Huge Meteor Left Crater Hidden Beneath Greenland Ice
The crater is 22 miles (36 km)
in diameter and is buried under 1.2 miles (2 km) of ice. It's located
close to the Hiawatha impact crater.
Credit: NASA Goddard
Lurking below more than a mile of ice in Greenland is a circular depression that was very likely left by an ancient impact with a space rock.
The meteor impact crater, reported Feb. 11 in the journal Geophysical Research Letters, is only the second ever discovered in Greenland. It's just 113 miles (183 kilometers) from the other crater in the country, which scientists reported last year.
Joseph MacGregor, um glaciologista do Centro de Vôo Espacial Goddard da NASA, estava na equipe que descobriu a primeira cratera, apelidada de Hiawatha. No final de 2016, quando a maior parte do trabalho identificando a cratera de Hiawatha foi feita, embora a pesquisa ainda não tivesse sido publicada, MacGregor já estava à procura de outra cratera. Ele encontrou um mais rápido do que ele esperava.. [Images: Greenland's Gorgeous Glaciers]
"I was like, 'Really, could there actually be another?'" MacGregor told
Live Science. "I sort of stood up from my desk and paced the hallways a
little bit."
A new crater
A nova cratera tem cerca de 22 milhas (36 km) de diâmetro, o que a torna a 22ª maior cratera de impacto já descoberta na Terra e um pouquinho menor que a cratera de Hiawatha, que mede 31 km (31 milhas) de diâmetro. Hiawatha fica a cerca de 930 metros de gelo, enquanto a nova cratera está enterrada a menos de 2 km. Ambas as crateras estão no noroeste da Groenlândia, e os cientistas têm uma quantidade desproporcional de informações sobre esta região remota e gelada, simplesmente porque muitos de seus voos de pesquisa se originam nas proximidades. Thule Air Base. [Photos: Top-Secret, Cold War-Era Military Base in Greenland]
A GIF showing the surface topography of the new meteor impact crater in Greenland.
Credit: Joe MacGregor, NASA Goddard Space Flight Center
To find the craters, the research team combined satellite imagery of
the Greenland ice sheet and radar-sounding data collected by aircraft.
With the radar data, scientists can "see" through the ice using radar
waves that hit the bedrock below and bounce back. Most of the data came
courtesy of NASA's Terra and Aqua satellites and the space agency's
IceBridge aerial survey program; all of that data is publicly available.
"Anyone could have found this," MacGregor said. In fact, some amateur
enthusiasts did. After the Hiawatha paper was published in November
2018, some members of the public contacted MacGregor to draw his
attention to the second crater, he said, not knowing he'd found it
before the Hiawatha crater paper went out.
Crater questions
A idade da nova cratera é difícil de avaliar, disse MacGregor. A camada de gelo mais antiga, datada acima da depressão, tem cerca de 79.000 anos, mas o gelo flui, o que não significa necessariamente muito. A utilização de relações profundidade-largura de crateras de impacto permitiu que a equipe estimasse a idade da cratera por sua taxa de erosão - mas apenas de maneira muito aproximada. Os pesquisadores têm entre 100 milhões e 100.000 anos de idade. Hiawatha é provavelmente mais jovem, disse MacGregor. [Photos: Craters Hidden Beneath the Greenland Ice Sheet]
Scientists are fairly certain the new crater really is from an impact.
The only other explanation for the newfound depression is that it's a
volcanic caldera, MacGregor said, but volcanic rocks create magnetic
anomalies that just aren't present in the new feature.
Though it was surprising to find the first known pair of Greenland
impact craters so close to one another, a sample size of two is too
small to alter the understanding of how many Arctic impacts
there were or how fast craters erode, MacGregor said. Most likely,
Hiawatha and the new crater are the "largest-slash-easiest ones that
there are to find," he said. Any additional craters will probably be
much smaller and harder to detect.
Answering questions about the craters' age and formation won't be easy, he added.
"You have to drill through 2 kilometers [1.2 miles] of ice, and then,
depending exactly what element of the crater's history you're interested
in, you might have to drill through 100 or 200 m [330 to 670 feet]
worth of rock," MacGregor said. He added that all the equipment would
have to be hauled more than 100 miles (160 km) inland across the ice.
"That's a technological challenge."
Nenhum comentário:
Postar um comentário
Observação: somente um membro deste blog pode postar um comentário.