Posted on by Matt Williams

What is the Transit Method?

In a series of papers, Professor Loeb and Michael Hippke indicate that conventional rockets would have a hard time escaping from certain kinds of extra-solar planets. Credit: NASA/Tim Pyle
In a series of papers, Professor Loeb and Michael Hippke indicate that conventional rockets would have a hard time escaping from certain kinds of extra-solar planets. Credit: NASA/Tim Pyle

Welcome all to the first in our series on Exoplanet-hunting methods. Today we begin with the most popular and widely-used, known as the Transit Method (aka. Transit Photometry).

For centuries, astronomers have speculated about the existence of planets beyond our Solar System. After all, with between 100 and 400 billion stars in the Milky Way Galaxy alone, it seemed unlikely that ours was the only one to have a system of planets. But it has only been within the past few decades that astronomers have confirmed the existence of extra-solar planets (aka. exoplanets).

Astronomers use various methods to confirm the existence of exoplanets, most of which are indirect in nature. Of these, the most widely-used and effective to date has been Transit Photometry, a method that measures the light curve of distant stars for periodic dips in brightness. These are the result of exoplanets passing in front of the star (i.e. transiting) relative to the observer.

Description:

These changes in brightness are characterized by very small dips and for fixed periods of time, usually in the vicinity of 1/10,000th of the star’s overall brightness and only for a matter of hours. These changes are also periodic, causing the same dips in brightness each time and for the same amount of time. Based on the extent to which stars dim, astronomers are also able to obtain vital information about exoplanets.

For all of these reasons, Transit Photometry is considered a very robust and reliable method of exoplanet detection. Of the 3,526 extra-solar planets that have been confirmed to date, the transit method has accounted for 2,771 discoveries – which is more than all the other methods combined.

Advantages:

One of the greatest advantages of Transit Photometry is the way it can provide accurate constraints on the size of detected planets. Obviously, this is based on the extent to which a star’s light curve changes as a result of a transit.  Whereas a small planet will cause a subtle change in brightness, a larger planet will cause a more noticeable change.

When combined with the Radial Velocity method (which can determine the planet’s mass) one can determine the density of the planet. From this, astronomers are able to assess a planet’s physical structure and composition – i.e. determining if it is a gas giant or rocky planet. The planets that have been studied using both of these methods are by far the best-characterized of all known exoplanets.

In addition to revealing the diameter of planets, Transit Photometry can allow for a planet’s atmosphere to be investigated through spectroscopy. As light from the star passes through the planet’s atmosphere, the resulting spectra can be analyzed to determine what elements are present, thus providing clues as to the chemical composition of the atmosphere.

Artist’s impression of an extra-solar planet transiting its star. Credit: QUB Astrophysics Research Center

Last, but not least, the transit method can also reveal things about a planet’s temperature and radiation based on secondary eclipses (when the planet passes behind it’s sun). On this occasion, astronomers measure the star’s photometric intensity and then subtract it from measurements of the star’s intensity before the secondary eclipse. This allows for measurements of the planet’s temperature and can even determine the presence of clouds formations in the planet’s atmosphere.

Disadvantages:

Transit Photometry also suffers from a few major drawbacks. For one, planetary transits are observable only when the planet’s orbit happens to be perfectly aligned with the astronomers’ line of sight. The probability of a planet’s orbit coinciding with an observer’s vantage point is equivalent to the ratio of the diameter of the star to the diameter of the orbit.

Only about 10% of planets with short orbital periods experience such an alignment, and this decreases for planets with longer orbital periods. As a result, this method cannot guarantee that a particular star being observed does indeed host any planets. For this reason, the transit method is most effective when surveying thousands or hundreds of thousands of stars at a time.

It also suffers from a substantial rate of false positives; in some cases, as high as 40% in single-planet systems (based on a 2012 study of the Kepler mission). This necessitates that follow-up observations be conducted, often relying on another method. However, the rate of false positives drops off for stars where multiple candidates have been detected.

Number of extrasolar planet discoveries per year through September 2014, with colors indicating method of detection – radial velocity (blue), transit (green), timing (yellow), direct imaging (red), microlensing (orange). Credit: Public domain

While transits can reveal much about a planet’s diameter, they cannot place accurate constraints on a planet’s mass. For this, the Radial Velocity method (as noted earlier) is the most reliable, where astronomers look for signs of “wobble” in a star’s orbit to the measure the gravitational forces acting on them (which are caused by planets).

In short, the transit method has some limitations and is most effective when paired with other methods. Nevertheless, it remains the most widely-used means of “primary detection” – detecting candidates which are later confirmed using a different method – and is responsible for more exoplanet discoveries than all other methods combined.

Examples of Transit Photometry Surveys:

Transit Photometry is performed by multiple Earth-based and space-based observatories around the world. The majority, however, are Earth-based, and rely on existing telescopes combined with state-of-the-art photometers. Examples include the Super Wide Angle Search for Planets (SuperWASP) survey, an international exoplanet-hunting survey that relies on the Roque de los Muchachos Observatory and the South African Astronomical Observatory.

There’s also the Hungarian Automated Telescope Network (HATNet), which consists of six small, fully-automated  telescopes and is maintained by the Harvard-Smithsonian Center for Astrophysics. The MEarth Project is another, a National Science Foundation-funded robotic observatory that combines the Fred Lawrence Whipple Observatory (FLWO) in Arizona with the Cerro Tololo Inter-American Observatory (CTIO) in Chile.

The SuperWasp Cameras at the South African Astronomical Observatory. Credit: SuperWASP project & David Anderson

Then there’s the Kilodegree Extremely Little Telescope (KELT), an astronomical survey jointly administered by Ohio State University, Vanderbilt University, Lehigh University, and the South African Astronomical Society (SAAO). This survey consists of two telescopes, the Winer Observatory in southeastern Arizona and the Sutherland Astronomical Observation Station in South Africa.

In terms of space-based observatories, the most notable example is NASA’s Kepler Space Telescope. During its initial mission, which ran from 2009 to 2013, Kepler detected 4,496 planetary candidates and confirmed the existence of 2,337 exoplanets. In November of 2013, after the failure of two of its reaction wheels, the telescope began its K2 mission, during which time an additional 515 planets have been detected and 178 have been confirmed.

The Hubble Space Telescope also conducted transit surveys during its many years in orbit. For instance, the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) – which took place in 2006 – consisted of Hubble observing 180,000 stars in the central bulge of the Milky Way Galaxy. This survey revealed the existence of 16 additional exoplanets.

Other examples include the ESA’s COnvection ROtation et Transits planétaires (COROT) – in English “Convection rotation and planetary transits” – which operated from 2006 to 2012. Then there’s the ESA’s Gaia mission, which launched in 2013 with the purpose of creating the largest 3D catalog ever made, consisting of over 1 billion astronomical objects.

NASA’s Kepler space telescope was the first agency mission capable of detecting Earth-size planets. Credit: NASA/Wendy Stenzel

In March of 2018, the NASA Transiting Exoplanet Survey Satellite (TESS) is scheduled to be launched into orbit. Using the transit method, TESS will detect exoplanets and also select targets for further study by the James Webb Space Telescope (JSWT), which will be deployed in 2019. Between these two missions, the confirmation and characterization or many thousands of exoplanets is anticipated.

Thanks to improvements in terms of technology and methodology, exoplanet discovery has grown by leaps and bounds in recent years. With thousands of exoplanets confirmed, the focus has gradually shifted towards the characterizing of these planets to learn more about their atmospheres and conditions on their surface.

In the coming decades, thanks in part to the deployment of new missions, some very profound discoveries are expected to be made!

We have many interesting articles about exoplanet-hunting here at Universe Today. Here’s What are Extra Solar Planets?, What are Planetary Transits?, What is the Radial Velocity Method?, What is the Direct Imaging Method?, What is the Gravitational Microlensing Method?, and Kepler’s Universe: More Planets in our Galaxy than Stars.

Astronomy Cast also has some interesting episodes on the subject. Here’s Episode 364: The COROT Mission.

For more information, be sure to check out NASA’s page on Exoplanet Exploration, the Planetary Society’s page on Extrasolar Planets, and the NASA/Caltech Exoplanet Archive.

