A Leap Forward in the Search for Life on Other Planets
By Darby Kendall
Space aliens. Little green men. Life on far planets.
From time out of hand, humankind has wondered whether life exists beyond Earth. For over 25 years, William Cochran has been trying to answer that question, and rapid advances in technology for scanning the cosmos today may have pushed his goal within reach.
“There’s nothing special about us,” said Cochran, an astronomy professor at the University of Texas at Austin. “Virtually every star has planets, so why can’t we assume they all have life?”
The very question marks a giant leap forward for science.
Until the early 1990s, researchers weren’t even sure whether planets existed outside our solar system. Now, thanks to Cochran and his fellow pioneers at NASA’s Kepler mission and at observatories around the world, we know there are tens of thousands of “exoplanets” in and beyond our own Milky Way galaxy.
Cochran and UT colleagues Phillip MacQueen and Michael Endl are advancing that search at the McDonald Observatory in Fort Davis, in West Texas, where their ground-based program uses state-of-the-art spectrography to detect planets that are most like Earth and therefore most capable of supporting life as we know it.
Spectrographs work by measuring the slight motion of stars that are often thousands of light-years away. Individual planets are invisible at such distances. If the star’s path wobbles, however, scientists theorize that gravity from an unseen planet is tugging on it. In measuring the movement, the spectrograph will tell Cochran and his team the size of the planet doing the tugging.
The UT team expects its study to benefit from $500,000 of improvements to McDonald’s 20-year-old Hobby-Eberly telescope that come on line this year and will help them draw a sharper bead on their exoplanet clientele.
“We’re very interested in finding rocky planets in the habitable zones of stars,” said MacQueen, a UT astronomy professor and chief scientist at the McDonald Observatory, because that is where researchers believe they stand the best chances of finding signs of life.
UT researchers also have been using the Hobby-Eberly telescope to collect data on a million galaxies that are up to 11 billion light-years away, information likely to yield the most detailed map of the universe ever produced. Funding for both Hobby-Eberly efforts comes to $33 million.
Cochran, 64, credits NASA’s 25-year, $600 million Kepler mission with kickstarting the field of exoplanet discovery. In addition to his university duties, he has spent much of the last two decades working as a co-investigator on Kepler, which is named after the pioneering 17th Century German astronomer Johannes Kepler. Since 2009, the Kepler space telescope has been orbiting our sun every 372.5 days and has spotted 4,000 exoplanets, 1,019 of which have been confirmed by other telescopes.
Astronomers now estimate the number of stars in the Milky Way at hundreds of billions, and each star could have at least one or two planets orbiting them. “There has to be life out there somewhere else,” Cochran said. “It’s kind of scary to think we’re as good as it gets.”
The planet Kepler-22b, for instance, was detected by Kepler and confirmed at the McDonald Observatory in 2011. That particular world, 600 light-years from Earth, was the first transiting exoplanet to be found within the habitable zone of a sun-like star, meaning it has great potential to support life.
The Kepler telescope works by taking snapshots of the same patch of sky, day in and day out, for years. Because planets far off in the universe are too small for a telescope to detect, Kepler instead looks for “transits”— planets crossing in front of a star that temporarily block its light. When the light goes out during one of Kepler’s 30-minute scans, scientists know they’ve discovered an exoplanet.
Public opinion polls consistently show that more than half of Americans surveyed believe extraterrestrial life exists. Yet Cochran warns that such life, if and when it’s discovered, is more likely to take the form of micro-organic ooze than Star Wars aliens.
“Life developed very quickly on Earth,” Cochran said. “But for most of that time, the life was microscopic.” Intelligent life, he says, formed slowly, and that is likely to be the case at other cosmic addresses.
Efforts to find Earth-like planets and any alien life pasturing there are doing more than just working to answer the age-old question, “Are we alone?” They also help scientists better understand our own solar system and the sun that allows Earth to sustain life.
“We want to understand the diversity of planetary systems that have formed,” Cochran said. “That can help us to understand the process of star formation in general.”
Cochran’s fascination with astronomy began when he was a boy growing up outside of Schenectady, N.Y. While studying physics at Duke University as an undergraduate, he decided to make a career out of his passion. “I figured if I can actually get paid to do my hobby, well, it would be great,” Cochran said. “What else do I want in life?”
Cochran received his Ph.D. in astrophysics from Princeton University in 1976 before coming to UT as a post-doctoral fellow. Although Cochran joined NASA’s hunt for exoplanets in 1995, he was detecting them on his own time years before. In the late 1980s, a small community of astronomers, including Cochran, discovered exoplanets by surveying the movement of stars.
“Cochran got involved in the Kepler mission because he was already very well known for his work on exoplanets,” MacQueen said.
Few expected Kepler to find such a huge number of planets. “It is absolutely astounding that the Kepler telescope has found over 4,000 planets around other stars,” said Geoff Marcy, an astronomy professor at the University of California at Berkeley. “Incredibly, most of these stars are roughly the size of our Earth, or somewhat larger by two or three times.”
“The universe is lousy with Earth-size planets,” Marcy said.
The next advances in telescope technology may allow scientists to zero in on which exoplanets contain life, such as Kepler-22b. NASA’s $8.7 billion James Webb Space Telescope, set for completion in 2018, will survey the chemical signatures of Earth-like planets from space to judge whether they might have life. The telescope will see if planets contain oxygen and methane and other gases that are essential to life.
The $700 million Giant Magellan Telescope project, involving a consortium of American universities, is scheduled to start operation in 2020 in Chile and will produce images 10 times the resolution of the Hubble Space Telescope, the world’s costliest telescope when it was launched in 1990. UT, one of the founding partners of the GMT, will fund 10 percent of the telescope’s cost to receive 10 percent of the viewing time, according to Cochran. The Giant Magellan will be unique due to its ability to create high-resolution images of planets from Earth.
Those telescopes will give astronomers a much more detailed view of exoplanet atmospheres, Cochran said. “This will completely revolutionize our study of exoplanets.”
Some experts in the field, such as Tom Murphy, a physics professor at the University of California at San Diego, wonder if the long-term goals of interstellar exploration are realistic enough to warrant the spending.
Murphy approves of the spending on Kepler but is skeptical about the success of what might follow: human interstellar travel. “It’s a catch-22; most people are energized by the human exploration side, so if it weren’t for that maybe NASA wouldn’t get enough funding to do the science part,” Murphy said. “We can look, but we can’t touch, and I don’t think most people understand the reality of that.”
Cochran said the spending is justified because exoplanet research produces vital knowledge and create jobs. “I believe it would be a serious mistake to not spend this money,” he said.
A shorter version of this story appears in the Insight section of the Austin American-Statesman