Astronomers have found a way to speed up the search for nearby planets, discovering a planetary system 54 light-years away as a proof of concept.
However, most of these newly discovered worlds have been far enough away to make study difficult. Consequently, the original method for finding planets beyond the solar system, which works best at close range (in galactic terms), continues to have a place.
Until now, the Doppler wobble, as this technique is called, has relied on human oversight, inevitably slowing progress. This has made astronomers at the Lick Observatory excited about the Automated Planet Finder (APF).
"We initially used APF like a regular telescope, staying up all night searching star to star,” says University of Hawaii graduate student B.J. Fulton. “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."
One of the stars the APF was instructed to investigate was HD 7924, which at 54 light-years away was far closer than most of the planets Kepler has revealed. In 2009, the Keck Observatory found a planet circling HD 7924 with an orbital period of just five days.
Our studies of extrasolar planets have taught us that where there is one planet, there are usually more, making HD 7924 a natural target for further study.
The Keck Observatory has continued to keep a mirror on HD 7924, and the combination of its observations and more recent ones from the APF have produced evidence of two further planets, soon to be published in the Astrophysical Journal (preprint here).
Both of the new discoveries are also very close to the star, with orbital periods of 15 and 24 days. By comparison, Mercury takes 88 days to orbit the sun. HD 7924 emits less than two-fifths as much light as the sun, but these planets are still close enough to be far too hot for life.
The interest in their discovery comes in part from the demonstration of techniques that could be used to assist astronomers in finding planets more like our own. However, the new discoveries also expand our limited knowledge of the category of planets known as “super-Earths,” those with masses between our home and Neptune.
"The three planets are unlike anything in our solar system, with masses 7-8 times the mass of Earth and orbits that take them very close to their host star," says University of California, Berkeley graduate student Lauren Weiss. Such planets have been found to be very common, but we are still largely speculating about their make-up.
Meanwhile, team leader Dr. Andrew Howard of the University of Hawaii is excited about the potential of the technology. "This level of automation is a game-changer in astronomy," he said. "It's a bit like owning a driverless car that goes planet shopping."