Space: Robotic planet-hunting telescope finds its first exoplanets

The Automated Planet Finder - Lick ObservatoryThe world’s first robotic planet-hunting telescope has bagged its first planets. The Automated Planet Finder (APF) – a 2.4-metre telescope located at Lick Observatory on Mount Hamilton in California – started its self-directed operation in January, and has just confirmed the existence of two new systems of planets.

“It’s just proof that it works. The planets are starting to come out,” says Steve Vogt at the University of California, Santa Cruz, who designed the spectrometer at the heart of the system.

Astronomers have found thousands of planets orbiting other stars, or exoplanets, in recent years. Most of them were spotted by NASA’s Kepler space telescope, which stared at a single patch of sky for more than four years to detect the telltale dimming of stars that occurs when planets cross, or transit, in front of them.

But before Kepler, the most prolific planet hunters relied on ground-based telescopes that observed stars one at a time, watching to see if they wobbled back and forth due to gravitational tugs from unseen planets. One of these ground-based telescopes, at the Keck Observatory in Hawaii, had been monitoring the potential exoplanets for many years, but it is APF that completed the characterising of their orbits.

Space-based and ground-based techniques are useful for different things. Kepler’s strategy can tell us a planet’s size, but not its mass. The ground-based technique yields a planet’s mass, but not its size. Astronomers need both to figure out a planet’s density, which in turn provides a clue to its composition.

But ground-based telescopes required constant supervision during observing time, and are mostly found in remote locations like the mountains of Hawaii and Chile.

“You had to man a telescope 365 nights a year,” Vogt says. “It takes a lot of manpower to do that. We thought it would just be too much for an army of undergrads, so we decided to try to automate APF fully.”

Every day, the APF wakes up in the early afternoon and calibrates itself, then opens the telescope dome by itself at sunset. It chooses stars from a list the researchers feed it, and steers itself from star to star until just before sunrise. “Now we can sleep at night!” Vogt says.

The ultimate goal is to find Earth-sized planets in the habitable zones of bright, nearby stars – stars that are close enough to us that we could perhaps receive messages from any intelligent beings that might live around them. Kepler mostly focused on faint, distant stars, and in the process showed that we should be able to find planets essentially everywhere.

“One of the things we’ve learned now that the Kepler data is flooding out is that nearly every star has planets,” Vogt says. “Now that you know that, you just need to look at the brightest, nearest stars. Those are going to be the most fun in the next 100 years or so.”

The first two star systems with planets confirmed by APF are not very exciting in themselves. One of them, a star called HD 141399, has four gas giant planets in close orbit. The second star, GJ 687, is a red dwarf star with a Neptune-sized planet orbiting it.

But these observations are an encouraging sign of things to come, says veteran planet-hunter Geoff Marcy at the University of California, Berkeley, whose team uses APF for about half of its available time. “We’re excited to be searching the nearest sun-like stars, and also many red dwarfs, for planets orbiting close to their host star, including nearly Earth-sized ones,” he says.

Journal reference: Publications of the Astronomical Society of the Pacific (in press, arxiv.org/abs/1402.6684)

Syndicated content: Lisa Grossman, New Scientist

Image: UCSC – The Automated Planet Finder (APF) is the newest telescope at UC’s Lick Observatory on Mt. Hamilton. (Photo by Laurie Hatch)

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