Sources:

Posted on by Matt Williams

There Could be Hundreds More Icy Worlds with Life Than on Rocky Planets Out There in the Galaxy

The moons of Europa and Enceladus, as imaged by the Galileo and Cassini spacecraft. Credit: NASA/ESA/JPL-Caltech/SETI Institute

In the hunt for extra-terrestrial life, scientists tend to take what is known as the “low-hanging fruit approach”. This consists of looking for conditions similar to what we experience here on Earth, which include at oxygen, organic molecules, and plenty of liquid water. Interestingly enough, some of the places where these ingredients are present in abundance include the interiors of icy moons like Europa, Ganymede, Enceladus and Titan.

Whereas there is only one terrestrial planet in our Solar System that is capable of supporting life (Earth), there are multiple “Ocean Worlds” like these moons. Taking this a step further, a team of researchers from the Harvard Smithsonian Center for Astrophysics (CfA) conducted a study that showed how potentially-habitable icy moons with interior oceans are far more likely than terrestrial planets in the Universe.

The study, titled “Subsurface Exolife“, was performed by Manasvi Lingam and Abraham Loeb of the Harvard Smithsonain Center for Astrophysics (CfA) and the Institute for Theory and Computation (ITC) at Harvard University. For the sake of their study, the authors consider all that what defines a circumstellar habitable zone (aka. “Goldilocks Zone“) and likelihood of there being life inside moons with interior oceans.

Cutaway showing the interior of Saturn’s moon Enceladus. Credit: ESA

To begin, Lingam and Loeb address the tendency to confuse habitable zones (HZs) with habitability, or to treat the two concepts as interchangeable. For instance, planets that are located within an HZ are not necessarily capable of supporting life – in this respect, Mars and Venus are perfect examples. Whereas Mars is too cold and it’s atmosphere too thin to support life, Venus suffered a runaway greenhouse effect that caused it to become a hot, hellish place.

On the other hand, bodies that are located beyond HZs have been found to be capable of having liquid water and the necessary ingredients to give rise to life. In this case, the moons of Europa, Ganymede, Enceladus, Dione, Titan, and several others serve as perfect examples. Thanks to the prevalence of water and geothermal heating caused by tidal forces, these moons all have interior oceans that could very well support life.

As Lingam, a post-doctoral researcher at the ITC and CfA and the lead author on the study, told Universe Today via email:

“The conventional notion of planetary habitability is the habitable zone (HZ), namely the concept that the “planet” must be situated at the right distance from the star such that it may be capable of having liquid water on its surface. However, this definition assumes that life is: (a) surface-based, (b) on a planet orbiting a star, and (c) based on liquid water (as the solvent) and carbon compounds. In contrast, our work relaxes assumptions (a) and (b), although we still retain (c).”

As such, Lingam and Loeb widen their consideration of habitability to include worlds that could have subsurface biospheres. Such environments go beyond icy moons such as Europa and Enceladus and could include many other types deep subterranean environments. On top of that, it has also been speculated that life could exist in Titan’s methane lakes (i.e. methanogenic organisms). However, Lingam and Loeb chose to focus on icy moons instead.

A “true color” image of the surface of Jupiter’s moon Europa as seen by the Galileo spacecraft. Image credit: NASA/JPL-Caltech/SETI Institute

“Even though we consider life in subsurface oceans under ice/rock envelopes, life could also exist in hydrated rocks (i.e. with water) beneath the surface; the latter is sometimes referred to as subterranean life,” said Lingam. “We did not delve into the second possibility since many of the conclusions (but not all of them) for subsurface oceans are also applicable to these worlds. Similarly, as noted above, we do not consider lifeforms based on exotic chemistries and solvents, since it is not easy to predict their properties.”

Ultimately, Lingam and Loeb chose to focus on worlds that would orbit stars and likely contain subsurface life humanity would be capable of recognizing. They then went about assessing the likelihood that such bodies are habitable, what advantages and challenges life will have to deal with in these environments, and the likelihood of such worlds existing beyond our Solar System (compared to potentially-habitable terrestrial planets).

For starters, “Ocean Worlds” have several advantages when it comes to supporting life. Within the Jovian system (Jupiter and its moons) radiation is a major problem, which is the result of charged particles becoming trapped in the gas giants powerful magnetic field. Between that and the moon’s tenuous atmospheres, life would have a very hard time surviving on the surface, but life dwelling beneath the ice would fare far better.

“One major advantage that icy worlds have is that the subsurface oceans are mostly sealed off from the surface,” said Lingam. “Hence, UV radiation and cosmic rays (energetic particles), which are typically detrimental to surface-based life in high doses, are unlikely to affect putative life in these subsurface oceans.”

Artist rendering showing an interior cross-section of the crust of Enceladus, which shows how hydrothermal activity may be causing the plumes of water at the moon’s surface. Credits: NASA-GSFC/SVS, NASA/JPL-Caltech/Southwest Research Institute

“On the negative side,’ he continued, “the absence of sunlight as a plentiful energy source could lead to a biosphere that has far less organisms (per unit volume) than Earth. In addition, most organisms in these biospheres are likely to be microbial, and the probability of complex life evolving may be low compared to Earth. Another issue is the potential availability of nutrients (e.g. phosphorus) necessary for life; we suggest that these nutrients might be available only in lower concentrations than Earth on these worlds.”

In the end, Lingam and Loeb determined that a wide range of worlds with ice shells of moderate thickness may exist in a wide range of habitats throughout the cosmos. Based on how statistically likely such worlds are, they concluded that “Ocean Worlds” like Europa, Enceladus, and others like them are about 1000 times more common than rocky planets that exist within the HZs of stars.

These findings have some drastic implications for the search for extra-terrestrial and extra-solar life. It also has significant implications for how life may be distributed through the Universe. As Lingam summarized:

“We conclude that life on these worlds will undoubtedly face noteworthy challenges. However, on the other hand, there is no definitive factor that prevents life (especially microbial life) from evolving on these planets and moons. In terms of panspermia, we considered the possibility that a free-floating planet containing subsurface exolife could be temporarily “captured” by a star, and that it may perhaps seed other planets (orbiting that star) with life. As there are many variables involved, not all of them can be quantified accurately.”

Exogenesis
A new instrument called the Search for Extra-Terrestrial Genomes (STEG)
is being developed to find evidence of life on other worlds. Credit: NASA/Jenny Mottor

Professor Leob – the Frank B. Baird Jr. Professor of Science at Harvard University, the director of the ITC, and the study’s co-author – added that finding examples of this life presents its own share of challenges. As he told Universe Today via email:

“It is very difficult to detect sub-surface life remotely (from a large distance) using telescopes. One could search for excess heat but that can result from natural sources, such as volcanos. The most reliable way to find sub-surface life is to land on such a planet or moon and drill through the surface ice sheet. This is the approach contemplated for a future NASA mission to Europa in the solar system.”

Exploring the implications for panspermia further, Lingam and Loeb also considered what might happen if a planet like Earth were ever ejected from the Solar System. As they note in their study, previous research has indicated how planets with thick atmospheres or subsurface oceans could still support life while floating in interstellar space. As Loeb explained, they also considered what would happen if this ever happened with Earth someday:

“An interesting question is what would happen to the Earth if it was ejected from the solar system into cold space without being warmed by the Sun. We have found that the oceans would freeze down to a depth of 4.4 kilometers but pockets of liquid water would survive in the deepest regions of the Earth’s ocean, such as the Mariana Trench, and life could survive in these remaining sub-surface lakes. This implies that sub-surface life could be transferred between planetary systems.”

The Drake Equation, a mathematical formula for the probability of finding life or advanced civilizations in the universe. Credit: University of Rochester

This study also serves as a reminder that as humanity explores more of the Solar System (largely for the sake of finding extra-terrestrial life) what we find also has implications in the hunt for life in the rest of the Universe. This is one of the benefits of the “low-hanging fruit” approach. What we don’t know is informed but what we do, and what we find helps inform our expectations of what else we might find.

And of course, it’s a very vast Universe out there. What we may find is likely to go far beyond what we are currently capable of recognizing!

