A Minute With...

Leslie Looney, expert on astronomy

2/13/2013  8:00 am

On Friday, Feb. 15, an asteroid named 2012 DA14 will pass very closely to Earth. The trajectory of the 150-foot-diameter rock is the nearest fly-by ever predicted for an asteroid this large – even closer than some satellites. In an interview with News Bureau physical sciences editor Liz Ahlberg, astronomy professor Leslie Looney discusses the asteroid and its looming approach.

Tell us about 2012 DA14. How is an asteroid different from a comet?

image of professor leslie looney2012 DA14 is an asteroid, which is a way of saying a big piece of rock orbiting in the solar system. In this case, 2012 DA14 is a special type of asteroid that orbits near Earth, so we call it a near-Earth asteroid. There is a congressional mandate to NASA to find all near-Earth asteroids bigger than 1 kilometer. Today, we know of nearly 10,000 asteroids ranging in size from 3 feet up to 20 miles

These are different than comets. Asteroids are metal and rocky material, while comets include ice. Both objects were formed in the early solar system about 4.5 billion years ago. Asteroids formed in regions where it was too warm for ice to remain solid, while comets formed farther out where it was cold enough for ice to exist. When a comet is in an orbit that approaches the sun, it will lose material as it heats up and some of the ice melts, becoming a tail.

What makes them both interesting to study is that they formed when Earth was forming, but they were not incorporated into a planet. They are the fossils of the solar system, allowing us to better understand the conditions of the early solar system.

How close will the asteroid come to Earth? Is there any chance of a collision?

2012 DA14 will come within 17,200 miles from the surface of Earth. That is close. 2012 DA14 will be so close that it will pass inside the ring of geosynchronous weather and communications satellites. This will be a great opportunity for scientist to study a near-Earth asteroid close up. Luckily, the asteroid has zero chance of hitting Earth. Because the asteroid has been tracked for nearly a year, we have a precision measurement of its orbit, even taking into account the pull of Earth’s gravity. Nonetheless, with an estimated diameter of 140 feet, 2012 DA14 is the largest recorded object to get this close. Such an event is only expected once every 40 years, and an impact of an object this size is only expected every 1,200 years or so on average.

Could it hit satellites in orbit? What would happen?

There is very little chance that 2012 DA14 will hit a satellite. The asteroid will pass lower than the geosynchronous satellites (which orbit near 22,200 miles) but higher than the larger number of satellites orbiting much closer to Earth. Remember that the International Space Station is orbiting at 250 miles. The estimate is that 2012 DA14 will not pass within 1,200 miles of any satellites. If it does hit a satellite, it will clearly smash that satellite.

How can it come so close to Earth and not be pulled in by gravity?

2012 DA14 is on its own orbit around the sun, and although it will be perturbed by the gravity of the Earth, it will not be pulled in. Although 17,200 miles is close astronomically speaking, it is still very distant. Even at the closest approach, the asteroid will still be more than twice the diameter of Earth away. At its closest approach to Earth, the asteroid will be moving 17,500 miles per hour, or 4.8 miles per second relative to Earth. With these orbital parameters the asteroid cannot be pulled in by gravity.

Will we be able to see it?

The asteroid will be so far away that it will still be invisible to the naked eye. Regardless, it is not visible from Illinois during closest approach. However, if you are in Indonesia, Eastern Europe, Asia or Australia, and have some good binoculars handy, it is possible to observe the asteroid; however, it will be moving twice the diameter of the moon every minute with respect to the background stars.


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