Little morethan a decade ago, astronomers Michel Mayor and Didier Queloz announced thediscovery of a planet in orbit about 51 Pegasi. It rushes around its sun injust over four days, seared to a temperature of 1,000degrees Celsius (about 1,800 degrees Fahrenheit).
Today, wecall this sort of planet a "hot Jupiter." This was the first planetfound orbiting a main sequence star — a star similar to our sun.
Almostweekly, there's an announcement of yet another extrasolar planet around aneighborhood star. This week, it's a triple system ofsuper-Earths discovered at the European Southern Observatory at La Sillausing the HARPS (High Accuracy Radial velocity Planet Searcher) instrument.
The planets, having 4.2, 6.7, and 9.4 times the mass of the Earth, orbit the star with periods of 4.3, 9.6, and 20.4 days, respectively.These short periods place the trio of new planets well within the orbit ofMercury around the sun. So, again, these are hot planets, well inside thehabitable zone of their star. This trio, and others, were announced this weekat the international conference, "Extra-solar Super-Earths," anddemonstrate that small planets are likely common.
"Clearlythese planets are only the tip of the iceberg," says Michel Mayor, team leaderfor this discovery. "The analysis of all the stars studied with HARPSshows that about one third of all solar-like stars have either super-Earth orNeptune-like planets with orbital periods shorter than 50 days."
Super-Earthsare beginning to be found with high-precision instruments like HARPS. Hints ofsmall planets have also been reported by the COROT (COnvection ROtation and planetary Transits) Mission and by thegravitational lensing experiments underway.
But theholy grail — an Earth-size planet in the habitable zone of its star— awaits NASA's Kepler Mission.
The Keplerspacecraft launches in February 2009, 400 years after Johannes Kepler publishedhis first two laws of planetary motion in Astronomia Nova, the "NewAstronomy," which first described planets orbiting on ellipses and atvarying speeds around the sun. Ten years later, he published his third law,which relates the period of the planet to its mean distance from the sun.Kepler used his discoveries to predict solar transits of Mercury and Venus, butdid not survive to observe them.
FindingEarth-size planets in Earth-like orbits requires patience, because observationsmust be repeated to confirm discoveries. If an alien astronomer in a distantsolar system werelooking for us, Earthly transits would be seen once per year, and that goodastronomer would require at least three transit observations to announce adiscovery. The same is true for the Kepler scientists. Kepler's scientificprospectors should be announcing discoveries of Earth-size planets in habitablezones by 2011-2012.
In myopinion, that's a short wait to answer the question, "Are there other planetslike Earth orbiting distant suns?" We're approaching the mother lode ofdistant solar systems, and the Kepler Mission promises a major advance towardunderstanding whether we are alone in this vast universe.
- Video Player: Mercury Transit
- Largest Known Exoplanet Discovered
- The Kepler Mission: The Search for Earth-like Planets
Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@space.com.
