August 9, 2017August 9, 2017 by Matt Williams

What are Gas Giants?

The outer planets of our Solar System at approximately relative sizes. From left, Jupiter, Saturn, Uranus and Neptune. Credit: Lunar and Planetary Institute

Between the planets of the inner and outer Solar System, there are some stark differences. The planets that resides closer to the Sun are terrestrial (i.e. rocky) in nature, meaning that they are composed of silicate minerals and metals. Beyond the Asteroid Belt, however, the planets are predominantly composed of gases, and are much larger than their terrestrial peers.

This is why astronomers use the term “gas giants” when referring to the planets of the outer Solar System. The more we’ve come to know about these four planets, the more we’ve come to understand that no two gas giants are exactly alike. In addition, ongoing studies of planets beyond our Solar System (aka. “extra-solar planets“) has shown that there are many types of gas giants that do not conform to Solar examples. So what exactly is a “gas giant”?

Definition and Classification:

By definition, a gas giant is a planet that is primarily composed of hydrogen and helium. The name was originally coined in 1952 by James Blish, a science fiction writer who used the term to refer to all giant planets. In truth, the term is something of a misnomer, since these elements largely take a liquid and solid form within a gas giant, as a result of the extreme pressure conditions that exist within the interior.

*The four gas giants of the Solar System (from right to left): Jupiter, Saturn, Uranus and Neptune. Credit: NASA/JPL*

What’s more, gas giants are also thought to have large concentrations of metal and silicate material in their cores. Nevertheless, the term has remained in popular usage for decades and refers to all planets – be they Solar or extra-solar in nature – that are composed mainly of gases. It is also in keeping with the practice of planetary scientists, who use a shorthand – i.e. “rock”, “gas”, and “ice” – to classify planets based on the most common element within them.

Hence the difference between Jupiter and Saturn on the one and, and Uranus and Neptune on the other. Due to the high concentrations of volatiles (such as water, methane and ammonia) within the latter two – which planetary scientists classify as “ices” – these two giant planets are often called “ice giants”. But since they are composed mainly of hydrogen and helium, they are still considered gas giants alongside Jupiter and Saturn.

Classification:

Today, Gas giants are divided into five classes, based on the classification scheme proposed by David Sudarki (et al.) in a 2000 study. Titled “Albedo and Reflection Spectra of Extrasolar Giant Planets“, Sudarsky and his colleagues designated five different types of gas giant based on their appearances and albedo, and how this is affected by their respective distances from their star.

Class I: Ammonia Clouds – this class applies to gas giants whose appearances are dominated by ammonia clouds, and which are found in the outer regions of a planetary system. In other words, it applies only to planets that are beyond the “Frost Line”, the distance in a solar nebula from the central protostar where volatile compounds – i.e. water, ammonia, methane, carbon dioxide, carbon monoxide – condense into solid ice grains.

*These cutaways illustrate interior models of the giant planets. Jupiter is shown with a rocky core overlaid by a deep layer of metallic hydrogen. Credit: NASA/JPL*

Class II: Water Clouds – this applies to planets that have average temperatures typically below 250 K (-23 °C; -9 °F), and are therefore too warm to form ammonia clouds. Instead, these gas giants have clouds that are formed from condensed water vapor. Since water is more reflective than ammonia, Class II gas giants have higher albedos.

Class III: Cloudless – this class applies to gas giants that are generally warmer – 350 K (80 °C; 170 °F) to 800 K ( 530 °C; 980 °F) – and do not form cloud cover because they lack the necessary chemicals. These planets have low albedos since they do not reflect as much light into space. These bodies would also appear like clear blue globes because of the way methane in their atmospheres absorbs light (like Uranus and Neptune).

Class IV: Alkali Metals – this class of planets experience temperatures in excess of 900 K (627 °C; 1160 °F), at which point Carbon Monoxide becomes the dominant carbon-carrying molecule in their atmospheres (rather than methane). The abundance of alkali metals also increases substantially, and cloud decks of silicates and metals form deep in their atmospheres. Planets belonging to Class IV and V are referred to as “Hot Jupiters”.

Class V: Silicate Clouds – this applies to the hottest of gas giants, with temperatures above 1400 K (1100 °C; 2100 °F), or cooler planets with lower gravity than Jupiter. For these gas giants, the silicate and iron cloud decks are believed to be high up in the atmosphere. In the case of the former, such gas giants are likely to glow red from thermal radiation and reflected light.

Artist’s concept of “hot Jupiter” exoplanet, a gas giant that orbits very close to its star. Credit: NASA/JPL-Caltech)

Exoplanets:

The study of exoplanets has also revealed a wealth of other types of gas giants that are more massive than the Solar counterparts (aka. Super-Jupiters) as well as many that are comparable in size. Other discoveries have been a fraction of the size of their solar counterparts, while some have been so massive that they are just shy of becoming a star. However, given their distance from Earth, their spectra and albedo have cannot always be accurately measured.

As such, exoplanet-hunters tend to designate extra-solar gas giants based on their apparent sizes and distances from their stars. In the case of the former, they are often referred to as “Super-Jupiters”, Jupiter-sized, and Neptune-sized. To date, these types of exoplanet account for the majority of discoveries made by Kepler and other missions, since their larger sizes and greater distances from their stars makes them the easiest to detect.

In terms of their respective distances from their sun, exoplanet-hunters divide extra-solar gas giants into two categories: “cold gas giants” and “hot Jupiters”. Typically, cold hydrogen-rich gas giants are more massive than Jupiter but less than about 1.6 Jupiter masses, and will only be slightly larger in volume than Jupiter. For masses above this, gravity will cause the planets to shrink.

