Last November, scientists were shaken by finding a crater 19 miles below Greenland. The crater was in a visible place only 150 miles from the main air base. Scientists flying through aerial studies with NASA's IceBridge operation accidentally discovered it as they tested their equipment during a collection of Arctic data. On Monday, the same group announced that it had uncovered another potential impact crater, which is even bigger and is just over 100 miles from the first.
This time they were looking for him.
NASA scientist Joe McGregor was in the team who discovered the first crater under the Hawaii glacier in northwest Greenland. He says that after the results of Haayavas he asks if there can be more craters on the ice sheet that have been neglected. It took only a few hours to scan a map of Greenland before he noticed a suspiciously circular geological feature near the newly discovered crater of Haiawa.
Under the ice
Ice sheets are pretty rough in landscapes. They are the cause of the US Midwest being so flat – everything that is on the ice-road is shattered. That's why scientists have long believed that geological features like craters, even if they ever existed, would be smooth with time if they were under the ice.
McGregor, a scientist and scientist in the NASA IceBridge project, explains that he has noticed the new crater of a topographic map that NASA has created several years ago from the Greenland landscape under the ice.
"When you look at this map in the northwest of Greenland, you can see depression – it's not the Hawa (crater)," McGregor explains. He says he has consulted several other cards and "it was quite clear that there was a round surface of this depression. And that was quite exciting. Somehow I got up from my desk and down the corridor as I approached myself, like, is there another crater?
Then the hard work came, McGregor said. The impact craters, unlike other rounded holes in the ground, for example from ancient collapsed volcanoes, often cause specific anomalies in the magnetic and gravitational fields. It is convenient that researchers have already done geophysical research in this area – meaning that they already had the data to investigate the potential crater.
The remains of volcanoes and impact craters leave different geophysical signatures on the landscape – anomalies in the magnetic and gravitational fields. The latter is related to the way the earth's crust precipitates after the impact – it becomes smaller than before. And in this case, the signature of the crater suggests that he really is a blow crater.
Ice, ice, baby
It is too early to set a real date for this crater, but there are some initial clues. The ice near the crater is at least 79,000 years old, but that may mean many things – for example, the ice near the crater may now have moved away from distant lands in millennia.
The ice questions are McGregor's specialty. "We can say with certainty that the layering of the ice over the second crater looks very different from what we saw in Hawa. Layering in Hiawatha was part of what motivated us to suspect young age. In the second potential crater the layering is much older and smoother, with no clear discrepancies; in this respect it seems like a good part of Greenland. So only that can be suspected of being older, he says.
The other big age hint is its depth – the crater is quite shallow for such a wide diameter that covers 22.7 miles. Scientists believe that the impact that would create a crater of this size would also create a crater nearly half a mile long, which means that the structure has disappeared very little. She is about twice as eroded as Hayward's neighbor. Based on how much ice is expected to have on the crater and how quickly the age of the new crater could be more than a hundred thousand to a hundred million years.
What are the chances, though
If you read this thinking, "what are the chances," do not worry that scientists are seriously worried. If the two structures are officially confirmed as shooters and confirmed as different ages, as the initial data suggests … what are the chances that two unrelated impacts will occur just 100 miles apart?
Fortunately, scientists are scientists, so they actually calculate the odds.
Only last month, Sara Mazrouei of the University of Toronto and my colleagues posted in science updated estimates of the speed of Earth's effects based on data from the two known craters of the Earth, as well as from a neighbor of our crater, the moon.
McGregor and his team used these estimates to estimate the probability that two unrelated craters would appear so close to each other. Given the size of the shells needed to create such a crater, the size of the Earth and the overall dimensions of objects close to the Earth, they estimate that an unrelated pair of large craters should emerge about once every seven billion years. Or, in other words, it is unlikely.
But they also looked at it in a different way, though in a way that reflects the "paradise of the birthday" that you may be familiar with. The birthday paradox refers to the likelihood of two people sharing one birthday; mathematically, this is more common than you think. In each casual group of 23 people, the chances of two sharing a birthday is about 50/50. In a group of 70 people it is almost 99.9% sure.
So how many craters need to be blown up in the Earth before two of them are near each other without sharing a birthday? The team again uses estimates from Mazurui: about 355 impacts are likely to have occurred over the last 650 million years, although only about 10% of the Earth's surface is stable enough to have such craters today. The team runs simulations that randomly allocate 355 meteor hits to the planet, and finds that there will be an average of 13 pairs of craters in the story that are unrelated but close to each other. Cut it to 10% of the craters that have survived today and you have one, maybe two pairs of craters.
Two such pair of craters have already been found: one in Quebec and one in Ukraine. But that does not mean that a third pair is out of the sphere of opportunity – sometimes three coins turn heads, even when you expect at least one "tail".
More about learning; Expect skeptics
"And Hiawatha, and this second possible crater fall into an unusual category of percussion craters," says MacGregor. "They are on Earth but covered with ice, making them relatively difficult to sample in any way you would like."
To confirm a true crater as a crater, McGregor explains, the terrestrial geological community will need much more than a gravitational anomaly. But the information they need is under a mile of ice.
"Maybe another way to think about it is that it takes about 10 seconds to convince a planetary scientist that these are crashing craters," McGregor jokes, "but it will probably take 10 years to convince earth geologists.
McGregor says there is talk of the kind of labor-intensive expedition that will be needed to study the craters, but there are still no hard plans. For now, he does not give up his daily work with IceBridge despite his new experience in studying craters.
"It's a lot of fun, but I'll be a gay scientist," says McGregor. "To hope that there are many good reasons, we still want to know a lot more about what ice will do in the future."