Searching for Other Earths

From earliest times, humans have contemplated the existence of other Earth-like worlds in the universe.

Now, NASA is turning conjecture into conclusion with its Kepler Mission, a first attempt to determine whether planets similar to earth are a rare or common occurrence in our galaxy.

"This is an important project in NASA's astrobiology path," said San Diego State astronomy professor Bill Welsh, the only Kepler Participating Scientist from Southern California. "It's asking, are there other planets like ours out there? That's the first question we need to answer."

The Kepler telescope, which launched March 6, will survey approximately 100,000 stars over three and a half years. It will use photometry to find planets by detecting the very slight change in brightness (only 0.008%) that occurs when a planet passes in front of its host star. Mission team members expect it may find as many as 50 Earth-like planets and become a stepping stone for further NASA missions to study these planets with more powerful telescopes.

A select group

When NASA announced  in February 2007 that it was looking for astronomers to assist with a new mission, Welsh jumped at the opportunity to become one of only nine astronomers nationwide to join the Kepler Mission Science Team. While the main science working group is highly focused on detecting Earth-sized planets, the Participating Scientists carry out complementary research on the detection, characterization and understanding of extrasolar planets.

Welsh's task is to complete a meticulously detailed analysis of planets similar to Jupiter using a cutting-edge analysis tool written by fellow SDSU astronomy professor Jerome Orosz.  Although Welsh's work is not directly focused on finding Earth-size planets, his research will greatly enhance understanding of the planets and possibly even detect a few Earth-like planets or moons.  He and Orosz have worked closely for the last few years on extrasolar planet research, and Orosz is a paid consultant for the Kepler Mission under Welsh's grant.

20 years of planning

Coincidentally, SDSU's ties to the Kepler Mission pre-date Orosz and Welsh. Kepler Principal Investigator Bill Borucki looked to SDSU adjunct astronomy professor Andy Young for guidance when he was getting started on this project back in the mid-1980s.

Borucki's idea of finding other planets through photometry was pushing the limits, but fortunately, Young was an expert in the field. He helped mentor Borucki through the difficult process of perfecting his technique for locating Earth-like planets.

Now Welsh is using his Kepler work as an opportunity to mentor current SDSU students. His astrobiology class watched the launch and answered NASA's request for essays explaining the importance of the Kepler Mission. The submissions were included in a DVD placed inside the Kepler spacecraft.

Blast off

Last month, Welsh attended the Kepler launch with other team members and their families. The crowd—close to 400 people—rode buses from Kennedy Space Center to their viewing spot five miles from the launch site. After much anticipation, the crowd cheered in unison as they watched the rocket successfully launch.

Although the final experience was joyous, Welsh had many anxious moments leading up to the launch. He described one night just before the event when, at 2 a.m., he suddenly had doubts about some of his computations. He spent three hours checking his results, not because anyone else questioned him, but because of his own high expectations.

"There's a lot of internal pressure—you know how important this is and you feel an obligation to do the best that can be done," he explained.

These days, Welsh is more relaxed as he watches Kepler's early successes. The telescope's dust cover was recently ejected, allowing starlight to enter Kepler's science instrument, the photometer.  Engineers will continue to calibrate the instrument using images of stars for another several weeks, after which science observations will begin.

Mission outcome

According to Welsh, there are two potential outcomes for the mission. One is the finding that there are many planets like Earth in the solar system, and therefore, life similar to ours may be common. The other is that Earth and life as we know it are indeed very rare.

Either outcome will have significant consequences, Welsh said. On one hand, scientists may hope to begin to detect other species and find that we are not alone in the universe; or, on the other hand, humans will realize just how important it is to preserve life and resources on our unique planet.

NASA will not begin to release results of the mission to Participating Scientists until extensive calibration and quality control have been completed, possibly sometime in the fall.  Welsh will work part-time on the mission this spring, then full-time starting this summer, making the most of his appointment, which will last at least three years.

"It is a privilege to be part of such an important and historic mission," Welsh said. "I am honored to have been selected to join the 45 or so Science Team members who will be working with the Kepler data to discover other worlds."