How Did the TRAPPIST-1 Planets Get Their Water?

Most exoplanets orbit red dwarf stars because they're the most plentiful stars. This is an artist's illustration of what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credits: NASA/JPL-Caltech

In 2017, an international team of astronomers announced a momentous discovery. Based on years of observations, they found that the TRAPPIST-1 system (an M-type red dwarf located 40 light-years from Earth) contained no less than seven rocky planets! Equally exciting was the fact that three of these planets were found within the star’s Habitable Zone (HZ), and that the system itself has had 8 billion years to develop the chemistry for life.

At the same time, the fact that these planets orbit tightly around a red dwarf star has given rise to doubts that these three planets could maintain an atmosphere or liquid water for very long. According to new research by an international team of astronomers, it all comes down to the composition of the debris disk that the planets formed from and whether or not comets were around to distribute water afterward.

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One of the TRAPPIST-1 Planets Has an Iron Core

In February of 2017, a team of European astronomers announced the discovery of a seven-planet system orbiting the nearby star TRAPPIST-1. Aside from the fact that all seven planets were rocky, there was the added bonus of three of them orbiting within TRAPPIST-1’s habitable zone. Since that time, multiple studies have been conducted to determine whether or not any of these planets could be habitable.

In accordance with this goal, these studies have focused on whether or not these planets have atmospheres, their compositions and their interiors. One of the latest studies was conducted by two researchers from Columbia University’s Cool Worlds Laboratory, who determined that one of the TRAPPIST-1 planets (TRAPPIST-1e) has a large iron core – a finding which could have implications for this planet’s habitability.

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TRAPPIST-1 Planets Might Actually Have Too Much Water to be Habitable

In February of 2017, the world was astounded to learn that astronomers – using data from the TRAPPIST telescope in Chile and the Spitzer Space Telescope – had identified a system of seven rocky exoplanets in the TRAPPIST-1 system. As if this wasn’t encouraging enough for exoplanet-enthusiasts, it was also indicated that three of the seven planets orbited within the stars’ circumstellar habitable zone (aka. “Goldilocks Zone”).

Since that time, this system has been the focus of considerable research and follow-up surveys to determine whether or not any of its planets could be habitable. Intrinsic to these studies has been the question whether or not the planets have liquid water on their surfaces. But according to a new study by a team of American astronomers, the TRAPPIST planets may actually have too much water to support life.

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Good News For The Search For Life, The Trappist System Might Be Rich In Water

When we finally find life somewhere out there beyond Earth, it’ll be at the end of a long search. Life probably won’t announce its presence to us, we’ll have to follow a long chain of clues to find it. Like scientists keep telling us, at the start of that chain of clues is water.

The discovery of the TRAPPIST-1 system last year generated a lot of excitement. 7 planets orbiting the star TRAPPIST-1, only 40 light years from Earth. At the time, astronomers thought at least some of them were Earth-like. But now a new study shows that some of the planets could hold more water than Earth. About 250 times more.

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New Study Claims that TRAPPIST-1 Could Also Have Gas Giants

Most exoplanets orbit red dwarf stars because they're the most plentiful stars. This is an artist's illustration of what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credits: NASA/JPL-Caltech

In February of 2017, NASA scientists announced the existence of seven terrestrial (i.e. rocky) planets within the TRAPPIST-1 star system. Since that time, the system has been the focal point of intense research to determine whether or not any of these planets could be habitable. At the same time, astronomers have been wondering if all of the system’s planets are actually accounted for.

For instance, could this system have gas giants lurking in its outer reaches, as many other systems with rocky planets (for instance, ours) do? That was the question that a team of scientists, led by researchers from the Carnegie Institute of Science, sought to address in a recent study. According to their findings, TRAPPIST-1 may be orbited by gas giants at a much-greater distance than its seven rocky planets.

