An asteroid exploded over Sudan’s Nubian desert last year with the force of a small atom bomb and sent a California astronomer and others racing into the rock-strewn sandy wilderness to recover tiny fragments of a space rock.

Now those ancient rocks, fragments of the demolished asteroid, are yielding new insights into the origins of our solar system, the astronomer and his team of scientists reported Wednesday.

The small asteroid was picked up by NASA meteor trackers last Oct. 6 tumbling in space about 23 miles above the Earth’s surface. Using an automated telescope, they determined its orbit, followed its course, and watched as it entered the Earth’s atmosphere and burst into a shower of fragments.

Peter Jenniskens of the SETI Institute and NASA’s Ames research center at Moffett Field in California said it was the first time scientists had observed the destruction of an asteroid and traced its meteorite fragments as they fell to Earth , onto the floor of the Nubian desert in Sudan.

In a teleconference call, he recalled that the brilliant light of the explosion just before sunrise that autumn day terrified villagers around the small Sudanese railroad town of Wadi Halfa.

No one there could explain it, he said. “The fireball was seen everywhere along the Nile.”

Jenniskens and his colleagues, however, recognized the event as an extraordinary scientific gift from the sky.

On Wednesday, Jenniskens told reporters how he led a team of Sudanese scientists and university students across miles of desert near the Egyptian border to gather nearly 300 unique asteroid fragments — one of which has already been analyzed by researchers.

“It’s the first time we’ve ever actually held an asteroid in our hands,” he said, adding that it makes a splendid replacement for a long-planned NASA space mission designed to seek and bring back a chunk of some other asteroid.

The conference call linked NASA headquarters in Washington with Jenniskens in his SETI Institute office in Mountain View, Calif.

From space to the lab

Michael Zolensky, a cosmic mineralogist at NASA’s Johnson Space Center in Houston who participated in the call, marveled at the scientists’ good fortune.

“For the first time we have a complete evidence chain — from an asteroid in space whose color and optical spectrum we obtained just before its impact, to a rock we can analyze in the lab,” he said.

Scientists and amateurs alike have long found meteorites — both large and small — all over the world, but no one had ever linked a single meteorite to a specific asteroid.

The asteroid belt lies between Mars and Jupiter and contains millions of objects left over from the giant cloud of dust and rocks that surrounded the sun as the solar system and all its planets were forming some 4.7 billion years ago.

Asteroids observed by telescope are divided into varied classes according to their optical characteristics, and the one that yielded Jenniskens’ fragments after exploding with the energy of 1,000 tons of TNT was a very rare F-class object called a ureilite. It was extremely fragile, fine-grained, porous and probably weighed nearly 90 tons before its sharp-edged fragments fell to Earth, Jenniskens said.

He and his team returned to the Nubian desert on a second trip only three weeks ago, and collected more rocks, bringing the total number of recovered fragments to 280 shards and rocks. Because of their porous nature, the entire collection weighs just 10 pounds. Some shards weigh only a few hundredths of an ounce, others nearly a half-pound, and all are as precious as jewels, Jenniskens said in an interview after the conference call.

Even now, tens of thousands of small pieces must be invisibly littering the Nubian desert, he said.

A report on the first round of discovery and analysis is being published today in the journal Nature.

The discovery

The first tiny chunk that was analyzed has been named Almahatta Sitta, the Arabic word for Station 6, a Sudanese railroad station near the discovery site where Jenniskens and Prof. Muawia Shaddad of the University of Khartoum collected the fragments. Jenniskens recalled that Mohammed Alameen, a sharp-eyed Sudanese university student, found the very first one.

The single fragment that Zolensky and other scientists are now analyzing contains widely varied and colored forms of carbon, including countless microscopic diamonds — “nanodiamonds,” they’re called — plus graphite and iron carbide. It holds organic chemicals too, possibly including amino acids.

The asteroid itself was detected by the Catalina Sky Survey Telescope atop Mount Lemmon in Arizona. The instrument is one of three telescopes worldwide designed to find and track “near-Earth objects” of all sizes that appear on course to approach or actually hit the Earth.

Because the telescope was able to determine its orbit precisely, said Steve Chesley of the Jet Propulsion Laboratory in Pasadena, it also could track all of the tiny meteorite fragments that fell to the Nubian desert 15 hours after the explosion.

Lucy McFadden, an astronomy professor at the University of Maryland who specializes in asteroid research, was not part of the team, but she joined Wednesday’s teleconference to note that the fragments are particularly significant because they show evidence of volcanic activity and melting in the distant past.

It was probably part of a much larger body — “I’d call it a planet,” she said — that formed and then crashed against other objects as the crowded early solar system was forming all those billions of years ago.

“There had to be hundreds if not thousands of them jostling in the congestion,” McFadden said. “Meteorites like this one are bringing us stories of the early solar system,” she said. “It gives us ground truth to study in the lab.”

There are many different types of asteroids, all classified from afar based on color and light wavelengths. This type is called class F and turns out to be mostly porous and fragile. McFadden said it’s unlikely that a class F asteroid could be any danger to Earth, even if it was bigger, because of its porous makeup, which would cause it to break up before hitting.

This asteroid was full of metals, such as iron and nickel, and organics such as graphites, Zolensky said.

And most interesting are the nanodiamonds. They are formed by collisions in space and high pressure and they are all over the rocks, making them glitter like geodes, he said. But they aren’t very big.

“If bacteria had engagement rings, these would be the right size for them,” Zolensky said.