The Man Who Guards The Planet

You don’t want Don Yeomans’ job, no matter how appealing it seems. He’s an astronomer at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., which is awfully cool. And he’s one of the lab’s top guys, which is even better. The problem with Yeomans’ job is the pressure. He is never really off duty, and his work is very straightforward: he guards the planet. Really. If morning dawns in your part of the world and all is still well, it’s on Yeomans’ watch. If your city or entire country is wiped out tomorrow, well, there’s a case to be made that it’s on Yeomans’ head.

Yeomans leads JPL’s prosaically named Near Earth Object Program Office, charged with the mission of watching the skies for errant asteroids that are always out there, always moving at dive-bombing speed and always capable–depending on the vagaries of gravity, physics and simple bad luck–of putting Earth in their crosshairs. After decades of being dismissed as apocalyptic nonsense, the threat from incoming space rubble is at last being taken seriously. Funding is up–way up–telescopes and satellites are being assigned to the hunt, and real progress is being made in a cosmic census taking like none before. It’s high time.

The dinosaurs could tell you how a serious asteroid hit turns out–except they can’t because they’re all dead, thanks to a 6-mile asteroid that crashed off the Yucatán Peninsula 65 million years ago, throwing up a globe-cooling shroud of dust and debris that made Earth uninhabitable, at least for them. It’s the same kind of event that flattened 830 sq. mi. of trees across the Tunguska region of Russia in 1908 and the same kind that on the morning of Feb. 15, 2013, clobbered Russia again, this time near the city of Chelyabinsk, injuring 1,600 people and damaging 7,300 buildings.

The enormous destructive power of space rocks is due to the enormous speed at which they travel–and thus the enormous energy they’re packing. The Chelyabinsk meteor was 66 ft. wide and exploded with the power of 33 Hiroshima bombs; the only thing that prevented 33 times the Hiroshima damage from being done was that the airburst took place so high in the atmosphere. The Tunguska meteor unleashed 330 Hiroshimas.

Someone has to keep an eye on all that cosmic ordnance, and Yeomans, 72, got the job. What air-raid wardens were in the days of the Cold War, he is in the modern era, except that air-raid wardens never had to shoot down enemy bombers. Yeomans does. He is responsible for figuring out ways to deflect rocks that are headed our way. Despite the deadly seriousness of the work, he treats it with as much sangfroid as he can.

“It’s our job to make sure the solar system is well behaved,” he says. “Asteroid strikes are what we call low-probability, high-consequence events. If we’re not investing in some kind of insurance, one of them, one day, could take us all out.”

Keeping Track: 11,000 Asteroids

The world got its most recent taste of what that might be like with the 2013 Chelyabinsk strike–and a taste too of the hubris of thinking we’re too smart to get blindsided that way. On the very day that Russia got rocked, NASA was tracking another asteroid, known as 2012 DA14, which had been getting a lot of press. Part of the coverage was driven by how big the thing was–about the size of a small office building. But mostly it was the asteroid’s altitude. It was supposed to pass Earth at a distance of just 17,200 miles, several thousand miles below the altitude of some of our highest-flying satellites.

That, however, didn’t matter. Thanks to its sophisticated sky-watching capabilities, NASA knew where 2012 DA14 was going and knew it would miss, and the agency was using that fact as a kind of case study of how sharp-eyed it had become. “We had the asteroid in the bag,” says Yeomans. “I was in Vienna at a conference and was going to talk about it at the end of my presentation. I had a nice graphic to go with it.”

But even before Yeomans took the stage, Chelyabinsk was hit. The asteroid sneaked through the same way that fighter pilots can get the jump on the enemy: by flying in from the direction of the sun. Just in case NASA and JPL needed any reminder of how completely they had been sandbagged, they learned about Chelyabinsk in the most proletarian way possible, via Twitter. “That was humbling,” Yeomans says, “and instructive.”

Yeomans and his team of six other astronomers are currently tracking over 600,000 asteroids, and something new is added to the tote board daily. Every day, we get hit by 100 tons of pebbly debris–all of which incinerates in the atmosphere–including at least one basketball-size object. Every eight months something comes in that’s as big as a small car.

Most of the objects the Near Earth Object (NEO) office is tracking are detected by one of three telescopes, which are in Arizona, New Mexico and Hawaii. From there, the data is sent to the Minor Planets Center in Cambridge, Mass., where the orbit and size of the objects are estimated. Those findings are then sent to both JPL and a team of astronomers working at the University of Pisa, in Italy, who refine the orbit predictions and estimate the odds of future collisions.

For all the devastation the crack-ups can cause, Yeomans has developed something of a fondness for space rocks. There are no plants on his office windowsill, but there are two large potato-like objects–both scale models of asteroids. One of them, Eros, which in real life measures 21 miles by 7.7 miles, is a place NASA knows well. In 2001 the agency’s NEAR Shoemaker spacecraft landed on Eros, where it remains today. Yeomans turns the model over and over in his hand, then points to a dimple on its side. “It’s right about there,” he says.

He came to his fascination with rogue cosmic bodies partly as a result of a big win early in his career. In 1986, Halley’s Comet was due to reappear, which it had done once every 76 years or so since its first reliably recorded appearance in 240 B.C. But the “or so” part presented a puzzle, and the comet could actually reappear anytime within a five-year window from 1984 to 1989. Predicting exactly when it would show itself and at exactly what point in the sky would not only be worth global astronomical bragging rights–a little like getting an NCAA bracket entirely right–but would also help validate modern orbital-prediction methods. By the early 1980s, astronomers around the world were at work on the puzzle. Yeomans, who had come to JPL in 1976 after a stint at NASA’s Goddard Space Flight Center, was part of the scrum. As it turned out, he was the one who called the shot correctly, telling the astronomers running Caltech’s Palomar Observatory where they should point their telescopes if they wanted the first look at Halley–and there the comet was. “That was gratifying,” Yeomans says. “That was fun.”

