Artist’s conception of the binary system with three giant planets discovered in this study. One star hosts two planets and the other hosts the third. The system represents the smallest-separation binary in which both stars host planets that has ever been observed. Image courtesy of Robin Dienel/Carnegie.
The more we look, the more we see the great diversity in planetary systems around other stars. And curiously, planet hunters are finding that most star systems are very different from our own.
An example is a recently discovered system that is extremely crowded. It consists of a three giant planets in a binary (two stars) system. One star hosts two planets and the other hosts the third. The system represents the smallest-separation binary in which both stars host planets that has ever been observed.
“The probability of finding a system with all these components was extremely small,” said Johanna Teske from the Carnegie Institution for Science, “so these results will serve as an important benchmark for understanding planet formation, especially in binary systems.”
An illustration of this highly unusual system, which features the smallest-separation binary stars that both host planets ever discovered. Only six other metal-poor binary star systems with exoplanets have ever been found. Illustration courtesy of Timothy Rodigas/Carnegie.
Teske and her team said this busy system might help explain the influence that giant planets like Jupiter have over a solar system’s architecture.
“We are trying to figure out if giant planets like Jupiter often have long and, or eccentric orbits,” Teske explained. “If this is the case, it would be an important clue to figuring out the process by which our Solar System formed, and might help us understand where habitable planets are likely to be found.”
The twin stars are named HD 133131A and HD 133131B. The former hosts two Jupiter-sized worlds and the latter a planet with a mass at least 2.5 times Jupiter’s. All three planets have “eccentric” or highly elliptical orbits. So far no smaller, rocky worlds have been detected but the team said those type of planets could be part of the system, or may have been part of the system in the past.
The two stars themselves are separated by only 360 astronomical units (AU – the distance between the Earth and the Sun, approximately 150,000,000 km or 93,000,000 miles). This is extremely close for twin stars with detected planets orbiting the individual stars. The next-closest known binary star system with planets has stars about 1,000 AU apart.
The two stars are more like fraternal twins rather than identical because they have slight different chemical compositions. The team said this could indicate that one star swallowed some baby planets early in its life, changing its composition slightly. Or another option is that the gravitational forces of the detected giant planets may have had a strong effect on fully-formed small planets, flinging them in towards the star or out into space.
But both stars are “metal poor,” meaning that most of their mass is hydrogen and helium, as opposed to other elements like iron or oxygen. This is another curious thing about this system, as most stars that host giant planets are “metal rich.”
The system was found using the Planet Finder Spectrograph, an instrument developed by Carnegie scientists and mounted on the Magellan Clay Telescopes at Carnegie’s Las Campanas Observatory. This finding represents the first exoplanet detection made based solely on data from the. PFS is able to find large planets with long-duration orbits or orbits that are very elliptical rather than circular.
Artist's impression of a system of exoplanets orbiting a low mass, red dwarf star. Credit: NASA/JPL
Finding exoplanets is hard work. In addition to requiring seriously sophisticated instruments, it also takes teams of committed scientists; people willing to pour over volumes of data to find the evidence of distant worlds. Professor Kipping, an astronomer based at the Harvard-Smithsonian Center for Astrophysics, is one such person.
Within the astronomical community, Kipping is best known for his work with exomoons. But his research also extends to the study and characterization of exoplanets, which he pursues with his colleagues at the Cool Worlds Laboratory at Columbia University. And what has interested him most in recent years is finding exoplanets around our Sun’s closest neighbor – Proxima Centauri.
Kipping describes himself as a “modeler”, combining novel theoretical modeling with modern statistical data analysis techniques applied to observations. He is also the Principal Investigator (PI) of The Hunt for Exomoons with Kepler (HEK) project and a fellow at the Harvard College Observatory. For the past few years, he and his team have been taking the hunt for exoplanets to the local stellar neighborhood.
The inspiration for this search goes back to 2012, when Kipping was at a conference and heard the news about a series of exoplanets being discovery around Kepler 42 (aka. KOI-961). Using data from the Kepler mission, a team from the California Institute of Technology discovered three exoplanets orbiting this red dwarf star, which is located about 126 light years from Earth.
At the time, Kipping recalled how the author of the study – Professor Philip Steven Muirhead, now an associate professor at the Institute for Astrophysical Research at Boston University – commented that this star system looked a lot like our nearest red dwarf stars – Barnard’s Star and Proxima Centauri.
In addition, Kepler 42’s planets were easy to spot, given that their proximity to the star meant that they completed an orbital period in about a day. Since they pass regularly in front of their star, the odds of catching sight of them using the Transit Method were good.
As Prof. Kipping told Universe Today via email, this was the “ah-ha moment” that would inspire him to look at Proxima Centauri to see if it too had a system of planets:
“We were inspired by the discovery of planets transiting KOI-961 by Phil Muirhead and his team using the Kepler data. The star is very similar to Proxima, a late M-dwarf harboring three sub-Earth sized planets very close to the star. It made me realize that if that system was around Proxima, the transit probability would be 10% and the star’s small size would lead to quite detectable signals.”
The MOST satellite, a Canadian built space telescope. Credit: Canadian Space Agency
In essence, Kipping realized that if such a planetary system also existed around Proxima Centauri, a star with similar characteristics, then they would very easy to detect. After that, he and his team began attempting to book time with a space telescope. And by 2014-15, they had been given permission to use the Canadian Space Agency’s Microvariability and Oscillation of Stars (MOST) satellite.
