Published in The Patriot Ledger May 17, 2013:
When I was a boy, I read many science fiction stories featuring alien civilizations on our neighboring planets, such as “A Princess of Mars” by Edgar Rice Burroughs, in which John Carter travels to Mars and meets a beautiful red Martian princess who falls in love with him. But over the last half-century, NASA has sent space ships to study all the planets and their moons, and although we’ve learned lots about the history of the solar system, we’ve found no signs of alien life. There seems to be no one out there.
NASA probes have found that Mars had much liquid water a few billion years ago, when life first arose on Earth, and bacteria may have evolved back then on Mars as well. And scientists think that Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, today have underground oceans of liquid water that may harbor early forms of life. If we ever find definitive evidence of bacterial life elsewhere in the solar system, that will be an important scientific discovery, but somehow bacteria are not as exciting as beautiful alien princesses.
We will now have to look farther out for advanced forms of life, including alien princesses. The next places to look for possible life are planets orbiting other stars, starting with our Sun’s neighbors, the billions of stars in our own Milky Way galaxy. Scientists had long assumed that other stars had planetary systems, and for about twenty years now, they have been finding them. The use of telescopes to search for planets orbiting other stars, called exoplanets, has become one of the most exciting frontiers of astronomical research. Nearly a thousand exoplanets have already been confirmed, and several thousand additional candidates have been identified.
It’s hard to see exoplanets directly – they’re smaller than stars and don’t emit their own light. Many have been observed indirectly by their gravitational effects on the star’s motion, which can be measured accurately by changes in the frequencies of the star’s emitted light. And a growing number have been observed through the periodic dimming of the star as exoplanets cross in front of it.
Large Jupiter-size planets are easiest to detect. But if we’re looking for possible life, we are most interested in planets that are near Earth-size, and that orbit their stars at a distance favorable to life, in the so-called “Goldilocks zone,” neither too hot nor too cold to hold liquid water. We think liquid water is required for the evolution of life.
In 2009, NASA launched the Kepler space telescope for the specific purpose of using the periodic-dimming technique to search for Earth-size exoplanets in the Goldilocks zone around their stars. Kepler is now many millions of miles from the Earth, reliably gathering data on variations in the light from distant stars. Although it has just suffered a malfunction, it has been getting important results for several years.
Current excitement is focused on Kepler-62, a star system in the constellation Lyra, which was reported last month to have at least five exoplanets, two of which (62e and 62f) are near Earth-size and in the Goldilocks zone. That makes Kepler-62 a prime target for SETI, Search for Extraterrestrial Life, the long-standing project that searches for promising radio signals from distant stars, as Jodie Foster did in the 1997 movie Contact.
The catch is that this star is so far away from Earth that radio signals take over a thousand years to get here, so any message they sent is now old news indeed. And we will have to develop a propulsion technique like Star Trek’s warp drive that produces speeds in excess of the speed of light, in violation of present-day physics. Otherwise, we won’t be able to meet the beautiful alien princess living on Kepler-62e.