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Hubble Spots First Indications of Water on TRAPPIST-1s Planets

This artist’s impression shows the view from the surface of one of the planets in the TRAPPIST-1 system. A powerful laser beacon using current and near-future technology could send a signal strong enough to be detected by any alien astronomers here. Credit: NASA/ESA/HST

In February of 2017, astronomers from the European Southern Observatory (ESO) announced the discovery of seven rocky planets around the nearby star of TRAPPIST-1. Not only was this the largest number of Earth-like planets discovered in a single star system to date, the news was also bolstered by the fact that three of these planets were found to orbit within the star’s habitable zone.

Since that time, multiple studies have been conducted to ascertain the likelihood that these planets are actually habitable. Thanks to an international team of scientists who used the Hubble Space Telescope to study the system’s planets, we now have the first clues as to whether or not water (a key ingredient

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Scientists Discover TRAPPIST-1 is Older Than Our Solar System

Most exoplanets orbit red dwarf stars because they're the most plentiful stars. This is an artist's illustration of what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credits: NASA/JPL-Caltech

In February of 2017, a team of European astronomers announced the discovery of a seven-planet system orbiting the nearby star TRAPPIST-1. Aside from the fact that all seven planets were rocky, there was the added bonus of three of them orbiting within TRAPPIST-1’s habitable zone. As such, multiple studies have been conducted that have sought to determine whether or not any planets in the system could be habitable.

When it comes to habitability studies, one of the key factors to consider is the age of the star system. Basically, young stars have a tendency to flare up and release harmful bursts of radiation while planets that orbit older stars have been subject to radiation for longer periods of time. Thanks to a new study by a pair of astronomers, it is now known that the TRAPPIST-1 system is twice as old as the Solar System.

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Even Though Red Dwarfs Have Long Lasting Habitable Zones, They’d be Brutal to Life

Artist's concept of the TRAPPIST-1 star system, an ultra-cool dwarf that has seven Earth-size planets orbiting it. We're going to keep finding more and more solar systemsl like this, but we need observatories like WFIRST, with starshades, to understand the planets better. Credits: NASA/JPL-Caltech

Ever since scientists confirmed the existence of seven terrestrial planets orbiting TRAPPIST-1, this system has been a focal point of interest for astronomers. Given its proximity to Earth (just 39.5 light-years light-years away), and the fact that three of its planets orbit within the star’s “Goldilocks Zone“, this system has been an ideal location for learning more about the potential habitability of red dwarf stars systems.

This is especially important since the majority of stars in our galaxy are red dwarfs (aka. M-type dwarf stars). Unfortunately, not all of the research has been reassuring. For example, two recent studies performed by two separate teams from Harvard-Smithsonian Center for Astrophysics (CfA) indicate that the odds finding life in this system are less likely than generally thought.

The first study, titled “Physical Constraints on the Likelihood of Life on Exoplanets“, sought to address how radiation and stellar wind would affect any planets located within TRAPPIST-1s habitable zone. Towards this end, the study’s authors – Professors Manasvi Lingam and Avi Loeb – constructed a model that considered how certain factors would affect conditions on the surface of these planets.

This artist’s concept shows what each of the TRAPPIST-1 planets may look like, based on available data about their sizes, masses and orbital distances. Credits: NASA/JPL-Caltech

This model took into account how the planets distance from their star would affect surface temperatures and atmospheric loss, and how this might affect the changes life would have to emerge over time. As Dr. Loeb told Universe Today via email:

“We considered the erosion of the atmosphere of the planets due to the stellar wind and the role of temperature on ecological and evolutionary processes. The habitable zone around the faint dwarf star TRAPPIST-1 is several tens of times closer in than for the Sun, hence the pressure of the stellar wind is several orders of magnitude higher than on Earth. Since life as we know it requires liquid water and liquid water requires an atmosphere, it is less likely that life exists around TRAPPIST-1 than in the solar system.”

Essentially, Dr. Lingam and Dr, Loeb found that planets in the TRAPPIST-1 system would be barraged by UV radiation with an intensity far greater than that experienced by Earth. This is a well-known hazard when it comes to red dwarf stars, which are variable and unstable when compared to our own Sun. They concluded that compared to Earth, the chances of complex life existing on planets within TRAPPIST-1’s habitable zone were less than 1%.

