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2012 Fall Issue 5 (October 19, 2012)

Asteroids Hitting the Earth Not As Ridiculous As It Sounds, Says Physicist

October 19, 2012
By Jonathan Lin

He introduced himself as a physics nerd who “takes pride in humorously debunking bad science.” In his convocation speech last Friday, Philip Plait, astronomer and author of the “Bad Astronomy” blog, discussed how astronomy is “constantly misused.”

People are interested in the “pretty pictures of space and the cosmos,” he said, but “are very easily scared of it.”

His presentation, titled “Death From The Skies”, covered the impact of asteroids hitting the earth as well as its inhabitants.

The far-fetched “death scenarios” that many associate with outer space – such as black holes and solar flares – Plait emphasized that asteroid impacts are actually “not some ridiculous sci-fi situation.”

He laid the groundwork about the Milky Way, explaining how the Asteroid Belt between Mars and Jupiter does not actually contain that much material: “if you compiled all the asteroid chunks out there, the result would be a mass smaller than the moon.” Via telescope images, Plait walked through the potato, dog-bone, and dumbbell shapes of various asteroid bodies, highlighting the challenge of studying them: “you have to really get up close and personal – that is, send a probe directly to the asteroid you want to study.”

Plait illustrated the many different asteroid orbits, some of which get very close to the earth; “100,000 tons of debris hit our planet each day,” he remarked. “The bigger ones are very rare.”

While passing out a fist-sized asteroid chunk from South America that he purchased from Ebay, Plait discussed the physical effects of impact with the earth, referring to diagrams of cascading air pressure, energy release in the form of heat and sound, explosions and craters, and airbursts.

He pointed to the scenario in Tunguska, Russia on June 30th 1908 and its status as a testimony to the threat that asteroids can pose.

Plait passionately lamented Hollywood depictions of asteroid impacts. “They’ve got a lot of it wrong,” he fumed while gesturing at Armageddon (1998): “The right stuff is actually a lot scarier than what they’ve shown.” In expressing a little more respect for the scientific accuracies of Deep Impact (1998), Plait addressed the common theme of detonating a bomb on the asteroid as the only viable solution.

“So being the nerd I am, I actually calculated how big the bomb would have to be,” Plait admitted. “Conclusion? It would need the same energy that the sun emits – and that assumes perfect energy.”

In addition he emphasized the warped logic of using explosions to split an incoming asteroid: “it’s way too difficult, and you’re turning one problem into a million problems.”

He talked about the 2004 discovery of the Apophis asteroid, which originally had about a 1/500 chance of colliding with the earth. Subsequent observations confirmed that the possibility was much lower, yet Plait emphasized the important lesson from the scenario.

“Apophis taught us about keyholes,” he remarked, referring to the small window in space where an asteroid passing through would miss the earth, but be sufficiently affected by its gravitational pull that an impact would nonetheless occur in the future.

“There is a two-pronged approach undergoing development,” Plait reassured the audience. “We could alter the velocity of the asteroid by detonating an explosion near it. Alternatively we could send out a probe and have its gravitational force nudge the incoming asteroid off course – into a newer, safer orbit.”

He highlighted that one of these probe projects costs less than a billion dollars, which is comparatively less than other solutions currently under discussion to a very real threat.

Plait concluded by reiterating the danger of asteroid impacts. “The dinosaurs are extinct because they didn’t have a space program,” he remarked. “On the other hand we today can vote: we have a choice.

“As scary as asteroids are, we can prevent them. Either we can sit and wait for the big one to hit and wipe us out, or we can save the world. We have a choice.” Coming from a scientist who has devoted much of his career to debunking bad science, this optimistic plight should be both reassuring and galvanizing for his audience.

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