Further Reading: arXiv

Posted on by Matt Williams

The Genesis Project: Using Robotic Gene Factories to Seed the Galaxy with Life

Project Genesis aims to seed "transiently habitable worlds" with life in order to create more life in the Universe. Credit: NASA/Serge Brunier

In the past decade, the rate at which extra-solar planets have been discovered and characterized has increased prodigiously. Because of this, the question of when we might explore these distant planets directly has repeatedly come up. In addition, the age-old question of what we might find once we get there – i.e. is humanity alone in the Universe or not? – has also come up with renewed vigor.

These questions have led to a number of interesting and ambitious proposals. These include Project Blue, a space telescope which would directly observe any planets orbiting Alpha Centauri, and Breakthrough Starshot – which aims to send a laser-driven nanocraft to Alpha Centauri in just 20 years. But perhaps the most daring proposal comes in the form of Project Genesis, which would attempt to seed distant planets with life.

This proposal was put forth by Dr. Claudius Gros, a theoretical physicist from the Institute for Theoretical Physics at Goethe University Frankfurt. In 2016, he published a paper that described how robotic missions equipped with gene factories (or cryogenic pods) could be used to distribute microbial life to “transiently habitable exoplanets – i.e. planets capable of supporting life, but not likely to give rise to it on their own.

Exogenesis
The purpose of Project Genesis would be to seed “transiently habitable” worlds with life, thus giving them a jump start on evolution. Credit: NASA/Jenny Mottor

Not long ago, Universe Today wrote about Dr. Gros’ recent study where he proposed using a magnetic sail to slow down an interstellar spacecraft. We were fortunate to catch up with Dr. Gros again and had a chance to ask him about Project Genesis. You can find our Q&A below, and be sure to check out his seminal paper that describes this project – “Developing Ecospheres on Transiently Habitable Planets: The Genesis Project“.

What is the purpose of Project Genesis?

Exoplanets come in all sizes, temperatures and compositions. The purpose of the Genesis project is to offer terrestrial life alternative evolutionary pathways on those exoplanets that are potentially habitable but yet lifeless. The basic philosophy of most scientists nowadays is that simple life is common in the universe and complex life is rare. We don’t know that for sure, but at the moment, that is the consensus.

If you had good conditions, simple life can develop very fast, but complex life will have a hard time. At least on Earth, it took a very long time for complex life to arrive. The Cambrian Explosion only happened about 500 million years ago, roughly 4 billion years after Earth was formed. If we give planets the opportunity to fast forward evolution, we can give them the chance to have their own Cambrian Explosions.

Early trilobite species (Eoredlichia takooensis) from the Lower Cambrian period, found in Emu Bay Shale, Kangaroo Island, Australia. Credit and ©: Royal Ontario Museum/David Rudkin

What worlds would be targeted?

The prime candidates are habitable “oxygen planets” around M-dwarfs like TRAPPIST-1. It is very likely that the oxygen-rich primordial atmosphere of these planets will have prevented abiogenesis in first place, that is the formation of life. Our galaxy could potentially harbor billions of habitable but lifeless oxygen planets.

Nowadays, astronomers are looking for planets around M-stars. These are very different from planets around Sun-like stars. Once a star forms, it takes a certain amount of time to contract to the point where fusion begins, and it starts to produce energy. For the Sun, this took 10 million years, which is very fast. For stars like TRAPPIST-1, it would take 100 million to 1 billion years. Then they have to contract to dissipate their initial heat.

The planets around TRAPPIST-1 would have been very hot, because the star was very hot for a long time. All the water that was in their stratospheres, the UV radiation would have disassociated it into hydrogen and oxygen – the hydrogen escaped, and the oxygen remained. All surveys have showed that they have oxygen atmospheres, but this is the product of chemical disassociation and not from plants (as with Earth).

There’s a good chance that oxygen planets are sterile, because oxygen planets eat up prebiotic conditions. We believe there may be billions of oxygen planets in our galaxy. They would have no life, and complex life needs oxygen. In science fiction, you have all these planets that look alike. We could imagine that in half a billion years, we could have this because we seeded oxygen planets (only we couldn’t travel there quickly since we have no FTL).

Illustration of what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credits: NASA/JPL-Caltech

What kind of organisms would be sent?

The first wave would consist of unicellular autotrophs. That is photo-synthesizing bacteria, like cyanobacteria, and eukaryotes (the cell type making up all complex life, that is animals and plants). Heterotrophs would follow in a second stage, organisms that feed on other organisms and can only exist after autotrophs exist and take root.

How would these organisms be sent?

That depends on the technology. If it can advance, we can miniaturize a gene factory. In principle, nature is a miniature gene factory. Everything we want to produce is very small. If it’s possible that would be the best option. Send in a gene bank, and then select the most optimal organism to send down. If that is not possible, you would have to have frozen germs. In the end, it depends on what would be the technically available.

You could also send in synthetic life. Synthetic biology is a very active research field, which involves reprogramming the genetic code. In science fiction, you have alien life with a different genetic code. Today, people are trying to produce this here on Earth. The end goal is to have new life forms that are based on a different code. This would be very dangerous on Earth, but on a far-distant planet, it would be beneficial.

What if these worlds are not sterile?

Genesis is all about life, not destroying life, so we’d want to avoid that. The probes would have to go into orbit, so we are pretty sure that from orbit, we could detect complex life on the surface. The Genesis Project was intended for planets that are not habitable for eternity. Earth is habitable for billions of years, but we are not sure about habitable exoplanets.

This illustration shows a star’s light illuminating the atmosphere of a planet. Credits: NASA Goddard Space Flight Center

Exoplanets come in all kinds of sized, temperatures, and habitabilities. Many of these planets will only be habitable for some time, maybe 1 billion years. Life there will not have time to evolve into complex life forms. So you have a decision: leave them like they are, or take a chance at developing complex life there.

Some believe that all bacteria are worth saving. On Earth, there is no protection for bacteria. But bacteria living on different planets are treated differently. Planetary protection, why do we do that? So we can study the life, or for the sake of protecting life itself? Mars most likely had life at one time, but now not, except for maybe a few bacteria. Still, we plan manned missions to Mars, which means planetary protection is off. It’s a contradiction.

I am very enthusiastic about finding life, but what about the planets where we don’t find life? This offers the possibility about doing something about it.

Could humanity benefit from this someday (i.e. colonize “seeded” planets)?

Yes and no. Yes, because nothing would keep our decedents (or any other intelligence living on Earth by then), to visit Genesis planets in 10-100 million years (the minimal time for the life initially seeded to fully unfold). No, because the involved time spans are so long, that it is not rational to speak of a ‘benefit’.

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org

How soon could such a mission be mounted?

Genesis probes could be launched by the same directed-energy launch system planned for the Breakthrough Starshot initiative. Breakthrough Starshot aims to send very fast, very small, very light probes of about 1 gram to another star system. The same laser technology could send something more massive, but slower. Slow is relative, of course. So the in the end it depends on what is optimal.

The magnetic sail paper I recently wrote was a sample mission to show that it was possible. The probe would be about the size of a car (1 tonne) and would travel at a speed of about 1000 km/s – slow for interstellar travel relative to speed of light, but fast for Earth. If you reduce the velocity by a factor of 100, the mass you can propel is 10,000 heavier. You could accelerate a 1-tonne Genesis Probe and it would still fit into the layout of Breakthrough Starshot.

Therefore, the launch facility could see dual use and you wouldn’t need to build something new. Once that is in place one would need to test the magnetic sail. A realistic time span would hence be in the 50-100 years window.

What counter-arguments are there against this?

There are three main lines of counter-arguments. The first is the religious counter-argument, which says that humanity should not play God. The Genesis project is however not about creating life, but to give life the possibility to further develop. Just not on Earth, but elsewhere in the cosmos.

Mars, according to multiple studies, could still support life, raising issues of “planetary protection”. Credit: YONHAP/EPA

The second is the Planetary protection argument, which argues that we should not interfere. Some people objecting to the Genesis Project cite the ‘first directive’ of the Star Trek TV series. The Genesis Project fully supports planetary protection of planets which harbor complex life and of planets on which complex life could potentially develop in the future. The Genesis project will target only planets on which complex life could not develop on its own.

The third argument is about the lack of benefit to humanity. The Genesis Project is expressively not for human benefit. It is reasonable to argue, from the perspective of survival, that the ethical values of a species (like humanity) has to put the good of the species at the center.  Ethical is therefore “what is good for our own species”. Spending a large amount of money on a project, like the Genesis Project, which is expressively not for the benefit of our own species, would then be unethical.