Exoplanet surveys have also turned up a class of planet known as “gas dwarfs”, which applies to hydrogen planets that are not as large as the gas giants of the Solar System. These stars have been observed to orbit close to their respective stars, causing them to lose atmospheric mass faster than planets that orbit at greater distances.

For gas giants that occupy the mass range between 13 to 75-80 Jupiter masses, the term “brown dwarf” is used. This designation is reserved for the largest of planetary/substellar objects; in other words, objects that are incredibly large, but not quite massive enough to undergo nuclear fusion in their core and become a star. Below this range are sub-brown dwarfs, while anything above are known as the lightest red dwarf (M9 V) stars.

*An artist’s conception of a T-type brown dwarf. Credit: Tyrogthekreeper/Wikimedia Commons*

Like all things astronomical in nature, gas giants are diverse, complex, and immensely fascinating. Between missions that seek to examine the gas giants of our Solar System directly to increasingly sophisticated surveys of distant planets, our knowledge of these mysterious objects continues to grow. And with that, so is our understanding of how star systems form and evolve.

We have written many interesting articles about gas giants here at Universe Today. Here’s The Planet Jupiter, The Planet Saturn, The Planet Uranus, The Planet Neptune, What are the Jovian Planets?, What are the Outer Planets of the Solar System?, What’s Inside a Gas Giant?, and Which Planets Have Rings?

For more information, check out NASA’s Solar System Exploration.

Astronomy Cast also has some great episodes on the subject. Here’s Episode 56: Jupiter to get you started!

Sources:

August 8, 2017 by Matt Williams

Standford Team Creates mDOT, a Mini-Starshade for Exoplanet Research

The new DARKNESS camera developed by an international team of researchers will allow astronomers to directly study nearby exoplanets. Credit: Stanford/SRL

NASA has turned a lot of heads in recent years thanks to its New Worlds Mission concept – aka. Starshade. Consisting of a giant flower-shaped occulter, this proposed spacecraft is intended to be deployed alongside a space telescope (most likely the James Webb Space Telescope). It will then block the glare of distant stars, creating an artificial eclipse to make it easier to detect and study planets orbiting them.

The only problem is, this concept is expected to cost a pretty penny – an estimated $750 million to $3 billion at this point! Hence why Stanford Professor Simone D’Amico (with the help of exoplanet expert Bruce Macintosh) is proposing a scaled down version of the concept to demonstrate its effectiveness. Known as mDot, this occulter will do the same job, but at a fraction of the cost.

The purpose behind an occulter is simple. When hunting for exoplanets, astronomers are forced to rely predominantly on indirected methods – the most common being the Transit Method. This involves monitoring stars for dips in luminosity, which are attributed to planets passing between them and the observer. By measuring the rate and the frequency of these dips, astronomers are able to determine the sizes of exoplanets and their orbital periods.

As Simone D’Amico, whose lab is working on this eclipsing system, explained in a Stanford University press statement:

“With indirect measurements, you can detect objects near a star and figure out their orbit period and distance from the star. This is all important information, but with direct observation you could characterize the chemical composition of the planet and potentially observe signs of biological activity – life.”

However, this method also suffers from a substantial rate of false positives and generally requires that part of the planet’s orbit intersect a line-of-sight between the host star and Earth. Studying the exoplanets themselves is also quite difficult, since the light coming from the star is likely to be several billion times brighter than the light being reflected off the planet.

The ability to study this reflected light is of particular interest, since it would yield valuable data about the exoplanets’ atmospheres. As such, several key technologies are being developed to block out the interfering light of stars. A spacecraft equipped with an occulter is one such technology. Paired with a space telescope, this spacecraft would create an artificial eclipse in front of the star so objects around it (i.e. exoplanets) can be clearly seen.

But in addition to the significant cost of building one, there is also the issue of size and deployment. For such a mission to work, the occulter itself would need to be about the size of a baseball diamond – 27.5 meters (90 feet) in diameter. It would also need to be separated from the telescope by a distance equal to multiple Earth diameters and would have to be deployed beyond Earth’s orbit. All of this adds up to a rather pricey mission!

Artist’s impression of the mDOT system. Much like the moon in a solar eclipse, one spacecraft would block the light from the star, allowing the other to observe objects near that star. Credit: Space Rendezvous Laboratory/Stanford University

As such, D’Amico – an assistant professor and the head of the Space Rendezvous Laboratory (SRL) at Stanford – and and Bruce Macintosh (a Stanford professor of physics) teamed up to create a smaller version called the Miniaturized Distributed Occulter/Telescope (mDOT). The primary purpose of mDOT is to provide a low-cost flight demonstration of the technology, in the hopes of increasing confidence in a full-scale mission.

As Adam Koenig, a graduate student with the SRL, explained:

“So far, there has been no mission flown with the degree of sophistication that would be required for one of these exoplanet imaging observatories. When you’re asking headquarters for a few billion dollars to do something like this, it would be ideal to be able to say that we’ve already flown all of this before. This one is just bigger.”

Consisting of two parts, the mDOT system takes advantage of recent developments in miniaturization and small satellite (smallsat) technology. The first is a 100-kg microsatellite that is equipped with a 3-meter diameter starshade. The second is a 10-kg nanosatellite that carries a telescope measuring 10 cm (3.937 in) in diameter. Both components will be deployed in high Earth orbit with a nominal separation of less than 1,000 kilometers (621 mi).

With the help of colleagues from the SRL, the shape of mDOT’s starshade was reformulated to fit the constraints of a much smaller spacecraft. As Koenig explained, this scaled down and specially-designed starshade will be able to do the same job as the large-scale, flower-shaped version – and on a budget!

