The NASA chief has discovered a possible second-stroke crater buried under more than a mile of ice in northwest Greenland.
its consequence of the finding, announced in November 2018, of a 19-millimeter crater under the Hawaii glacier, the first meteor crater ever to have been found under the ice layers of the Earth. Although the newly discovered sites of impact in the northwest of Greenland are only 114 miles away, they do not appear to have formed at the moment.
If the second crater, which is over 22 miles in width, is eventually confirmed as a result of a meteorite, it will be the 22nd largest crater hit on the Earth.
"We have explored the Earth in many different ways, from land, air and space – it is exciting that such discoveries are still possible," said Joe McGregor, a NASA space flight scientist at Greenbelt, Maryland. both findings.
Before discovering the Hiawatha crater, scientists generally assume that most evidence of past impacts in Greenland and Antarctica would be erased by inexorable erosion from the ice. After discovering the first crater, McGregor checked the topographic maps of the rock under the ice of Greenland for signs of other craters. Using icons on the moderate resolution moderation tools on NASA's Terra and Aqua satellites, he soon noticed a circular pattern about 114 miles southeast of the Hiawatha glacier. The same circular pattern appears in ArcticDEM, a high-resolution digital model across the Arctic, derived from commercial satellite imagery.
"I started to ask," Is this another crater of the blow? Are the underlying data supporting this idea? "Said MacGregor. "Help in identifying a big crater under the ice was already very exciting, but now it seemed that there might be two of them.
McGregor reported on the discovery of this second possible crater Geophysical studies on 11 February.
To confirm his suspicion of the possible existence of a second crater, McGregor studied the raw radar images that are used to map the ice-based topography, including those collected from NASA's Ice Bridge. What he saw beneath the ice was a few distinctive features of a complicated impact crater: flat, cup-shaped depression in the rock foundation that was surrounded by a raised edge and centrally located peaks that formed when the crater floor balanced after the impact . Although the structure is not as circular as the Hayave crater, McGregor calculates the diameter of the second crater at 22.7 miles. Measurements from the IceBridge operation also reveal a negative gravity anomaly on the area that is characteristic of the impact craters.
"The only other circular structure that could reach this size would be the collapsed volcanic caldera," McGregor said. "But areas with some volcanic activity in Greenland are a few hundred miles. Besides, the volcano must have a clear positive magnetic anomaly, and we do not see it at all. "
Although newly discovered shooters in northwestern Greenland are only 114 miles away, they seem not to be formed at the same time. From the same radar data and ice cores that were collected nearby, McGregor and his colleagues found that the ice in the area was at least 79,000 years old. The ice sheets were smooth, suggesting that the ice was not very disturbed during this time. This means that either the impact occurred more than 79 000 years ago, or – if it has happened recently – any ice that has been struck by the impact has long escaped from the area and been replaced by ice from within the country.
The researchers then looked at the degree of erosion: they calculated that a crater of this size would initially have been more than half a mile deep between the edge and the floor, which is much larger than its current depth. Considering a number of probable erosion rates, they estimated it would take somewhere between a hundred thousand years and a hundred million years to allow the ice to erode the crater to its present form – the faster the rate of erosion, the more – the milky crater will be within the plausible range and vice versa.
"The ice layers above this second crater are unmistakably older than those above the Hawa, and the second crater is about twice as eroded," McGregor said. "If the two were formed at the same time, then perhaps more thick ice over the second crater would have to be balanced with the crater much faster than the Haayavas.
In order to calculate the statistical probability that the two craters are caused by unrelated impacts, McGregor's team used recently published estimates that increase the rate of the lunar stroke to understand the more difficultly recorded impact of the Earth. By using computer models that can track the production of large Earth craters, they find that the abundance of said craters, which naturally have to be formed close together without the need for double impact, is consistent with the Earth's record craters.
"This does not rule out the possibility that two new Greenland craters have been made in one event, such as the impact of a well-separated binary asteroid, but we can not make any case for it," says William Botke, a planetary scientist. the Southwest Research Institute in Boulder, Colorado, and co-author of MacGregor paper and the new study of the lunar impact record.
In fact, two pairs of unrelated but geographically close craters are already found in Ukraine and Canada, but the age of craters in pairs is different.
"The existence of a third pair of unrelated craters is modestly surprising, but we do not think it's unlikely," says McGregor. "In general, the evidence we have gathered shows that this new structure is very likely a shooter, but at the moment it seems unlikely to be a twin with Hawa."