___

Our thanks go out to Dr. Gros for taking the time to talk to us! We hope to hear more from him in the future and wish him the best of luck with Project Genesis.

Posted on by Matt Williams

Astronomers Think They Know Why Hot Jupiters Get So Enormous

Artist's impression of the K2-132 system, along with schematics of the star during its main sequence and Red Branch Phase. Credit: Karen Teramura/UH IfA

The study of extra-solar planets has revealed some fantastic and fascinating things. For instance, of the thousands of planets discovered so far, many have been much larger than their Solar counterparts. For instance, most of the gas giants that have been observed orbiting closely to their stars (aka. “Hot Jupiters”) have been similar in mass to Jupiter or Saturn, but have also been significantly larger in size.

Ever since astronomers first placed constraints on the size of a extra-solar gas giant seven years ago, the mystery of why these planets are so massive has endured. Thanks to the recent discovery of twin planets in the K2-132 and K2-97 system – made by a team from the University of Hawaii’s Institute for Astronomy using data from the Kepler mission – scientists believe we are getting closer to the answer.

The study which details the discovery – “Seeing Double with K2: Testing Re-inflation with Two Remarkably Similar Planets around Red Giant Branch Stars” – recently appeared in The Astrophysical Journal. The team was led by Samuel K. Grunblatt, a graduate student at the University of Hawaii, and included members from the Sydney Institute for Astronomy (SIfA), Caltech, the Harvard-Smithsonian Center for Astrophysics (CfA), NASA Goddard Space Flight Center, the SETI Institute, and multiple universities and research institutes.

Artist’s concept of Jupiter-sized exoplanet that orbits relatively close to its star (aka. a “hot Jupiter”). Credit: NASA/JPL-Caltech)

Because of the “hot” nature of these planets, their unusual sizes are believed to be related to heat flowing in and out of their atmospheres. Several theories have been developed to explain this process, but no means of testing them have been available. As Grunblatt explained, “since we don’t have millions of years to see how a particular planetary system evolves, planet inflation theories have been difficult to prove or disprove.”

To address this, Grunblatt and his colleagues searched through the data collected by NASA’s Kepler mission (specifically from its K2 mission) to look for “Hot Jupiters” orbiting red giant stars. These are stars that have exited the main sequence of their lifespans and entered the Red Giant Branch (RGB) phase, which is characterized by massive expansion and a decrease in surface temperature.

As a result, red giants may overtake planets that orbit closely to them while planets that were once distant will begin to orbit closely. In accordance with a theory put forth by Eric Lopez – a member of NASA Goddard’s Science and Exploration Directorate – hot Jupiter’s that orbit red giants should become inflated if direct energy output from their host star is the dominant process inflating planets.

So far, their search has turned up two planets – K2-132b and K2-97 b – which were almost identical in terms of their orbital periods (9 days), radii and masses. Based on their observations, the team was able to precisely calculate the radii of both planets and determine that they were 30% larger than Jupiter. Follow-up observations from the W.M. Keck Observatory at Maunakea, Hawaii, also showed that the planets were only half as massive as Jupiter.

The life-cycle of a Sun-like star from protostar (left side) to red giant (near the right side) to white dwarf (far right). Credit: ESO/M. Kornmesser

The team then used models to track the evolution of the planets and their stars over time, which allowed them to calculate how much heat the planets absorbed from their stars. As this heat was transferring from their outer layers to their deep interiors, the planets increased in size and decreased in density. Their results indicated that while the planets likely needed the increased radiation to inflate, the amount they got was lower than expected.

While the study is limited in scope, Grunblatt and his team’s study is consistent with the theory that huge gas giants are inflated by the heat of their host stars. It is bolstered by other lines of evidence that hint that stellar radiation is all a gas giant needs to dramatically alter its size and density. This is certainly significant, given that our own Sun will exit its main sequence someday, which will have a drastic effect on our system of planets.

As such, studying distant red giant stars and what their planets are going through will help astronomers to predict what our Solar System will experience, albeit in a few billion years. As Grunblatt explained in a IfA press statement:

“Studying how stellar evolution affects planets is a new frontier, both in other solar systems as well as our own. With a better idea of how planets respond to these changes, we can start to determine how the Sun’s evolution will affect the atmosphere, oceans, and life here on Earth.”

It is hoped that future surveys which are dedicated to the study of gas giants around red giant stars will help settle the debate between competing planet inflation theories. For their efforts, Grunblatt and his team were recently awarded time with NASA’s Spitzer Space Telescope, which they plan to use to conduct further observations of K2-132 and K2-97, and their respective gas giants.

The search for planets around red giant stars is also expected to intensify in the coming years with he deployment of NASA’s Transiting Exoplanet Survey Satellite (TESS) and the  James Webb Space Telescope (JWST). These missions will be launching in 2018 and 2019, respectively, while the K2 mission is expected to last for at least another year.

Further Reading: IfA, The Astronomical Journal

Posted on by Matt Williams

Planet With Lava Oceans Also has an Atmosphere, Says New Study

This illustration shows the super-Earth exoplanet 55 Cancri e with its star. What would our Solar System be like if it was home to a super-Earth like this one? Credit: NASA/JPL

The super-Earth 55 Cancri e (aka. Janssen) is somewhat famous, as exoplanet go. Originally discovered in 2004, this world was one of the few whose discovery predated the Kepler mission. By 2016, it was also the first exoplanet to have its atmosphere successfully characterized. Over the years, several studies have been conducted on this planet that revealed some rather interesting things about its composition and structure.

For example, scientists believed at one time that 55 Cancri e was a “diamond planet“, whereas more recent work based on data from the Spitzer Space Telescope concluded that its surface was covered in lakes of hot lava. However, a new study conducted by scientists from NASA’s Jet Propulsion Laboratory indicates that despite its intense surface heat, 55 Cancri e has an atmosphere that is comparable to Earth’s, only much hotter!

The study, titled “A Case for an Atmosphere on Super-Earth 55 Cancri e“, recently appeared in The Astrophysical Journal. Led by Isabel Angelo (a physics major with UC Berkeley) with the assistance of Renyu Hu – a astronomer and Hubble Fellow with JPL and Caltech – the pair conducted a more detailed analysis of the Spitzer data to determine the likelihood and composition of an atmosphere around 55 Cancri e.

Artist’s impression of the super-Earth 55 Cancri e in front of its parent star. Credit: ESA/NASA

Previous studies of the planet noted that this super-Earth (which is twice as large as our planet), orbits very close to its star. As a result, it has a very short orbital period of about 17 hours and 40 minutes and is tidally locked (with one side constantly facing towards the star). Between June and July of 2013, Spitzer observed 55 Cancri e and obtained temperature data using its special infrared camera.

Initially, the temperature data was seen as being an indication that large deposits of lava existed on the surface. However, after re-analyzing this data and combining it with a new model previously develop by Hu, the team began to doubt this explanation. According to their findings, the planet must have a thick atmosphere, since lava lakes exposed to space would create hots spots of high temperatures.

What’s more, they also noted that the temperature differences between the day and night side were not as significant as previously thought – another indication of an atmosphere. By comparing changes in the planet’s brightness to energy flow models, the team concluded that an atmosphere with volatile materials was the best explanation for the high temperatures. As Renyu Hu explained in a recent NASA press statement:

“If there is lava on this planet, it would need to cover the entire surface. But the lava would be hidden from our view by the thick atmosphere. Scientists have been debating whether this planet has an atmosphere like Earth and Venus, or just a rocky core and no atmosphere, like Mercury. The case for an atmosphere is now stronger than ever.”

Using Hu’s improved model of how heat would flow throughout the planet and radiate back into space, they found that temperatures on the day side would average about 2573 K (2,300 °C; 4,200 °F). Meanwhile, temperatures on the “cold” side would average about 1573 – 1673 K (1,300 – 1,400 °C; 2,400 – to 2,600 °F). If the planet had no atmosphere, the differences in temperature would be far more extreme.

