Tuesday, May 24, 2005
Looking For Distant Earths In All The Right Places.
Cox was in San Diego to speak at the Aerospace Museum as part of its mysteries of aviation series. (Click here for museum website.) The mystery Cox talked about was "are there other Earths in our galaxy?"
Cox is just coming off a stint as part of the Mars Rover team. In that job she helped to answer the question whether liquid water ever flowed on the surface of Mars. The Rovers answered that question with a resounding "yes!" Now Cox is moving on to an even greater mystery.
The search for extra-solar planets is just beginning. The first such planet was discovered revolving around a neutron star in 1992. To date, the search for planets outside our solar system has relied on a technique called "radial velocity." That technique measures the wobble of a star caused by the presence of a planet.
Radial velocity is good for detecting large gas giants. It's not so good at detecting smaller rocky planets like Earth, Mars and Venus. Kepler will use a new technique to search for those planets, called the "transit method." It will look at stars to detect the slight dimming to the face of the star caused when a planet passes in front of it. In essence, Kepler will be looking for spots on distant stars to detect small planets.
This is no easy task. For example, Earth casts a shadow on the sun that makes a circle covering only 0.01 percent of the sun's surface. When you combine this small shadow with the fact that other stars have sunspots, just like our sun does, it's easy to recognize the difficulty of Kepler's mission.
Kepler will have a 100 megapixel camera for its mission. It will have to stare at its targets continuously to determine what is a sunspot and what might be a planet. To provide the best vantage with the least interference from the Earth for viewing the distant stars, Kepler will be launched into an orbit that trails the Earth on its voyage around the sun.
When Kepler detects a likely candidate its data will be shared with other astronomers to do the follow up work to confirm whether a planet exists. Kepler's job is a census mission. It will try to detect a statistically significant number of objects to help determine the frequency of Earth like planets around other stars. Kepler's instruments will be precise enough to detect whether the planet is within the so-called Goldilocks Zone of the other star where liquid water could exist -- about 1 A.U., or the distance of Earth's orbit, for a sun like ours.
Cox is optimistic about her new mission. Today, we know that 144 planets circle around other stars in our galaxy, a fact that was mere speculation before 1992. She told her San Diego audience that 6 years from now we will know whether there are other Earths in our galaxy.
We won't know whether these other Earths can sustain life. All we will know is whether there are planets like Earth orbiting other stars in the zone where liquid water could exist. In searching for life here in the Heliosphere, we have adopted the strategy of following the water. Kepler is taking that strategy beyond the solar system to look for places where water could exist and life could find a home.
Are we alone in the universe? Stay tuned.