Roughly the same size as a suitcase, the MOST satellite weighs only 54 kg and is equipped with an ultra-high definition telescope that measures just 15 cm in diameter. It is the first Canadian scientific satellite to be placed in orbit in 33 years, and was the first space telescope to be entirely designed and built in Canada.
Despite its size, MOST is ten times more sensitive than the Hubble Space Telescope. In addition, Kipping and his team knew that a mission to look for transiting exoplanets around Proxima Centauri would be too high-risk for something like Hubble. In fact, the CSA initially rejected their applications for this same reason.
“MOST initially denied us because they wanted to look at Alpha Centauri following the announcement by Dumusque et al. of a planet there,” said Kipping. “So understandably Proxima, for which no planets were known at the time, was not as high priority as Alpha Cen. We never even tried for Hubble time, it would be a huge ask to stare HST at a single star for months on end with just a a 10% chance for success.”
Artist’s impression of the Earth-like exoplanet discovered orbiting Alpha Centauri B iby the European Southern Observatory on October 17, 2012. Credit: ESO
By 2014 and 2015, they secured permission to use MOST and observed Proxima Centauri twice – in May of both years. From this, they acquired a month and half’s-worth of space-based photometry, which they are currently processing to look for transits. As Kipping explained, this was rather challenging, since Proxima Centauri is a very active star – subject to star flares.
“The star flares very frequently and prominently in our data,” he said. “Correcting for this effect has been one the major obstacles in our analysis. On the plus side, the rotational activity is fairly subdued. The other issue we have is that MOST orbits the Earth once every 100 minutes, so we get data gaps every time MOST goes behind the Earth.”
Their efforts to find exoplanets around Proxima Centauri are especially significant in light of the European Southern Observatory’s recent announcement about the discovery of a terrestrial exoplanet within Proxima Centauri’s habitable zone (Proxima b). But compared to the ESO’s Pale Red Dot project, Kipping and his team were relying on different methods.
“Essentially, we seek planets which have the right alignment to transit (or eclipse) across the face of the star, whereas radial velocities look for the wobbling motion of a star in response to the gravitational influence of an orbiting planet. Transits are always less likely to succeed for a given star, because we require the alignment to be just right. However, the payoff is that we can learn way more about the planet, including things like it’s size, density, atmosphere and presence of moons and rings.”
Artist’s impression of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Credit: ESO/M. Kornmesser
In the coming months and years, Kipping and his team may be called upon to follow up on the success of the ESO’s discovery. Having detected Proxima b using the Radial Velocity method, it now lies to astronomers to confirm the existence of this planet using another detection method.
In addition, much can be learned about a planet through the Transit Method, which would be helpful considering all the things we still don’t know about Proxima b. This includes information about its atmosphere, which the Transit Method is often able to reveal through spectroscopic measurements.
Suffice it to say, Kipping and his colleagues are quite excited by the announcement of Proxima b. As he put it:
“This is perhaps the most important exoplanet discovery in the last decade. It would be bitterly disappointing if Proxima b does not transit though, a planet which is paradoxically so close yet so far in terms of our ability to learn more about it. For us, transits would not just be the icing on the cake, serving merely as a confirmation signal – rather, transits open the door to learning the intimate secrets of Proxima, changing Proxima b from a single, anonymous data point to a rich world where each month we would hear about new discoveries of her nature and character.”
This coming September, Kipping will be joining the faculty at Columbia University, where he will continue in his hunt for exoplanets. One can only hope that those he and his colleagues find are also within reach!
Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO
The ESO’s recent announcement that they have discovered an exoplanet candidate orbiting Proxima Centauri – thus confirming weeks of speculation – has certainly been exciting news! Not only is this latest find the closest extra-solar planet to our own Solar System, but the ESO has also indicated that it is rocky, similar in size and mass to Earth, and orbits within the star’s habitable zone.
However, in the midst of this news, there has been some controversy regarding certain labels. For instance, when a planet like Proxima b is described as “Earth-like”, “habitable”, and/or “terrestrial“, there are naturally some questions as to what this really means. For each term, there are particular implications, which in turn beg for clarification.
For starters, to call a planet “Earth-like” generally means that it is similar in composition to Earth. This is where the term “terrestrial” really comes into play, as it refers to a rocky planet that is composed primarily of silicate rock and metals which are differentiated between a metal core and a silicate mantle and crust.
This applies to all planets in the inner Solar System, and is often used in order to differentiate rocky exoplanets from gas giants. This is important within the context of exoplanet hunting, as the majority of the 4,696 exoplanet candidates – of which 3,374 have been confirmed (as of August 18th, 2016) – have been gas giants.
What this does not mean, at least not automatically, is that the planet is habitable in the way Earth is. Simply being terrestrial in nature is not an indication that the planet has a suitable atmosphere or a warm enough climate to support the existence of liquid water or microbial life on its surface.
What’s more, Earth-like generally implies that a planet will be similar in mass and size to Earth. But this is not the same as composition, as many exoplanets that have been discovered have been labeled as “Earth-sized” or “Super-Earths” – i.e. planets with around 10 times the mass of Earth – based solely on their mass.
This term also distinguishes an exoplanet candidate from those that are 15 to 17 masses (which are often referred to as “Neptune-sized”) and those that have masses similar to, or many times greater than that of Jupiter (i.e. Super-Jupiters). In all these cases, size and mass are the qualifiers, not composition.