Simone D’Amico’s Space Rendezvous Laboratory, pictured inside the room where they test space navigation in highly realistic illumination conditions. Credit: Space Rendezvous Laboratory/Stanford University

“With this special geometric shape, you can get the light diffracting around the starshade to cancel itself out,” he said. “Then, you get a very, very deep shadow right in the center. The shadow is deep enough that the light from the star won’t interfere with observations of a nearby planet.”

However, since the shadow created by mDOT’s starshade is only tens of centimeters in diameter, the nanosatellite will have do some careful maneuvering to stay within it. For this purpose, D’Amico and the SRL also designed an autonomous system for the nanosatellite, which would allow it to conduct formation maneuvers with the starshade, break formation when needed, and rendezvous with it again later.

An unfortunate limitation to the technology is the fact that it won’t be able to resolve Earth-like planets. Especially where M-type (red dwarf) stars are concerned, these planets are likely to orbit too close to their parent stars to be observed clearly. However, it will be able to resolve Jupiter-sized gas giants and help characterize exozodiacal dust concentrations around nearby stars – both of which are priorities for NASA.

In the meantime, D’Amico and his colleagues will be using the Testbed for Rendezvous and Optical Navigation (TRON) to test their mDOT concept. This facility was specially-built by D’Amico to replicate the types of complex and unique illumination conditions that are encountered by sensors in space. In the coming years, he and his team will be working to ensure that the system works before creating an eventual prototype.

*Artist’s concept of the prototype starshade, a giant structure designed to block the glare of stars so that future space telescopes can take pictures of planets. Credit: NASA/JPL*

As D’Amico said of the work he and his colleagues at the SNL perform:

“I’m enthusiastic about my research program at Stanford because we’re tackling important challenges. I want to help answer fundamental questions and if you look in all current direction of space science and exploration – whether we’re trying to observe exoplanets, learn about the evolution of the universe, assemble structures in space or understand our planet – satellite formation-flying is the key enabler.”

Other projects that D’Amico and the SNL are currently engaged in include developing larger formations of tiny spacecraft (aka. “swarm satellites”). In the past, D’Amico has also collaborated with NASA on such projects as GRACE – a mission that mapped variations in Earth’s gravity field as part of the NASA Earth System Science Pathfinder (ESSP) program – and TanDEM-X, an SEA-sponsored mission which yielded 3D maps of Earth.

These and other projects which seek to leverage miniaturization for the sake of space exploration promise a new era of lower costs and greater accessibility. With applications ranging from swarms of tiny research and communications satellites to nanocraft capable of making the journey to Alpha Centauri at relativistic speeds (Breakthrough Starshot), the future of space looks pretty promising!

Be sure to check out this video of the TRON facility too, courtesy of Standford University:

Further Reading: Standford University

July 20, 2017April 14, 2020 by Matt Williams

Advanced Civilizations Could Build a Galactic Internet with Planetary Transits

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

Decades after Enrico Fermi’s uttered his famous words – “Where is everybody?” – the Paradox that bears his name still haunts us. Despite repeated attempts to locate radio signals coming from space and our ongoing efforts to find visible indications of alien civilizations in distant star systems, the search extra-terrestrial intelligence (SETI) has yet to produce anything substantive.

June 20, 2017 by Matt Williams

NASA Announces 10, That’s Right 10! New Planets in Their Star’s Habitable Zone

Artist's impression of rocky exoplanets orbiting Gliese 832, a red dwarf star just 16 light-years from Earth. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).

The Kepler space telescope is surely the gift that keeps on giving. After being deployed in 2009, it went on to detect a total of 2,335 confirmed exoplanets and 582 multi-planet systems. Even after two of its reaction wheels failed, it carried on with its K2 mission, which has discovered an additional 520 candidates, 148 of which have been confirmed. And with yet another extension, which will last beyond 2018, it shows no signs of stopping!

In the most recent catalog to be released by the Kepler mission, an additional 219 new planet candidates have been added to its database. More significantly, 10 of these planets were found to be terrestrial (i.e. rocky), of comparable in size to Earth and orbited within their star’s habitable zone – the distance where surface temperatures would be warm enough to support liquid water.

These findings were presented at a news conference on Monday, June 19th, at NASA’s Ames Research Center. Of all the catalogs of Kepler candidates that have been released to date, this one is the most comprehensive and detailed. The eighth in a series of Kepler exoplanet catalogs, this one is based on data that was obtained from the first four years of the mission and is the final catalog that covers the spacecraft’s observations of the Cygnus constellation.

Since 2014, Kepler has ceased looking at a set starfield in the Cygnus constellation and has been collecting data on its second mission – observing fields on the plane of the ecliptic of the Milky Way Galaxy. With the release of this catalog, there are now 4,034 planet candidates that have been identified by Kepler – of which 2,335 have been verified.

An important aspect of this catalog were the methods that were used for producing it, which were the most sophisticated to date. As with all planets detected by Kepler, the latest finds were all made using the transit method. This consists of monitoring stars for occasional dips in brightness, which is used to confirm the presence of planets transiting between the star and the observer.

To ensure that the detections in this latest catalog were real, the team relied on two approaches to eliminate false positives. This consisted of introducing simulated transits into the dataset to make sure the dips that Kepler detected were consistent with planets. Then, they added false signals to see how often the analysis mistook these for planet transits. From this, they were able to tell which planets were overcounted and which were undercounted.

This led to another exciting find, which was the indication that for all of the smaller exoplanets discovered by Kepler, most fell within one of two distinct groupings. Essentially, half the planets that we know of in the galaxy are either rocky in nature and larger than Earth (i.e. Super-Earth’s), or are gas giants that are comparable in size to Neptune (i.e. smaller gas giants).

This conclusion was reached by a team of researchers who used the W.M. Keck Observatory to measure the sizes of 1,300 stars in the Kepler field of view. From this, they were able to determine the radii of 2,000 Kepler planets with extreme precision, and found that there was a clear division between rocky, Earth-sized planets and gaseous planets smaller than Neptune – with few in between.

