The Planet Hunters
NASA grant launches UM effort to discover new worlds
By Cary Shimek
To a certain extent, UM’s planned telescope to search for planets around other stars can be traced to pickup basketball games a dozen years ago at the University of California, Berkeley.
Back then, UM Associate Professor Nate McCrady was a graduate student who regularly met with other budding astrophysicists to shoot hoops. They would play on university courts or parks in the Berkeley Hills overlooking campus.
And it wasn’t nerd ball. “Some of us were pretty good athletes,” McCrady contends (perhaps a tad defensively).
Those games helped forge lifelong friendships, and a few times they were joined by Geoff Marcy, one of their Berkeley professors and a rock star of the astronomy world. Starting in 1995, Marcy and his research team discovered 70 of the first 100 exoplanets orbiting other stars. Their total has since risen to more than 300.
So, sure, Marcy can find new planets. But could he play?
“He wasn’t big, but he was a good athlete,” McCrady says. “I couldn’t dunk on him or anything. Of course, I can’t dunk on anyone.”
Marcy, a scientist pushing the boundaries of human knowledge, made a big impression on McCrady and his friends, who eventually dispersed to various astronomy programs across the country. Then last year, one of the pickup players, John Johnson from Harvard, approached McCrady at a professional conference in Texas.
Johnson knew McCrady wanted to build a new modern research observatory for UM. He announced that he and another former pickup player, Jason Wright at Penn State, planned to build a multi-telescope observatory to search for exoplanets around nearby stars. Did UM want in on the game?
“I couldn’t say no to that,” McCrady says. “It was a tremendous opportunity for UM, our students and myself. This will really get us involved in cutting-edge science, and we fully intend to add to the list of planets that have been discovered.”
The former Berkeley ballers created a project called Minerva to hunt for rocky planets similar to the Earth around 100 nearby stars. The project involves four telescopes, each worth about $250,000 and owned by a different institution. McCrady says the telescopes, each with a 0.7-meter collecting mirror, will work together — flying in formation — to create the power of a telescope with a 1.4-meter mirror, an instrument that would cost $7 million.
The owners are UM, Harvard, Penn State and the University of New South Wales in Australia. Harvard and Penn State paid for their telescopes directly, while UM received a $1.125 million NASA grant this summer through the Experimental Program to Stimulate Competitive Research, which will fund Montana’s telescope and three years of research. New South Wales received funding in December.
“EPSCoR provides resources to states that normally don’t get a lot of government funding or have universities with deep pockets,” McCrady says. “This was an unexpected advantage of being in Montana.”
Harvard also funded a $1 million spectrometer that will analyze starlight collected by the Minerva telescopes. “That’s of course a huge benefit for us,” he says. “All I can say is, ‘Thanks, Harvard!’”
The Minerva telescopes will be placed at the Fred Lawrence Whipple Observatory atop 8,600-foot Mount Hopkins, located about 35 miles south of Tucson, Ariz. McCrady says Montana is a poor location for such an observatory, with its high latitude and weather-limited observing days.
Penn State’s telescope already has been assembled and tested at the California Institute of Technology, home to Jon Swift, another friend who played pickup ball at Berkeley. Swift and his Caltech colleagues are working to roboticize the telescopes with software that will automate Minerva observations. McCrady says the momentous “first light” of observing with one of the telescopes happened at Caltech, and he expects UM’s telescope to be delivered directly to Arizona in the first half of next year. Observations should start in mid-2014.
“This will be the largest research telescope that anyone in the state of Montana has ever owned,” McCrady says. “With the big national facilities, you apply for time, you get a specific time, and if it rains you apply again next year. Now, UM and our partners will have dedicated access to this telescope 365 days a year.”
He’s especially excited that undergraduate students from towns across Montana will join the hunt for exoplanets.
“Our students will be walking the front lines with colleagues and students at other prestigious institutions,” McCrady says. “It really will give our students an inroad into the world of professional astrophysics.”
