Astronomers shared a collective sighofrelief last week when a 100-foot asteroid hurtling toward Earth missed by50,000 milesjusta fifth of the distanceto the moon. As comforting as the avoided terrestrial calamity was,what remains disturbing is that no one knew it was coming.
The near misscamejust days before NASA plansto launch an $800 million probe that will land ona much largerasteroid, a remnant from the beginning of the solar system that should provide clues to Earths origins.
The mission OSIRIS-REx, which actually stands for something (Origins Spectral Interpretation Resource Identification SecurityRegolith Explorer), is slated to blast offon Sept. 8, from Cape Canaveral, Fla.
The mission advances our more practical goals of understanding the resources of the near earth Solar Systemas well as the hazards, Jeffrey Grossman, a mission scientist, said at a press conference lastmonth.
The probe will visit a near-Earth object that tracesan orbit around the Sun similar to the Earths. The asteroid, called Bennunamed by a nine year-old from North Carolinarecommended itself for several reasons. Its oldbasically leftover pizza dough from the beginning of the solar system. As a result, it might contain some of the chemical secrets about how the Earth was seeded with the potential for life.
Being a near-Earth object, however, doesnt make Bennu a pal of our home planet. By beingin the neighborhood, itpasses Earthevery six years, comingso close that scientists give it a 1-in-2,700 chance of hitting us over the next two centuries.
It's tempting to believethatKepler's laws of planetary motiondescribes heavenly objects, including asteroids and comets, as taking immutable, precisely calculable tours around the sun. But there's more to it than that. OSIRIS-REx will be measuring a phenomenon known by the spy-novel sounding moniker, the Yarkovsky effect. Abig chunk of rock can pick up speed as sunlight heats it up and the blackness of space cools it off. This acceleration can nudge its heading slightly. The effect acts like a thruster and changes the trajectory of theasteroid, Dante Lauretta, the mission's principal investigator and a professor at the University of Arizona, said last month. So if you want to predict where an object like Bennu is going to be in the future, you have to account for this phenomenon.
What itmeans is that Bennu, which was discovered in 1999, mightstill surprise astronomers when its orbit starts to more closely trackEarth's in 160 years.By collecting precise data on its composition, shape, and surface features, NASA hopes it will be able to document the Yarkovsky effect in greater detail, and consequently get a better sense of the risk asteroids pose to Earthlike "2016 QA2," the recent near-miss.
|Scientists and engineers gather around Lockheed Martins thermal vacuum chamber to watch the OSIRIS-REx spacecraft enter one of its last phases of testing.
Photo: University of Arizona/ Symeon Platts
NASA, directed by Congress, takes impact-risk seriously, maintaining adatabase of possible hazards and a scientific scale for categorizing their threats. The National Research Councilin 2010 published a report about asteroid risks and what to do about them. That research suggests that a rock the sizeof 2016 QA2 mighthave had some serious local impacts:
Many dozens of people work for years to launch a mission that has thecomplexity of OSIRIS-REx. Often, its a lifelong dream. As Canadian Space Agencys Tim Haltiginsaid in this NASA video, I grew up playing video games about shooting lasers at asteroids, and now its my job to shoot lasers at asteroids. It never stops amazing me.
The sample-return spacecraft can carry up to 4.4 pounds of space rock. The minimum amountscientists expect is about 2 ounces. It's a lot of work for what seems like a little materialand yet a much better idea than waiting to see if the whole 1,600-foot-wide asteroid slams into earth at the end of the next century.