As Benjamin Fulton, a doctoral candidate at the University of Hawaii in Manoa and the lead author of this study, explained:

“We like to think of this study as classifying planets in the same way that biologists identify new species of animals. Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree.”

These results are sure to have drastic implications when it comes to knowing the frequency of different types of planets in our galaxy, as well as the study of planet formation. For instance, they noted that most rocky planets discovered by Kepler are up to 75% larger than Earth. And for reasons that are not yet clear, about half of them take on hydrogen and helium, which swells their size to the point that they become almost Neptune-sized.

*Histogram shows the number of planets per 100 stars as a function of planet size relative to Earth. Credits: NASA/Ames Research Center/CalTech/University of Hawaii/B.J. Fulton*

These findings could similarly have significant implications in the search for habitable planets and extra-terrestrial life. As Mario Perez, Kepler program scientist in the Astrophysics Division of NASA’s Science Mission Directorate, said during the presentation:

“The Kepler data set is unique, as it is the only one containing a population of these near Earth-analogs – planets with roughly the same size and orbit as Earth. Understanding their frequency in the galaxy will help inform the design of future NASA missions to directly image another Earth.”

From this information, scientists will be able to know with a greater degree of certainty just how many “Earth-like” planets exist within our galaxy. The most recent estimates place the number of planets in the Milky Way at about 100 billion. And based on this data, it would seem that many of these are similar in composition to Earth, albeit larger.

Combined with a statistical models of how many of these can be found within a circumstellar habitable zone, we should have a better idea of just how many potentially-life-bearing worlds are out there. If nothing else, this should simplify some of the math in the Drake Equation!

In the meantime, the Kepler space telescope will continue to make observations of nearby star systems in order to learn more about their exoplanets. This includes the TRAPPIST-1 system and its seven Earth-sized, rocky planets. Its a safe bet that before it is finally retired after 2018, it will have some more surprises in store for us!

Further Reading: NASA, NASA Kepler and K2

May 23, 2017June 20, 2020 by Matt Williams

We Have More Details on the Outermost Trappist-1 Planet!

An artist’s conception shows the planet TRAPPIST-1h. (NASA / JPL-Caltech)

The announcement of a seven-planet system around the star TRAPPIST-1 earlier this year set off a flurry of scientific interest. Not only was this one of the largest batches of planets to be discovered around a single star, the fact that all seven were shown to be terrestrial (rocky) in nature was highly encouraging. Even more encouraging was the fact that three of these planets were found to be orbiting with the star’s habitable zone.

Since that time, astronomers have been seeking to learn all they can about this system of planets. Aside from whether or not they have atmospheres, astronomers are also looking to learn more about their orbits and surface conditions. Thanks to the efforts of a University of Washington-led international team of astronomers, we now have an accurate idea of what conditions might be like on its outermost planet – TRAPPIST-1h.

Continue reading “We Have More Details on the Outermost Trappist-1 Planet!”

May 11, 2017May 11, 2017 by Evan Gough

Rise of the Super Telescopes: The Large UV Optical Infrared Surveyor (LUVOIR) aka Hubble 2.0

An artist's illustration of a 16 meter segmented mirror space telescope. There are no actual images of LUVOIR because the design hasn't been finalized yet. Image: Northrop Grumman Aerospace Systems & NASA/STScI

We humans have an insatiable hunger to understand the Universe. As Carl Sagan said, “Understanding is Ecstasy.” But to understand the Universe, we need better and better ways to observe it. And that means one thing: big, huge, enormous telescopes.

In this series we’ll look at the world’s upcoming Super Telescopes:

The Giant Magellan Telescope
The Overwhelmingly Large Telescope
The 30 Meter Telescope
The European Extremely Large Telescope
The Large Synoptic Survey Telescope
The James Webb Space Telescope
The Wide Field Infrared Survey Telescope
The Large UV Optical Infrared Surveyor (LUVOIR)

The Large UV Optical Infrared Surveyor Telescope (LUVOIR)

There’s a whole generation of people who grew up with images from the Hubble Space Telescope. Not just in magazines, but on the internet, and on YouTube. But within another generation or two, the Hubble itself will seem quaint, and watershed events of our times, like the Moon Landing, will be just black and white relics of an impossibly distant time. The next generations will be fed a steady diet of images and discoveries stemming from the Super Telescopes. And the LUVOIR will be front and centre among those ‘scopes.

If you haven’t yet heard of LUVOIR, it’s understandable; LUVOIR is in the early stages of being defined and designed. But LUVOIR represents the next generation of space telescopes, and its power will dwarf that of its predecessor, the Hubble.

LUVOIR (its temporary name) will be a space telescope, and it will do its work at the LaGrange 2 point, the same place that JWST will be. L2 is a natural location for space telescopes. At the heart of LUVOIR will be a 15m segmented primary mirror, much larger than the Hubble’s mirror, which is a mere 2.4m in diameter. In fact, LUVOIR will be so large that the Hubble could drive right through the hole in the center of it.

This not-to-scale image of the Solar System shows the LaGrangian points. LUVOIR will be located in a halo orbit at L2, along with the JWST. Image: By Xander89 - File:Lagrange_points2.svg, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=36697081 — This not-to-scale image of the Solar System shows the LaGrangian points. LUVOIR will be located in a halo orbit at L2, along with the JWST. Image: By Xander89 – File:Lagrange_points2.svg, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=36697081

While the James Webb Space Telescope will be in operation much sooner than LUVOIR, and will also do amazing work, it will observe primarily in the infrared. LUVOIR, as its name makes clear, will have a wider range of observation more like Hubble’s. It will see in the Ultra-Violet spectrum, the Optical spectrum, and the Infrared spectrum.

