Kenneth Change NYTimes Article on 2008 TC3

Here is the complete article from Kenneth Chang that summarizes the 2008 TC3 discovery.

Scientists Examine Asteroid Remains
Kenneth Chang
New York Times
25 March 2009

Scientists who for the first time tracked an asteroid on a collision course with Earth, and watched as it exploded in the atmosphere, have now picked up some of the remnants on the ground. The discovery and analysis of the meteorites, reported in Thursday’s issue of the journal Nature, give scientists solid data on the composition of meteorites that originate from what are known as F-class asteroids.

Millions of asteroids, mostly small, whirl around the solar system. It is not uncommon for the fireball of an incoming asteroid to light up the night sky and then for people find meteorites — the surviving rock fragments. But in most cases, scientists can only guess what kind of asteroid the meteorites came from.

“We now have the first samples in hand of a known asteroid, characterized in a way other asteroids are,” said Petrus M. Jenniskens, a scientist at the SETI Institute in Mountain View, Calif., who organized the search teams for the meteorites and is the lead author of the Nature paper.

Richard Kowalski first spotted the asteroid on Oct. 5 at an observatory on Mount Lemmon in Arizona. He noticed a white dot moving on his computer screen and sent the coordinates to the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics.

The next morning, Timothy B. Spahr, director of the Minor Planet Center, got to work. The asteroid, designated 2008 TC3, was passing so close that the Earth’s gravity was greatly distorting its orbit. In fact, the asteroid looked as if it was being pulled directly into Earth.

Dr. Spahr woke up a colleague, Gareth Williams, who calculates the probabilities of impacts. Based on the initial sparse data, Mr. Williams calculated 80 percent. With some more data, the probability rose to 100 percent.

From the brightness, Dr. Spahr and Mr. Williams knew that the asteroid was small — about the size of a car and 70 tons — and would not cause any damage. Notice of 2008 TC3 quickly spread. By the time the asteroid disintegrated about 23 miles over the Nubian desert of northern Sudan, 20 hours after Mr. Kowalski spotted it, both professional and amateur asteroid watchers had pointed their telescopes to it.

Even a KLM pilot alerted to the asteroid was able to spot the fireball from more than 800 miles away. The expectation was that none of 2008 TC3 survived the passage through the atmosphere. But still, Dr. Jenniskens, an expert on meteor showers, wondered.

In December, he flew to Sudan and organized a team of 45 students and staff members from the University of Khartoum to search through the desert for fragments of 2008 TC3. And they found them — shiny black fragments, about 280 of them, weighing several pounds in total. The meteorites turned out to be a strange type known as ureilites — a hodgepodge of different minerals that had been heated but not totally melted.

The observations of 2008 TC3 before impact showed that it belonged to the F-class of meteorites. Thus, for the first time, scientists has direct evidence that ureilite meteorites originate from F-class asteroids.

Link: NYTimes Article