Ergo, finding a planet that is greater in size and mass than Earth, but significantly less than that of a gas giant, does not mean it is terrestrial. In fact, some scientists have recommended that the term “mini-Neptune” be used to describe planets that are more massive than Earth, but not necessarily composed of silicate minerals and metals.
And estimates of size and mass are not exactly metrics for determining whether or not a planet is “habitable”. This term is especially sticky when it comes to exoplanets. When scientists attach this word to extra-solar planets like Proxima b, Gliese 667 Cc, Kepler-452b, they are generally referring to the fact that the planet exists within its parent star’s “habitable zone” (aka. Goldilocks zone).
This term describes the region around a star where a planet will experience average surface temperatures that allow for liquid water to exist on its surface. For those planets that orbit too close to their star, they will experience intense heat that transforms surface water into hydrogen and oxygen – the former escaping into space, the latter combining with carbon to form CO².
This is what scientists believe happened to Venus, where thick clouds of CO² and water vapor triggered a runaway greenhouse effect. This turned Venus from a world that once had oceans into the hellish environment we know today, where temperatures are hot enough to melt lead, atmospheric density if off the charts, and sulfuric acid rains from its thick clouds.
Kepler-62f, an exoplanet that is about 40% larger than Earth. It’s located about 1,200 light-years from our solar system in the constellation Lyra. Credit: NASA/Ames/JPL-Caltech
For planets that orbit beyond a star’s habitable zone, water ice will become frozen solid, and the only liquid water will likely be found in underground reservoirs (this is the case on Mars). As such, finding planets that are just right in terms of average surface temperature is intrinsic to the “low-hanging fruit” approach of searching for life in our Universe.
But of course, just because a planet is warm enough to have water on its surface doesn’t mean that life can thrive on it. As our own Solar System beautifully demonstrates, a planet can have the necessary conditions for life, but still become a sterile environment because it lacks a protective magnetosphere.
This is what scientists believe happened to Mars. Located within our Sun’s Goldilocks zone (albeit on the outer edge of it), Mars is believed to have once had an atmosphere and liquid water on its surface. But today, atmospheric pressure on the surface of Mars is only 1% that of Earth’s, and the surface is dry, cold, and devoid of life.
The reason for this, it has been determined, is because Mars lost its magnetosphere 4.2 Billion years ago. According to NASA’s MAVEN mission, this resulted in Mars’ atmosphere being slowly stripped away over the course of the next 500 million years by solar wind. What little atmosphere it had left was not enough to retain heat, and its surface water evaporated.
Billions of years ago, Mars was a very different world. Liquid water flowed in long rivers that emptied into lakes and shallow seas. A thick atmosphere blanketed the planet and kept it warm. Credit: NASA
By the same token, planets that do not have protective magnetospheres are also subject to an intense level of radiation on their surfaces. On the Martian surface, the average dose of radiation is about 0.67 millisieverts (mSv) per day, which is about a fifth of what people are exposed to here on Earth in the course of a year.
We can expect similar situations on extra-solar planets where a magnetosphere does not exist. Essentially, Earth is fortunate in that it not only orbits in a pretty cushy spot around our Sun, but that its core is differentiated between a solid inner core and a liquid, rotating outer core. This rotation, it is believed, is responsible for creating a dynamo effect that in turn creates Earth’s magnetic field.
However, using our own Solar System again as a model, we find that magnetic fields are not entirely uncommon. While Earth is the only terrestrial planet in our Solar System to have on (all the gas giants have powerful fields), Jupiter’s moon Ganymede also has a magnetosphere of its own.
Similarly, there are orbital parameters to consider. For instance, a planet that is similar in size, mass and composition could still have a very different climate than Earth due to its orbit. For one, it may be tidally-locked with its star, which would mean that one side is permanently facing towards it, and is therefore much warmer.
An artist’s depiction of planets transiting a red dwarf star in the TRAPPIST-1 System. Credit: NASA/ESA/STScl
On the other hand, it may have a slow rotational velocity, and a rapid orbital velocity, which means it only experiences a few rotations per orbit (as is the case with Mercury). Last, but certainly not least, its distance from its respective star could mean it receives far more radiation than Earth does – regardless of whether or not it has a magnetosphere.
This is believed to the be the case with Proxima Centauri b, which orbits its red dwarf star at a distance of 7 million km (4.35 million mi) – only 5% of the Earth’s distance from the Sun. It also orbits Proxima Centauri with an orbital period of 11 days, and either has a synchronous rotation, or a 3:2 orbital resonance (i.e. three rotations for every two orbits).
Because of this, the climate is likely to be very different than Earth’s, with water confined to either its sun-facing side (in the case of a synchronous rotation), or in its tropical zone (in the case of a 3:2 resonance). In addition, the radiation it receives from its red dwarf star would be significantly higher than what we are used to here on Earth.
So what exactly does “Earth-like” mean? The short answer is, it can mean a lot of things. And in this respect, its a pretty dubious term. If Earth-like can mean similarities in mass, size, composition, and can allude to the fact that planet orbits within its star’s habitable zone – but not necessarily all of the above – then its not a very reliable term.
Artist’s impression of the Earth-like planets that have been observed in other star systems. Image Credit: JPL
In the end, the only way to keep things clear would be to describe a planet as “Earth-like” if it in fact shows similarities in terms of size, mass and composition, all at the same time. The word “terrestrial” can certainly be substituted in a pinch, but only where the composition of the planet is known with a fair degree of certainty (and not just its size and mass).