But what’s gratifying can also be terrifying, a point that asteroid scholars had been trying to make for a long time. Finally, in 1998, Congress agreed to begin allocating funds–just $4 million per year–to the business of searching for dangerous asteroids. In 2012 the figure was bumped to $20 million, and since then–post-Chelyabinsk–it’s been doubled to $40 million, a lot of which will go to upgrading ground-based telescopes and maintaining the NEO Wise satellite, which also searches for asteroids. But already we’re a lot safer than we once were.

JPL astronomers have now found and plotted the trajectories of nearly 11,000 so-called near Earth asteroids, defined as those that come within 1.3 astronomical units of the sun. A single astronomical unit is the distance from the sun to Earth–93 million miles. So 1.3 AUs means close, but with a 30 million-mile margin of error. To qualify as what’s known as a potentially hazardous asteroid, the object must measure 460 ft. and come within 0.05 AU of Earth–or 4.65 million miles. Currently NASA knows of slightly fewer than 1,500 of these bruisers. The objective is to project orbital cycles at least a century into the future.

“NASA’s plan from the start has been to find the largest of these bodies first–those 1 km or more,” says Yeomans, “and we’ve found 95% of those.” But they’ve found less than 40% of the 460-ft. class. With the new bump in funding, Congress expects JPL to get that number up to 90%. “By finding them,” Yeomans says, “we will have addressed 90% of the remaining overall risk.”

A Good Hard Shove?

Of course, the point of the work isn’t just to watch all the near misses fly by but also to do something about the ones that are heading our way. Paul Chodas, an astronomer who specializes in asteroid motion and impact probabilities, works both with Yeomans and with NASA’s manned space program developing a method to steer an asteroid to the vicinity of the moon and use it as a research base for astronauts. The same system that could be used to move a rock to a spot where we want it to be could also be used to deflect it from a path we very much want it to avoid. Chodas is cheekily aware of those dual purposes. “Asteroids,” he says, “are nature’s way of asking, ‘How’s that space program going?'”

The problem is that the engine system he’s using in his work is solar electric propulsion, which relies on an exceedingly gentle thrust to accelerate an object gradually. It’s a perfectly nice way to go when you have the luxury of time and must be very precise with your steering, but asteroids threatening Earth don’t need such tender handling. There has long been talk about using a spacecraft carrying explosives–either conventional or nuclear–to simply blow the thing out of the sky. But nobody much likes the idea of launching nukes, and an imprecise blast could merely reduce one very large object to several smaller but still dangerous ones–turning a bomb into a cluster bomb.

A better solution, Yeomans and others say, is just to give the asteroid a good, hard shove, changing its trajectory a little when it’s far away from Earth so that by the time it reaches us, it flies wide–the way a fractional change in heading when you’re setting out to sail east across the Atlantic could determine whether you wind up in Europe or Africa. “Depending on distance,” says Yeomans, “you might have to change an asteroid’s velocity by only 1 cm per sec.”

Such a course correction could be achieved by hitting the rock with a cannonball-like projectile or even a spacecraft. NASA has already accomplished something similar, firing an 816-lb. impactor into comet Tempel 1 in 2005 to gouge out a crater that permitted the Deep Impact spacecraft to observe the interior. The impactor did not affect Tempel 1’s trajectory much, but a larger collider–say, a few tons–could do it.

The hard fact remains, however, that no asteroid-deflecting spacecraft exists, and it takes time to design one, build it and send it out on its mission. At the moment, Yeomans estimates we’d need a 10-year window between the discovery of a killer rock and deflection if we wanted to avoid disaster.

For now, JPL is working on boosting its observational game and is getting yet more help from Washington. Government surveillance satellites that typically look down rather than up are being reprogrammed to scan for atmospheric flashes that suggest a meteor incinerating itself. Tallying those airbursts will provide a better estimate of how often Earth gets hit and of the odds of more-serious strikes.

Washington has geopolitical interests at stake too. In 2008, JPL spotted an asteroid that had a fair chance of striking northern Sudan and alerted the White House that it should notify the Sudanese–fast. “They needed to know that this was a natural phenomenon and not something coming from a neighbor,” Yeomans says.

In May, JPL conducted a pair of tabletop exercises, or simulations, with both FEMA and the Defense Advanced Research Projects Agency, war-gaming what would happen if an asteroid were discovered this year that was on track to hit us in 2021. A range of experts from spacecraft designers to civil-defense experts to social psychologists worked on problems of deflection and evacuation–and did so under exceedingly high pressure, with the entire seven-year cycle playing out in a single day. There are more such drills to come, and the U.S. hopes to press other countries to get more involved as well. Yeomans estimates that with the exception of the University of Pisa group, 98% of all detection and tracking work is being done by the U.S. “This is an international problem,” he says. “It calls for an international solution.”

Actually, it’s a bigger problem than that–a potentially existential one. Not all forms of life succumbed to the dino-killing event 65 million years ago, but the dominant one on the planet did. We have long since become heir to that position. The goal is to avoid falling to that fate.