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When a body meets a body…

What would happen if a hunk of space rock crashed into the planet? Purdue’s Impact Earth site lets you find out

By Michael Summers


Fort Wayne Reader


It’s a tried-and-true scenario of many a science fiction/disaster tale: the massive comet or asteroid hurtling towards Earth, unstoppable, implacable, and mankind can only brace for the environmental and geological havoc its imminent impact will unleash…

Henry Jay Melosh, Distinguished Professor of Earth and Atmospheric Sciences at Purdue University, has studied the “real world” version of that scenario for years. With help from colleagues Melosh developed Impact Earth, an interactive website that allows users to discover just what might happen if a big object from space collided with our planet. Visitors can set parameters for the projectile, like size, speed, and density; choose an impact angle; and select what sort of surface the object crashes into, such as water, land, the type of land, etc.

Then you watch the disaster unfold in the form of earthquakes, tidal waves, dust clouds…

“We don’t understand every possible aspect of big impacts until something like that happens,” Melosh explains. “But for those of us who study it, this incorporates the best and latest of what we do.”

He adds that to make sure Impact Earth is really a scientific website and not just some “video game,” there’s a link to a scientific paper that was peer-reviewed and published in a scientific journal, describing in detail all the calculations and various approximations used in the website. So, anybody who is deeply interested in the subject and wants to find out the science behind it, it’s all there.

That said, it also makes a pretty interesting and fun video game. For example, you can choose the size of your threatening chunk of space rock using kilometers/miles (or yards/meters), but for those of us not up on our weights and measures, the site also uses more descriptive sizeings, like a school bus, or a humpback whale, or Asia.

Melosh and his colleagues Robert Marcus and Gareth Collins developed an earlier version of Impact Earth while at the University of Arizona. Major impacts are Melosh’s area of expertise: he’s studied the impact that created the moon, the impact that killed off the dinosaurs… “So, anytime impacts of some kind, or asteroids, or any threatening object was in the news, I’d get a call from media people and they‘d all ask similar questions.”

Everyone wanted to know “what would happen if…” If an asteroid the size of a Wal-Mart crashed into the Rocky Mountains… if an asteroid as big as Rhode Island splashed down 200 miles off the Eastern seaboard… if a huge asteroid covered with active volcanoes…

“The object was always crashing down somewhere you weren’t,” Melosh laughs. “But I found myself doing the same things, consulting the same tables, doing the same calculations to answer these questions. It occurred to me that this could be automated and we could put it into a program that almost anybody could access.”

Melosh says the original site was very Spartan; no graphics at all. “But it would give answers and descriptions of what would happen, both in scientific terms and more expressive language,” he adds.

The site garnered over a million hits, and when Melosh moved to Purdue over a year ago, the university’s information technology group was interested in upgrading it, giving Melosh the opportunity to fix a few bugs and add some other features, including much better graphics. “When we wrote the first one people had relatively slow internet connections, so heavy graphics was not a good idea then, but things have changed,” Melosh says.

Advances in science and research were also taken into account. An example: when Impact Earth was first developed, Meloshi and his colleagues were asked to add tsunamis to ocean impacts. “We didn’t know how to calculate them reliably at first, but a lot of research has been done since then. We at least know shape of the ocean bottom. Still, there are a lot of variables, and you just can’t really say what the effects would be for every place, but we’ve incorporated what we can into the new calculator.”

A newer version is on the horizon that will link to Google Maps. “It’ll draw concentric rings around the impact site you choose with all the different effects,” explains Melosh.

“That feature has actually been requested as a civil defense tool,” he adds. “I’ve been involved with a National Research Council Panel evaluating the possible threat of asteroids and comets and what we should do about them. I learned on that panel that one of the things that was really needed was something that will give you an aerial map, mainly for civil defense folks.”

Once again, it sounds like the stuff of which disaster movies are made. And, to be frank, chances are indeed pretty slim that the Earth will be struck by a sizeable asteroid or comet; the probability is about 1 in a million that anything half-a-mile wide or greater would hit the Earth in any given year (smaller objects burn up in the atmosphere all the time). But Melosh emphasizes that civil defense agencies are taking this pretty seriously. “At one time, there was what was called ‘the giggle factor’,” says Melosh. “It seemed absolutely ridiculous that there would be big impacts on the Earth, it seemed so remote that it was not something that would effect our daily lives. What we’ve learned since then is that we can detect some impacts before they happen, and we’re seeing some pretty big objects out there that have a moderate probably of hitting the Earth. Unlike Earthquakes and hurricanes, asteroids are a threat that we can predict in advance, and it’s also something we can do something about.”

Like what? Well, Melosh was part of a group that looked at the possibility of deflecting an object headed our way. They impacted a small space craft into a comet. In that instance, the comet was too big to be deflected (we weren’t in any danger). “If it had been pointing towards the Earth, we wouldn’t have moved it any significant amount. But if it was an asteroid, say, a few hundred yards across, something that would wipe out a town, we could have moved that out of collision with the Earth by doing exactly what we did.”

There’s also a survey underway to find all big objects — about half-a-mile across — that are threatening Earth. The survey is almost wrapped up, and Melosh says it’s found maybe 85% or 90% of those objects. In 2005, the Brown Amendment required NASA to detect any object larger than about 100 yards. NASA was supposed to have this finished up to 90% by 2020, but Melosh explains there was no appropriation to do it. “We can’t do it by 2020, but 2030, maybe 2025, if we deem it a high priority.”

The biggest threat that we know of out there right now is a 1/2-mile wide object called Apophis. There’s a 1 in 100,000 probability Apophis will hit the Earth… in the year 2036. Melosh says worrying about it is a little premature — something that size we can deflect anyway — but considering the possibility of a big impact on Earth is not as silly as it sounds. “I often say we now know big impacts happen,” he continues. “They’re part of the Earth and our environment. They’ve happened in the past, they’ll happen in the future. They’re something we have to learn to live with. But unlike dinosaurs, we have brains and can maybe do something about it.”


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