Now, Schultz and Crawford have demonstrated that many of these impactors may have been much more substantial than past research has imagined.
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However, 3.8 billion years ago during a period known as the Late Heavy Bombardment, they frequently smashed the surfaces of the inner planets and their moons.
“This was a time when Jupiter and Saturn were changing their position in the Solar System, and as a result it stirred the pot, so to speak”, Schultz said.
Scientists investigated the area surrounding Mare Imbrium – Latin for “The Sea of Showers”.
Location of Imbrium basin.
“The large basins we see on the Moon and elsewhere are the record of lost giants”, Schultz added. Planetary collisions created colossal craters like Mare Imbrium, and also launched new material into orbit that would have smashed into the paths of the inner planetary bodies over and over. “Its scarred face can tell us quite a lot about what was happening in our neighborhood 3.8 billion years ago”. “The mystery has been why didn’t the grooves all come from the centre of the basin?” Instead, they apparently came from a region northwest of the basin’s center.
Those calculations yielded an estimated diameter of 150 miles or 250 kilometers across, large enough for the object to be classified as a protoplanet.
They used the Vertical Gun Range at the Nasa Ames Research Center. The bottom of the projectile would create a crater, while the sides and top of the projectile would shear off and continue traveling at high speeds along the projectile’s original trajectory to scour the surface.
“The key point is that the grooves made by these chunks aren’t radial to the crater”, Schultz said.
Having worked out where the grooves came from, the scientists could measure the features and work backwards to calculate the minimum size of the asteroid that thumped into the moon.
Previous studies used computer models to estimate the size of the asteroid that led to the 750-mile-wide Mare Imbrium.
“The previous estimate for the Imbrium asteroid was in the order of 80km, and we’ve increased that by a factor of three”, Professor Schultz said. During his experiments with low-angle impacts, Schultz noticed that impactors tend to start breaking apart when they first make contact with the surface. Physical processes affecting the fate of the projectile observed in the lab experiments at high speeds also apply at much larger scale. “It’s possible that it could have been as large as 300 kilometers [185 miles]”.
All in all, the researchers suggest that protoplanets may have once been common in the asteroid belt. “This is the first estimate for the Imbrium impactor’s size that is based largely on the geological features we see on the Moon”. “What we don’t know is what happened to all these objects that hit the moon”. This was especially true of the Apollo 16 mission, which landed downrange from the Imbrium impact.
A team from Brown University teamed up with NASA to explore the origins of the Imbrium Basin, which forms the right hand peeper of the moon man’s face.
“These chips off the old blocks could have contributed significantly to the impact record we see on the moon and other terrestrial planets”, mentioned Schultz.
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Earth dwellers no longer have to worry about collisions of this magnitude anymore: All of the giant objects are gone, Schultz said, and the last big impact on the moon was about 3.78 billion years ago. According to research published in today’s Nature, that impactor was so big that as it broke up, it sent chunks of debris spewing in all directions, helping fuel the 200-million year-long hard rain.