“We showed that Earth-sized exoplanets in the habitable zone around M-dwarfs display much lower prospects of being habitable relative to Earth, owing to the higher incident ultraviolet fluxes and closer distances to the host star,” said Loeb. “This applies to the recently discovered exoplanets in the vicinity of the Sun, Proxima b (the nearest star four light years away) and TRAPPIST-1 (ten times farther), which we find to be several orders of magnitude smaller than that of Earth.”

Three of the TRAPPIST-1 planets – TRAPPIST-1e, f and g – dwell in their star’s so-called “habitable zone. CreditL NASA/JPL

The second study – “The Threatening Environment of the TRAPPIST-1 Planets“, which was recently published in The Astrophysical Journal Letters – was produced by a team from the CfA and the Lowell Center for Space Science and Technology at the University of Massachusetts. Led by Dr. Cecilia Garraffo of the CfA, the team considered another potential threat to life in this system.

Essentially, the team found that TRAPPIST-1, like our Sun, sends streams of charged particles outwards into space – i.e. stellar wind. Within the Solar System, this wind exerts force on the planets and can have the effect of stripping away their atmospheres. Whereas Earth’s atmosphere is protected by its magnetic field, planets like Mars are not – hence why it lost the majority of its atmosphere to space over the course of hundreds of million of years.

As the research team found, when it comes to TRAPPIST-1, this stream exerts a force on its planets that is between 1,000 to 100,000 times greater than what Earth experiences from solar wind. Furthermore, they argue that TRAPPIST-1’s magnetic field is likely connected to the magnetic fields of the planets that orbit around it, which would allow particles from the star to directly flow onto the planet’s atmosphere.

Illustration showing the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Credits: NASA/JPL-Caltech
Illustration showing the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Credits: NASA/JPL-Caltech

In other words, if TRAPPIST-1’s planets do have magnetic fields, they will not afford them any protection. So if the flow of charged particles is strong enough, it could strip these planets’ atmospheres away, thus rendering them uninhabitable. As Garraffo put it:

“The Earth’s magnetic field acts like a shield against the potentially damaging effects of the solar wind. If Earth were much closer to the Sun and subjected to the onslaught of particles like the TRAPPIST-1 star delivers, our planetary shield would fail pretty quickly.”

As you can imagine, this is not exactly good news for those who were hoping that the TRAPPIST-1 system would hold the first evidence of life beyond our Solar System. Between the fact that its planets orbit a star that emits varying degrees of intense radiation, and the proximity its seven planets have to the star itself, the odds of life emerging on any planet within it’s “habitable zone” are not significant.

The findings of the second study are particularly significant in light of other recent studies. In the past, Prof. Loeb and a team from the University of Chicago have both addressed the possibility that the TRAPPIST-1 system’s seven planets – which are relatively close together – are well-suited to lithopanspermia. In short, they determined that given their close proximity to each other, bacteria could be transferred from one planet to the next via asteroids.

An artist’s depiction of planets transiting a red dwarf star in the TRAPPIST-1 System. Credit: NASA/ESA/STScl

But if the proximity of these planets also means that they are unlikely to retain their atmospheres in the face of stellar wind, the likelihood of lithopanspermia may be a moot point. However, before anyone gets to thinking that this is bad news as far as the hunt for life goes, it is important to note that this study does not rule out the possibility of life emerging in all red dwarf star systems.

As Dr. Jeremy Drake – a senior astrophysicist from the CfA and one of Garraffo’s co-authors – indicated, the results of their study simply mean that we need to cast a wide net when searching for life in the Universe.  “We’re definitely not saying people should give up searching for life around red dwarf stars,” he said. “But our work and the work of our colleagues shows we should also target as many stars as possible that are more like the Sun.”

And as Dr. Loeb himself has indicated in the past, red dwarf stars are still the most statistically-likely place to find habitable worlds:

“By surveying the habitability of the Universe throughout cosmic history from the birth of the first stars 30 million years after the Big Bang to the death of the last stars in 10 trillion years, one reaches the conclusion that unless habitability around low-mass stars is suppressed, life is most likely to exist near red dwarf stars like Proxima Centauri or TRAPPIST-1 trillions of years from now.”

