The first picture has been released from Kepler, NASA’s $600m planet-hunting satellite. This latest eye-in-the-sky is pointing its 95 mega-pixel camera at the same patch of sky and staring at it for three and a half years. Hidden deep within this cosmic window are over 100,000 suns that astronomers have identified as possible host stars for Earth like planets. The aim of the mission is to get a handle on just how many Earth like planets there are out there in our galaxy.
To do this the Kepler team are utilising what is known as the transit method, one of three main techniques for looking at so-called extra-solar planets. Of course, planets like our own are far too dim compared to their luminous gravitational masters and so can’t be seen directly. Instead Kepler is looking for small dips in the star’s brightness as the planet passes or ‘transits’ in front of it. Kepler’s instrumentation is so sensitive that it can detect dips in brightness of just one part in 50,000 or 0.002%. This is actually more sensitive than required to find planets the size of the Earth. If there were some alien blogging astronomer out there staring back at us, they would see our Sun dim by 0.008% as our planet glided across our star.
With Kepler scrutinising this patch of sky for around 42 months it should be able to catch approximately three orbits of such Earth-like planets. And there is good reason to look for planets with the same orbital period as our own. Johannes Kepler, the 16th century astronomer after whom the satellite is named, formulated three laws of planetary motion, one of which says the time it takes a planet to orbit its star is precisely related to its distance from it. Planets that take a year to traverse their elliptical path around their Sun will be in the habitable zone, the small window of space around a star where water is liquid. Sometimes referred to as the Goldilocks Hypothesis, where the Earth is porridge that’s temperature, instead of being too hot or too cold to have liquid water, instead is just right, this region around a star is the most likely place to find life.
And so the search to answer the age-old question of whether we are alone in the Universe has entered a new and I have to admit an exciting phase. When the data from this mission is released, probably in the middle of the next decade, we should have a much better idea of just how rare watery blue marbles like our own are. Perhaps, as always in science, the most intriguing outcome will be the unexpected. The question of just how rare Earths are formed a part of my undergraduate dissertation (which you can read here). At the time I approximated that there should be around 10 million Earths in our Milky Way galaxy. Whether this prediction is in itself a form of Goldilocks’ porridge, being too low, too high or just right, I really can’t wait to find out.