You don't need a multi-million-dollar budget to find alien worlds – off-the-shelf scopes rigged together can spot our cosmic neighbours too
A NEW search for our nearest cosmic neighbours is just beginning. Under construction now on an Arizona mountaintop, the Minerva observatory will look for small worlds around bright, nearby stars. By using off-the-shelf equipment, rather than bespoke scopes, Minerva – the Miniature Exoplanet Radial Velocity Array – offers a novel and cheap way to hunt for our solar system's closest companions.
Exoplanet science has exploded since the first discovery of a world outside the solar system in 1995. More recently, between 2009 and 2013, NASA's Kepler space telescope raked in thousands of probable worlds.
But most such planets have been spotted from space or with giant telescopes on remote mountaintops, which cost millions of dollars and require repeated observations over several years to confirm sightings.
By contrast, Minerva and a collection of other small observatories use relatively simple off-the-shelf telescopes. That makes this planet-hunting vanguard wholly unlike marquee observatories such as the W. M. Keck Observatory in Hawaii and the Kepler telescope – and that is precisely its advantage.
"We're looking at a small number of bright stars every night, all the time, for years. That's normally very hard," says Jason Wright, Minerva's co-investigator and an astronomer at Penn State University. "Because we've designed this observatory and it's ours, there's no one to compete with."
Minerva uses four 0.7-metre-wide, 2.5-metre-tall commercial telescopes built by a company called PlaneWave, which also sells them to hobbyists for about $200,000 – Amazon founder Jeff Bezos bought one just before Minerva's team. The light from all four scopes is collected and fed into a spectrograph, which splits it into different wavelengths and enables astronomers to see tiny variations in a given star's movement with respect to Earth. Such variations show something orbiting the star is exerting a faint gravitational tug on it and lets astronomers determine the orbiting object's mass.
Minerva will also be able to watch stars for brief dips in brightness that indicate something crossing in front of them. Seeing a regular pattern of dips reveals an orbiting object, such as a planet. This technique, called the transit method, is Kepler's strategy, and allows astronomers to calculate the planet's size. Combining size and mass gives the planet's density – a clue to its composition.
But both methods take time, especially for small worlds orbiting close to their stars, which Minerva will focus on.
"As we get toward truly Earth-like planets and truly Earth-like orbits, it's a very tough detection problem," says Greg Laughlin, an astronomer at the University of California at Santa Cruz who uses another dedicated planet-hunter, the Automated Planet Finder.
When Minerva's lead scientist, astronomer John Johnson of the Harvard-Smithsonian Center for Astrophysics in Massachusetts, designed the observatory, he wasn't aiming for speedy science. As a graduate student at Lick Observatory in southern California, he used a neglected older telescope to hunt for planets over a long stretch of time, choosing patience over precision and observing power.
"If you have high precision, more people want it. If it has crappy precision, it's probably on an old telescope nobody cares about," he says. "Typically, the more time you have, the less precision. Minerva is the first facility to have very high precision, and lots and lots of time. It's an unexplored territory."
Off the shelf
In other respects, Minerva is not so unique. It's the latest in a succession of amateur telescopes used for very big science. Gamma-ray astronomers already use such networks to scrutinise distant galactic explosions, for instance. Minerva will be able to do that, as well as observe asteroids crossing in front of stars, Wright says.
Funding has been one major motivation to try off-the-shelf tech, says Dave Charbonneau, also at the Harvard-Smithsonian Center, who was one of the first to build a planet-hunting system using commercially available telescopes. His MEarth project has been searching for small planets orbiting red dwarf stars since 2008 and has notched one discovery so far. "If you associate cost with a telescope – like one night of Keck time, or a few hours of Hubble time – that same cost would allow you to buy your own observatory," he says.
Astronomer Gáspár Bakos at Princeton University has been remotely operating the HATNet (Hungarian-made Automated Telescope Network) project for 10 years, and has published findings on 56 planets.
The six HATNet telescopes are each just 10 centimetres wide, but they function as a network. A companion project, HATSouth, has 24 telescopes spread across Chile, Namibia and Australia. This provides unprecedented coverage for transit searches, Bakos says. "The planets don't honour the rotation of Earth, they transit at their leisure. With a network, you catch all the transits."
Strategic search
Meanwhile Laughlin's custom-designed Automated Planet Finder has been hunting planets from a mountaintop in California since last January. It has already bagged two exoplanet systems. Its most promising finds will be candidates for follow-up searches with telescopes like the Transiting Exoplanet Survey Satellite (TESS), set to launch in August 2017.
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