The crater's location, in the Wilkes Land region of East Antarctica, south of Australia, suggests it might have instigated the breakup of the so-called Gondwana supercontinent, which pushed Australia northward, the researchers said.

"This Wilkes Land impact is much bigger than the impact that killed the dinosaurs, and probably would have caused catastrophic damage at the time," said Ralph von Frese, a professor of geological sciences at Ohio State University.

How they found it

The crater is about 300 miles wide. It was found by looking at differences in density that show up in gravity measurements taken with NASA's GRACE satellites. Researchers spotted a mass concentration, which they call a mascon-dense stuff that welled up from the mantle, likely in an impact.

"If I saw this same mascon signal on the Moon, I'd expect to see a crater around it," Frese said. (The Moon, with no atmosphere, retains a record of ancient impacts in the visible craters there.)

So Frese and colleagues overlaid data from airborne radar images that showed a 300-mile wide sub-surface, circular ridge. The mascon fit neatly inside the circle.

"And when we looked at the ice-probing airborne radar, there it was," he said today.

Smoking gun?

The Permian-Triassic extinction, as it is known, wiped out most life on land and in the oceans. Researchers have long suspected a space rock might have been involved. Some scientists have blamed volcanic activity or other culprits.

The die-off set up conditions that eventually allowed dinosaurs to rule the planet.

The newfound crater is more than twice the size of the Chicxulub crater in the Yucatan peninsula, which marks the impact that may have ultimately killed the dinosaurs 65 million years ago. The Chicxulub space rock is thought to have been 6 miles wide, while the Wilkes Land meteor could have been up to 30 miles wide, the researchers said.

Confirmation needed

Postdoctoral researcher Laramie Potts assisted in the discovery.

The work was financed by NASA and the National Science Foundation. The discovery, announced today, was initially presented in a poster paper at the recent American Geophysical Union Joint Assembly meeting in Baltimore.

The researchers say further work is needed to confirm the finding. One way to do that would be to go there and collect rock from the crater to see if its structure matches what would be expected from such a colossal impact.

Itokawa has two parts resembling the head and body of a sea otter, according to Akira Fujiwara and his colleagues in Friday's issue of the journal Science.

Previously studied asteroids appeared to be lumps of solid rock, but Itokawa is made up of loosely packed bits of sand and boulders, they said.

Their findings could have implications for deflecting asteroids that might pass too closely to the Earth in the future.

"We've never had a close-up look at such a small asteroid until now," said Takahiro Hiroi of Brown University in Rhode Island, who worked on the study, a joint U.S.-Japanese effort.

"Large asteroids such as Eros are completely covered with a thick regolith - a blanket of looser material created by space weathering. With Itokawa, we believe we have witnessed a developing stage of the formation of this regolith."

Itokawa is very small, just 500 yards (metres) long. But it is close, orbiting just 321 million miles away from Earth. Although it does not threaten to collide with Earth, it makes a tempting scientific target.

NEAR MISS

Hayabusa very nearly did not make it.

The little spacecraft, now bringing a capsule of samples back to Earth, uses an electronic ion propulsion system, whose efficiency should be critical to future missions in deep space.

At one point, Hayabusa lost communication with its controllers, wrote Erik Asphaug of the University of California, Santa Cruz in a commentary in Science.

"Its hydrazine (fuel) had leaked away shortly after the second sample collection attempt. Two of the reaction wheels had failed and the battery was dead. Adding insult to injury, Minerva - intended to be the first asteroid surface robot - had been released during an unexpected maneuver and was lost to space," he added.

"Yet despite these heartbreaking setbacks, Hayabusa has been a stunning success both for asteroid science and for deep space concept testing."

Asphaug said information delivered by the spacecraft "enhances our understanding of near-Earth objects. Near-Earth objects are not only important scientifically - our planet formed from them - but have also become political hot potatoes, given the growing pressure to do something to mitigate the risks they may pose to Earth."

The spacecraft, launched in 2003, is expected to glide back to Earth in 2010 and crash-land in the Australian desert.

Bryan Parker, an investigator for the Senate Indian affairs committee, told a U.S. District Court jury that early last March Safavian told him by telephone that "he had paid for his part on the ground but not including the air fare."

Parker was to be the last witness for the prosecution.

Abramoff chartered a Gulfstream jet for the August 2002 trip to the famed St. Andrews golf course in Scotland and on to London.

Parker said Safavian, who was chief of staff at the General Services Administration in 2002, also volunteered that GSA ethics officers had authorized him to take the trip because his ex-partner Abramoff had no business dealings with GSA.

