In August 2010, NASA’s Kepler Mission announced the latest series of results from the Kepler space telescope. The new findings actually included a number of new planets in several different star systems. However, the most immediate returns – and the highlight of the most recent press conference – was the discovery of a pair of new Saturn-sized planets imaged crossing in front of their star at the same time, now named Kepler-9a and Kepler-9b.
The Kepler space telescope is now just over a year old and the $600 million satellite has already been living up to many of the great expectations placed upon it. Finding planets orbiting other stars, hundreds or even thousands of light-years away, is extremely difficult and requires a number of sophisticated tricks, measuring changes in light levels of distant stars as their planets cross in front of them and then circle behind them. The difficulties involved have meant that, since the first extrasolar planets were discovered in the early 1990s, the growing catalogue of known planets has been extremely heavily biased towards very large planets, orbiting very close to their Sun. The surprising discovery of these so-called “super-Earths” and “hot Jupiters” (respectively, very large but probably solid planets, and large gas giants orbiting closer to their own stars than Mercury does our Sun) was unexpected, given that neither are present in our own solar system.
At the same time, astronomers long suspected that, extrapolating from our own solar system, the apparent prevalence of these hulking planets was an artifact of our sensor technology rather than an accurate reflection of the galaxy. In short, the theory went, we were finding very large Jupiter-like planets in unusual locations not because these planets were necessarily the majority of planets out there, but simply because those were the easiest planets to see with our current technology.
When the Kepler space telescope launched in 2009, it quickly established that these skeptics were correct. Kepler carries the most advanced technology for finding planets yet – in its first months of operation, it identified more potential planets than had been confirmed by any other planet-finding surveys to date. Moreover, this technology was sensitive enough to identify Earth-like planets (or so it was hoped).
NASA’s latest announcement was preceded by several days of space agency hype about “intriguing” new data, leading some to believe that perhaps Kepler had finally discovered a genuinely Earth-like planet. This is not (yet) the case, and in any case a planet in an Earth-like orbit would probably require more than a single year of observation to confirm its existence. What has been discovered, however, is a bizarre system in which two new planets, both roughly the size of Saturn in our own solar system, orbit their star with orbits of 19 and 38 days, respectively. Kepler was able to image both planets crossing in front of their star at the same time. This alignment is, so far, unique in the extrasolar planetary catalogue.
In addition, interestingly, Kepler seems to have found a third planet orbiting the same star, Kepler-9. This planet, designated Kepler-9c, is believed to be only slightly larger than Earth itself. However, there will almost certainly be no extraterrestrial life forms of any kind on this body. Instead of being in an Earth-like orbit, it orbits an extremely short distance from the surface of its star. Kepler-9c is so close to its star that it completes one orbit, or year, in less than two Earth-days. In contrast, the nearest-in planet in our own solar system, Mercury, takes 88 days to circle the Sun.