As for the composition of this atmosphere, Angelo and Hu revealed that it is likely similar to Earth’s – containing nitrogen, water and even oxygen. While much hotter, the atmospheric density also appeared to be similar to that of Earth, which suggests the planet is most likely rocky (aka. terrestrial) in composition. On the downside, the temperatures are far too hot for the surface to maintain liquid water, which makes habitability a non-starter.

Ultimately, this study was made possible thanks to Hu’s development of a method that makes the study exoplanet atmospheres and surfaces easier. Angelo, who led the study, worked on it as part of her internship with JPL and adapted Hu’s model to 55 Cancri e. Previously, this model had only been applied to mass gas giants that orbit close to their respective suns (aka. “Hot Jupiters”).

Naturally, there are unresolved questions that this study helps to raise, such as how 55 Cancri e has avoided losing its atmosphere to space. Given how close the planet orbits to its star, and the fact that it’s tidally locked, it would be subject to intense amounts of radiation. Further studies may help to reveal how this is the case, and will help advance our understanding of large, rocky planets.

The application of this model to a Super-Earth is the perfect example of how exoplanet research has been evolving in recent years. Initially, scientists were restricted to studying gas giants that orbit close to their stars (as well as their respective atmospheres) since these are the easiest to spot and characterize. But thanks to improvements in instrumentation and methods, the range of planets we are capable of studying is growing.

Further Reading: NASA, The Astrophysical Journal

Posted on by Matt Williams

Closest Potentially-Habitable World Found Around “Quiet” Star

This artist's impression shows the temperate planet Ross 128 b, with its red dwarf parent star in the background. Credit: ESO/M. Kornmesser

In August of 2016, the European Southern Observatory (ESO) announced the discovery of a terrestrial (i.e. rocky) extra-solar planet orbiting within the habitable zone of the nearby Proxima Centauri star system, just 4.25 light-years away. Naturally, news of this was met with a great deal of excitement. This was followed about six months later with the announcement of a seven-planet system orbiting the nearby star of TRAPPIST-1.

Well buckle up, because the ESO just announced that there is another potentially-habitable planet in our stellar neighborhood! Like Proxima b, this exoplanet – known as Ross 128b – is relatively close to our Solar System (10.8 light years away) and is believed to be temperate in nature. But on top of that, this rocky planet has the added benefit of orbiting a quiet red dwarf star, which boosts the likelihood of it being habitable.

The discovery paper, titled “A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs“, was recently released by the ESO. The discovery team was led by Xavier Bonfils of the University of Grenoble Alpes, and included members from the Geneva Observatory, the National Scientific and Technical Research Council (CONICET), the University of Buenos Aires, the University of Laguna, the Instituto de Astrofísica de Canarias (IAC), and the University of Porto.

This artist’s impression shows the temperate planet Ross 128b, with its red dwarf parent star in the background. Credit: ESO/M. Kornmesser

The discovery was made using the ESO’s High Accuracy Radial velocity Planet Searcher (HARPS), located at the La Silla Observatory in Chile. This observatory relies on measurements of a star’s Doppler shift in order to determine if it moving back and forth, a sign that it has a system of planets. Using the HARPS data, the team determined that a  rocky planet orbits Ross 128 (an M-type red dwarf star) at a distance of about 0.05 AU with a period of 9.9 days.

Despite its proximity to its host star, Ross 128b receives only 1.38 times more irradiation than the Earth. This is due to the cool and faint nature of red dwarf stars like Ross 128, which has a surface temperature roughly half that of our Sun. From this, the discovery team estimated that Ross 128b’s equilibrium temperature is likely somewhere between -60 and 20°C – i.e. close to what we experience here on Earth.

As Nicola Astudillo-Defru of the Geneva Observatory – and a co-author on the discovery paper – indicated in an ESO press release:

“This discovery is based on more than a decade of HARPS intensive monitoring together with state-of-the-art data reduction and analysis techniques. Only HARPS has demonstrated such a precision and it remains the best planet hunter of its kind, 15 years after it began operations.”

But what is most encouraging is the fact that Ross 128 is the “quietest” nearby star that is also home to an exoplanet. Compared to other classes of stars, M-type red dwarfs are particularly low in mass, dimmer and cooler. They are also the most common type of star in the Universe, accounting for 70% of the stars in spiral galaxies and more than 90% of all stars in elliptical galaxies.

Unfortunately, they are also variable and unstable compared to other classes of star, which means they experience regular flare ups. This means that any planets which orbit them will be periodically subjected to deadly ultraviolet and X-ray radiation. In comparison, Ross 128 is much quieter, meaning it experiences less in the way of flare activity, and planets orbiting it are therefore exposed to less radiation over time.

This means that, relative to Proxima b or those planets located within TRAPPIST-1’s habitable zone – Ross 128b is more likely to retain an atmosphere and support life. For those who are engaged in searches for exoplanets around M-type stars – or are of the opinion that red dwarfs are the best bet for finding habitable worlds – this latest discovery would seem to confirm that they are looking in the right spots!

As noted, red dwarfs are the most common in the Universe, and in recent years, many rocky planets (sometimes even a multi-planet system) have been found orbiting these stars. Combined with their natural longevity – which can remain in their main sequence phase for up to 10 trillion years – red dwarf stars have understandably become a popular target for exoplanet-hunters.

In fact, lead author Xavier Bonfils named their HARPS program “The Shortcut to Happiness” for this very reason. As he and his colleagues indicated, it is easier to detect small cool planets of Earth around smaller, dimmer M-type stars than it is around stars that are more similar to the Sun.

However, many in the scientific community have remained skeptical about the likelihood that any of these planets could be habitable (again, due to their variable nature). But this most recent discovery, along with recent research that indicates how tidally-locked  planets that orbit red dwarf stars could hold onto their atmospheres, is another possible indication that these fears may be for naught.

Being at a distance of about 11 light-years from Earth, Ross 128b is currently the second-closest exoplanet to our Sun. However, Ross 128 itself is slowly moving closer towards us and will become our nearest stellar neighbor in roughly 79,000 years. At this point, Ross 128b will replace Proxima b and become the closest exoplanet to Earth!

But of course, much remains to be found about this latest exoplanet. While the discovery team consider Ross 128b to be a temperate planet based on its orbit, it remains uncertain as to whether it lies within, beyond, or on the cusp of the star’s habitable zone. However, further studies are expected to shed more light on this and other questions relating this potentially-habitable world.

Astronomers also anticipate that more temperature exoplanets will be discovered in the coming years, and that future surveys will be able to determine a great deal more about their atmospheres, composition and chemistry. Instruments like the James Webb Space Telescope (JWST) and the ESO’s Extremely Large Telescope (ELT) are expected to play a major role.

Not only will these and other instrument help turn up more exoplanet candidates, they will also be used in the hunt for biosignatures in planet’s atmospheres (i.e. oxygen, nitrogen, water vapor, etc.). As Bonfils concluded:

“New facilities at ESO will first play a critical role in building the census of Earth-mass planets amenable to characterization. In particular, NIRPS, the infrared arm of HARPS, will boost our efficiency in observing red dwarfs, which emit most of their radiation in the infrared. And then, the ELT will provide the opportunity to observe and characterize a large fraction of these planets.”

At this juncture, the process of exoplanet discovery is moving beyond detection and getting into the process of characterization and detailed study. Even so, it is nice that we are still making groundbreaking discoveries in the field of detection. In the coming years, we may transition from looking for an Earth 2.0 to a point where weare actively studying several at once!

Further Reading: ESO, ESO (2)

Posted on by Matt Williams

Proxima Centauri has a Cold Dust Belt that Could Indicate Even More Planets

This artist’s impression shows how the newly discovered belts of dust around the closest star to the Solar System, Proxima Centauri, may look. Credit: ESO/M. Kornmesser

Proxima Centauri, in addition to being the closest star system to our own, is also the home of the closest exoplanet to Earth. The existence of this planet, Proxima b, was first announced in August of 2016 and then confirmed later that month. The news was met with a great deal of excitement, and a fair of skepticism, as numerous studies followed t were dedicated to determining if this planet could in fact be habitable.

Another important question has been whether or not Proxima Centauri could have any more objects orbiting it. According to a recent study by an international team of astronomers, Proxima Centauri is also home to a belt of cold dust and debris that is similar to the Main Asteroid Belt and Kuiper Belt in our Solar System. The existence of this dusty belt could indicate the presence of more planets in this star system.

