Science & Environment

Greenland ice sheet hides huge ‘impact crater’

The 31km-wide depression came to light when scientists examined radar images of the island's bedrock.

Investigations suggest the feature was probably dug out by a 1.5km-wide iron asteroid sometime between about 12,000 and three million years ago.

But without drilling through nearly 1km of ice to sample the bed directly, scientists can't be more specific.

"We will endeavour to do this; it would certainly be the best way to get the 'dead fish on the table' (acknowledge the issue, rather than leaving it), so to speak," Prof Kurt Kjær, from the Danish Museum of Natural History, told BBC News.

If confirmed, the crater would be the first of any size that has been observed under one of Earth's continental ice sheets.

The discovery is reported in the journal Science Advances.

How Greenland scorched its underside How Greenland would look without its ice Hunt for Antarctica's 'lost meteorites'

What does the crater look like? The putative impact crater is located right on the northwest margin of the Greenland Ice Sheet, underneath what is known as Hiawatha Glacier.

Additional high-resolution radar imagery gathered by Prof Kjær's team clearly shows a circular structure that is elevated at its rim and at its centre - both classic traits. But because the depression is covered by up to 980m of ice, the scientists have so far had to rely on indirect studies.

What is the supporting evidence? Meltwaters running out from under Hiawatha Glacier into the Nares Strait carry sediments from the depression. In these sediments are quartz grains which have been subjected to enormous shock pressures, of the type that would be experienced in an impact.

Other river sediments have revealed unusual ratios in the concentrations of different metals.

"The profile we saw was an enrichment of rhodium, a depletion of platinum, and an enrichment of palladium," explained team-member Dr Iain McDonald, from Cardiff University, UK.

"We got very excited about this because we realised we weren't looking at a stony meteorite, but an iron meteorite - and not just any old iron meteorite; it had to be quite an unusual composition."

Such metal objects that fall to Earth are thought to be the smashed up innards of bodies that almost became planets at the start of the Solar System.

The signatures identified by Dr McDonald are relatively close to those in iron meteorite fragments collected at Cape York not far from the Hiawatha site. It's not inconceivable, the team argues, that the Cape York material represents pieces that came away from the main asteroid object as it moved towards its collision with Earth.

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California wildfires: Number of missing leaps to 631

The number of people missing in northern California's devastating wildfire has leapt to more than 600, and seven more bodies have been found, according to local authorities.

The missing persons' list has doubled since earlier on Thursday.

The Camp Fire, the state's deadliest and most destructive blaze, has killed at least 63 people. Nearly 12,000 buildings have been destroyed.

Three more people have also died in the Woolsey Fire, further south.

Wildfire survivors: 'We swam to safety' Before and after snapshots President Donald Trump will travel to California on Saturday to survey the damage and meet those affected.

About 9,400 firefighters are currently battling wildfires across the state.

The Camp Fire - which broke out eight days ago - swept through a swathe of the north at high speed, leaving residents little time to escape.

Why such a big jump in the missing? The official list more than doubled from 300 to 631 on Thursday.

At a news briefing, Butte County Sheriff Kory Honea said this was because investigators had thoroughly cross-checked their information, including emergency calls made since the Camp Fire started on 8 November.

"I want you to understand that the chaos we were dealing with was extraordinary," Mr Honea said.

He stressed that the number of the missing would most likely fluctuate.

"If you look at that list and see your name, or the name of a friend or loved one, please call to let us know," Mr Honea appealed to the public.

What's the latest on the firefighting operation? The California Fire Department says it has now contained about 40% of the Camp Fire blaze.

"We continue to engage in the fire fight. We continue to keep our eye on the ball," chief fire department official Ken Pimlott said.

Officials say they do not expect to fully contain the blaze - which has razed 145,000 acres (56,600 ha) - until the end of the month.

They are also battling several other fires. The Woolsey Fire in Ventura County near Los Angeles covers nearly 100,000 acres and is 62% contained.

The smaller Hill Fire, also in Ventura County, covers 4,530 acres and is 99% contained. The Morgan Fire in Contra Costa County, near San Francisco, covers 20 acres and is 60% contained.

Before and after snapshots Is it advisable to escape a wildfire by car? Red carpets cancelled after wildfires The worst-hit area is the town of Paradise, with officials saying it will need a "total rebuild" job that will take several years.