One year lasts a day in alien solar system

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Astronomers have been investigating the secrets of an alien solar system that has planets orbiting its star so tightly that one of them has a year that lasts only as long as an Earth day.

The system, dubbed Kepler-80, is about 1,100 light-years away from Earth and consists of five planets, which travel around their star in one, three, four, seven and nine Earth days. 

The planets are rocky and all have similar masses (four- to six-times that of Earth) and are crammed into an area about 150 times smaller than the Earth’s orbit around the sun.

The outer two planets are almost twice as big as the others due, scientists believe, to an expansive atmosphere made up of hydrogen and helium.  

The system was first seen by the Kepler space telescope in 2012, but this new study into the system was led by Mariah MacDonald and Darin Ragozzine of the Florida Institute of Technology. The paper has been accepted for publication by the Astronomical Journal, but can be accessed here.

MacDonald and Ragozzine used transit timings – when a planet passes in front of its star – to observe when the brightness of the star decreased to investigate their orbits. 

“Because the planets are so close to each other, a planet can gravitationally perturb the orbits of the other planets, causing it to transit either early or late,” they write. 

“These transit timing variations, or TTVs, can be used to fit the orbits and masses of the planets. 

“Unfortunately, the inner-most planet is dynamically decoupled from the other planets and has a very weak TTV signal, so we can only estimate its mass.”

Kepler-80 is known as a STIP – System with Tightly-spaced Inner Planets – which astronomers are studying for hints as to how the Earth was formed.

Unusually the planets have “synchronised” orbits, in which the outer four return to almost exactly the same configuration every 27 days.

This effect is known as a “resonance” and helps the system remain gravitationally stable, says Ragozzine.

Kepler has observed hundreds of other STIPs with planets with orbits lasting from one to 100 days.

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