The study, titled “ALMA Discovery of Dust Belts Around Proxima Centauri“, recently appeared online and is scheduled to appear in the Monthly Notices of the Astronomical Society. The study was led by Guillem Anglada from the Astrophysical Institute of Andalusia (CSIS), and included members from the Institute of Space Sciences (IEEC), the European Southern Observatory (ESO), the Joint ALMA Observatory, and multiple universities.

View of the Atacama Large Millimeter/submillimeter Array (ALMA) site in the Atacama Desert of northern Chile. Credit: A. Marinkovic/X-Cam/ALMA (ESO/NAOJ/NRAO)

For their study, the team relied on data obtained by the Atacama Large Millimeter/submillimter Array (ALMA) at the ALMA Observatory in Chile. These observations revealed the glow of a cold dust belt that is roughly 1 to 4 AUs from Proxima Centauri – one to four times the distance between the Earth and the Sun. This puts it significantly further out than Proxima b, which orbits its sun at a distance of 0.0485 AU (~5% of Earth’s distance from the Sun).

Dust belts are essentially the leftover material that did not form into larger bodies withing a star system. The particles of rock and ice in these belts vary in size from being smaller than a millimeter across to asteroids that are many kilometers in diameter. Based on their observations, the team estimated that the belt in Proxima Centauri has a total mass that is about one-hundredth the mass of Earth.

The team also estimated that this belt experiences temperatures of about 43 K (-230°C; -382 °F), making it as cold as the Kuiper Belt. As Dr. Anglada explained the significance of these findings in a recent ESO press release:

“The dust around Proxima is important because, following the discovery of the terrestrial planet Proxima b, it’s the first indication of the presence of an elaborate planetary system, and not just a single planet, around the star closest to our Sun.”

This infographic compares the orbit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System. Credit: ESO

The ALMA data also provided indications that Proxima Centauri might also have another belt located about ten times further out. In other words, Proxima Centauri may have two belts, just like our Solar System. If confirmed, this could indicate that this neighboring star also has a system of planets that fall within and between belts of unconsolidated material, which in turn is leftover from the early days of planet formation. As Dr. Anglada explained:

“This result suggests that Proxima Centauri may have a multiple planet system with a rich history of interactions that resulted in the formation of a dust belt. Further study may also provide information that might point to the locations of as yet unidentified additional planets.”

The very cold environment of this outer belt could also have some interesting implications, since its parent star is much dimmer than our own. Pedro Amado, who also hails from the Astrophysical Institute of Andalusia, was similarly enthusiastic about these findings. As he indicated, they are just the beginning of what is sure to be a long process of discovery about this system.

“These first results show that ALMA can detect dust structures orbiting around Proxima,” he said. “Further observations will give us a more detailed picture of Proxima’s planetary system. In combination with the study of protoplanetary discs around young stars, many of the details of the processes that led to the formation of the Earth and the Solar System about 4600 million years ago will be unveiled. What we are seeing now is just the appetiser compared to what is coming!”

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org

This study is also likely to be of interest to those planning on conducting direct observations of the Alpha Centauri system, such as Project Blue. In the coming years, they hope to deploy a space telescope that will observe Alpha Centauri directly to study any exoplanets it may have. With a slight adjustment, this telescope could also take a gander at Proxima Centauri and aid in the hunt for a system of planets there.

And then there’s Breakthrough Starshot, the first proposed interstellar voyage which hopes to send a laser sail-driven nanocraft to Alpha Centauri in the coming decades. Recently, the scientists behind Starshot discussed the possibility of extending the mission to include a stopover in Proxima Centauri. Before such a mission can take place, the planners need to know what kind of dusty environment awaits it.

And of course, future studies will benefit from the deployment of next-generation instruments, like the James Webb Space Telescope (scheduled for launch in 2019) and the ESO’s Extremely Large Telescope (ELT) – which is expected to collect its first light in 2024.

Further Reading: ESO, arXiv

Posted on by Matt Williams

“Monster Planet” Discovered, Makes Scientists Rethink Theories of Planetary Formation

Artist’s impression of the cool red star and gas-giant planet NGTS-1b against the Milky Way. Credit: University of Warwick/Mark Garlick.

When it comes to how and where planetary systems form, astronomers thought they had a pretty good handle on things. The predominant theory, known as the Nebular Hypothesis, states that stars and planets form from massive clouds of dust and gas (i.e. nebulae). Once this cloud experiences gravitational collapse at the center, its remaining dust and gas forms a protoplanetary disk that eventually accretes to form planets.

However, when studying the distant star NGTS-1 – an M-type (red dwarf) located about 600 light-years away – an international team led by astronomers from the University of Warwick discovered a massive “hot Jupiter” that appeared far too large to be orbiting such a small star. The discovery of this “monster planet” has naturally challenged some previously-held notions about planetary formation.

The study, titled “NGTS-1b: A hot Jupiter transiting an M-dwarf“, recently appeared in the Monthly Notices of the Royal Astronomical Society. The team was led by Dr Daniel Bayliss and Professor Peter Wheatley from the University of Warwick and included members from the of the Geneva Observatory, the Cavendish Laboratory, the German Aerospace Center, the Leicester Institute of Space and Earth Observation, the TU Berlin Center for Astronomy and Astrophysics, and multiple universities and research institutes.

Artist’s impression of the cool red star above NGTS-1b. Credit: University of Warwick/Mark Garlick.

The discovery was made using data obtained by the ESO’s Next-Generation Transit Survey (NGTS) facility, which is located at the Paranal Observatory in Chile. This facility is run by an international consortium of astronomers who come from the Universities of Warwick, Leicester, Cambridge, Queen’s University Belfast, the Geneva Observatory, the German Aerospace Center, and the University of Chile.

Using a full array of fully-robotic compact telescopes, this photometric survey is one of several projects meant to compliment the Kepler Space Telescope. Like Kepler, it monitors distant stars for signs of sudden dips in brightness, which are an indication of a planet passing in front of (aka. “transiting”) the star, relative to the observer.  When examining data obtained from NGTS-1, the first star to be found by the survey, they made a surprising discovery.

Based on the signal produced by its exoplanet (NGTS-1b), they determined that it was a gas giant roughly the same size as Jupiter and almost as massive (0.812 Jupiter masses). Its orbital period of 2.6 days also indicated that it orbits very close to its star – about 0.0326 AU – which makes it a “hot Jupiter”. Based on these parameters, the team also estimated that NGTS-1b experiences temperatures of approximately 800 K (530°C; 986 °F).

The discovery threw the team for a loop, as it was believed to be impossible for planets of this size to form around small, M-type stars. In accordance with current theories about planet formation, red dwarf stars are believed to be able to form rocky planets – as evidenced by the many that have been discovered around red dwarfs of late – but are unable to gather enough material to create Jupiter-sized planets.

Artist’s concept of Jupiter-sized exoplanet that orbits relatively close to its star (aka. a “hot Jupiter”). Credit: NASA/JPL-Caltech)

As Dr. Daniel Bayliss, an astronomer with the University of Geneva and the lead-author on the paper, commented in University of Warwick press release:

“The discovery of NGTS-1b was a complete surprise to us – such massive planets were not thought to exist around such small stars. This is the first exoplanet we have found with our new NGTS facility and we are already challenging the received wisdom of how planets form. Our challenge is to now find out how common these types of planets are in the Galaxy, and with the new NGTS facility we are well-placed to do just that.”

What is also impressive is the fact that the astronomers noticed the transit at all. Compared to other classes of stars, M-type stars are the smallest, coolest and dimmest. In the past, rocky bodies have been detected around them by measuring shifts in their position relative to Earth (aka. the Radial Velocity Method). These shifts are caused by the gravitational tug of one or more planets that cause the planet to “wobble” back and forth.

In short, the low light of an M-type star has made monitoring them for dips in brightness (aka. the Transit Method) highly impractical. However, using the NGTS’s red-sensitive cameras, the team was able to monitored patches of the night sky for many months. Over time, they noticed dips coming from NGTS-1 every 2.6 days, which indicated that a planet with a short orbital period was periodically passing in front of it.