Safavian is charged with concealing from the Senate and GSA officials the extent of his assistance to Abramoff, particularly just weeks before the trip on the lobbyist's efforts to acquire a piece of GSA land in Maryland for a school he started and to give an Indian tribe client a leg up on winning a GSA contract to redevelop the Old Post Office here.

But Parker said Safavian told a different story when he sent the Senate panel the ethics ruling on his trip and other documents March 17, 2005. In that letter, Safavian said even though the GSA ethics office said he could accept the free air travel - as Safavian had initially requested - he nevertheless gave Abramoff a check for the full cost, including air fare.

This $3,100 check was delivered to Abramoff at the beginning of the 2002 trip and Safavian's lawyer, Barbara Van Gelder, has said that Abramoff told Safavian that was his full share of all costs.

Prosecutors have scoffed at that notion and introduced evidence of $500-a-night hotel rooms, $100 rounds of drinks and $400 rounds of golf to suggest that it was obvious that each traveler's costs were much higher.

Parker also testified that Safavian never mentioned his contacts with Abramoff about the two GSA properties in three telephone calls, a letter and a packet of documents that purported to respond to the committee's request for any material related to the golf trip.

He testified he would have wanted to know about those for the Senate investigation because investigators had learned that some client fees from Indian tribes to Abramoff had helped pay for the trip.

Among others on the golf trip were Rep. Bob Ney, R-Ohio, and two of his aides. Prosecutors have introduced evidence that Ney was helping Abramoff in his efforts to obtain the land in Maryland.

Prosecutors also introduced a copy of a handwritten note on White House stationery that Safavian attached to his letter and packet of documents offering any additional assistance needed. In the intervening years, Safavian had been promoted from GSA to chief federal procurement officer at the Office of Management and Budget in the White House.

Van Gelder tried to suggest that Parker's interest in Safavian was outside the committee's jurisdiction, implying that if Safavian paid his way no Indian money benefited him.

She also pointed out that Parker never pursued the matter with Safavian, but he said he would have gotten to Safavian eventually had he not been indicted first.

Previously, two GSA ethics lawyers and an inspector general investigator said they too never heard from Safavian about his aid to Abramoff on the two GSA properties, would have wanted to know that and that it could have affected their decision to approve his trip and to close a later investigation of it.

Abramoff entered guilty pleas early this year in Washington and Florida.

Jan Peter Valheim, financial director of Norwegian company Fred Olsen Energy, told AFP, "The drilling rig was attacked this morning at 0400 GMT, eight members of the crew were kidnapped, one American, one Canadian, six British, the rest of the crew is safe"

"There were about 40 to 50 people on the rig" when the attack came, he said by telephone from Oslo, adding, "The emergency procedures are on."

A company statement said a group of people had boarded the Bulford Dolphin facility off Nigeria's southern coast and seized the employees.

"National and other authorities are co-operating in solving the situation... The drilling operation has been temporarily terminated. The incident has not caused any pollution nor damage to the rig," the company said.

Nigerian national police spokesman Haz Iwendi said, "Eight workers of TEC petroleum company were kidnapped from an oilfield where they were working. They are six Britons, one American and one Canadian."

"Nobody has claimed responsibility yet and no ransom asked," he added. "We combine the efforts of the security agents and we are on their trail and trying to secure their release as soon as possible."

Iwendi said the incident "took place at Bilabre near Dodo river in Ekeremor local government area" of southern Bayelsa State.

A spokesman for the Foreign Office in London said, "These types of situations are not unusual in Nigeria, and we take them very seriously.

"Our colleagues in Nigeria are contacting local officials in order to discover what has happened."

A US diplomat said, "We are investigating, but right now we don't have any element or information."

The rig, some 20 kilometres (12 miles) off the coast, is operated by Fred Olsen Energy's subsidiary, Dolphin Drilling, based in the Scottish city of Aberdeen, the spokesman for the firm said.

Kidnappings of foreign workers have become increasingly frequent occurrences in the oil-rich Niger Delta.

Nine were seized on February 18 by heavily-armed militants fighting for control of the delta's oil resources.

Hostage-takers the Movement for the Emancipation of the Niger Delta (MEND) released six after just a week but three others -- a Briton and two Americans -- were held for more than five weeks.

The kidnappers demanded that Nigeria pulls all its military forces out of the delta, which is home to the 14-million-strong Ijaw ethnic group, most of whom live in abject poverty despite the vast wealth created by the oil and gas industry.

Nigeria, Africa's largest oil producer and world's sixth oil exporter with around 2.6 million barrels a day, derives more than 95 percent of its foreign exchange earnings from oil.

The continuing attacks on the oil industry, however, have cut production by more than a fifth.

Despite its massive income from oil, most of the country's population lives on the poverty line.