Kepler probe finds two Saturn-sized planets orbiting a single star 2,000 light years away
By Niall Firth
Two giant Saturn-sized planets have been spotted passing in front of the same star, Nasa scientists announced today.
It is the first time more than one planet has ever been discovered ‘transiting’ a single star.
The two planets were discovered by the space telescope Kepler and will give scientists vital information about how planets were formed and how they interact with each other.
Kepler scientists have also identified what appears to be a third, much smaller possible planet which is around 1.5 times the size of Earth but which is orbiting in a scorching 1.6 day-orbit very close to the sun.
The planets were named Kepler 9b and 9c and orbit a star around 2,000 light years away. The gravity of the planets acting upon one another means that their orbits are close to a 2-to-1 ratio, in what is known as a planetary resonance.
It is the first time this phenomenon of planets pushing and pulling each other out of orbit has been observed.
The discovery follows seven months of observations of more than 156,000 stars as part of an ongoing search for Earth-sized planets outside our solar system.
The observations show Kepler-9b is the larger of the two planets, and both have masses similar to that of Saturn. Kepler-9b lies closest to the star with an orbit of about 19 days, while Kepler-9c has an orbit of about 38 days.
The third ‘Earth-sized’ planet candidate will have to be analysed further before scientists can decide whether it is a planet or merely astronomical phenomenon that mimics the appearance of one..
Kepler has already discovered around 700 planetary candidates, or objects that could be planets in its first year of operation.
Kepler was designed to look for evidence of planets in the ‘Goldilocks zone’ around the stars, so named by scientists because conditions there are not too hot, not too cold, but just right for liquid water – and therefore life – to exist.
The telescope finds planets by detecting almost imperceptible ‘winks’ – the tiny amount of dimming that occurs each time a planet moves across the face of a star.
The distance of the planet from the star can be calculated by measuring the time between successive ‘winks’ as the planet orbits the star.
Small variations in the regularity of these dips can be used to determine the masses of planets and detect other non-transiting planets in the system.
Kepler has already announced five additional candidate systems that appear to have more than one transiting planet.
The Kepler team have also recently identified a sixth target exhibiting multiple possible planets and accumulated enough follow-up data to confirm this multi-planet system.
‘Kepler’s high quality data and round-the-clock coverage of transiting objects enable a whole host of unique measurements to be made of the parent stars and their planetary systems,’ said Doug Hudgins, the Kepler program scientist at NASA Headquarters in Washington.
Scientists refined the estimates of the masses of the planets using observations from the W.M. Keck Observatory in Hawaii.
‘This discovery is the first clear detection of significant changes in the intervals from one planetary transit to the next, what we call transit timing variations,’ said Matthew Holman, a Kepler mission scientist from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
‘This is evidence of the gravitational interaction between the two planets as seen by the Kepler spacecraft.’
Information such as a planet’s size and the extent of its orbit can be calculated from the amount of dimming, the length of time between ‘winks’ and the star’s mass.
Kepler will be searching the heavens for day and night without any interruption for the next 4 years.