And words like “habitable” should probably only be used when chaperoned by words like “potentially”. After all, being within a star’s habitable zone certainly means there’s the potential for life. But it doesn’t not necessarily entail that life could have emerged there, or that humans could live there someday.
And should these words apply to Proxima b? Perhaps, but one should consider the fact that the ESO has announced the detection of a exoplanet using the Radial Velocity method. Until such time as it is confirmed using direct detection methods, its remains a candidate exoplanet (not a confirmed one).
But even these simple measures would likely not be enough to erase all the ambiguity or controversy. When it comes right down to it, planet-hunting – like all aspects of space exploration and science – is a divisive issue. And new findings always have a way of drawing criticism and disagreement from several quarters at once.
And you thought Pluto’s classification confused things! Well, Pluto has got nothing on the exoplanet database! So be prepared for many years of classification debates and controversy!
Artist’s impression of Proxima b, which was discovered using the Radial Velocity method. Credit: ESO/M. Kornmesser
For years, astronomers have been observing Proxima Centauri, hoping to see if this red dwarf has a planet or system of planets around it. As the closest stellar neighbor to our Solar System, a planet here would also be our closest planetary neighbor, which would present unique opportunities for research and exploration.
So there was much excitement when, earlier this month, an unnamed source claimed that the ESO had spotted an Earth-sized planet orbiting within the star’s habitable zone. And after weeks of speculation, with anticipation reaching its boiling point, the ESO has confirmed that they have found a rocky exoplanet around Proxima Centauri – known as Proxima b.
Located just 4.25 light years from our Solar System, Proxima Centauri is a red dwarf star that is often considered to be part of a trinary star system – with Alpha Centauri A and B. For some time, astronomers at the ESO have been observing Proxima Centauri, primarily with telescopes at the La Silla Observatory in Chile.
Their interest in this star was partly due to recent research that has shown how other red dwarf stars have planets orbiting them. These include, but are not limited to, TRAPPIST-1, which was shown to have three exoplanets with sizes similar to Earth last year; and Gliese 581, which was shown to have at least three exoplanets in 2007.
The ESO also confirmed that the planet is potentially terrestrial in nature (i.e. rocky), similar in size and mass to Earth, and orbits its star with an orbital period of 11 days. But best of all are the indications that surface temperatures and conditions are likely suitable for the existence of liquid water.
It’s discovery was thanks to the Pale Red Dot campaign, a name which reflects Carl Sagan’s famous reference to the Earth as a “pale blue dot”. As part of this campaign, a team of astronomers led by Guillem Anglada-Escudé – from Queen Mary University of London – have been observing Proxima Centauri for signs of wobble (i.e. the Radial Velocity Method).
After combing the Pale Red Dot data with earlier observations made by the ESO and other observatories, they noted that Proxima Centauri was indeed moving. With a regular period of 11.2 days, the star would vary between approaching Earth at a speed of 5 km an hour (3.1 mph), and then receding from Earth at the same speed.
Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO
This was certainly an exciting result, as it indicated a change in the star’s radial velocity that was consistent with the existence of a planet. Further analysis showed that the planet had a mass at least 1.3 times that of Earth, and that it orbited the star at a distance of about 7 million km (4.35 million mi) – only 5% of the Earth’s distance from the Sun.
The discovery of the planet was made possible by the La Silla’s regular observation of the star, which took place star between mid-January and April of 2016, using the 3.6-meter telescope‘s HARPS spectrograph. Other telescopes around the world conducted simultaneous observation in order to confirm the results.
One such observatory was the San Pedro de Atacama Celestial Explorations Observatory in Chile, which relied on its ASH2 telescope to monitor the changing brightness of the star during the campaign. This was essential, as red dwarfs like Proxima Centauri are active stars, and can vary in ways that would mimic the presence of the planet.
Guillem Anglada-Escudé described the excitement of the past few months in an ESO press release:
“I kept checking the consistency of the signal every single day during the 60 nights of the Pale Red Dot campaign. The first 10 were promising, the first 20 were consistent with expectations, and at 30 days the result was pretty much definitive, so we started drafting the paper!”
Infographic comparing the orbit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System. Credit: ESO/M. Kornmesser/G. Coleman
Two separate papers discuss the habitability of Proxima b and its climate, both of which will be appearing soon on the Institute of Space Sciences (ICE) website. These papers describe the research team’s findings and outline their conclusions on how the existence of liquid water cannot be ruled out, and discuss where it is likely to be distributed.
Though there has been plenty of excitement thanks to words like “Earth-like”, “habitable zone”, and “liquid water” being thrown around, some clarifications need to be made. For instance, Proxima b’s rotation, the strong radiation it receives from its star, and its formation history mean that its climate is sure to be very different from Earth’s.
For instance, as is indicated in the two papers, Proxima b is not likely to have seasons, and water may only be present in the sunniest regions of the planet. Where those sunny regions are located depends entirely on the planet’s rotation. If, for example, it has a synchronous rotation with its star, water will only be present on the sun-facing side. If it has a 3:2 resoncance rotation, then water is likely to exist only in the planet’s tropical belt.
In any case, the discovery of this planet will open the door to further observations, using both existing instruments and the next-generation of space telescopes. And as Anglada-Escudé states, Proxima Centauri is also likely to become the focal point in the search for extra-terrestrial life in the coming years.
