In August 2010, NASA released the next major discovery by its highly-touted Kepler Mission space telescope: another solar system with multiple planets, like our own. This discovery was long expected, but until the launch of the Kepler telescope, available technology simply did not generally have the sensitivity necessary to carry out advanced planet-finding surveys.
The Kepler space telescope is a $600 million satellite and the first purpose-built planet-finding space telescope. It was launched in 2009 with the intention of surveying the largest-yet catalogue of candidate stars which may host extrasolar planets, and in particular to find what scientists believe must exist but which, until now, we have not been able to see: Earth-sized planets in Earth-like orbits. It is these rocky extrasolar planets which, it is believed, would be most likely to host intelligent species of their own, if in fact, our galaxy is home to more than just ourselves. The telescope’s powerful contribution to science can be seen in the early results: today, there are about 450 known extrasolar planets, but in its first year Kepler has already found over half again that number of potential planets.
Unfortunately, at the vast distances involved, it takes a number of sophisticated tricks to detect the presence of any extrasolar planets orbiting other stars, even large ones. For this reason, until quite recently, generally only very large planets with very close orbits to their stars were found by astronomers. This led to an extrasolar planetary catalogue dominated by so-called super-Earths and Hot Jupiters – very large planets, orbiting closer to their stars than Mercury does in our own solar system. Scientists long suspected, based on the composition of our solar system (home to four large gas giants, four small rocky planets, and numerous smaller rocky planetoids) that other star systems must also be home to large numbers of smaller rocky planets. In its first year of operation, Kepler’s primary achievement was to prove that small rocky planets are as common as large gas giants, not just in our own solar system but in others as well. This discovery was not unexpected, but until 2010 the existence of large numbers of small rocky planets was merely theoretical.
In August 2010, the Kepler Mission made another long-awaited announcement, preceded by several days of hype about “intriguing” new findings. Some doubtless hoped that this sort of vague reference meant the Kepler telescope had finally discovered the holy grail of extrasolar planet science – an Earth-like world in an Earth-like orbit. Instead, however, the NASA Kepler team announced on schedule the discovery of something even more bizarre.
Kepler, it turns out, has discovered a number of new star systems with roughly Earth-sized planets in them. The highlight of the new set of released findings, however, is a truly bizarre system now named Kepler-9, located over 2000 light-years from the Earth. The Kepler-9 system includes a pair of Saturn-sized gasgiants orbiting in what is known as gravitational resonance with one another, one which completes an orbit in just 38 Earth-days and another which completes an orbit in just half that time. A third planet in the same system, Kepler-9c, is believed to be Earth-sized, but is far too close to its star to support life of its own. It completes one orbit, or year, in an astonishingly brief 1.6 Earth-days.
The new Saturn-like planets offer little new insight into the search for extraterrestrial life, but they do provide interesting information about the evolution of star systems. Other discoveries seemed to indicate that very large planets orbiting very close to their stars (of which there are none in our system, but a surprising number elsewhere) had formed elsewhere in their system, and then spiralled down into close orbits. The discovery of the twin gas giants at Kepler-9 provide further evidence about how this occurs.
Kepler’s capabilities are theoretically great enough to detect planets somewhat like our own. However, it will likely be years before enough data has been gathered for such planets to actually be found. This is because, even with very fine resolution, Kepler confirms planets’ existence by watching differences in light reception from stars as planets pass in front of them. From the perspective of any single distant observer, a planet in an Earth-like orbit will only do so once per Earth-year. It is easy to confirm the existence of a planet when its orbit brings it in front of its star every few days, or every few weeks. Planets with orbits stretching to one year or more take correspondingly longer to identify.
