Prof. Lisa Kaltenegger's research focuses on detecting possible habitable worlds TRAPPIST-1.

Courtesy of NASA/Caltech

Prof. Lisa Kaltenegger's research focuses on detecting possible habitable worlds TRAPPIST-1.

January 28, 2019

Head of Carl Sagan Institute is Searching the Stars For Life

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As the hunt for life in the universe continues, the planets being found are getting smaller and smaller thanks to new technologies that have identified thousands of planets for closer examination.

Prof. Lisa Kaltenegger, astronomer and director of the Carl Sagan Institute, presented about the discovery of these exoplanets — planets outside Earth’s solar system — in a lecture on Monday in Rockefeller Hall’s Schwartz Auditorium.

“We have nearly 4,000 confirmed exoplanets [that we can test] so far,” she told the crowd. “We have about 5,000 more candidates that we are still evaluating.”

Kaltenegger and her team at NASA are evaluating whether or not these planets are worth future study to determine if they might contain organic material. If so, the first step is to measure the planets’ oxygen and methane contents. If enough of both are present, it’s a “tell-tale sign of life” on the light-years-away planetary bodies.

However, because these planets are so far away, there is no direct way to sample their atmospheric makeup. Instead, researchers can only observe the planets when they pass in front of their respective suns.

“Part of the stellar light gets filtered through the atmosphere of the planet before it gets to us,” Kaltenegger said. “We can actually start to characterize the atmosphere, the air, of other planets through this technique.”

By analyzing the light that makes its way back to Earth, the team can determine whether the planets have the combination of gases that they are looking for.

Kaltenegger specializes in more diminutive, rockier exoplanets, which “by chance” became the main focus of the study.

“Even though it’s way easier to find the big or massive planets, we are finding many, many more of the smaller planets,” she said.

Most of these planets were found through the Kepler telescope mission, which focused a massive telescope at the same area of the sky for three and a half years in order to chart the movement and orbits of all the planets within that zone.

Because the planets are detected when they pass in front of solar bodies, smaller planets actually have a disadvantage.

“Big planets have an advantage because they block more of the stellar light. It’s really hard to pick up anything smaller than the Earth,” Kaltenegger added.

Kaltenegger’s team then calculates the density of each planet, which yields more clues to the likely makeup of the planet. After “hundreds and hundreds” of geochemical equations, the researchers decide whether it falls within that “habitable zone.”

“This concept of a habitable zone is something we use to prioritize planets for follow-up,” Kaltenegger said. “By no means is the habitable zone where there can be life. It’s just where we can find life, where we can pick up life.”

However, in this search, her team tries not to be too “human-centric,” as life can take many different shapes even on Earth.

“If you just look around, there’s a lot of really interesting life on Earth that you don’t think about,” she said.

Despite the progress, scientists still don’t have a good estimate about how many planets might contain some form of life. Kaltenegger quipped that she has an answer ready whenever people ask how many planets may be habitable.

“Fifty percent,” she said. “Plus or minus fifty.”