A view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile, showing the location of Proxima Centauri in the sky. Credit: Y. Beletsky (LCO)/ESO/ESA/NASA/M. Zamani
“Many exoplanets have been found and many more will be found, but searching for the closest potential Earth-analogue and succeeding has been the experience of a lifetime for all of us,” he said. “Many people’s stories and efforts have converged on this discovery. The result is also a tribute to all of them. The search for life on Proxima b comes next…”
As we noted in a previous article on the subject, Project Starshot is currently developing a nanocraft that will use a laser-driven sail to make the journey to Alpha Centauri in 20 years time. But a mission to Proxima Centuari would take even less time (19.45 years at the same speed), and could study this newly-found exoplanet up-close.
One can only hope they are planning on altering their destination to take advantage of this discovery. And one can only imagine what they might find if and when they get to Proxima b!
Artist's renditions of a terrestrial planet orbiting a red dwarf star. Credit: Harvard-Smithsonian Center for Astrophysics (CfA)
For years, exoplanet hunters have been busy searching for planets that are similar to Earth. And when earlier this month, an unnamed source indicated that the European Southern Observatory (ESO) had done just that – i.e. spotted a terrestrial planet orbiting within the star’s habitable zone – the response was predictably intense.
The unnamed source also indicated that the ESO would be confirming this news by the end of August. At the time, the ESO offered no comment. But on the morning of Monday, August 22nd, the ESO broke its silence and announced that it will be holding a press conference this Wednesday, August 24th.
No mention was made as to the subject of the press conference or who would be in attendance. However, it is safe to assume at this point that it’s main purpose will be to address the burning question that’s on everyone’s mind: is there an Earth-analog planet orbiting the nearest star to our own?
Artist’s impression of a sunset seen from the surface of an Earth-like exoplanet. Credit: ESO/L. Calçada
For years, the ESO has been studying Proxima Centauri using the La Silla Observatory’s High Accuracy Radial velocity Planet Searcher (HARPS). It was this same observatory that reported the discovery of a planet around Alpha Centauri B back in 2012 – which was the “closest planet to Earth” at the time – which has since been cast into doubt.
Relying on a technique known as the Radial Velocity (or Doppler) Method, they have been monitoring this star for signs of movement. Essentially, as planets orbit a star, they exert a gravitational influence of their own which causes the star to move in a small orbit around the system’s center of mass.
Ordinarily, a star would require multiple exoplanets, or a planet of significant size (i.e. a Super-Jupiter) in order for the signs to be visible. In the case of terrestrial planets, which are much smaller than gas giants, the effect on a star’s orbit would be rather negligible. But given that Proxima Centauri is the closest star system to Earth – at a distance of 4.25 light years – the odds of discerning its radial velocity are significantly better.
Artist’s impression of the Earth-like exoplanet discovered orbiting Alpha Centauri B iby the European Southern Observatory on October 17th, 2012. Credit: ESO
According to the source cited by the German weekly Der Speigel, which was the first to report the story, the unconfirmed exoplanet is not only believed to be “Earth-like” (in the sense that it is a rocky body) but also orbits within it’s stars habitable zone (i.e. “Goldilocks Zone”).
Because of this, it would be possible for this planet to have liquid water on its surface, and an atmosphere capable of supporting life. However, we won’t know any of this for certain until we can direct the next-generation of telescopes – like the James Webb Space Telescope or Transiting Exoplanet Survey Satellite (TESS) – to study it more thoroughly.
This is certainly an exciting development, as confirmation will mean that there is planet similar to Earth that is within our reach. Given time and the development of more advanced propulsion systems, we might even be able to mount a mission there to study it up close!
The press conference will start at 1 p.m. Central European Time (CET) – 1 p.m. EDT/10 a.m. PDT. And you bet that we will be reporting on the results shortly thereafter! Stay tuned!
Artist's impression of the "Venus-like" exoplanet GJ 1132b. Credit: cfa.harvard.edu
Last year, astronomers discovered a terrestrial exoplanet orbiting GJ 1132, a red dwarf star located just 12 parsecs (39 light years) away from Earth. Though too close to its parent star to be anything other than extremely hot, astronomers were intrigued to note that it appeared to still be cool enough to have an atmosphere. This was quite exciting, as it represented numerous opportunities for research.
In essence, the planet appeared to be “Venus-like” – i.e. very hot, but still in possession of an atmosphere. What’s more, it was close enough to our Solar System that its atmosphere could be studied in detail. However, a debate began over whether its atmosphere would be hot and wet, or thin and tenuous. And after a year of study, a team of astronomers from the CfA believe they have unlocked that mystery.
In addition to being relatively close to our own Solar System in astronomical terms, the Venus-like exoplanet GJ 1132b also has a relatively small orbital period around its star. This means that opportunities to spot it as it passes in front of its star (i.e. the Transit Method), occur quite often.
Artist’s concept of exoplanets orbiting a young, red dwarf star. Credit: NASA/JPL-Caltech
This makes it an excellent target for detailed observation and study, which in turn will help astronomers to learn more about terrestrial exoplanets that orbit close to red dwarf stars. But as noted already, astronomers were divided on the issue of GJ 1132b’s atmosphere.
Thanks to the research efforts of Laura Schaefer and her colleagues from the Harvard-Smithsonian Center for Astrophysics (CfA), it now appears that the case for a thin atmosphere is the far more likely. Interestingly enough, this was confirmed by determining just how much oxygen the planet has in its atmosphere.