Recently, Brad Peterson spoke with Fraser Cain on a weekly Space Hangout, where he outlined the plans for the LUVOIR. Brad is a recently retired Professor of Astronomy at the Ohio State University, where served as chair of the Astronomy Department for 9 years. He is currently the chair of the Science Committee at NASA’s Advisory Council. Peterson is also a Distinguished Visiting Astronomer at the Space Telescope Science Institute, and the chair of the astronomy section of the American Association for the Advancement of Science.

Different designs for LUVOIR have been discussed, but as Peterson points out in the interview above, the plan seems to have settled on a 15m segmented mirror. A 15m mirror is larger than any optical light telescope we have on Earth, though the Thirty Meter Telescope and others will soon be larger.

“Segmented telescopes are the technology of today when it comes to ground-based telescopes. The JWST has taken that technology into space, and the LUVOIR will take segmented design one step further,” Peterson said. But the segmented design of LUVOIR differs from the JWST in several ways.

“…the LUVOIR will take segmented design one step further.” – Brad Peterson

JWST’s mirrors are made of beryllium and coated with gold. LUVOIR doesn’t require the same exotic design. But it has other requirements that will push the envelope of segmented telescope design. LUVOIR will have a huge array of CCD sensors that will require an enormous amount of electrical power to operate.

The Hubble Space Telescope on the left has a 2.4 meter mirror and the James Webb Space Telescope has a 6.5 meter mirror. LUVOIR, not shown, will dwarf them both with a massive 15 meter mirror. Image: NASA

LUVOIR will not be cryogenically cooled like the JWST is, because it’s not primarily an Infrared observatory. LUVOIR will also be designed to be serviceable. In fact, the US Congress now requires all space telescopes to be serviceable.

“Congress has mandated that all future large space telescopes must be serviceable if practicable.” – Brad Peterson

LUVOIR is designed to have a long life. It’s multiple instruments will be replaceable, and the hope is that it will last in space for 50 years. Whether it will be serviced by robots, or by astronauts, has not been determined. It may even be designed so that it could be brought back from L2 for servicing.

LUVOIR will contribute to the search for life on other worlds. A key requirement for LUVOIR is that it do spectroscopy on the atmospheres of distant planets. If you can do spectroscopy, then you can determine habitability, and, potentially, even if a planet is inhabited. This is the first main technological challenge for LUVOIR. This spectroscopy requires a powerful coronagraph to suppress the light of the stars that exoplanets orbit. LUVOIR’s coronagraph will excel at this, with a ratio of starlight suppression of 10 billion to 1. With this capability, LUVOIR should be able to do spectroscopy on the atmospheres of small, terrestrial exoplanets, rather than just larger gas giants.

“This telescope is going to be remarkable. The key science that it’s going to do be able to do is spectroscopy of planets in the habitable zone around nearby stars.” – Brad Peterson

This video from NASA’s Goddard Space Flight Center talks about the search for life, and how telescopes like LUVOIR will contribute to the search. At the 15:00 mark, Dr. Aki Roberge talks about how spectroscopy is key to finding signs of life on exoplanets, and how LUVOIR will take that search one step further.

Using spectroscopy to search for signs of life on exoplanets is just one of LUVOIR’s science goals.

LUVOIR is tasked with other challenges as well, including:

Mapping the distribution of dark matter in the Universe.
Isolating the source of gravitational waves.
Imaging circumstellar disks to see how planets form.
Identifying the first starlight in the Universe, studying early galaxies and finding the first black holes.
Studying surface features of worlds in our Solar System.

To tackle all these challenges, LUVOIR will have to clear other technological hurdles. One of them is the requirement for long exposure times. This puts enormous constraints on the stability of the scope, since its mirror is so large. A system of active supports for the mirror segments will help with stability. This is a trait it shares with other terrestrial Super Telescopes like the Thirty Meter Telescope and the European Extremely Large Telescope. Each of those had hundreds of segments which have to be controlled precisely with computers.

A circumstellar disk of debris around a matured stellar system may indicate that Earth-like planets lie within. LUVOIR will be able to see inside the disk to watch planets forming. Credit: NASA — A circumstellar disk of debris around a matured stellar system may indicate that Earth-like planets lie within. LUVOIR will be able to see inside the disk to watch planets forming.
Credit: NASA

LUVOIR’s construction, and how it will be placed in orbit are also significant considerations.

According to Peterson, LUVOIR could be launched on either of the heavy lift rockets being developed. The Falcon Heavy is being considered, as is the Space Launch System. The SLS Block 1B could do it, depending on the final size of LUVOIR.

“I’s going to require a heavy lift vehicle.” – Brad Peterson

Or, LUVOIR may never be launched into space. It could be assembled in space with pre-built components that are launched one at a time, just like the International Space Station. There are several advantages to that.

With assembly in space, the telescope doesn’t have to be built to withstand the tremendous force it takes to launch something into orbit. It also allows for testing when completed, before being sent to L2. Once the ‘scope was assembled and tested, a small ion propulsion engine could be used to power it to L2.

It’s possible that the infrastructure to construct LUVOIR in space will exist in a decade or two. NASA’s Deep Space Gateway in cis-lunar space is planned for the mid-20s. It would act as a staging point for deep-space missions, and for missions to the lunar surface.

LUVOIR is still in the early stages. The people behind it are designing it to meet as many of the science goals as they can, all within the technological constraints of our time. Planning has to start somewhere, and the plans presented by Brad Peterson represent the current thinking behind LUVOIR. But there’s still a lot of work to do.

