“I think we’re going to have strong indications of life beyond Earth within a decade, and I think we’re going to have definitive evidence within 20 to 30 years.”
— Ellen Stofan, NASA chief scientist, April 7
As NASA beefs up its search for life elsewhere, it has selected two teams of astronomers, planetary scientists and other specialists, led by the University of Arizona and Arizona State University, to join in a systematic search for Earth-like planets.
The Arizona investigations are among 16 new projects in a NASA program called the Nexus for Exoplanet System Science, or NExSS.
It aims to coordinate exoplanet searches, find habitable planets and identify signatures of extraterrestrial life.
At the UA, astronomers and planetary scientists were awarded a $5.7 million, five-year grant to identify the optimum conditions for extraterrestrial life and the planets around nearby stars that are capable of hosting it.
ASU astronomers will join with geophysicists and geochemists in a $6.1 million grant to ASU’s School of Earth and Space Exploration that will try to explore how to tell whether chemical signs of life on distant planets arose from geological processes or biological ones.
“The excitement is palpable,” said Steve Desch of ASU’s School of Earth and Space Exploration. “We are really poised to answer the question of life elsewhere.”
Desch leads a team that will focus on whether the “biosignatures” of life, such as oxygen and methane, that may be discovered on distant planets are actually the result of biology.
The UA-led team includes researchers from Tucson-based Planetary Science Institute, geophysicists from the University of Chicago, the National Optical Astronomy Observatory in Tucson and Catholic University of Chile.
It is led by Steward Observatory and the Lunar and Planetary Lab at the UA. Daniel Apai of Steward is the principal investigator.
Apai said the team will combine study of the composition of various classes of meteorites with measurements of the chemical composition of planet-forming dust disks into a “Genesis database” that can be compared with the composition, age and size of “habitable planet” candidates.
“One of the questions is: ‘When planets are created, what comes in the box? Does it come with useful ingredients in an environment conducive to life,’” said Joan Najita of NOAO. Najita will use infrared and radio telescopes to answer those questions.
Tom Zega conducts similar investigations on meteorites found on Earth that contain the compositional record of the formation of our own solar system.
“In order to find Earth-like planets, we have to look for certain signatures,” said Zega, a cosmochemist at the UA’s Lunar and Planetary Lab.
“Some are physical, such as how big a planet is, how close to its star. Is it in the habitable zone?
“But there are also chemical signatures. Does it have an atmosphere? Does it contain water? Does it contain organic compounds?
“We really have to look for a chemical biosignature because we’re never going to be able to measure little green men running around on the surface of a planet,” Zega said.
Exoplanets, while theoretically abundant in the universe, are not easy to see.
Most have been discovered because they caused a wobble or a slight diminution of a star’s light as they passed by. Few have been directly imaged, though the UA team includes astronomers who have accomplished that. Still, determining their chemical compositions eludes even the largest telescopes on Earth.
NASA has led the way in discovering thousands of these exoplanets — planets that orbit near and distant stars.
Scientists have extrapolated from those successful searches that billions of planets exist in the “habitable zones” of their stars — close enough to be warmed by their suns and far enough away to keep water and biological life from being vaporized.
NASA is basically “crowd-sourcing” its planet hunt to clarify where to look and what to look for with its next generation of space telescopes.
Apai said finding exoplanets has become relatively easy. “Searching for life is a different and difficult endeavor.”
The work of all the teams will aid NASA in deciding the capabilities needed for a space telescope that could do the job, he said.
The NASA program enlists a variety of disciplines in the hunt.
Christy B. Till is one of them. Till is a petrologist, who studies the origin, composition and structure of rocks. In her lab, she simulates the formation of magma under extreme pressure and temperature.
After joining ASU’s School of Earth and Space Exploration a year ago, she was easily lured into extending that research to other planets.
“Most of the research I’ve done so far is on the Earth. We’re now realizing how we can use it to understand other things. It adds a much bigger scope to your research. It makes you excited to get out of bed and come to work.”