How to Catch an Asteroid
BU astronomers ponder how to save earth
Last February’s atmospheric blowup of a meteor over Russia injured 1,500 people, mostly from glass smashed by the blast, whose force was estimated at 30 times that of the atom bomb dropped on Hiroshima. A month later, the US Senate heard former astronaut Edward Lu advocate for beefing up asteroid detection, warning that the casualties in Russia would have been incalculably greater had the meteor exploded closer to a big city. The Russian rock, a NASA scientist noted at the hearing, snuck by Earth’s telescopes, whose sites are set on projectiles much larger than that 60-foot-diameter meteor.
Is NASA worried? Sufficiently so that it has announced an asteroid Grand Challenge, inviting ideas from the global scientific community about how to spot and stop asteroids that threaten our planet.
At BU, our sky-gazing capabilities include a partnership with the $50 million Discovery Channel Telescope, at the Lowell Observatory, in Arizona, as well as the Perkins Telescope, at the same site. But even the Discovery Channel equipment, which doubled the distance in space that BU astronomers could see, is not an asteroid watchdog per se.
“You might pick one up, but that’s not what you’re intending to look for,” says W. Jeffrey Hughes, a College of Arts & Sciences professor of astronomy and an associate dean. “And you’re unlikely to pick up one of the very small ones, because it requires, essentially, a long time exposure.”
How exactly does one stop an asteroid? First, Hughes says, we should distinguish between planet-killers—asteroids so massive that we could kiss our posteriors good-bye—and smaller, potential city-killers like the Russian meteor. The former, he says, are hard to miss. Current scopes pick up 95 percent of those believed to be lurking near us, none of which currently threatens Earth, and improved technology will move that detection rate closer to 100 percent. Hughes and Andrew West, a CAS assistant professor of astronomy, concur that strikes from such monster rocks happen only once in tens of millions of years.
City-killers, the asteroids small enough to go undetected by telescopes, strike once every 1,000 years. That sounds disturbing, but Hughes points out that “tsunamis, super storms, and major earthquakes also can come close to obliterating cities or even small countries, and they happen far more frequently than once a millennium, so are a far more dangerous threat.” It’s better to invest in preparing for those more likely catastrophes, he says. “I don’t think detecting small asteroids should be a NASA priority.”
West agrees, saying that given Earth’s vast uninhabited real estate, from oceans to wilderness, “the real chances of them hitting a populated city…are very small.”
But Hughes also knows that human nature is easily frazzled by even the most unlikely events: “Tell people about a risk they’ve never heard about or thought about, and they get excited.”
Obviously, he notes, the best scenario would provide lots of warning—“ideally a decade or more”—of a coming collision, and the astronomer thinks such lead times are becoming possible as scientists’ ability to calculate orbits improves. The hard part is figuring out what to do once the heavenly threat is identified. Hughes’ preferred approach would be to knock it off course by hijacking its steering.
He proposes landing a spacecraft equipped with an engine propulsion system on the asteroid. “Then we can switch on the engine. A low continuous-thrust engine, such as an ion propulsion engine that can get its energy from solar cells, is the most efficient for this kind of task. Not very dramatic, but effective.”
Drama, he and West say, is what you don’t want, anymore than you want Bruce Willis–style explosives, as seen in the film Armegeddon. That’s because blowing up asteroids just makes lots of little asteroids, most of which will continue hurtling toward Earth.
Punching the asteroid off course by shooting an object into it—one option mentioned at the Senate hearing—might work, says Hughes, but it won’t be easy to fire a missile that has enough momentum to do that. Another possibility would be hitting the object with a radar beam to heat up one side, causing it to release more gas and veer slightly off course.
These tactics all may sound like science fiction, but in the opinion of astronaut Lu, the menu of choices makes deflection easier than detection. “The key,” he told the Senate committee, “is if you don’t know where they are, there’s nothing you can do.”
Just a question on the first option of using an explosion near an asteroid to deflect its course: how does this work in the vacuum of space where there is nothing to transmit a shock wave? Am I missing something? Thanks.
There might be a small shock wave from the material in the explosion and that might cause some change to the asteroid’s trajectory but you are correct that it won’t propagate very far in space due to the near vacuum. So if you were close enough, you could get push – but it’s my understanding is that in an explosion you also release high-energy particles (and light) that heat up the surface of the asteroid. The heated up rock (some of which is vaporized) can act like a rocket and propel the asteroid off course.
The vacuum really doesn’t have a lot to do with it. It’s the same if you detonated a nuclear bomb at 30,000 ft. It has to do with the explosion going in all directions with no matter to create a shockwave. In space there is still a large Gamma Ray Burst which will cause the asteroid surface to become ablated. The bomb facing side of the asteroid would have surface material vaporizing at 10km/sec or greater creating an impulse shockwave that would move the asteroid off course. This has to be done way in advance of the potential impact for it to make a difference.
I recommend keeping an eye on the asteroid at the left of the screen once you get towards the end of the article. What occurs caught me quite by surprise.
Oh that’s cool– when you scroll down fast!
This was a great entertaining article. Loved the videos too! Great job to the editors
Excellent, concise article! Love the videos. My book club just read “Space Chronicles” by Neil deGrasse Tyson and he supports ‘nudging’ larger asteroids off course as well. The event in Russia moved this to our collective awareness.
One of the best things we could perhaps do is to make a serious investment in expanding our civilization. We seem to have lost the collective will and drive to explore space that we had during the space race and it is both a shame and a serious threat to our existence. We have a beautiful place to live here on Earth but it has a serious downside: it is at the bottom of a gravity well, and that is a dangerous position to be in.
We know it has happened and that it will happen again. We are simply playing the odds. But if we aren’t ready it won’t just take out you and I. It will take out Mozart, Newton, Plato and Einstein and all that will remain will be decaying ruins and some worn out space debris.
I suggest watching some of the videos of Neil degass Tyson about how little we invest in NASA and science.
Very creative presentation! I enjoyed the story and the video component.
Nudge the asteroid off track, and how many years, hundreds of years, thousands of years are you going to research for the nudge, to make certain you haven’t altered the asteroid into a direct impact with Earth?
The main questions are what is the accuracy of the prediction and what is maximum achievable deflection? Could we end up turning a near miss into an impact? I’d also suggest picking a deflection that smashes the asteroid into another body like the moon. Less risk of it coming back again.
We really need to have something ready before we spot a problem object. The problem is that politicians will expect the thing to be solved from start to finish in the months we have between first sighting and impact. Doh.
A consortium of nations should plan, fund and build an autonomous installation on the moon that would use multiple asteroid detection technologies and multiple defenses including a device that would intercept and attach to the asteroid and then fire powerful thrusters to alter the trajectory of the threatening asteroid.
Asteroids were once viewed as the vermin of the sky, disrupting astronomical observations by leaving streaks on long-exposure photographic plates used to take pictures of the stars. How times have changed. These remnants of the early solar system are now seen as key targets for space science and, just possibly, for future space commerce.