If there is one takeaway from these studies, it is that the existence of life within a star system does not simply require planets orbiting within the circumstellar habitable zones. The nature of the stars themselves and the role played by solar wind and magnetic fields also have to be taken into account, since they can mean the difference between a life-bearing planet and a sterile ball of rock!

Further Reading: CfA, International Journal of Astrobiology, The Astrophysical Journal Letters.

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

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.

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NASA Brings Trappist-1 Into Focus… Kinda Sorta

TRAPPIST-1 is probably the most well-known ultra-cool, or red dwarf, star. It is host to several rocky, roughly Earth-sized planets. Astronomers think it's no accident that ultra-cool stars and red dwarfs are host to so many smaller, rocky planets, and they hope that SPECULOOS will find them. Credit: NASA/JPL-Caltech

On February 22nd, 2017, NASA announced the discovery of a seven-planet system around the red dwarf star known as TRAPPIST-1. Since that time, a number of interesting revelations have been made. For starters, the Search for Extra-Terrestrial Intelligence (SETI) recently announced that it was already monitoring this system for signs of advanced life (sadly, the results were not encouraging).

In their latest news release about this nearby star system, NASA announced the release of the first images taken of this system by the Kepler mission. As humanity’s premier planet-hunting mission, Kepler has been observing this system since December 2016, a few months after the existence of the first three of its exoplanets were announced.

These observations took place between December 15th, 2016 and March 4th, 2017, as part of Kepler’s extended mission (known as K2). During this 74-day period, K2 collected data on minuscule changes in the star’s brightness, which were caused by transits made by the star’s exoplanets. And as of Wednesday, March. 8th, this information is now available to the scientific community.

Artist’s impression of of the exoplanets orbiting the ultracool dwarf star TRAPPIST-1. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).

These observations constituted the longest continuous set of observations of the star system to date. But in truth, the initial coordinates designated for this observation (known as Campaign 12) were set back in Oct. 2015, and did not focus on TRAPPIST-1. But as of May 2016, when the system’s first three planets were announced, the science teams adjusted their focus to observe them.

As Michael Haas, the science office director for the Kepler and K2 missions at NASA’s Ames Research Center, explained:

“We were lucky that the K2 mission was able to observe TRAPPIST-1. The observing field for Campaign 12 was set when the discovery of the first planets orbiting TRAPPIST-1 was announced, and the science community had already submitted proposals for specific targets of interest in that field. The unexpected opportunity to further study the TRAPPIST-1 system was quickly reconized and the agility of the K2 team and science community prevailed once again.”

While the data is raw and uncalibrated, it is expected to help astronomers learn more about this system of planets. In particular, it could help astronomers to place constraints on the seventh planet’s orbital period and mass (which are currently unknown). Additional information about the other six planets, particularly their size and mass, could also help astronomers make more accurate assessments about their composition.

Raw data from the K2 Category 12 survey. Credit: NASA/Kepler/K2 Campaign12

The magnetic activity of the host star, which is important in determining if any of its planets could be habitable, is also something that astronomers would like to learn more about. Last, but not least, the new data will help astronomers to prepare proposals for the use Earth-based telescopes next winter to further investigate TRAPPIST-1.

These proposals are due this month, and the timely arrival of this data ought to help research teams to refine their research objectives for next year. Any refinements made using this data will also help astronomer plan for follow-up studies using next-generations telescopes like the James Webb Space Telescope. As Geert Barentsen, a K2 research scientist at NASA’s Ames Research Center, explained:

“Scientists and enthusiasts around the world are invested in learning everything they can about these Earth-size worlds. Providing the K2 raw data as quickly as possible was a priority to give investigators an early look so they could best define their follow-up research plans. We’re thrilled that this will also allow the public to witness the process of discovery.

By the end of May 2017, the data will be fully processed and calibrated, which will also be made available to the public. As you can see from the images above, it was a little on the pixelated side! Still, we can expect some interesting finds to come out of this crowded star system in the coming months. Hopefully, some of that information will help us to determine if there’s any real chance of life forming there.

Further Reading: NASA, Kepler and K2