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HATSouth telescopes search for dim planets orbiting the stars in Chile’s Atacama desert sky. (Gáspár Bakos)

Pint-Size Sky Watchers

While monster telescopes get the attention, the little guys quietly — and cheaply — rack up cosmic finds.

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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.

After the instruments completed observations on October 5, 2008, the project’s software reported the night’s findings to the Minor Planet Center at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, an international clearinghouse for asteroid and comet data. The center’s computers calculated preliminary orbits for the new discoveries, and found that one of them, 2008 TC3, was headed straight for Earth. Scientists at NASA’s Jet Propulsion Laboratory in Pasadena, California, quickly confirmed the orbit.

“I got an e-mail about 10 o’clock that morning from Donald Yeomans at JPL saying that we’d found one that was going to hit the Earth that night,” recalls Ed Beshore. Calculations showed the asteroid, which was about the size of an SUV, would enter the atmosphere above Sudan (see “Fireball!” Apr./May 2009). “A couple of KLM pilots saw it,” says Beshore, “and so did a couple of men at a railroad station out in the desert. A few months later, an expedition went out into the desert and found about 10 kilograms [22 pounds] of fragments. It was the first time anyone had found meteorites from an object that had been observed before it hit Earth.”

A couple of years ago, astronomers from the California Institute of Technology realized the Catalina database contained other valuable nuggets: observations of events so violent or energetic they can be seen only for a short time. The two teams compiled a list of thousands of these objects, known as transients. They are giant stars that pulse light like beating hearts, or titanic stellar explosions known as supernovas, or even flickers of gas spiraling into a supermassive black hole at the center of a galaxy. “The transient universe is the new big thing,” says Larson.

The most enigmatic transients were the targets of another early small telescope network, ROTSE (Robotic Optical Transient Search Experiment). Established by University of Michigan physicist Carl Akerlof, it highlights a couple of the traits that small telescope operators must have to be successful: perseverance and adaptability.

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