Using a robotic telescope at Lick Observatory that scans the sky night after night, astronomers have discovered three planets – supersized Earths ‑ around a nearby star.
“The three planets are unlike anything in our solar system, with masses seven to eight times the mass of Earth and orbits very close to their host star,” said UC Berkeley graduate student Lauren Weiss.
She is the leader of the UC Berkeley component of the team that discovered the planets with the help of the Automated Planet Finder, a relatively new telescope atop Mt. Hamilton near San Jose dedicated to finding super-Earths and Earth-size planets.
To date, most of the planets discovered outside our solar system have been the size of Neptune — 17 times the mass of Earth — or larger, with the majority gas giants like Jupiter, which are several hundred times the mass of Earth. The goal of the APF is to find small planets around the nearest stars, some of which might have temperatures and surface conditions suitable for life.
“The discovery demonstrates the APF’s ability to find low-mass planets around nearby stars,” Weiss said. “Robotic telescopes are going to be the way we find planets in the future.”
The planets, invisible to the naked eye, betrayed their existence by the slight wobble they created in their host star, detected by the Doppler technique pioneered by Weiss’s adviser, Berkeley professor of astronomy Geoff Marcy. The new APF facility offers a way to speed up the search for exoplanets, Weiss said.
“We initially used the 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,” said University of Hawaii at Manoa graduate student Benjamin “BJ” Fulton.
The W.M Keck Observatory in Hawaii found the first evidence of planets orbiting HD 7924 in 2009. It took five years of additional observations at Keck Observatory and the year-and-a-half campaign by the APF Telescope to find the two additional planets orbiting HD 7924. The planets pinpointed by the APF were confirmed via the Keck Observatory and the Automatic Photometric Telescope at Fairborn Observatory in Arizona.
“This level of automation is a game-changer in astronomy,” said Andrew Howard, a professor of astronomy at the University of Hawaii. “It’s a bit like owning a driverless car that goes planet-shopping.”
All three planets orbit their star at a distance closer than Mercury orbits the sun, completing their orbits in just five, 15 and 24 days. The star is 54 light-years distant, close enough to be considered part of Earth’s neighborhood.
The robotic observations of HD 7924 are the start of a systematic survey for super-Earth planets orbiting nearby stars. Fulton will lead this two-year search with the APF as part of his research for his doctoral dissertation.
“When the survey is complete we will have a census of small planets orbiting sun-like stars within approximately 100 light-years of Earth,” says Fulton.
Their paper has been accepted for publication in the Astrophysical Journal.