Pint-Size Sky Watchers
While monster telescopes get the attention, the little guys quietly — and cheaply — rack up cosmic finds.
- By Damond Benningfield
- Air & Space magazine, November 2012
(Page 2 of 4)
“The amount of time you have on a small telescope is orders of magnitude more than you could have on a big one,” Bakos says; he can set the HATNet telescopes to gaze in one direction for as long as he wants, having them collect as many exoplanets as he thinks the little mirrors will find. The MMT is used for everything from projects that hunt for the exotic, like quasars and dark matter, to in-depth study of common stars and even exoplanets, so “you get a few nights per year. But [the HATNet] telescopes are dedicated to just this one thing. They’re small and cheap, and one can afford to dedicate them to one field.”
Some of the first small telescope networks were put to work looking for changes not in distant stars but inside our own solar system. They take snapshots of the same area of sky every few minutes or hours and look for objects that have moved against the background of stars, indicating the objects are close by. The goal is to find near-Earth objects (NEOs): asteroids or comets that approach or cross Earth’s orbit and thus have the potential for a collision.
In 1992, Congress asked NASA to gather astronomers from around the world to discuss NEOs; the result was a report that became known as the Spaceguard Survey (after the asteroid tracking system in Arthur C. Clarke’s novel Rendezvous with Rama). In it, scientists recommended an international NEO survey as “a modest investment to insure our planet against the ultimate catastrophe.” Congress agreed, and asked NASA to find and plot the orbits of at least 90 percent of NEOs measuring one kilometer (0.6 mile) in diameter or larger—those big enough to cause global devastation.
Engineers at the Massachusetts Institute of Technology’s Lincoln Laboratory were ready for the challenge. “We had developed technology that helps the Air Force find and track stuff in Earth orbit, and we realized that technology would be really good for the asteroid search enterprise,” says Grant Stokes, who directs the survey LINEAR (Lincoln Near Earth Asteroid Research). The project uses a pair of 40-inch telescopes in New Mexico to scan different patches of sky every night, taking a series of short exposures. Software identifies objects that move from one exposure to the next.
When LINEAR began operating, in 1996, astronomers had discovered and computed the orbits of fewer than 10,000 asteroids, most of which reside in the asteroid belt, just beyond Mars. As long as they stay there, they pose no threat to Earth. Today the total is more than 600,000, with almost a quarter-million discovered by LINEAR, including about 2,500 of the potentially dangerous NEOs. “We changed the model” for discovering asteroids, says Stokes. “It’s all automated. It’s not craft astronomy, it’s industrial astronomy.”
In 2005, Congress ordered the search expanded. Astronomers were tasked with finding and cataloging NEOs the next size down, at least 450 feet in diameter, which are still large enough to devastate a large swath of Earth. The Catalina Sky Survey, headquartered in Tucson, Arizona, began operating in 1998 with funding from NASA through the mandate. Since then it has chalked up, like LINEAR, about a quarter-million asteroids of both sizes.
Catalina got its start when current director Steve Larson was looking for a new project for a mothballed 16-inch telescope. “I had a couple of undergraduates who were interested in looking for asteroids, so I set them up with that telescope,” he says. “It was an old-style, hand-slewed telescope. These young guys were exhausted by the end of the night. They had to move the telescope every time they took an image. It was hard work.”
The hard work, though, proved the concept that a small telescope could be useful for asteroid hunting. The project was soon upgraded to a 27-inch telescope, and two others were added to the network: a second in Arizona and one in Australia. Of Catalina’s asteroid haul, about 4,000 are NEOs. None is currently on a collision course with Earth, but one of its discoveries did hit the planet a few years ago.