University of Pennsylvania astronomers are celebrating the dedication of a new planet-hunting telescope known as Minerva-Red. Installed at the Fred Lawrence Whipple Observatory in Arizona, Minerva-Red is part of the Minerva project, an array of low-cost telescopes that are designed to discover planets orbiting stars other than the sun.
Thousands of potential exoplanets have been identified, the vast majority within the past five years. New telescopes and instruments are increasingly capable of detecting rocky, Earth-like planets, with astronomers around the world hoping to be the first to find the chemical signatures of life in their atmospheres.
In Minerva’s search, Cullen Blake, an associate professor in the School of Arts & Sciences’Department of Physics and Astronomy, along with graduate student David Sliski, join astronomers from Harvard University, the University of New South Wales, the University of Montana, the Smithsonian Institution and Pennsylvania State University to operate five robotic telescopes.
Penn’s Minerva-Red telescope has special capabilities that make it well suited for finding planets orbiting some of Earth’s nearest stellar neighbors. The “Red” in the name is what sets it apart from the other telescopes in the project; it is designed to look for planets around low-mass stars, light from which is mostly in the infrared part of the spectrum.
“Over the last 20 years,” Blake said, “the pace of discovery in terms of finding planets around other stars has been incredible. But most of those efforts have been focused on finding planets around stars that are broadly like the sun. The sun isn’t an unusual star, but most stars are much smaller and much cooler than it is.”
“If you made a list our 100 nearest stellar neighbors,” Sliski said, “many of them are small stars and we essentially don’t know anything about the planetary systems most of them might have. Over the last few years, however, we’ve seen some tantalizing results that suggest that these types of stars might have a lot of planets.”
The search for Earth-like planets has historically focused on sun-like stars, but smaller, cooler stars could also host potentially habitable worlds. Even though there are many such stars in Earth’s proverbial backyard, their dimness has limited astronomers’ ability to detect and study their planets.
“Cool stars tend to emit more of their radiation in the infrared, at wavelengths of light longer than what we can see with our eyes,” Blake said. “Usually, our telescopes and instruments are tuned for green light, which is right in the middle of our visual range. Looking through those telescopes, these small stars would look very faint, but, if you could see in those longer wavelengths, they might be a hundred times brighter.”
A telescope specifically matched to those small stars’ traits has several advantages. Because it will focus on a specific sample of some of the closest small stars, Minerva-Red can be much less expensive than the ground- and space-based telescopes currently used in the hunt for exoplanets.
“The telescope is essentially the biggest amateur telescope you can get,” Sliski said, “and the data-collecting instrument is custom-built, almost entirely out of parts you can order from a catalog. That really cuts down on costs and time and makes it easier for other groups to replicate our work.”
Automation also boosts Minerva-Red’s efficiency. The telescope can be remotely operated over the Internet but can also be programmed to run itself.
“You can tell it to wake up at sunset and look at a list of 20 stars,” Sliski said. “It will do its thing all night, shut itself down in the morning and email you the results.”
The planets that orbit those nearby, small, dim stars are also of particular interest in the search for Earth’s twin. Planets in such systems would need to orbit closer to their host star to have Earth-like temperatures, a quality that would make detecting them easier. Even the most powerful telescopes do not have the ability to directly see most exoplanets, so one of the two main techniques for identifying them involves measuring how they tug on their host stars as they orbit. The closer the orbit, the more the star wobbles due to the planet’s gravitational pull.
The Kepler space telescope, which has identified the majority of the nearly 5,000 exoplanet candidates, and some of the larger ground-based projects use a different technique, one which measures the minute dip in the brightness of a star as a planet passes in front of it. Kepler’s planet-finding mission is drawing to a close, but its successor, the Transiting Exoplanet Survey Satellite, or TESS, will also use this technique.
Working within this ecosystem of planet-hunters, telescopes like Minerva-Red can help astronomers pick the best targets for future studies with larger telescopes, as well as follow up others’ discoveries.
“TESS is going to find thousands of planets,” Blake said, “but you need to measure the wobble to get the planet candidate’s mass and therefore its density. There's going to be a ton of work for different telescopes to do, and small telescopes like Minerva-Red will be able to make big contributions.”