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"Those gravity variations have been known ...
"Those gravity variations have been known for some time, but not with the precision we have now," says Jay Melosh, a professor of earth, atmospheric, and planetary sciences at Purdue University.
and colleagues, who published their findings in Science, made the measurements as part of NASA's
GRAIL mission, which launched two satellites to the moon in 2011.
"The warmer, deeper rocks in the moon were more fluid and moved inward after the impact, carrying the crustal rocks inward toward the center, and that's what made the faults," says Melosh
Understanding the cratering of the moon 3.85 billion years ago can give scientists clues about the formation of other planets, including Earth.
"If the moon was getting smacked up by all these different impacts, the Earth absolutely had to as well," Melosh
"The early Earth probably looked just like the moon.
We're looking back in time and seeing what the Earth would have looked like had it not had plate tectonics and subsequent geologic activity that erased any major trace of those early impacts."
Some theories even include the idea that the bombardment of Earth by asteroids and other objects may have led to life on the planet, adds Melosh
In an era when the size ...
In an era when the size of the atomic-weapons stockpile has been shrinking as a result of arms-control treaties and other factors, asteroid defense "may be an excuse for keeping the nuclear arsenal together," said Jay Melosh, a professor of earth, atmospheric and planetary sciences at Purdue University.
But he thinks there are better, nonnuclear ways for defending the planet.
Among possible options: a "gravity tractor" or an "impactor.
Both the Earth and moon are ...
Both the Earth and moon are safe - "this time", said Jay Melosh, professor of Earth and atmospheric sciences at Purdue University.
PBT Consulting: Astronomy
Jay Melosh, an expert in impact cratering and a distinguished professor of earth and atmospheric sciences, physics, and aerospace engineering at Purdue University, said the asteroid's orbit and trajectory meant there was zero chance of an impact. Melosh said.
used the asteroid impact effects calculator he
developed to estimate what would happen if the asteroid, which is a quarter mile in diameter, hit the Earth.
The calculator, "Impact: Earth!
Although it would begin to disintegrate as it passed through the atmosphere, the fragments would strike in a compact cluster that would blast out a crater 4 miles in diameter and 1,700 feet deep, Melosh
Sixty miles away from the impact site the heat from the fireball would cause extensive first-degree skin burns, the seismic shaking would knock down chimneys and the blast wave would shatter glass windows.
If YU55 were to strike a large city like Chicago, it would obliterate the entire city and leave few survivors. Fortunately, the chance of a large impact targeted on a city is very small, he
The most recent impact of this size is not known, but there are about 20 similar craters known in the geologic record, including the Wetumka crater in Alabama and the Rock Elm crater in Wisconsin. Of the known large craters, the most recent are the six-mile-wide Bosumtwi crater in Ghana, which is about 1 million years old, and the nine-mile-diameter Zhamanshin crater in Kazakhstan, which is about 900,000 years old, Melosh
is a co-author of a 2010 NRC report "Defending Planet Earth" that explores the feasibility of detecting all Earth-crossing asteroids down to a diameter of 140 meters, or about one-tenth of a mile, and of ways to mitigate their hazard.
"How the Earth lost its primordial ...
"How the Earth lost its primordial atmosphere has been a longstanding problem, and this paper goes a long way toward solving this enigma," says Jay Melosh, a professor of earth, atmospheric, and planetary sciences at Purdue University, who did not contribute to the research.
says Schlichting's conclusion is a surprising one, as most scientists have assumed the Earth's atmosphere was obliterated by a single, giant impact.
Other theories, he
says, invoke a strong flux of ultraviolet radiation from the sun, as well as an "unusually active solar wind."