February 3, 2011
First, a little about the mission, The Kepler spacecraft is a mission launched in March 2009 which was designed to search for small exoplanets by measuring almost constantly the brightness of more than 156,000 stars in a small patch of the sky. The 0.95m-telescope is able to detect a dip in the light coming from the host stars which could be due to the transit of an exoplanet passing between its star and us, like the Moon passes between the Earth and the Sun during a solar eclipse. When this happens it can give us a direct estimate of the size and orbit of the eoxplanet.
The Kepler mission has released 1,200 exoplanet candidates from data collected with the Kepler spacecraft around 150 days of observation time. This marks a new age in astronomy, there will be before and after Kepler era.
The Kepler team released the data from the first 150 or so days of operation. A careful statistical analysis done by the team concludes that 80-90% of these candidates are probably real. The total count of explanets currently contains 519 exoplanets which were discovered over 15 years of observations. In almost 4 months of operation, the Kepler mission has found 1,200 exoplanets!
Many of these exoplanets orbit around smaller and cooler stars than our Sun. The surface temperature of the exoplanets could allow liquid water to exist on the surface of these planets. In their paper, the Kepler team lists ~60 candidates with sizes ranging from Earth-size to larger than that of Jupiter which are in the Habitability Zone of their host star. This is one of the most extraordinary result of this survey! If we wish to find Earth-like planets with water on them, we need to look for exoplanets in the Habitability Zone, an area which isn’t too hot or too cold for water to exist. This zone is also called the Goldilocks Zone.
With these results, we can now say that stars in the Milky Way galaxy are more likely to have small exoplanets since 70% of the exoplanets discovered are smaller than Neptune, with a peak of exoplanets only 2-3 times larger than Earth. Using model predictions the team calculated that 6% of the stars in our Milky way have Earth and super-Earth size exoplanets. Since the Milky Way has around ~200 billion stas, that makes it ~12,000,000,000 stars with Earth-like planets!
The Kepler mission is still in operation and collecting new data. In a few years time, we can expect to have a more accurate and complete catalogue, which might contain smaller exoplanets, exoplanets orbiting further from their host star and even the exomoons of these exoplanets. Different groups of astronomers are now going to go through the catalogue and study the vast variety of worlds found. We can expect a lot of exciting news in the coming weeks. To start it off, here’s a very cool mini solar system with a lot more still to come.
If you go out tonight, take some time out to look at the sky and think that among the 2,500 stars that you can see with the naked eye, a third of them may have an exoplanet. Worlds which might be very different or very similar to ours, how many different worlds can you think of?
There are a lot of interesting worlds out there, now we just need to explore them. Welcome to the golden age of astronomy.