Three-planet system discovered

A planetary system has been found orbiting a star 54 lightyears away

Artist’s impression of a view from the HD 7924 planetary system looking back toward our sun, which would be easily visible to the naked eye. Since HD 7924 is in our northern sky, an observer looking back at the sun would see objects like the Southern Cross and the Magellanic Clouds close to our sun in their sky. Art by Karen Termaura and BJ Fulton, UH IfA

Artist’s impression of the HD 7924 planetary system looking back towards our Sun. Credit: Karen Teramura & BJ Fulton, UH IfA.

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A planetary system has been discovered orbiting a star just 54 lightyears away by the Automated Planet Finder (APF) at the University of California’s Lick Observatory.

The system was discovered following the detection of a wobble in star HD 7924. This was concluded to be an effect of the gravitational pull of planets orbiting it.

In total, three planets have been discovered, all at a distance to the star closer than Mercury orbits the Sun, completing their orbits in five, 15 and 24 days.

The APF is a fully robotic telescope, enabling it to search every night of the year unmanned, speeding up the rate at which planets and their orbits can be discovered.

The team located the planets using a combination of the APF and telescopes in Hawaii and Arizona.

“We initially used APF like a regular telescope, staying up all night searching star to star.

But the idea of letting a computer take the graveyard shift was more appealing after months of little sleep.

So we wrote software to replace ourselves with a robot,” says Benjamin ‘BJ’ Fulton, a graduate of the University of Hawaii.

The first of the planets orbiting HD 7924 was discovered in 2009 using the HIRES (High Resolution Echelle Spectrometer) on the Keck-I telescope.

Five years of additional searches at Keck in Hawaii plus an 18-month APF campaign later and two new planets had been found.

“The three planets are unlike anything in our Solar System, with masses seven to eight times the mass of Earth and orbits that take them very close to their host star,” explains UC Berkeley graduate student Lauren Weiss.

The discovery of the planetary system marks the beginning of a survey searching for super-Earth planets (larger than Earth but smaller than Neptune) orbiting nearby stars.

So far, most extrasolar planets discovered in the Milky Way have been found far from our Solar System.

Fulton is leading the two-year search with the APF.

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“When the survey is complete we will have a census of small planets orbiting sun-like stars within approximately 100 light-years of Earth,” he says.