The Search for Life in the Universe Just Got a Lot More Interesting

Discovering several Earth-size planets around TRAPPIST-1 means the likelihood of finding life within the habitable zones of other star systems could be much greater than previously thought.

The discovery of seven Earth-sized worlds orbiting a star 40 light-years away is certainly exciting news for exoplanet hunters and enthusiasts. But with three of these planets in the habitable zone of the cool, dwarf star TRAPPIST-1, this new discovery is definitely increasing our odds of finding other life in our galaxy.

Experts say that finding multiple planets in the "Goldilocks zone" of a star is a great discovery because there can be even more potentially habitable planets per star than originally thought.

"Finding several potential habitable planets per star is generally great news for our search for life," Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University, said in an email. "In our own solar system, we have two planets in the Habitable Zone (Earth and Mars), and this new system has three planets in the Habitable Zone. So far, it holds the record for number of rocky planets in the HZ."

Even though these planets are Earth-sized, that doesn't mean they are Earth-like. But several research teams are planning follow-up observations, so that means the fun is just beginning.

"I think the detection of the new planets in the TRAPPIST-1 system is a groundbreaking discovery," said Thomas Barclay, director of the Kepler/K2 mission Guest Observer program. "This has given us an example of temperate planets in our own backyard that we will be able to study in the coming years. So many opportunities to learn new things in one planetary systems is extremely compelling. Following along with the study of these planets is going to be thrilling. Within a few years this planetary system will be the second best studied, after our own solar system."

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Sara Seager, a planet hunter and professor of planetary science and physics at Massachusetts Institute of Technology, said that since the discovery of TRAPPIST-1 astronomers have used every telescope available to conduct follow-up observations. The Spitzer Space Telescope was instrumental in making confirmation studies of these worlds, which is especially interesting since Spitzer was never designed to observe exoplanets.

The Hubble Space Telescope is screening the six innermost planets looking for evidence of atmospheres. These observations, in the infrared and performed with the Wide Field Camera 3, will provide further information about the nature of the planets. In addition, Hubble's Space Telescope Imaging Spectrograph already observed the two innermost planets in the ultraviolet to determine the amount of irradiation they receive from their parent star.

But the best observatories for finding out more about these worlds - especially for determining their habitability - have yet to be launched.

"Looking for atmospheric bio-signatures - meaning the presence of ozone that would shield the surface and indicate biology in combination with a reduced gas like methane - could be detected with the James Webb Space Telescope, which will launch next year," Kaltenegger said.

JSWT's study of atmospheres to assess the greenhouse gas content can also provide information about a planet's surface.

Another upcoming mission is the Transiting Exoplanet Survey Satellite that will attempt to detect small planets with bright host stars in our nearby solar neighborhood, so that detailed characterizations of the planets and their atmospheres can be performed.

"This new discovery is just a taster for planets that the TESS mission will find, which is due for launch in March 2018," Barclay said. "The goal of this is to find new worlds that we can study with future telescopes like JWST. I hope that within a decade we will have a clear picture of the atmospheric chemistry of planets like those around TRAPPIST-1."

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The search for life around the star, Barclay said, requires the use of transit spectroscopy.

"We use starlight shining through the atmosphere of a planet to tell us about the chemical makeup of that planet," he explained. "What we are looking for is telltale signs of chemicals we think are evidence of biological processes. Examples might be methane, oxygen and carbon dioxide. In the near future, observations from the James Webb Space Telescope will be key to this discovery."

Barclay added that up until now almost all the planets we know about are not actually seen, but astronomers use proxy observations, like transits, to understand their characteristics. But that will change with new observatories and techniques.

"In the future we want to directly image earth-like planets," he said. "This involves using technology called coronagraphs to block out the starlight and leave only the light from the planet. Future NASA space experiments like the Wide Field Infrared Survey Telescope mission will allow us to image planets like Earth."

WFIRST is expected to launch in the mid-2020's.

Kaltnegger explained that the new discovery of exoplanets orbiting TRAPPIST-1 won't change where astronomers look for planets in the Habitable Zone because it is easiest to find small Earth-size or Earth-mass planets around the coolest smallest stars.

"We know small stars are more likely to make more rocky planets," she said. "Now we found three of them, and at the right distance too. That is exciting!"

Thomas Zurbuchen at NASA Headquarters said that the TRAPPIST-1 discovery is a major step forward in answering that age-old question of whether or not humans are alone in the universe.

"How do we get the data we need to answer these questions?" he asked. "For me it is all about the thought I have when I go to bed at night; the fact that there are worlds out there that have some commonality with Earth. These questions of if we are alone in the universe are being answered as we speak."