Artist’s impression of the planet orbiting a red dwarf star. Credit: ESO/M. Kornmesser

They then tracked the planet’s orbit around the star and combined the transit data with Radial Velocity measurements to determine its size, position and mass. As Professor Peter Wheatley (who leads NGTS) indicated, finding the planet was painstaking work. But in the end, its discovery could lead to the detection of many more gas giants around low-mass stars:

“NGTS-1b was difficult to find, despite being a monster of a planet, because its parent star is small and faint. Small stars are actually the most common in the universe, so it is possible that there are many of these giant planets waiting to found. Having worked for almost a decade to develop the NGTS telescope array, it is thrilling to see it picking out new and unexpected types of planets. I’m looking forward to seeing what other kinds of exciting new planets we can turn up.”

Within the known Universe, M-type stars are by far the most common, accounting for 75% of all stars in the Milky Way Galaxy alone. In the past, the discovery of rocky bodies around stars like Proxima Centauri, LHS 1140, GJ 625, and the seven rocky planets around TRAPPIST-1, led many in the astronomical community to conclude that red dwarf stars were the best place to look for Earth-like planets.

The discovery of a Hot Jupiter orbiting NGTS-1 is therefore seen as an indication that other red dwarf stars could have orbiting gas giants as well. Above all, this latest find once again demonstrates the importance of exoplanet research. With every find we make beyond our Solar System, the more we learn about the ways in which planets form and evolve.

Every discovery we make also advances our understanding of how likely we may be to discover life out there somewhere. For in the end, what greater scientific goal is there than determining whether or not we are alone in the Universe?

Further Reading: UofWarwick, RAS, MNRAS

Posted on by Matt Williams

Astronomers Find Comets Orbiting a Star 800 Light-Years Away

An artist’s conception of a view from within the Exocomet system KIC 3542116.. Credit: Danielle Futselaar

In the past thirty years, thousands of extra-solar planets have been discovered beyond our Solar System. For the most part, they have been detected by the Kepler Space Telescope using a technique called Transit Photometry. For this method, astronomers measure periodic dips in a star’s brightness – which are the result of planets passing in front of them relative to an observer – to confirm the presence of planets.

Thanks to a new research effort conducted by a team of professional and amateur astronomers, something much smaller than planets were recently detected orbiting a distant star. According to a new study published by the research team, six exocomets were observed orbiting around KIC 3542116, a spectral type F2V star located 800 light years from Earth. These comets are the smallest objects to date detecting the Transit Photometry method.

The study which details their findings, titled “Likely Transiting Exocomets Detected by Kepler“, recently appeared in the Monthly Notices of the Royal Astronomical Society. Led by Saul Rappaport of MIT’s Kavli Institute for Astrophysics and Space Research, the team also consisted of amateur astronomers, members of the Harvard-Smithsonian Center for Astrophysics (CfA), the University of Texas, Northeastern University, and NASA’s Ames Research Center.

Artist’s impression of an orbiting swarm of dusty comet fragments around Tabby’s Star. Credit: NASA/JPL-Caltech

This is the first time that Transit Photometry has been used to detect object as small as comets. These comets were balls of ice and dust – comparable in size to Halley’s Comet – that were found to be traveling at speeds of about 160,934 km/h (100,000 mph) before they vaporized. The researchers were able to detect them by picking out their tails, the clouds of dust and gas that form when comets get closer to their star and begin to sublimate.

This was no easy task, since the tails managed to obscure only about a tenth of 1% of the star’s light. As Saul Rappaport, who is also the professor emeritus of physics at the Kavli Institute for Astrophysics and Space Research, explained in an MIT press release:

“It’s amazing that something several orders of magnitude smaller than the Earth can be detected just by the fact that it’s emitting a lot of debris. It’s pretty impressive to be able to see something so small, so far away.”

Credit for the original detection goes to Thomas Jacobs, an amateur astronomer who lives in Bellevue, Washington, and is a member of Planet Hunters. This citizen scientist project was first established by Yale University and consists of amateur astronomers who dedicated their time to the search for exoplanets. Members are given access to data from the Kepler Space Telescope in the hopes that they would notice things that computer algorithms might miss.

NASA’s Kepler space telescope was the first agency mission capable of detecting Earth-size planets. Credit: NASA/Wendy Stenzel

Back in January, Jacobs began scanning four years of data obtained during Kepler‘s main mission. During this phase, which lasted from 2009 to 2013, Kepler scanned over 200,000 stars and conducted measurements of their light curves. After five months of sifting through the data (on March 18th), he noticed several curious light patterns amid background noise coming from KIC 3542116. As Jacobs said:

“Looking for objects of interest in the Kepler data requires patience, persistence, and perseverance. For me it is a form of treasure hunting, knowing that there is an interesting event waiting to be discovered. It is all about exploration and being on the hunt where few have traveled before.”

Specifically, Jacobs was searching for signs of single transits, which are not like those that are caused by planets orbiting a star (i.e. periodic). While looking at KIC 3542116, he noticed three single transits, and then alerted Rappaport and Andrew Vanderburg, as astrophysicist at University of Texas and member of the CfA. Jacobs had worked with both men in the past, and wanted their opinion on these findings.

As Rapport recalled, the process of interpreting the data was challenging, but rewarding. Initially, they noted that the lightcurves did not resemble those caused by planetary transits, which are characterized by a sudden and sharp drop in light, followed by a sharp rise. In time, Rapport noted the asymmetry in the three lightcurves resembled those of disintegrated planets, which they had observed before.

Artist’s impression of the Epsilon Eridani system, showing Epsilon Eridani b (a Jupiter-mass planet) and a series of asteroid belts and comets. Credit: NASA/SOFIA/Lynette Cook.

“We sat on this for a month, because we didn’t know what it was — planet transits don’t look like this,” said Rappaport. “Then it occurred to me that, ‘Hey, these look like something we’ve seen before’… We thought, the only kind of body that could do the same thing and not repeat is one that probably gets destroyed in the end. The only thing that fits the bill, and has a small enough mass to get destroyed, is a comet.”

Based on their calculations, which indicated that each comet blocked out about one-tenth of 1% of the star’s light, the research team concluded that the comet likely disintegrated entirely, creating a dust trail that was sufficient to block out light for several months before it disappeared. After conducting additional observations, they also noted three more transits in the same time period that were similar to the ones noticed by Jacobs.

The fact that these six exocomets appear to have transited very close to their star in the past four years raises some interesting questions, and answering them could have drastic implications for extra-solar research. It could also advance our understanding of our own Solar System. As Vanderburg explained:

“Why are there so many comets in the inner parts of these solar systems? Is this an extreme bombardment era in these systems? That was a really important part of our own solar system formation and may have brought water to Earth. Maybe studying exocomets and figuring out why they are found around this type of star… could give us some insight into how bombardment happens in other solar systems.”

This artist’s conception illustrates a storm of comets around a star near our own. Credit: NASA/JPL-Caltech

Between 4.1 and 3.8 billion years ago, the Solar System also experienced a period of intense comet activity known as the Late Heavy Bombardment. During this time, asteroids and comets are believed to have impacted bodies in the inner Solar System on a regular basis. Interestingly, this period of heavy bombardment is believed to be what was responsible for the distribution of water to Earth and the other terrestrial planets.

As noted, KIC 3542116 belongs to the spectral type F2V, a yellow-white class of star that is typically 1 to 1.4 times as massive as our Sun and quite bright. Since it is comparable in size and mass to our Sun, it is possible that the bombardment period it is experiencing is similar to what the Solar System went through. Watching it unfold could therefore tell us much about how similar activity influenced the evolution of our Solar System billions of years ago.

In addition to the study’s significance to the study of astrophysics and astronomy, it also demonstrates the important role citizen scientists play today. Were it not for the tireless work performed by Jacobs, who sifts through Kepler data between working his day job and on the weekends, this discovery would not have been possible.

“I could name 10 types of things these people have found in the Kepler data that algorithms could not find, because of the pattern-recognition capability in the human eye,” said Rappaport. “You could now write a computer algorithm to find this kind of comet shape. But they were missed in earlier searches. They were deep enough but didn’t have the right shape that was programmed into algorithms. I think it’s fair to say this would never have been found by any algorithm.”