“Typical time scale from selection to launch of a flagship mission is something like 20 years.” – Brad Peterson

As Peterson explains, LUVOIR will have to be chosen as NASA’s highest priority during the 2020 Decadal Survey. Once that occurs, then a couple more years are required to really flesh out the design of the mission. According to Peterson, “Typical time scale from selection to launch of a flagship mission is something like 20 years.” That gets us to a potential launch in the mid-2030s.

Along the way, LUVOIR will be given a more suitable name. James Webb, Hubble, Kepler and others have all had important missions named after them. Perhaps its Carl Sagan’s turn.

“The Carl Sagan Space Telescope” has a nice ring to it, doesn’t it?

April 28, 2017June 20, 2020 by Matt Williams

TRAPPIST-1 System Ideal For Life Swapping

Back in February of 2017, NASA announced the discovery of a seven-planet system orbiting a nearby star. This system, known as TRAPPIST-1, is of particular interest to astronomers because of the nature and orbits of the planets. Not only are all seven planets terrestrial in nature (i.e. rocky), but three of the seven have been confirmed to be within the star’s habitable zone (aka. “Goldilocks Zone”).

But beyond the chance that some of these planets could be inhabited, there is also the possibility that their proximity to each other could allow for life to be transferred between them. That is the possibility that a team of scientists from the University of Chicago sought to address in a new study. In the end, they concluded that bacteria and single-celled organisms could be hopping from planet to planet.

Continue reading “TRAPPIST-1 System Ideal For Life Swapping”

April 21, 2017April 28, 2017 by Evan Gough

Are Drylanders The Minority On Habitable Worlds?

Artist's depiction of a waterworld. A new study suggests that Earth is in a minority when it comes to planets, and that most habitable planets may be greater than 90% ocean. Credit: David A. Aguilar (CfA)

If we want to send spacecraft to exoplanets to search for life, we better get good at building submarines.

A new study by Dr. Fergus Simpson, of the Institute of Cosmos Sciences at the University of Barcelona, shows that our assumptions about exo-planets may be wrong. We kind of assume that exoplanets will have land masses, even though we don’t know that. Dr. Simpson’s study suggests that we can expect lots of oceans on the habitable worlds that we might discover. In fact, ocean coverage of 90% may be the norm.

At the heart of this study is something called ‘Bayesian Statistics’, or ‘Bayesian Probability.’

Normally, we give something a probability of occurring—in this case a habitable world with land masses—based on our data. And we’re more confident in our prediction if we have more data. So if we find 10 exoplanets, and 7 of them have significant land masses, we think there’s a 70% chance that future exoplanets will have significant land masses. If we find 100 exoplanets, and 70 of them have significant land masses, then we’re even more confident in our 70% prediction.

Is Earth in the range of normal when it comes to habitable planets? Or is it an outlier, with both large land masses, and large oceans? Image: Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC

But the problem is, even though we’ve discovered lots of exoplanets, we don’t know if they have land masses or not. We kind of assume they will, even though the masses of those planets is lower than we expect. This is where the Bayesian methods used in this study come in. They replace evidence with logic, sort of.

In Bayesian logic, probability is assigned to something based on the state of our knowledge and on reasonable expectations. In this case, is it reasonable to expect that habitable exoplanets will have significant landmasses in the same way that Earth does? Based on our current knowledge, it isn’t a reasonable expectation.

According to Dr. Simpson, the anthropic principle comes into play here. We just assume that Earth is some kind of standard for habitable worlds. But, as the study shows, that may not be the case.

“Based on the Earth’s ocean coverage of 71%, we find substantial evidence supporting the hypothesis that anthropic selection effects are at work.” – Dr. Fergus Simpson.

In fact, Earth may be a very finely balanced planet, where the amount of water is just right for there to be significant land masses. The size of the oceanic basins is in tune with the amount of water that Earth retains over time, which produces the continents that rise above the seas. Is there any reason to assume that other worlds will be as finely balanced?

Dr. Simpson says no, there isn’t. “A scenario in which the Earth holds less water than most other habitable planets would be consistent with results from simulations, and could help explain why some planets have been found to be a bit less dense than we expected.” says Simpson.

Simpson’s statistical model shows that oceans dominate other habitable worlds, with most of them being 90% water by surface area. In fact, Earth is very close to being a water world. The video shows what would happen to Earth’s continents if the amount of water increased. There is only a very narrow window in which Earth can have both large land masses, and large oceans.

Dr. Simpson suggests that the fine balance between land and water on Earth’s surface could be one reason we evolved here. This is based partly on his model, which shows that land masses will have larger deserts the smaller the oceans are. And deserts are not the most hospitable place for life, and neither are they biodiverse. Also, biodiversity on land is about 25 times greater than biodiversity in oceans, at least on Earth.

Simpson says that the fine balance between land mass and ocean coverage on Earth could be an important reason why we are here, and not somewhere else.

“Our understanding of the development of life may be far from complete, but it is not so dire that we must adhere to the conventional approximation that all habitable planets have an equal chance of hosting intelligent life,” Simpson concludes.

April 4, 2017April 28, 2017 by Matt Williams

Venus 2.0 Discovered In Our Own Back Yard

Artist's impression of Kepler-1649b, the "Venus-like" world orbiting an M-class star 219 light-years from Earth. Credit: Danielle Futselaar

It has been an exciting time for exoplanet research of late! Back in February, the world was astounded when astronomers from the European Southern Observatory (ESO) announced the discovery of seven planets in the TRAPPIST-1 system, all of which were comparable in size to Earth, and three of which were found to orbit within the star’s habitable zone.

And now, a team of international astronomers has announced the discovery of an extra-solar body that is similar to another terrestrial planet in our own Solar System. It’s known as Kepler-1649b, a planet that appears to be similar in size and density to Earth and is located in a star system just 219 light-years away. But in terms of its atmosphere, this planet appears to be decidedly more “Venus-like” (i.e. insanely hot!)

