What will the James Webb Space Telescope reveal about the newly discovered exoplanets?
The discovery of seven habitable planets just 40 light years away is certainly impressive, but the fact is, they are still 40 light years away. Unless we're willing and able to spend thousands of years traveling through space, we won't be rolling into the TRAPPIST-1 system anytime soon. This means that over the coming decades, advanced scientific instruments closer to home will play very important roles in exploring these distant worlds – perhaps none more so than the James Webb Space Telescope. So what can we expect when it is fired into orbit next year? We checked in with some of the scientists behind yesterday's hugely exciting discovery to learn how astronomers will use NASA's next-generation space telescope to probe the secrets of the TRAPPIST-1 system.
The James Webb Space Telescope (JWST) has been almost two decades in the making and, spanning the size of a tennis court, will be the largest space telescope ever assembled. Poised to take the reins from Hubble as NASA's premier orbiting telescope in 2018, it will boast seven times the light-collecting capacity of its predecessor and will be sensitive enough to spot a single firefly one million kilometers away.
Astronomers plan to put its capabilities to use in a number of exciting ways, such as looking back over 13.5 billion years to unravel the mysteries of the early universe, exploring how early stars and galaxies formed, and studying the atmospheres of planets outside our solar system. But as Adam Burgasser, an astrophysicist at UC San Diego and co-author on yesterday's groundbreaking paper tells us, the new discovery will place the TRAPPIST-1 system among its top science priorities.
"I suspect TRAPPIST-1 will be one of the first targets for the facility," he says. "I know several of the scientists on the instrument teams. Those that helped build and test the cameras on the telescope are eager to flex their muscles on this exciting system, and of course we will be proposing to observe the sources as soon as we can."
According to Katherine Deck, study co-author and research fellow at Caltech (the research institute behind NASA's Jet Propulsion Laboratory), promptly pointing the JWST in the direction of TRAPPIST-1 makes a lot of sense.
"One major research priority for JWST is to characterize the atmospheres of Earth-sized planets, and Trappist-1, with six Earth-sized planets – three of which are in the nominal habitable zone of the star – is an excellent target for this research goal," she tells New Atlas.
One of the inherent difficulties in exoplanet research is the blinding light that comes from the parent star. This makes it impossible to directly image the circling exoplanets. Instead, they are detected through what is known in astronomy circles as transiting, where orbiting planets create dips in the star's light as they pass in front, revealing their presence to exoplanet hunters here on Earth. TRAPPIST-1, the system's parent star, is dim and small (around the size of Jupiter), but not dim enough to directly image its planetary system.
"The planets are too close to their star to resolve even with a large telescope like JWST, so we'll still be relying on the transit method," Burgasser says. "However, JWST will allow us to search not just for starlight blocked by the planets, but starlight that filters through their atmospheres, which will allow us to measure the temperatures and chemical compositions of those atmospheres in more detail, necessary to search for life."
This technique is called transit spectroscopy and will be the main approach used to study the atmospheres of the TRAPPIST-1 system through the JWST. Deck explained to us how it works.
"When a planet passes in front of a star, it blocks light from that star," she says. "A bigger planet will block more light. If a planet has an atmosphere, that atmosphere extends the size of the planet past the size of the rocky core, and so planets with atmospheres block additional light, compared with those with the same size rocky core, without an atmosphere.
"The key point is that the atmosphere only blocks light of certain colors, or wavelengths, which correspond to particular wavelengths of light that excite particular molecules in the atmosphere. Effectively, JWST will look at a host star with different filters on, isolating particular colors of light from the star. When the transit happens, the amount of light blocked by the planet will be different in each of the filters, depending on which molecules are present in the atmosphere and on other characteristics of the atmosphere."
Of light and life
Scanning this light for atmospheric molecules could reveal all kinds of secrets about the planets in the TRAPPIST-1 system, including possibly the building blocks of life.
"By spreading out that light like a rainbow, we can look for signatures of molecules and atoms in the atmosphere, including oxygen, methane and water vapor, all potential signatures of life," says Burgasser. "JWST can also be used to measure the reflection of starlight off of the planets when they pass behind the star. This is called a 'secondary eclipse.' This would potentially allow us to study the surfaces of the planets."
While it will be a big player in exoplanet research in the coming decades, the JWST is just one of a number of tools scientists will use to search these worlds for signs of life. The Giant Magellan Telescope, for example, will feature an aperture 15 times that of JWST and will start scanning the night sky from Chile's Atacama Desert sometime in the mid-2020s. With these, plus other larger telescopes and yet-to-be developed technologies entering the fray, how much will we learn about the TRAPPIST-1 system without ever actually going there?
"Quite a lot," says Burgasser. "In addition to the atmosphere and surface measurements, we have some earlier measurements of mass, but with higher precision instruments and larger telescopes, we could improve those measurements and get a firm measure of the planets' average density, which in turn would tell us if they are mostly rocky, like Earth, or a mixture of rock and ice, like Jupiter's moon Ganymede. There is a chance one or more of these planets have moons, which may show up in more detailed transit measurements."
And as Burgasser explains, the things discovered in the TRAPPIST-1 system might be just as vital in answering key questions as the things that are not.
"We are also looking for evidence that the planets may be losing their atmospheres due to magnetic winds coming from the star, an important consideration to determine whether water is retained on their surfaces," he says. "And of course the big question is life itself, did it arise on any of these planets? Are they even hospitable to life? All of the measurements above are important ingredients to answering these truly big questions."
The video below (provided by the European Southern Observatory) offers a few early and interesting facts about these newly discovered worlds.