Asteroid That Might Hit Earth Next Century to Be Visited by U of A Spacecraft in 2018

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One real-life version already is unfolding, albeit on a comfortably long timescale.

Bennu, which used to have the eye-glazing name of "101955 (1999 RQ36)" before 9-year-old Michael Puzio from North Carolina won a naming contest last year, has a diameter of almost 1,600 feet. That's taller than the vertical gain of Camelback Mountain. Its orbit occasionally crosses the Earth's orbit.

During eight close calls of Earth the asteroid will make between 2169 and 2199, it has a 1-in-1,410 chance of hitting this planet, according to NASA's Sentry Risk Table.

Nothing to lose sleep over now. But those odds, combined with the sheer size of the thing, make it the perfect target for observation. Bennu's the largest object known that might hit the Earth the soonest. It's the number-two body on the NASA risk table. Number one is 1950 DA, nearly three times bigger and with a 1-in-4,000 chance of slamming into Earth — but not until the year 2880, when our ability to deal with such things may be much improved.

Bennu's not a dreaded "planet killer," like the six-mile-wide rock believed to have done in the dinosaurs. But it's big enough to cause real damage. If Bennu had hit Chelyabinsk, the city would have been wiped off the map as if from a thermonuclear weapon, minus the poisonous radiation and fallout.

The online simulator Impact Earth!, created by Purdue University scientists in 2010, helps estimate the potential destruction. Plug in Bennu's size, estimated density (currently unknown, but thought to be somewhere between "ice" and "porous rock" on the impact calculator), estimated speed at impact, and how far you'd be standing from the blast site.

Ten kilometers (6.2 miles) would be much too close. Nearly everything at that distance would burst into flame, the site calculates. A shock blast would follow 30 seconds later, flattening buildings and tossing cars like soccer balls.

Learning more about Bennu clearly is prudent, especially if the people of Earth want to prevent such a disaster. Since it's an object that orbits the sun near Earth, Bennu will teach humans how not only to deflect its trajectory but ward off other potential threats.

About 94 percent of the estimated number of near-Earth objects of truly scary size — about a kilometer across — already have been located in space. But that leaves quite a few potential Earth-smackers, and there are endless opportunities for bodies from farther out to move closer, kicked in by the gravity of Jupiter and other planets or nearby stars.

If an Earth-bound asteroid is spotted far enough out, scientists are laboring to give humans plenty of time to nudge it a little, changing its trajectory just enough to make a difference over millions of miles traveled.

NASA is funding plans to use nuclear weapons for just that purpose, similar to the plot of Armageddon, released in 1998.

But before anything like this can happen, scientists must learn more about these super-abundant space objects. Enter OSIRIS-REx, a boxy spacecraft with wing-like solar panels, a movable appendage that blows air like an elephant's trunk, and a saucer-shaped cargo carrier.

For scientists and astronomy lovers, the most interesting part of the mission isn't the chance of an impact by Bennu but the far better odds of advancing scientific knowledge. While asteroids have been known since the first one, Ceres, was discovered in 1801 by Giuseppe Piazzi, the field of study matured in the 1990s, as computer-aided astronomy began taking off. Scientists have learned that asteroids, comets, and other minor bodies are far more interesting and varied, and that near-Earth objects are more common than first thought. Some believe asteroids are responsible for Earth's water — and, indirectly, its life.

What Bennu's made of, how calculations of its orbit can be refined, and whether the recovered physical sample will match up with other astronomical observations are questions that OSIRIS-REx will help answer.

That, in turn, will fill in some blanks of one of the most pressing mysteries in the study of the outer space: How the solar system's planets, moons, and other bodies formed into their present compositions out of spinning gas and dust nearly five billion years ago.

Much has been learned in the past 20 years, with the detection and discovery of numerous planets outside our solar system around nearby stars and by the intense focus on smaller objects in our own system. Previous theories of solar system formation don't match up with what's now seen in these faraway planets and nearby asteroids and comets.

The view of the solar system still is under development, and asteroids figure large in the new theories. They can be as small as boulders or as large as Ceres, which is more like a planet. They're shaped like crude spheres, but also like dumbbells or bowling pins. Some appear reddish, deep black, or brown, and some consist of rubble held together loosely by gravity instead of solid rock or metals. They might be rich in precious metals like platinum. Even small asteroids might have one or more smaller moons orbiting about them.

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Ray Stern has worked as a newspaper reporter in Arizona for more than two decades. He's won numerous awards for his reporting, including the Arizona Press Club's Don Bolles Award for Investigative Journalism.