The team’s study, titled “Kepler-1649b: An Exo-Venus in the Solar Neighborhood“, was recently published in The Astronomical Journal. Led by Isabel Angelo – of the SETI Institute, NASA Ames Research Center, and UC Berkley – the team included researchers also from SETI and Ames, as well as the NASA Exoplanet Science Institute (NExScl), the Exoplanet Research Institute (iREx), the Center for Astrophysics Research, and other research institutions.

*Diagram comparing the Solar System to Kepler 69 and its system of exoplanets. Credit: NASA Ames/JPL-Caltech*

Needless to say, this discovery is a significant one, and the implications of it go beyond exoplanet research. For some time, astronomers have wondered how – given their similar sizes, densities, and the fact that they both orbit within the Sun’s habitable zone – that Earth could develop conditions favorable to life while Venus would become so hostile. As such, having a “Venus-like” planet that is close enough to study presents some exciting opportunities.

In the past, the Kepler mission has located several extra-solar planets that were similar in some ways to Venus. For instance, a few years ago, astronomers detected a Super-Earth – Kepler-69b, which appeared to measure 2.24 times the diameter of Earth – that was in a Venus-like orbit around its host the star. And then there was GJ 1132b, a Venus-like exoplanet candidate that is about 1.5 times the mass of Earth, and located just 39 light-years away.

In addition, dozens of smaller planet candidates have been discovered that astronomers think could have atmospheres similar to that of Venus. But in the case of Kepler-1649b, the team behind the discovery were able to determine that the planet had a sub-Earth radius (similar in size to Venus) and receives a similar amount of light (aka. incident flux) from its star as Venus does from Earth.

However, they also noted that the planet also differs from Venus in a few key ways – not the least of which are its orbital period and the type of star it orbits. As Dr. Angelo told Universe Today via email:

“The planet is similar to Venus in terms of it’s size and the amount of light it receives from it’s host star. This means it could potentially have surface temperatures similar to Venus as well. It differs from Venus because it orbits a star that is much smaller, cooler, and redder than our sun. It completes its orbit in just 9 days, which places it close to its host star and subjects it to potential factors that Venus does not experience, including exposure to magnetic radiation and tidal locking. Also, since it orbits a cooler star, it receives more lower-energy radiation from its host star than Earth receives from the Sun.”

*Artist’s impression of a Venus-like exoplanet orbiting close to its host star. Credit: CfA/Dana Berry*

In other words, while the planet appears to receive a comparable amount of light/heat from its host star, it is also subject to far more low-energy radiation. And as a potentially tidally-locked planet, the surface’s exposure to this radiation would be entirely disproportionate. And last, its proximity to its star means it would be subject to greater tidal forces than Venus – all of which has drastic implications for the planet’s geological activity and seasonal variations.

Despite these differences, Kepler-1649b remains the most Venus-like planet discovered to date. Looking to the future, it is hoped that next-generations instruments – like the Transiting Exoplanet Survey Satellite (TESS), the James Webb Telescope and the Gaia spacecraft – will allow for more detailed studies. From these, astronomers hope to more accurately determine the size and distance of the planet, as well as the temperature of its host star.

This information will, in turn, help us learn a great deal more about what goes into making a planet “habitable”. As Angelo explained:

“Understanding how hotter planets develop thick, Venus-like atmospheres that make them inhabitable will be important in constraining our definition of a ‘habitable zone’. This may become possible in the future when we develop instruments sensitive enough to determine chemical compositions of planet atmospheres (around dim stars) using a method called ‘transit spectroscopy’, which looks at the light from the host star that has passed through the planet’s atmosphere during transit.”

The development of such instruments will be especially useful given joust how many exoplanets are being detected around neighboring red dwarf stars. Given that they account for roughly 85% of stars in the Milky Way, knowing whether or not they can have habitable planets will certainly be of interest!

Further Reading: The Astronomical Journal

March 8, 2017May 2, 2017 by Evan Gough

Rise of the Super Telescopes: The James Webb Space Telescope

A full-scale model of the JWST went on a bit of a World Tour. Here it is in Munich, Germany. Image Credit: EADS Astrium

The Giant Magellan Telescope
The Overwhelmingly Large Telescope
The 30 Meter Telescope
The European Extremely Large Telescope
The Large Synoptic Survey Telescope
The James Webb Space Telescope
The Wide Field Infrared Survey Telescope

The James Webb Space Telescope

The James Webb Space Telescope“>James Webb Space Telescope (JWST, or the Webb) may be the most eagerly anticipated of the Super Telescopes. Maybe because it has endured a tortured path on its way to being built. Or maybe because it’s different than the other Super Telescopes, what with it being 1.5 million km (1 million miles) away from Earth once it’s operating.

The JWST will do its observing while in what’s called a halo orbit at L2, a sort of gravitationally neutral point 1.5 million km from Earth. Image: NASA/JWST

If you’ve been following the drama behind the Webb, you’ll know that cost overruns almost caused it to be cancelled. That would’ve been a real shame.

The JWST has been brewing since 1996, but has suffered some bumps along the road. That road and its bumps have been discussed elsewhere, so what follows is a brief rundown.

Initial estimates for the JWST were a $1.6 billion price tag and a launch date of 2011. But the costs ballooned, and there were other problems. This caused the House of Representatives in the US to move to cancel the project in 2011. However, later that same year, US Congress reversed the cancellation. Eventually, the final cost of the Webb came to $8.8 billion, with a launch date set for October, 2018. That means the JWST’s first light will be much sooner than the other Super Telescopes.

