LINEAR accounted for the bulk of new discoveries in the late ’90s and early 2000s before being overtaken by the Catalina Sky Survey, another NASA-funded effort at the University of Arizona. Catalina and Spacewatch have informally divided responsibilities—Spacewatch focuses on better determining the orbits of objects that are already known, while Catalina focuses on finding new hazards.
All of these programs used roughly the same technique—take many pictures of the sky and look for things that move. NEOWISE, a systematic space-based effort to scan the skies for danger in 2010 and 2011, used the same basic idea, but had several advantages. Unlike the ground-based telescopes, which take pictures in the visible spectrum, NEOWISE used an infrared telescope. As NASA explains, “optical telescopes observe reflected sunlight so they cannot easily tell the difference between a small bright object and large dark object.” Infrared telescopes can thus better estimate the crucial question of how big potentially dangerous objects in space are.
WISE, the telescope part of NEOWISE, was launched in 2009 and hadn’t even been intended to hunt for hazardous objects. Its purpose was just to comprehensively scan the sky in the infrared spectrum, looking for luminous galaxies; finding new, dim stars; and doing basic astronomy research in how planets form.
After its main mission ended, astronomers realized they could use the 40-centimeter telescope to search nearby in the solar system. Because it is based in space, the NEOWISE mission can search more of the sky at once than ground-based detectors. Comparing how many such objects it found with the number of objects that had already been discovered from the ground let the NEOWISE scientists at NASA’s Jet Propulsion Laboratory in California estimate how many “unknown unknowns” are out there. They estimate that only 20-30 percent of large (that is, bigger than 100 meter) PHAs have been found already.
As for the smaller ones, the numbers are much larger. Events like today’s Siberian blaze are actually common. A similarly sized rock blew over Western Canada in November 2008, entering the atmosphere just east of Lloydminster. “Tens of thousands of people … saw it streak across the sky, saw its arc-welding blue flash, or heard the subsequent explosions,” a news report from the time said. But Twitter and YouTube weren’t so widely used then, and no one was reported injured, so it didn’t create the same international sensation. Something on the order of 10 fireballs of the size of the 2008 Canadian one—a bit smaller than today’s Russian fireball—occur every year. We just don’t see all of them. Many, for instance, fly over oceans.
It is probably not cost-effective to mount a large effort to track and develop the ability to deflect small space rocks like today’s. But such objects can serve as a wake-up call that more must be done to find and deal with their larger, rarer, and potentially far more hazardous brethren.
This article arises from Future Tense, a collaboration among Arizona State University, the New America Foundation, and Slate. Future Tense explores the ways emerging technologies affect society, policy, and culture. To read more, visit the Future Tense blog and the Future Tense home page. You can also follow us on Twitter.