For the sake of their study, which was outlined in a paper that approved for publication in The Astrophysical Journal – titled “Predictions of the atmospheric composition of GJ 1132b” – they explain how they used a “magma ocean-atmosphere” model to determine what would happen to GJ 1132b over time if it began with a water-rich atmosphere.
They began with the knowledge that a planet like GJ 1132b – which orbits its star at a distance of 2.25 million km (1.4 million mi) – would be subjected to intense amounts of ultraviolet light. This would result in any water vapor in the atmosphere being broken down into hydrogen and oxygen (a process known as photolysis), with the hydrogen escaping into space and the oxygen being retained.
Size comparison of the exoplanet GJ 1132 b with Earth, as reported in the Open Exoplanet Catalogue as of 2015-11-14. Credit: Open Exoplanet Catalogue/AldaronAt the same time, they determined that the planet’s atmosphere and proximity to its star would lead to a severe greenhouse effect that would leave the surface molten for a long time. This “magma ocean” would likely interact with the atmosphere by absorbing some of the oxygen. How much would be absorbed and how much would be retained was the big question.
They concluded that the planet’s magma ocean would absorb about one-tenth of the oxygen in the atmosphere. The majority of the remaining 90 percent, according to their model, would be lost to space while a small margin would linger around the planet. This proved to be very much consistent with measurements made of the planet thus far.
As Dr. Laura Schaefer explained to Universe Today via email:
“We determined that the planet would likely have a thin atmosphere by doing a suite of models looking at atmospheric loss and interaction with a surface magma ocean. For the allowable composition range (esp. the abundance of water) based on the current mass measurement, nearly all of the allowed compositions resulted in thin atmospheres, except at the very extreme upper end of the range.”
This magma ocean-atmosphere model could not only help scientists to study terrestrial exoplanets that orbit close to their parent stars, but also to understand how our own planet Venus came to be. For some time, scientists have theorized that Venus began with significant amounts of water on its surface, but that it then underwent a significant change.
Artist’s impression of three newly-discovered exoplanets orbiting an ultracool dwarf star TRAPPIST-1. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).
This ocean is believed to have evaporated due to Venus’ closer proximity to the Sun, with the ensuing water vapor triggering a runaway greenhouse effect. Over time, ultraviolet radiation from the Sun broke apart the water molecules, resulting in the hot, virtually waterless atmosphere we see today. However, what happened to all the oxygen has remained a mystery.
“We also have plans to use this model in the future to study Venus, which may have once had about the same amount of water as the Earth but is now very dry,” said Schaefer. “There is very little O2 left in Venus’ atmosphere, so this model would help us understand what happened to that oxygen (whether it was lost to space or absorbed by the planet’s mantle).”
Schaefer predicts that their model will also assist researchers with the study of other, similar exoplanets. One example is the TRAPPIST-1 system, which contains three planets that may lie with the star’s the habitable zone. But as Schaefer put it, the real value lies in the fact that we are more likely to find “Venus-like” worlds down the road:
“Most of the rocky planets that we know of and will discover in the near future will likely be hotter than the Earth or even Venus, just because it is easier to detect hotter planets. So there are a lot of planets out there similar to GJ 1132b just waiting to be studied!”
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. It’s scientists are dedicated to studying the origin, evolution and future of the universe.
And be sure to check out this video, courtesy of MIT news:
Artist’s impression of a sunset seen from the surface of an Earth-like exoplanet. Credit: ESO/L. Calçada
The hunt for exoplanets has been heating up in recent years. Since it began its mission in 2009, over four thousand exoplanet candidates have been discovered by the Kepler mission, several hundred of which have been confirmed to be “Earth-like” (i.e. terrestrial). And of these, some 216 planets have been shown to be both terrestrial and located within their parent star’s habitable zone (aka. “Goldilocks zone”).
But in what may prove to be the most exciting find to date, the German weekly Der Spiegel announced recently that astronomers have discovered an Earth-like planet orbiting Proxima Centauri, just 4.25 light-years away. Yes, in what is an apparent trifecta, this newly-discovered exoplanet is Earth-like, orbits within its sun’s habitable zone, and is within our reach. But is this too good to be true?
For over a century, astronomers have known about Proxima Centauri and believed that it is likely to be part of a trinary star system (along with Alpha Centauri A and B). Located just 0.237 ± 0.011 light years from the binary pair, this low-mass red dwarf star is also 0.12 light years (~7590 AUs) closer to Earth, making it the closest star system to our own.
In the past, the Kepler mission has revealed several Earth-like exoplanets that were deemed to be likely habitable. And recently, an international team of researchers narrowed the number of potentially-habitable exoplanets in the Kepler catalog down to the 20 that are most likely to support life. However, in just about all cases, these planets are hundreds (if not thousands) of light years away from Earth.
Knowing that there is a habitable planet that a mission from Earth could reach within our own lifetimes is nothing short of amazing! But of course, there is reason to be cautiously optimistic. Citing anonymous sources, the magazine stated:
“The still nameless planet is believed to be Earth-like and orbits at a distance to Proxima Centauri that could allow it to have liquid water on its surface — an important requirement for the emergence of life. Never before have scientists discovered a second Earth that is so close by.”
In addition, they claim that the discovery was made by the European Southern Observatory (ESO) using the La Silla Observatory‘s reflecting telescope. Coincidentally, it was this same observatory that announced the discovery of Alpha Centauri Bb back in 2012, which was also declared to be “the closest exoplanet to Earth”. Unfortunately, subsequent analysis cast doubt on its existence, claiming it was a spurious artifact of the data analysis.
