About 2,500 light-years away is Kepler-90 (formerly known as KOI-351): a star with a planetary system that is set up a lot like ours. Information about the system comes from observations by the Kepler Space Telescope. The discovery of the seventh planet (though it is fifth in the sequence away from the star) was made by citizen scientists using Zooniverse’s Planet Hunter and was published on arXiv.org. Other details of the system were published by lead author Juan Cabrera of the DLR Institute of Planetary Research in the Astrophysical Journal.
Kepler-90 is a main sequence star (which is a bit brighter than our sun) has at least seven planets orbiting it, more than any other discovered system. It is set up much like ours with the rocky ones closer to the star and much larger gas planets around the exterior of the system. A distinct difference between Kepler-90 and our system is that the planetary orbits are much more compact than ours. The innermost planet, Kepler-90b, has a period of only 7 Earth days. As a comparison, Mercury takes 88 days to travel around the sun. The outermost planet, Kepler-90h is about one AU away from its star. This means that the entire system would fit inside of Earth’s orbit. All of the planets have smaller radii than Neptune.
The other planets all have relatively tight orbits as well. The rest of the planets have orbits that take 9, 60, 92, 125, 211, and 331 days respectively. However, the orbital periods aren’t precise. There is a 25.7 hour variation, which is larger than any other planetary system discovered. This could be because there are actually more planets than we have confirmed. Also, because the planets are so close to the host star, fluctuations in gravitational pull could also be affecting the orbital periods.
Despite any possible gravitational fluctuations, the system is believed to be very stable. Many astronomers may be able to use this planetary setup to learn more about planetary formation and also about what makes a stable system. The European Space Agency is deliberating on a mission called Planetary Transits and Oscillations of Stars (PLATO) which would allow for more in-depth analysis of exoplanets orbiting bright stars. It could also potentially provide information about the atmosphere of exoplanets and determine if there is the possibility for alien life. The ESA is expected to make a decision about the mission within the next few months.
Tour of the Seven-Planet System Around the Star Kepler-90 from Robert Simpson on Vimeo.
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