The business end of the James Webb Space Telescope is its 18-segment primary mirror. The gleaming, gold-coated beryllium mirror has a collecting area of 25 square meters. Image: NASA/Chris Gunn

The Webb was envisioned as a successor to the Hubble Space Telescope, which has been in operation since 1990. But the Hubble is in Low Earth Orbit, and has a primary mirror of 2.4 meters. The JWST will be located in orbit at the LaGrange 2 point, and its primary mirror will be 6.5 meters. The Hubble observes in the near ultraviolet, visible, and near infrared spectra, while the Webb will observe in long-wavelength (orange-red) visible light, through near-infrared to the mid-infrared. This has some important implications for the science yielded by the Webb.

The Webb’s Instruments

The James Webb is built around four instruments:

The Near-Infrared Camera (NIRCam)
The Near-Infrared Spectrograph (NIRSpec)
The Mid-Infrared Instrument(MIRI)
The Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS)

This image shows the wavelengths of the infrared spectrum that Webb’s instruments can observe. Image: NASA/JWST

The NIRCam is Webb’s primary imager. It will observe the formation of the earliest stars and galaxies, the population of stars in nearby galaxies, Kuiper Belt Objects, and young stars in the Milky Way. NIRCam is equipped with coronagraphs, which block out the light from bright objects in order to observe dimmer objects nearby.

NIRSpec will operate in a range from 0 to 5 microns. Its spectrograph will split the light into a spectrum. The resulting spectrum tells us about an objects, temperature, mass, and chemical composition. NIRSpec will observe 100 objects at once.

MIRI is a camera and a spectrograph. It will see the redshifted light of distant galaxies, newly forming stars, objects in the Kuiper Belt, and faint comets. MIRI’s camera will provide wide-field, broadband imaging that will rank up there with the astonishing images that Hubble has given us a steady diet of. The spectrograph will provide physical details of the distant objects it will observe.

The Fine Guidance Sensor part of FGS/NIRISS will give the Webb the precision required to yield high-quality images. NIRISS is a specialized instrument operating in three modes. It will investigate first light detection, exoplanet detection and characterization, and exoplanet transit spectroscopy.

The Science

The over-arching goal of the JWST, along with many other telescopes, is to understand the Universe and our origins. The Webb will investigate four broad themes:

First Light and Re-ionization: In the early stages of the Universe, there was no light. The Universe was opaque. Eventually, as it cooled, photons were able to travel more freely. Then, probably hundreds of millions of years after the Big Bang, the first light sources formed: stars. But we don’t know when, or what types of stars.
How Galaxies Assemble: We’re accustomed to seeing stunning images of the grand spiral galaxies that exist in the Universe today. But galaxies weren’t always like that. Early galaxies were often small and clumpy. How did they form into the shapes we see today?

The Birth of Stars and Protoplanetary Systems: The Webb’s keen eye will peer straight through clouds of dust that ‘scopes like the Hubble can’t see through. Those clouds of dust are where stars are forming, and their protoplanetary systems. What we see there will tell us a lot about the formation of our own Solar System, as well as shedding light on many other questions.

Planets and the Origins of Life: We now know that exoplanets are common. We’ve found thousands of them orbiting all types of stars. But we still know very little about them, like how common atmospheres are, and if the building blocks of life are common.

These are all obviously fascinating topics. But in our current times, one of them stands out among the others: Planets and the Origins of Life.

The recent discovery the TRAPPIST 1 system has people excited about possibly discovering life in another solar system. TRAPPIST 1 has 7 terrestrial planets, and 3 of them are in the habitable zone. It was huge news in February 2017. The buzz is still palpable, and people are eagerly awaiting more news about the system. That’s where the JWST comes in.

One big question around the TRAPPIST system is “Do the planets have atmospheres?” The Webb can help us answer this.

The NIRSpec instrument on JWST will be able to detect any atmospheres around the planets. Maybe more importantly, it will be able to investigate the atmospheres, and tell us about their composition. We will know if the atmospheres, if they exist, contain greenhouse gases. The Webb may also detect chemicals like ozone and methane, which are biosignatures and can tell us if life might be present on those planets.

You could say that if the James Webb were able to detect atmospheres on the TRAPPIST 1 planets, and confirm the existence of biosignature chemicals there, it will have done its job already. Even if it stopped working after that. That’s probably far-fetched. But still, the possibility is there.

Launch and Deployment

The science that the JWST will provide is extremely intriguing. But we’re not there yet. There’s still the matter of JWST’s launch, and it’s tricky deployment.

The JWST’s primary mirror is much larger than the Hubble’s. It’s 6.5 meters in diameter, versus 2.4 meters for the Hubble. The Hubble was no problem launching, despite being as large as a school bus. It was placed inside a space shuttle, and deployed by the Canadarm in low earth orbit. That won’t work for the James Webb.

This image shows the Hubble Space Telescope being held above the shuttle’s cargo bay by the Canadian-built Remote Manipulator System (RMS) arm, or Canadarm. A complex operation, but not as complex as JWST’s deployment. Image: NASA

The Webb has to be launched aboard a rocket to be sent on its way to L2, it’s eventual home. And in order to be launched aboard its rocket, it has to fit into a cargo space in the rocket’s nose. That means it has to be folded up.

The mirror, which is made up of 18 segments, is folded into three inside the rocket, and unfolded on its way to L2. The antennae and the solar cells also need to unfold.

Unlike the Hubble, the Webb needs to be kept extremely cool to do its work. It has a cryo-cooler to help with that, but it also has an enormous sunshade. This sunshade is five layers, and very large.

We need all of these components to deploy for the Webb to do its thing. And nothing like this has been tried before.

The Webb’s launch is only 7 months away. That’s really close, considering the project almost got cancelled. There’s a cornucopia of science to be done once it’s working.

But we’re not there yet, and we’ll have to go through the nerve-wracking launch and deployment before we can really get excited.