Artist’s impression of the Earth-like exoplanet discovered orbiting Alpha Centauri B by the European Southern Observatory on October 17, 2012. Credit: ESO
However, according to Der Spiegel’s unnamed source – whom they claim was involved with the La Silla team that made the find – this latest discovery is the real deal, and was the result of intensive work. “Finding small celestial bodies is a lot of hard work,” the source was quoted as saying. “We were moving at the technically feasible limit of measurement.”
The article goes on to state that the European Southern Observatory (ESO) will be announcing the finding at the end of August. But according to numerous sources, in response to a request for comment by AFP, ESO spokesman Richard Hook refused to confirm or deny the discovery of an exoplanet around Proxima Centauri. “We are not making any comment,” he is reported as saying.
What’s more, the folks at Project Starshot are certainly excited by the news. As part of Breakthrough Initiatives – a program founded by Russian billionaire Yuri Milner to search for intelligent life (with backing from Stephen Hawking and Mark Zuckerberg) – Starshot intends to send a laser-sail driven-nanocraft to Alpha Centauri in the coming years.
This craft, they claim, will be able to reach speeds of up to 20% the speed of light. At this speed, it will able to traverse the 4.37 light years that lie between Earth and Alpha Centauri in just 20 years. But with the possible discovery of an Earth-like planet orbiting Proxima Centauri, which lies even closer, they may want to rethink that objective.
Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org
As Professor Phillip Lubin – a professor at the University of California, Santa Barbara, the brains behind Project Starshot, and a key advisor to NASA’s DEEP-IN program – told Universe Today via email:
“The discovery of possible planet around Proxima Centauri is very exciting. It makes the case of visiting nearby stellar systems even more compelling, though we know there are many exoplanets around other nearby stars and it is very likely that the Alpha Centauri system will also have planets.”
Naturally, there is the desire (especially amongst exoplanet enthusiasts) to interpret the ESO’s refusal to comment either way as a sort of tacit confirmation. And knowing that industry professionals are excited it about it does lend an air of legitimacy. But of course, assuming anything at this point would be premature.
If the statements made by the unnamed source, and quoted by Der Speigel, are to be taken at face value, then confirmation (or denial) will be coming shortly. In the meantime, we’ll all just need to be patient. Still, you have to admit, it’s an exciting prospect: an Earth-like planet that’s actually within reach! And with a mission that could make it there within our own lifetimes. This is the stuff good science fiction is made of, you know.
Artist’s impression of how an an Earth-like exoplanet might look. Credit: ESO.
The ongoing hunt for exoplanets has yielded some very interesting returns in recent years. All told, the Kepler mission has discovered more than 4000 candidates since it began its mission in March of 2009. Amidst the many “Super-Jupiters” and assorted gas giants (which account for the majority of Kepler’s discoveries) astronomers have been particularly interested in those exoplanets which resemble Earth.
And now, an international team of scientists has finished perusing the Kepler catalog in an effort to determine just how many of these planets are in fact “Earth-like”. Their study, titled “A Catalog of Kepler Habitable Zone Exoplanet Candidates” (which will be published soon in the AstrophysicalJournal), explains how the team discovered 216 planets that are both terrestrial and located within their parent star’s “habitable zone” (HZ).
The international team was made up of researchers from NASA, San Francisco State University, Arizona State University, Caltech, University of Hawaii-Manoa, the University of Bordeaux, Cornell University and the Harvard-Smithsonian Center for Astrophysics. Having spent the past three years looking over the more than 4000 entries, they have determined that 20 of the candidates are most like Earth (i.e. likely habitable).
Figure showing the habitable zone for different types of stars, as well as the location of terrestrial size Kepler candidates. Credit: Chester Harman
As Stephen Kane, an associate professor of physics and astronomy at San Fransisco University and lead author of the study, explained in a recent statement:
“This is the complete catalog of all of the Kepler discoveries that are in the habitable zone of their host stars. That means we can focus in on the planets in this paper and perform follow-up studies to learn more about them, including if they are indeed habitable.”
In addition to isolating 216 terrestrial planets from the Kepler catalog, they also devised a system of four categories to determine which of these were most like Earth. These included “Recent Venus”, where conditions are like that of Venus (i.e. extremely hot); “Runaway Greenhouse”, where planets are undergoing serious heating; “Maximum Greenhouse”, where planets are within their star’s HZ; and “Recent Mars”, where conditions approximate those of Mars.
From this, they determined that of the Kepler candidates, 20 had radii less than twice that of Earth (i.e. on the smaller end of the Super-Earth category) and existed within their star’s HZ. In other words, of all the planets discovered in our local Universe, they were able to isolate those where liquid water can exist on the surface, and the gravity would likely be comparable to Earth’s and not crushing!
Earlier today, NASA announced that Kepler had confirmed the existence of 1,284 new exoplanets, the most announced at any given time. Credit: NASA
This is certainly exciting news, since one of the most important aspects of exoplanet hunting has been finding worlds that could support life. Naturally, it might sound a bit anthropocentric or naive to assume that planets which have similar conditions to our own would be the most likely places for it to emerge. But this is what is known as the “low-hanging fruit” approach, where scientists seek out conditions which they know can lead to life.
“There are a lot of planetary candidates out there, and there is a limited amount of telescope time in which we can study them,” said Kane. “This study is a really big milestone toward answering the key questions of how common is life in the universe and how common are planets like the Earth.”
