The past year has been a thrilling time for astronomers, even as NASA closed another chapter in its history with the launching of the agency’s final space shuttle. With the era of shuttles and moon walks coming to a close, a fresh, exciting age has arrived to replace it, with discoveries that may lead to the confirmation of life outside of Earth.
NASA’s newest focus now goes beyond the moon, the sun and even our solar system as a whole. Officially initiated in 2001, the Kepler Mission is the newest frontier into planetary exploration, focused on discovering Earth-sized planets outside our familiar eight-planet solar system. Kepler scientists, including a UC Berkeley professor, have so far identified over 2,300 new planets, nearly quintupling the number of known planets. Eventually, they hope to identify planets hospitable to life and perhaps even find life — microbial or otherwise.
Since January of 2010, Kepler scientists have regularly announced the identification of a number of possible new planets, including the groundbreaking confirmation this past September of planets that orbit two stars at oncerather than simply a single star.
Scientists have confirmed that 35 of the 2,326 possibilities identified thus far are certainly planets — an astounding number, considering that not too long ago scientists questioned the frequency of planets orbiting stars at all.
They now know that such systems are fairly common, and some even contain planets in the habitable zone, where a planet could potentially support life.
“Kepler has really opened up things as far as looking for life in the universe,” said Laurance Doyle of the SETI Institute, who led the team that discovered the first confirmed case of circumbinary planets — planets that orbit two stars rather than just one.
Scientists are specifically searching for a so-called “Goldilocks planet” — one that is neither too hot nor too cold and has the right physical traits for life.
“We are desperate to find a planet that is Earth-like,” said Geoff Marcy, a campus professor of astronomy and a co-investigator on the Kepler Team. “We’re still looking for a planet that is rocky like the Earth, has a hard surface (and is) lukewarm like the Earth.”
The Kepler spacecraft finds planets by detecting the temporary dimming of a star, allowing scientists to deduce that some object, often a planet, has passed in front of it, much akin to a speck of dust falling on a light bulb. Scientists can then figure out the size of the planet by watching to see if the star wobbles in space, which only occurs if a planet is exerting a gravitational force on it.
“We can determine masses by how strongly (a planet) yanks on a star,” Marcy explained. “(It’s like) a dog owner on the end of a leash. A strong dog will yank on its owner’s leash so that the owner gets yanked around. So you can kind of tell how big a dog is by watching the owner.”
Yet as scientists continue to identify stars by the dozen, none have yet proven to be conducive to life. Of the 2,326 possible planets, only 54 are in the habitable zone, and none has yet shown the traits necessary for supporting life.
But the real question, many researchers stress, is not if extraterrestrial life exists but what constitutes life at all?
The conventional answer is that life is carbon-based and requires water in the form of liquid. However, many scientists have pointed out that the current understanding of life is very Earth-centric, and humans essentially have no idea what they are looking for when searching for alien life forms.
“Maybe there’s life that doesn’t need water, maybe life doesn’t have to be carbon-based,” Marcy said. “Life out there that might be completely different from the type of biology we have on Earth.”
Not only are scientists looking for life, but they are also looking for signs that life ever existed — or could potentially exist — on a planet. Life on Earth, after all, is relatively recent, and only 10 percent of Earth’s history has witnessed life big enough to see with the naked eye.
“You can just imagine the typical (alien) space traveler coming to Earth at a random point in Earth’s history,” said Don Brownlee, who co-authored Rare Earth, a book that explored the extent to which Earth is unique in the universe. “They would say ‘Ah, no life here,’ and get up and leave.”
Human forays into space are just getting started, and scientists have more questions than answers as to the possibility of extraterrestrial life.
“At Cal, we pride ourselves on doing research that’s challenging and beyond the imagination,” Marcy said. “The search for life is made even more difficult because we don’t even know what we’re searching for.”