The Minerva observatory won’t image planets directly. Instead it will detect them using the Doppler technique that Geoff Marcy helped pioneer. (The Swiss team of Didier Queloz and Michel Mayor are credited with finding the first exoplanet using the Doppler technique in 1995, scooping Marcy and partner Paul Butler by a few days.) Scientists know that the gravity of stars tug on planets and planets tug on their stars in return, creating a slight wobble called reflex motion. This motion can be detected by passing starlight through a spectrometer, which breaks the light into prismatic lines of colors. As the star moves away from and toward us — getting Doppler shifted — the lines move back and forth across the spectrum. By repeatedly measuring the starlight and the spectrum, astrophysicists can reproduce the motion of a star.
“If there is a wobble, it’s a smoking gun,” says McCrady, an expert in high-resolution spectroscopy of stars. “It gives us the mass of the planet, its distance from its star and the length of its year.”
Finding these wobbles requires incredibly precise measurements. A huge planet the size of Jupiter creates a 12-meter-per-second signal. For a rocky planet the size of the Earth, the wobble is only 9 centimeters per second, which will be below Minerva’s ability to detect. But the observatory will find wobbles of 1 meter per second or greater, allowing them to find worlds a few times more massive than Terra — so-called Super Earths. Minerva can detect Earth-mass planets, but only if they orbit close to their host stars.
NASA’s Kepler Spacecraft spent four years monitoring more than 170,000 stars in one section of sky. McCrady says Kepler was a statistics mission trying to discover how common planets are in our galaxy. The results show that our Milky Way Galaxy contains at least as many planets as it does stars, meaning there are 100 billion to 400 billion exoplanets waiting to be discovered.
Kepler, however, didn’t study nearby stars in our stellar neighborhood, which is where Minerva comes in. The team will select about 100 or so stars to monitor that are about 10 to 100 light years from Earth. Most of these stars range from 70 percent the size of our sun to slightly larger. McCrady says much larger stars burn through their fuel more quickly, giving potential life and evolution less time to take root. Smaller stars are much more abundant in our neighborhood, but many would be too faint for Minerva to work with. So the researchers will target sun-like stars.
The Holy Grail for the Minerva scientists would be finding rocky planets slightly larger than Earth in the “Goldilocks Zone” — the area around each star where liquid water (and potentially life as we understand it) is possible.
Discovering exoplanets sometimes takes years. Scientists have discovered strange “hot Jupiters” that scream around their suns in days, but it would take two years to discover the Earth using the Doppler technique, even if one had an instrument capable of finding a planet so small. The wobble has to be repeated at least once before a planet is confirmed. So Minerva will need more funding to find worlds with orbits longer than two years.
“What we learned from the Kepler Mission will guide the target list for Minerva,” McCrady says. “We anticipate finding about 14 new planets during our three-year mission.”
Incredible new telescopes will become available in the next decade. The famed Hubble Space Telescope, with its 2.4-meter collecting mirror, likely will be supplanted by the James Webb Space Telescope, with a 6.5-meter mirror, in 2018. The largest Earth-based telescopes are currently about 11 meters across, but a 30-meter behemoth is coming to Hawaii. These new giants will reveal the atmospheres of exoplanets, and signs of water or oxygen may indicate life.
“The time on these massive instruments will be precious, and they will need targets,” McCrady says. “When Minerva identifies planets around nearby stars, we essentially become a scouting mission for the next generation of large telescopes coming online.”
He says other scientific teams are studying the nearby stars that Minerva will target. However, these teams are either using small-aperture equipment — basically Nikon camera lenses — or they are using the big national observatories with limited observing time. Minerva will offer the only high-precision spectroscopic observatory with access to the same stars every clear night of the year.
“We are going to be doing some of the hottest science going,” McCrady says. “When I was an undergraduate, we knew of eight planets in our solar system and maybe 10 other planetary systems. Now 15 years later, we know of more than 3,000 planets that have been identified.
“And we are going to find more. It’s a really exciting time to be alive.”
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