Professor Kane is renowned for being one of the world’s leading “planet-hunters”. In addition to discovering several hundred exoplanets (using data obtained by the Kepler mission) he is also a contributor to two upcoming satellite missions – the NASA Transiting Exoplanet Survey Satellite (TESS) and the European Space Agency’s Characterizing ExOPLanet Satellite (CHEOPS).
These next-generation exoplanet hunters will pick up where Kepler left off, and are likely to benefit greatly from this recent study.
Artist's impression of an exoplanet orbiting a low-mass star. Credit: ESO/L. Calçada
The Fermi Paradox essentially states that given the age of the Universe, and the sheer number of stars in it, there really ought to be evidence of intelligent life out there. This argument is based in part on the fact that there is a large gap between the age of the Universe (13.8 billion years) and the age of our Solar System (4.5 billion years ago). Surely, in that intervening 9.3 billion years, life has had plenty of time to evolve in other star system!
An artist’s depiction of planets transiting a red dwarf star in the TRAPPIST-1 System. Credit: NASA/ESA/STScl
When Hubble first observed the atmospheric conditions of an extrasolar planet in 2000, it opened up that entire field of study. Now, Hubble has conducted the first preliminary study of the atmospheres of Earth-sized, relatively nearby worlds and found “indications that increase the chances of habitability on two exoplanets,” say the researchers.
The planets, TRAPPIST-1b and TRAPPIST-1c, were discovered earlier this year and are approximately 40 light-years away. At the time of their discovery, it was unknown if the worlds were gas planets or rocky worlds, but Hubble’s most recent observations suggest that both planets have compact atmospheres, similar to those of rocky planets such as Earth, Venus, and Mars instead of thick, puffy atmospheres, similar to that of the gas planets like Jupiter.
“Now we can say that these planets are rocky. Now the question is, what kind of atmosphere do they have?” said Julien de Wit of the Massachusetts Institute of Technology, who led a team of scientists to observe the planets in near-infrared light using Hubble’s Wide Field Camera 3. “The plausible scenarios include something like Venus, with high, thick clouds and an atmosphere dominated by carbon dioxide, or an Earth-like atmosphere dominated by nitrogen and oxygen, or even something like Mars with a depleted atmosphere. The next step is to try to disentangle all these possible scenarios that exist for these terrestrial planets.”
Structure of the TRAPPIST-1 exosystem. The green is the star’s habitable zone. Credit: Planetary Habitability Lab.
The exoplanets were originally discovered by the TRAPPIST telescope at ESO’s La Silla observatory in Chile, which, like the Kepler telescope, looks for planetary transits (TRAPPIST stands for Transiting Planets and Planetesimals Small Telescope) observing dips in a star’s light from planets passing in front of it from Earth’s point of view.
The star, TRAPPIST-1, is an ultracool dwarf star and is very small and dim. TRAPPIST-1b completes an orbit around the star in just 1.5 days and TRAPPIST-1c in 2.4 days, and the planets are between 20 and 100 times closer to their star than the Earth is to the sun. Both are tidally locked, where one side of these worlds might be hellish and uninhabitable, but conditions might permit a limited region of habitability on the other side. And because of the star’s faintness, researchers think that TRAPPIST-1c may be within the star’s habitable zone, where moderate temperatures could allow for liquid water to pool.
“A rocky surface is a great start for a habitable planet, but any life on the TRAPPIST-1 planets is likely to have a much harder time than life on Earth,” said Joanna Barstow, an astrophysicist at University College London, who was not involved with the research. “Of course, our ideas of habitability are very narrow because we only have one planet to look at so far, and life might well surprise us by flourishing in what we think of as unlikely conditions.”
The researchers used spectroscopy to decode the light and reveal clues to the chemical makeup of the planets’ atmospheres. While the content of the atmospheres is unknown and are scheduled for more observations, the low concentration of hydrogen and helium has scientists excited about the implications.
The team realized a rare double transit was going to take place, when the two planets would almost simultaneously pass in front of their star, but they only knew two weeks in advance. They took a chance, and taking advantage of Hubble’s ability to do observations on short notice, they wrote up a proposal in a day.
“We thought, maybe we could see if people at Hubble would give us time to do this observation, so we wrote the proposal in less than 24 hours, sent it out, and it was reviewed immediately,” de Wit said. “Now for the first time we have spectroscopic observations of a double transit, which allows us to get insight on the atmosphere of both planets at the same time.”
Using Hubble, the team recorded a combined transmission spectrum of TRAPPIST-1b and c, meaning that as first one planet then the other crossed in front of the star, they were able to measure the changes in wavelength as the amount of starlight dipped with each transit.
“The data turned out to be pristine, absolutely perfect, and the observations were the best that we could have expected,” de Wit says. “The force was certainly with us.”
“These initial Hubble observations are a promising first step in learning more about these nearby worlds, whether they could be rocky like Earth, and whether they could sustain life,” says Geoff Yoder, acting associate administrator for NASA’s Science Mission Directorate in Washington. “This is an exciting time for NASA and exoplanet research.”
![Comparison of best-fit size of the exoplanet GJ 1132 b with the Solar System planet Earth, as reported in the Open Exoplanet Catalogue[1] as of 2015-11-14. Open Exoplanet Catalogue (2015-11-14). Retrieved on 2015-11-14. Aldaron, a.k.a. Aldaro](https://www.universetoday.com/wp-content/uploads/2016/08/Exoplanet_Comparison_GJ_1132_b-e1471628608145.png)
