Could the Apophis Asteroid Strike Earth in 2036?

On December 26, 2004, the world's eyes were fixed in horror and compassion on the appalling tragedy happening around the Indian Ocean, where a tsunami triggered by a massive earthquake claimed the lives of over 200,000 people.

Astronomers, meanwhile, were grappling with a future horror: a 1 in 37 chance that the newly-discovered asteroid Apophis could hit Earth on Friday, April 13, 2029, raising 800-foot-tall tsunamis if it struck the ocean, or wiping out a city-sized area if it struck land. In addition to millions of casualties, a terrestrial strike could produce a year of no winter like theTambora volcanic eruption of 1815.

On December 27, 2004, astronomers breathed a sigh of relief: a previously-unrecognized photo of Apophis from a few years earlier let them plot its course more precisely, ruling out a 2029 impact. However, it will come so close — 18,000 miles away — that it will be inside the orbits of Earth's geosynchronous satellites.

Luckily, those satellites orbit the Earth's equator, whereas Apophis' tilted angle of approach means it will not cross that plane. So we are not expected to have our satellites shaved off by a close buzz. But Apophis should briefly be visible to the naked eye in Europe, Asia and Africa, which is pretty incredible for a rock as opposed to a shiny metal satellite.

Unfortunately, Apophis will be back, and we're not out of the woods quite yet.

When Apophis wings by Earth in 2029, Earth's gravity will alter its course slightly. It's extremely difficult to predict this course alteration precisely without knowing the asteroid's exact shape and spin: it's like guessing a baseball's path before the bat hits it. At the moment, the window of uncertainty includes a remote (1 in 250,000, downgraded from 1 in 45,000) possibility that Apophis could impact Earth in 2036 (or, even less likely, 2053).

When the uncertainty window was greater, astronaut Rusty Schweickart startedlobbying NASA to launch a mission to Apophis to get an accurate prediction of its course as soon as possible. It's much easier to alter an asteroid's course a few decades ahead of impact. The Russians are still thinking about plans to deflect it, which might not be a bad idea as a trial run for the next Near Earth Orbit asteroid that threatens us. The only problem with a dress rehearsal is the risk of accidentally sending it towards us due to a miscalculation, glitch or programming error like the last several failed Russian space probes.

The risk of Apophis hitting Earth in 2036 is tiny. But if it did hit, the effects could be catastrophic, worldwide, and last for decades, or even centuries. If it hits land, it could wipe out a small country and throw up enough of a dust cloud to block sunlight for several years, which could play havoc on climate and the world's food supply.

If it hits ocean, it could send several hundred-foot-tall tsunamis crashing around all the low-lying cities of the Atlantic or Pacific. Even with a few years' warning, there's no way to mitigate the economic impact of losing, say, New York and London, or the port of Los Angeles. The early projected risk area for impact also includes oil-producing countries in South America, and perhaps the Panama Canal.

Even though the possibility of Apophis hitting anywhere is extremely low, the result of such an impact is so devastating that we need plans in place. We should have more information in the next year or so, as Apophis emerges from the sun's glare and allows ground-based telescopes to take new sightings and get a better fix on which way it's spinning and exactly where it's headed. This is one case where even a foot or two now can make a big difference 20 years from now.

Apophis can probably be deflected, if world governments decide that the threat is serious and commit to a deflection mission soon enough. If we wait until 2029, when Apophis swings by, it will be too late to alter its course enough to miss in 2036.

The only technology we've tested that works is to ram it with a spacecraft at least a decade ahead of of impact, creating a minute course change that would add up to enough deviation to miss Earth in 2036. NASA successfully hit a comet with the Deep Impact mission in 2005, so we know it can be done.

Any other asteroid-deflection plan is merely theoretical, and we won't have much time to test theory before putting it into practice. Space is still not 100% routine. The U.S. and other countries have had their share of failures. Intercepting a small, irregularly-shaped asteroid, tumbling and moving at thousands of miles an hour, is tricky even for modern space technology.

One asteroid defense method that's popular in Hollywood, but which probably would not work in reality, is to detonate the asteroid with nuclear or conventional bombs. It's unlikely that explosives would reduce an asteroid to harmless dust: there are just too many unknown factors like its shape, weak points, varying composition, and so on to plan a controlled demolition. Such an attempt would be far more likely to break an asteroid into fragments, some of which might be too large to burn up in the atmosphere. This 1994 photo of Jupiter shows what happens when fragments of a comet hit a planet.

Our best bet is to place something on or near the asteroid that gives it continuous small nudges (like a rocket nozzle or a jackhammer that thumps it continually), or slamming a spacecraft into it. Each of these methods would create a small deviation that would add up to a miss with enough lead time— hopefully a decade or more. Since a major mission like this would have to be organized, funded, designed, and built from scratch, we would be cutting it very close with Apophis if it turns out something needs to be done.

[Recommended Article: Five Plans to Head Off Killer Asteroid Apophis in Popular Mechanics Magazine]

It's a good thing we already know about it— what if it hadn't been spotted in 2004?

I'm not very worried about Apophis hitting Earth in 2036; at this points the odds are pretty good that we'll just be treated to a couple of dramatically close fly bys. That's actually exciting: telescopes are going to get a great look at an asteroid at extremely close range, and some space agencies may be able to get a probe up there and take samples, if they hurry!

I'm more interested in Apophis as a learning experience and trial run. It's close enough to galvanize public interest and (I hope) encourage space agencies to prepare and test asteroid-deflecting methods, so that we'll be ready if and when a direct threat arises. There are a lot of Near Earth Objects out there, and sooner or later, one is going to hit us and cause major destruction, unless we prepare for it. Unlike volcanic eruptions and most natural disasters, asteroid impacts are one threat that we can avert, if we have several decades to prepare.

Let's take this chance to learn all we can and get ready. And let's also be crossing our fingers that U.S. budget cuts don't shut down the Aricebo Observatory, whose highly accurate radar measurements are expected to help astronomers lock down Apophis' precise path once it emerges from the sun's glare. Near Earth Object Detection is one NASA mission where budget cuts to save money now may wind up costing us bigtime in the future.