Russian asteroid highlights astronomers' challenge: predicting such space objects

Astronomers have cataloged about 95 percent of the space objects wider than half a mile – those that could destroy civilization. But they have found less than 1 percent of the objects 100 feet across or larger, a class that includes the asteroid that flitted past Earth on Friday.

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Yet despite the respectable amount of telescope glass aimed at the night sky, ground-based observations have their limits, notes Russell Schweickart, a former NASA astronaut who has spent much of his post-Apollo-9 career focusing on asteroid hazards and planetary defense.

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Earthbound telescopes tend to take their observations at visible wavelengths. But the amount of light reaching a telescope – assuming good weather – depends on the size and distance of an asteroid, as well as its composition.

By some estimates most near-Earth objects reflect about as much light as dark, wet soil, while the darkest reflect about as much light as a charcoal briquette.

The toughest asteroids to spot until they are very close are the ones that are small and dark.

Moreover, if an asteroid's orbital period is close to that of Earth's, "you get less information than you want for tracking," Mr. Schweickart says.

The reason: The closer the orbital periods, the longer orbital mechanics keeps the asteroid out of view for Earthbound observers.

If an asteroid completes one circuit around the sun in 360 days, for instance, "for five or 10 years, it's relatively close to you every year. But for the next 30 or 40 you don't get any data, so you don't know what's going on," Schweickart says.

For Schweickart and other planetary-defense specialists, it's time to take detection into space using telescopes that scan the skies at infrared wavelengths – making them sensitive to the heat asteroids give off from sunlight the objects have intercepted. Such telescopes not only can pick out the harder-to-detect asteroids, they also can lead to better estimations of an asteroid’s diameter compared with estimates derived from visible-light observations.

NASA's WISE satellite, an infrared telescope launched in December 2009 and designed for multiple research programs, has given researchers a taste of what's possible. It bagged 130 near-Earth asteroids, 21 potentially hazardous objects, and 17 comets before its detectors ran out of coolant in late 2011.

The B612 Foundation, a nonprofit, independent group of near-Earth asteroid specialists, is wrapping up design work on an infrared telescope to be placed on orbit around the sun the same distance away as Venus. The design is based on NASA's highly successful Kepler planet-hunting spacecraft. From that vantage point, it can look back at Earth and see clearly objects that cross or come near Earth's orbit – the heat signatures of the objects shining against the cold, black expanse of space in the background.

The mission, whose goal is to detect 90 percent of near-Earth objects about 460 feet across or larger, represents the first privately funded craft for asteroid detection. If all goes well, the group anticipates launching the craft in 2018, says Schweickart, a founder and former chairman of the group's board of directors. (Schweickart still sits on the board.)

In addition, the newly formed company Deep Space Industries, which aims to mine asteroids, has proposed a squadron of small "FirefFly" satellites in Earth orbit to hunt for prospecting asteroids to mine as well as search for potentially hazardous objects.