In the future, the research team expects that the deployment Transiting Exoplanet Survey Satellite (TESS) – which will be led by MIT – will continue to conduct the type of research performed by Kepler.

Further Reading: MIT, MNRAS

Posted on by Matt Williams

Project Blue: Building a Space Telescope that Could Directly Observe Planets Around Alpha Centauri

Artist's concept of the Project Blue space telescope, which the organization hopes to use to spot exoplanets in Alpha Centauri beginning in 2020. Credit: projectblue.org

In the past few decades, thousands of exoplanets have been discovered in neighboring star systems. In fact, as of October 1st, 2017, some 3,671 exoplanets have been confirmed in 2,751 systems, with 616 systems having more than one planet. Unfortunately, the vast majority of these have been detected using indirect means, ranging from Gravitational Microlensing to Transit Photometry and the Radial Velocity Method.

What’s more, we have been unable to study these planets up close because the necessary instruments do not yet exist. Project Blue, a consortium of scientists, universities and institutions, is looking to change that. Recently, they launched a crowdfunding campaign through Indiegogo to finance the development of a space telescope that will start looking for exoplanets in the Alpha Centauri system by 2021.

In addition to its commercial and academic partners, Project Blue is a collaborative effort between the BoldlyGo Institute, Mission Centaur, the SETI Institute, and the University of Massachusetts Lowell. It is steered by a Science & Technology Advisory Committee (STAC) composed of science and technology experts who are dedicated to space exploration and the search for life in our Universe.

Artist’s impression of a planet orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. Credit: ESO

To accomplish their goal of directly studying exoplanets, Project Blue is seeking to leverage recent changes in space exploration, which include improved instruments and methodology, the rate at which exoplanet have been discovered in recent years, and increased collaboration between the private and public sector. As SETI Institute President and CEO Bill Diamond explained in a recent SETI press statement:

“Project Blue builds on recent research in seeking to show that Earth is not alone in the cosmos as a planet capable of supporting life, and wouldn’t it be amazing to see such a planet in our nearest neighboring star system? This is the fundamental reason we search.”

As noted, virtually all exoplanet discoveries that have been made in the past few decades were done using indirect methods – the most popular of which is Transit Photometery. This method is what the Kepler and K2 missions relied on to detect a total of 5,017 exoplanet candidates and confirm the existence of 2,470 exoplanets (30 of which were found to orbit within their star’s habitable zone).

This method consists of astronomers monitoring distant stars for periodic dips in brightness, which are caused by a planet transiting in front of the star.  By measuring these dips, scientists are able to determine the size of planets in that system. Another popular technique is the Radial Velocity (or Doppler) Method, which measures changes in a star’s position relative to the observer to determine how massive its system of planets are.

Project Blue’s mission concept, showing the telescope, its launch and deployment. Credit: projectblue.org

These and other methods (alone or in combination) have allowed for the many discoveries that have been made to take place. But so far, no exoplanets have been directly imaged, which is due to the cancelling effect stars have on optical instruments. Basically, astronomers have been unable to spot the light being reflected off of an exoplanet’s atmosphere because the light coming from the star is up to ten billion times brighter.

The challenge has thus become how to go about blocking this light so that the planets themselves can become visible. One proposed solution to this problem is NASA’s Starshade concept, a giant space structure that would be deployed into orbit alongside a space telescope (most likely, the James Webb Space Telescope). Once in orbit, this structure would deploy its flower-shaped foils to block the glare of distant stars, thus allowing the JWST and other instruments to image exoplanets directly.

But since Alpha Centauri is a binary system (or trinary, if you count Proxima Centauri), being able to directly image any planets around them is even more complicated. To address this, Project Blue has developed plans for a telescope that will be able to suppress light from both Alpha Centauri A and B, while simultaneously taking images of any planets that orbit them. It’s specialized starlight suppression system consists of three components.

First, there is the coronagraph, an instrument which will rely on multiple techniques to block starlight. Second, there’s the deformable mirror, low-order wavefront sensors, and software control algorithms that will manipulate incoming light. Last, there is the post-processing method known as Orbital Differntial Imaging (ODI), which will allow the Project Blue scientist to enhance the contrast of the images taken.

Project Blue’s mission timeline, which woudl commence at the end of the decade and run for six years. Credit: projectblue.org

Given its proximity to Earth, the Alpha Centauri system is the natural choice for conducting such a project. Back in 2012, an exoplanet candidate – Alpha Centauri Bb – was announced. However, in 2015, further analysis indicated that the signal detected was an artefact in the data. In March of 2015, a second possible exoplanet (Alpha Centauri Bc) was announced, but its existence has also come to be questioned.

With an instrument capable of directly imaging this system, the existence of any exoplanets could finally be confirmed (or ruled out). As Franck Marchis – the Senior Planetary Astronomer at the SETI Institute and Project Blue Science Operation Lead – said of the Project:

“Project Blue is an ambitious space mission, designed to answer to a fundamental question, but surprisingly the technology to collect an image of a “Pale Blue Dot” around Alpha Centauri stars is there. The technology that we will use to reach to detect a planet 1 to 10 billion times fainter than its star has been tested extensively in lab, and we are now ready to design a space-telescope with this instrument.”

If Project Blue meets its crowdfunding goals, the organization intends to deploy the telescope into Near-Earth Orbit (NEO) by 2021. The telescope will then spend the next two years observing the Alpha Centauri system with its corongraphic camera. All told, between the development of the instrument and the end of its observation campaign, the mission will last six years, a relatively short run for an astronomical mission.

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org

However, the potential payoff for this mission would be incredibly profound. By directly imaging another planet in the closest star system to our own, Project Blue could gather vital data that would indicate if any planets there are habitable. For years, astronomers have attempted to learn more about the potential habitability of exoplanets by examining the spectral data produced by light passing through their atmospheres.

However, this process has been limited to massive gas giants that orbit close to their parent stars (i.e. “Super-Jupiters”). While various models have been proposed to place constraints on the atmospheres of rocky planets that orbit within a star’s habitable zone, none have been studied directly. Therefore, if it should prove to be successful, Project Blue would allow for some of the greatest scientific finds in history.

What’s more, it would provide information that could a long way towards informing a future mission to Alpha Centauri, such as Breakthrough Starshot. This proposed mission calls for the use of a large laser array to propel a lightsail-driven nanocraft up to relativistic speeds (20% the speed of light). At this rate, the craft would reach Alpha Centauri within 20 years time and be able to transmit data back using a series of tiny cameras, sensors and antennae.

As the name would suggest, Project Blue hopes to capture the first images of a “Pale Blue Dot” that orbits another star. This is a reference to the photograph of Earth that was taken by the Voyager 1 probe on February 19th, 1990, after the probe concluded its primary mission and was getting ready to leave the Solar System. The photos were taken at the request of famed astronomer and science communicator Carl Sagan.

The “Pale Blue Dot” photograph taken by the Voyager 1 probe. Credit: NASA/JPL

When looking at the photographs, Sagan famously said: “Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.” Thereafter, the name “Pale Blue Dot” came to be synonymous with Earth and capture the sense of awe and wonder that the Voyage 1 photographs evoked.

More recently, other “Pale Blue Dot” photographs have been snapped by missions like the Cassini orbiter. While photographing Saturn and its system of rings in the summer of 2013, Cassini managed to capture images that showed Earth in the background. Given the distance, Earth once again appeared as a small point of light against the darkness of space.

Beyond relying on crowdfunding and the participation of multiple non-profit organizations, this low-cost mission also seeks to capitalize on a growing trend in space exploration, – which is open participation and collaborations between scientific institutions and citizen scientists. This is one of the primary purposes behind Project Blue, which is to engage the public and educate them about the importance of space exploration.

As Jon Morse, the CEO of the BoldlyGo Institute, explained:

“The future of space exploration holds boundless potential for answering profound questions about our existence and destiny. Space-based science is a cornerstone for investigating such questions. Project Blue seeks to engage a global community in a mission to search for habitable planets and life beyond Earth.”

As of the penning of this article, Project Blue has managed to raise $125,561 USD of their goal of $175,000. For those interesting in backing this project, Project Blue’s Indiegogo campaign will remain open for another 11 days. And be sure to check out their promotional video as well:

Further Reading: SETI, Project Blue, Indiegogo