In the search for life on another planet, NASA and UC Berkeley astronomers from the Kepler mission announced Wednesday the discovery of 1,235 possible planets, which would triple the number of known planets in the universe.
Although the planet candidates have not yet been confirmed, astronomers believe that most will prove to be planets. But even more thrilling to scientists than the sheer number of new planets is the possibility that 54 of those planets happen to fall in the habitable zone, where the temperature is suitable for life.
“We’ve worked 16-hour days, 7 days a week toward this,” said Geoff Marcy, co-investigator of the mission and a campus professor of astronomy, in an e-mail. “We’re exhausted … but this is a watershed moment in human history.”
The mission’s planet-hunting satellite has only actively been on the prowl since March 2009, but Alex Filippenko, campus astronomy professor, said it has already made fundamental advances.
Over the last 15 years, traditional methods yielded about 400 confirmed exoplanets. In just over a year, the Kepler mission, which instead finds planets by measuring how much the host star’s light dims as a potential planet passes by, has located more than 1,200 candidates.
“The traditional way in the past was to take a spectra of stars over the course of time and see if those stars were wobbling in response to a planet orbiting them,” Filippenko said.
Most planets found before this group were far too large to support life, as greater size generally indicates an inhabitable composition, such as of gas or liquid. However, among the planets announced this week, more than 600 are smaller than four times the size of Earth, Marcy said in the e-mail.
“These numerous worlds of nearly Earth-size indicate that the prospects of finding habitable, Earth-like planets are very good,” he said in the e-mail.
The planets are not confirmed and life on any one of the 54 planets in the habitable zone has yet to be found. Confirming that the planets are, in fact, planets will require years more of work, using data collected from telescopes on the ground to measure planets’ masses, among other methods.
Only then can astronomers begin the actual search for life on another planet. According to Filippenko, there are a variety of indicators that suggest life, such as the contents of the planet’s atmosphere.
“The composition of Earth’s atmosphere … could be used by aliens to strongly argue that there’s life on Earth,” he said. “You don’t have to get tweets from aliens in order to know that they’re there. You can figure out that life is present based on the effect it has on the planet’s atmosphere.”
Indicators could include an abundance of atmospheric oxygen and methane, the former allowing life to survive and the latter a byproduct of life’s existence.
Even without confirmation, the certainty scientists have that most of the 1,235 are planets makes the discovery historical, akin to when the first exoplanet was found, Filippenko said.
“When you look up tonight at the night sky, gazing at those twinkling lights, you are the first people in human history to know that most of them contain planets, big ones and small ones,” Marcy said in the e-mail. “Surely some of those planets are rocky with a temperature just right for life.”