NASAs Kepler Telescope Finds Probable Earth-Size Planet
Scientists working with NASA’s Kepler satellite reported Thursday that they might have spotted a planet just 1.5 times the diameter of Earth around a Sun-like star 2,000 light-years away.
“We’re still in the process of confirming this candidate is a planet,” said Matthew Holman, of the Harvard-Smithsonian Center for Astrophysics, at a NASA-sponsored news conference on Thursday. Dr. Holman is the lead author of an article describing the discoveries that the journal Science published on its Web site.
This is the first announcement of a candidate Earth-size planet by the Kepler mission, which in March 2009 launched a one-ton spacecraft to search for planets like ours that just might harbor life. The planet was among more than 700 candidate planets that the team announced in June. If it is made of similar stuff as Earth, its mass would be three to four times as much.
The planet discovered should probably be called a “Super-Mercury”, as it is so close to its star that it will be quite hot.
Nevertheless, this is the first non-gas-giant that Kepler has discovered.
Here is the actual science paper’s abstract:
The Kepler spacecraft is monitoring over 150,000 stars for evidence of planets transiting those stars. We report the detection, based on 7 months of Kepler observations, of two Saturn-size planets that transit the same Sun-like star. Their 19.2- and 38.9-day periods are presently increasing and decreasing at respective average rates of 4 and 39 min per orbit, and in addition the transit times of the inner body display an alternating variation of smaller amplitude. These signatures are characteristic of gravitational interaction of two planets near a 2:1 orbital resonance. Six radial velocity observations show that these two planets are the most massive objects orbiting close to the star and substantially improve the estimates of their masses. After removing the signal of the two conrmed giant planets, we identify an additional transiting super-Earth-size planet candidate with a period of 1.6 days.
So the rocky planet discovery was as a result of finding the dual Saturn size planets.
Nevertheless, from the first 700 candidate list there will no doubt be many rocky, Earth-size planets.
Since this first candidate list only includes items from the first 7 months of observation, and because it takes three transits to measure the orbital period, all the planets on the first list are quite close to their host star, and thus are too hot to be Earth-like, even if Earth sized.
And, since each candidate discovered by transiting needs to be confirmed by other methods - specifically radial velocity methods, it will take several months to work through the list, employing Earth based telescopes.
Also, the standard accepted by the Kepler team is that they won’t announce that they have discovered a planet unless they are confident to the seven-sigma level of noise. As the NYT article mentions in quoting an astronomer, even a 99% probability isn’t good enough for them. In this regard the exoplanetologists have set a very high bar for confidence, more so than many other scientific disciplines.
What this all means is that this discovery announced today is barely the tip of the iceberg, and there will be many, very many future announcements of rocky planet discoveries.