If you've wondered why so many Extrasolar Planet(Exoplanet) begin with the name Kepler, wonder no more. The reason why they are called Kepler followed by a number and a letter occasionally is because they were spotted using the Kepler space telescope. The telescope is a National Aeronautics and Space Administration (N.A.S.A.) that was put into space on March 7th, 2009. Its planned mission was to be three and a half years but at the time of writing, in 2016, it still going strong after nearly seven years. It has discovered many new confirmed and possible exoplanets that are orbiting far and distant worlds.
The satellite is fixed to a certain area of space in the Cygnus, the Swan constellation overlapping with Lyra. The area was chosen because it has a rich amount of stars within the area and that light from the Sun would not affect the readings. The area had to be constantly in view during the whole time so it had to be an area in the northern hemisphere rather than the southern because of the location of mission control. The planets are calculated using a transition method, when a planet moves in front of a star, it causes the star to dim a little and that difference is what Kepler is looking out for.
Given that there are so many planets in such a small area of space increases the likelihood of there being life out there. If you unscientifically multiplied the amount of planets out there discovered with how big space is compared to the area of space watched, you realise that there are a truly unbelievable amount of exoplanets out there. The stars selected for watching are predominately small stars, ones where the temperature is more likely to be similar to our own. A star that is a giant such as Betelgeuse which is a red giant star is a dying star, one that will almost certainly have destroyed any orbiting planets. Also that star is in another part of the galaxy so it won't be monitored.
At the heart of the satellite is the main Photometer which is what takes the photos and uses those to calculate the difference in brightness. Once a month, the information is collated and sent down to mission control for analysis. The satellite is looking at stars that are roughly about 600 to 3,000 light years away. Anything further, the star would be too far away for proper readings to take place. Unless we had wormhole technology, the chances of visiting them are zero. Less than 1% of the stars that are being studied are closer than 600 LYs. The total area that the satellite is looking at is 3,000 light years across.
The satellite will be observing a total of about 100,000 stars simultaneously, looking for any change that could indicate a planet.
Kepler space mission was named after Johannes Kepler, who was a German astronomer who lived between 27th December 1571 and November 15th, 1630. His most famous contribution was his three laws of planetary motion, they are :-
- Law of Orbit - Planets move in elliptical orbits with the star in the centre,
- Law of Areas - A line that connects a planet to the Star sweeps out equal areas in equal times, when its closer, it moves faster.
- Law of Period - The square of any planets orbital period (sidereel) is proportional to cube of its mean distance (semi-major axis) from the Star.Hopefully the below picture will try and explain things about this to you. Ignore the quality of the picture, I'm no artist. The star is in the middle and the green planet is the same planet at different points in orbit.
So far, as of Jan 2016, the Kepler mission has discovered 1,032 confirmed planets and 4,696 candidate planets. Of those, 12 planets are less than twice the size of Earth and are in the hospitable, Goldilocks Zone. Anything more than twice the size of the Earth would result in the planet being a gas giant because of its gravitational pull on te gasses such as Hydrogen and Helium. Ref:N.A.S.A. Any planets larger than twice Earth is possiby a gas giant and one which we probably wouldn't be able to survive on because the gravity on the planet would be stronger than here on Earth. No alien life has yet been discover, only possible locations of where they might be living.
The smallest exoplanet that has been discovered so far as at Jan 2016 is Kepler 37-b which is on a par size with the moon. As it is small, it probably a rocky planet like moon. 37-b along with the other planets in the solar system are likely to be inhabitable as they are close to its star and therefore to hot for life as we know. Ref: Space
On the other scale, the largest exoplanet that it has discovered so far is Kepler 12b which is roughly 1.69 times the size of Jupiter and is therefore most likely to be a gas giant. Kepler 12b is small compared to HD 100546 b which orbits the star KR Muscae which is estimated to be about over six times bigger than Jupiter but that was not discovered by Kepler. In the picture below from N.A.S.A., it will show you how big the planets are roughly in size compared to the RE (Radius of Earth). More information can be found at the NASA Kepler Section of their website.