trappist-1

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Observing the Atmospheres of TRAPPIST-1 Planets

Posted by admin on February 16, 2018
Posted in: Journal Club. Tagged: , , , .

Comparing the TRAPPIST-1 system to the solar system. From http://www.spitzer.caltech.edu/images/6294-ssc2017-01h-The-TRAPPIST-1-Habitable-Zone.

In astronomy, when you look for evidence supporting a hypothesis and don’t find it, that’s called a “null result“. The null result is usually not all that exciting, but last week, an attempt to detect the atmospheres of potentially habitable exoplanets came up null, and that, as it turns out, may mean the planets are habitable.

In a recent study published last week in Nature Astronomy, Dr. Julien de Wit of MIT and colleagues observed the transits of four of the planets in the TRAPPIST-1 system. The discovery of this system was announced last year and generated a lot of interest — it comprises seven Earth-sized planets orbiting a red-dwarf star, and at least four of the planets orbit in the star’s habitable zone. So astronomers are scrambling to determine the climatic conditions on these planets and find out whether they host life.

Key to those conditions is the composition of the planets’ atmospheres, and the best way to probe atmospheres lightyears distant is to detect the colors of the planets’ shadows as they pass in front of their host stars, i.e. as they transit. When light from the star passes through a planet’s atmosphere, the cool gases can imprint spectral signatures, which we can then detect using a very sensitive telescope — de Wit used the Hubble Space Telescope.

Now, even though the TRAPPIST planets are Earth-sized, that doesn’t mean their atmospheres are Earth-like — astronomers have founds lots of weird planets in the last several years. The atmospheres could be hydrogen-rich like Jupiter, hydrocarbon-rich like Neptune, or rich in nitrogen and oxygen like Earth.

In principal, each kind of atmosphere would give a distinct spectrum, but in practice, atmospheres rich in hydrocarbons or nitrogen, potentially good atmospheres for life, are difficult to detect because they are weighty and drape over the planet like a heavy blanket. By contrast, a hydrogen-rich atmosphere, although probably not great for life, can be light and fluffy, relatively easy to detect.

When de Wit and colleagues analyzed transit data they collected from Hubble showing transits for planets TRAPPIST-1 d, e and f, they found no atmospheric signals down to their detection limits. The spectra below show this lack of atmospheric coloration and what they would have detected if the atmosphere was hydrogen-rich.

Now, of course, this non-detection does NOT mean the planets are habitable or even Earth-like. As the figure shows, their atmospheres could still be radically different from the Earth’s (drenched in water vapor or carbon dioxide-rich like Venus), but it rules out the possibility that they are Jupiter-like — potentially good news for life there.

Very likely, when the James Webb Space Telescope finally launches next year, the TRAPPIST-1 system will be one of its first targets. JWST’s vastly improved sensitivity will help reveal not just a potent null result for the TRAPPIST-1 system but may also reveal the glimmer of distant Earth-like worlds.

Spectra for TRAPPIST-1 d, e, f, and g. From de Wit et al. (2018) – https://www.nature.com/articles/s41550-017-0374-z.

Habitable Planets of the TRAPPIST-1 System

Posted by admin on April 4, 2017
Posted in: Public Outreach. Tagged: , , .

Google’s TRAPPIST-1 doodle.

UPDATE: KBSX ran a story about our event this morning – http://boisestatepublicradio.org/post/bsu-and-university-washington-part-search-life-nearby-planets.

The seven Earth-sized planets orbiting the nearby star TRAPPIST-1 reveal that rocky worlds are common in our galactic neighborhood. Three of the planets are in the habitable zone, the region around a star in which liquid water is possible. However, planets that are Earth-sized and in the habitable zone have merely cleared the first two hurdles for a planet to support life!

Join the Boise State Physics Department and Prof. Rory Barnes from University of Washington on Friday, April 7 at 7:30p in the Multi-Purpose Classroom Building, room 101 to learn about how these planets were discovered, what it means to us, and the potential of discovering life beyond our Solar System.

Contact Prof. Brian Jackson (bjackson@boisestate.edu) with any questions.

The TRAPPIST-1 System

Posted by admin on February 28, 2017
Posted in: BSU Journal Club. Tagged: , , .

Unless you were living under a very large and heavy rock last week, you probably heard about the discovery of seven planets in the TRAPPIST-1 system by Michaël Gillon and colleagues.

Although this system was already known to host three, roughly Earth-sized transiting planets, the discovery of four more throws the door wide open for habitability – all seven planets receive the right amount of starlight from their diminutive red-dwarf host that liquid water might be stable on their surfaces.

There are so many interesting questions to explore for this system – What are the planets’ atmospheres like? How did this system of tightly-packed planets form and how do their orbits remain stable? And, of course, are they habitable?

Fortunately, concerted follow-up observations and theoretical studies can probably a lot of these questions. The fact that the planets all transit their small host star means their atmospheres are ideal for study by the James Webb Space Telescope. Strong gravitational tugs among the planets caused their orbits to change visibly over the course of the observations, so we have strong constraints on how exactly the planets interact.

The last and probably most important question is going to be a lot more difficult to answer. But since a detailed understanding of this system is likely (and probably inevitable, given the enormous enthusiasm for this system), we’ll soon be very close to answering the question of whether the TRAPPIST-1 system is habitable and maybe even inhabited.

One bit of trivia: the TRAPPIST survey that discovered this system was named in honor of the contemplative Roman Catholic religious order of Trappists, and the astronomers reportedly celebrated their discovery with a round of Trappist beer. Maybe this should be the start of a new tradition of naming new planetary systems after beers.