23Feb2012

To Nuke An Asteroid/Meteor Makeup

What an asteroid hitting the Earth might look like. Image credit: NASA/Don Davis.

Scientists aren’t entirely sure when the last major asteroid hit the Earth, but it’s certain to happen again. Alan Harris, asteroid researcher at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), is hoping to head the next one off. Last month, Harris established an international collaboration of 13 researchers to investigate methods of shielding the Earth from near Earth objects (NEOs). The project is, appropriately, called NEOShield.

Asteroids approaching the planet typically travel between 5 and 30 kilometres (about 5 to 19 miles) per second. As that speed, a moderate sized body can have major consequences. The Barringer Crater in Arizona, often referred to as Meteor Crater, is a 1,200 metre crater (about 3,950 feet or 0.7 miles) that scientists hypothesize was caused by a 50 metre (164 feet) meteor.

The bad news is that there are thousands of known NEOs just like the one that made Meteor Crater, leading experts to posit that a dangerous collision could occur as often as every two hundred years. The good news is that it’s possible to stop an asteroid hitting the Earth. You just have to be in the right place at the right time to give the object the right push in another direction.

Scientists are focusing on possible methods of redirecting threatening asteroids so they miss the Earth. “In order to modify their orbit and prevent a collision with Earth, a force must be exerted on them,” explains Alan Harris. “And at the precise time, as well.” One way to do this is to have a spacecraft impact a threatening asteroid, imparting enough force to change its orbit. “In my opinion, this is a very practical method,” said Harris. But there are still questions to answer, like how to guide the spacecraft to a moving target at the right angle for the right impact and how to minimize the effects of fuel movement on the spacecraft’s path.

Another way is to use the spacecraft’s gravitational pull to nudge the asteroid into a different orbit. If the object is far enough away, a tiny tug could have a big effect. But so far, “this method only exists on paper,” said Harris, “but it could work.”

Meteor Crater near Winslow, Arizona. Image credit: NASA.

Another third, less appealing prospect, is to use explosive power to break up an Earth-bound asteroid. But this could be disastrous, creating a shower of debris instead of one solid piece. As such, Harris considers this method a last resort. “If a very large, dangerous object with a diameter of one kilometre [0.6 miles] or more is discovered,” explains Harris, changing its orbit won’t be a option. “The greatest force we would be able to use to divert the asteroid from its path would be a nuclear explosion. This technique is regarded as a very controversial.”

Over the next three years, during which the European Union will support the project with four million Euros and international partners will contribute an additional 1.8 million Euros, the NEOShield project will research these defence methods. The scientists will focus on data from asteroid observations and lab experiments to generate computer simulations, ultimately determining how best to protect the Earth from future devastating impacts. Source: Universe Today

 

 Not All Meteors The Same

Fast-traveling meteors tend to burn up once they strike Earth's atmosphere. Click to enlarge this image. Tony Hallas/Science Faction/Corbis

Scientists have unravelled the mystery of why some meteors flash across the night sky burning up as shooting stars, while others survive raining gently down to the ground.

The discovery by David Nesvorny from the Southwest Research Institute in Boulder, Colo. and colleagues was made during a study of an astronomcical feature known as the Zodiacal Cloud.

The Zodiacal Cloud is a diffuse glow of scattered sunlight in the night sky. Models predict that micro-meteoroids enter the Earth’s atmosphere at relatively low speeds, gently raining down onto the ground. But meteor radars consistently see the sky filled with rapidly speeding meteors flying too fast to survive.

Nesvorny and colleagues found the inconsistency was caused by some meteor radars not being able to see the slower, smaller meteors, instead only detecting the bigger faster ones which people see as shooting stars.

Reporting in the Astrophysical Journal and on the pre-press website ArXiv.org, Nesvorny and colleagues found that 90 percent of the dust in the Zodiacal Cloud comes from Jupiter family comets such as 2P/Encke, whose orbits are influenced by the giant gas planet.

These appear to have compositions which cause them to slow down rapidly once they enter the Earth’s atmosphere, allowing them to survive and reach the ground often as micrometeorites no bigger than grains of dust.

The remaining 10 percent of material in the Zodiacal Cloud comes from Oort Cloud comets, Halley-type comets and asteroid collisions.

They are usually associated with cometary debris trails seen as meteor showers, and because they’re traveling faster when they hit the Earth’s atmosphere, they’re more likely to burn up as shooting stars.

 Meteoroids and their tiny counter parts micro-meteoroids often fly through space at speeds of 40,000 kilometers per hour (25,000 miles per hour). Meteors that enter the Earth’s atmosphere and reach the ground are called meteorites.

Astronomer Dr Fred Watson from the Australian Astronomical Observatory says the study provides a new insight into the amount of dust and debris falling into the Earth’s atmosphere every year.

“Their figure of 15,000 tons a year is considerably more than previously thought,” said Watson. “When you think about it, that’s an extraordinary amount of stuff falling down to the Earth’s surface. It’s a train’s worth of stuff.”

The study also provides an important contribution to our understanding of the Earth’s environment, said Watson.

“It’s an area of study that hasn’t been examined over the past couple of decades, and we’re now starting to see real scientific measurements being brought to the process rather than just the guesstimates,” he said. “We now have a much better picture of what’s happening.” Source: Discovery Channel

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