By Jonny Lupsha, Wondrium Staff Writer
A Chinese rocket launched a decade ago hit the Moon, causing a crater. The rocket had long since broken up into countless piece of debris, striking at 5,800 mph. Naturally formed craters tell another tale.
On Friday, a bevy of space junk hit the Moon at speeds exceeding 5,800 miles per hour. The debris was originally a rocket that China launched nearly 10 years ago, though it broke up and has been drifting through space ever since. The impact site will be hidden from view for weeks, if not months, but it’s believed that the impact formed a crater up to 65 feet across.
The other craters on the Moon occurred naturally, and they contain several mysteries of their own. In his video series Understanding the Universe: An Introduction to Astronomy, 2nd Edition, Dr. Alex Filippenko, Professor of Astronomy at the University of California, Berkeley, reveals the secrets of the Moon’s craters.
For the Crater Good
“If you look at the Moon, you notice that it’s heavily cratered—lots of craters [and] lots of seas or basins, or maria, as they were called,” Dr. Filippenko said. “Initially, people didn’t really know what they were; they were called seas. Now we know that they are frozen or solidified lava flows.”
According to Dr. Filippenko, when looking at the Moon’s craters near its sunrise or sunset, the shadows are long and reveal the sheer number of craters that exist on the lunar surface. Many big craters have a peak in the middle. Almost all the craters are circular; though, some look deformed due to a crater being formed on top of an another crater. In contrast, there are fewer craters on the maria.
“For a long time, there was a debate: Are the craters impact craters or are they of volcanic origin?” asked Dr. Filippenko. “Their shape gives one clue. First of all, the lunar craters have less steep sides than terrestrial volcanoes; second of all, the lunar craters have this [little blip] in the middle. Both of these features of the profile of a crater suggest that they are predominantly of impact origin.”
Dr. Filippenko said that there’s very little erosion on the Moon and there is no water or atmosphere. The areas of the Moon that have excessive craters on them are likely to be older than the areas with no craters. Why?
“We think that the cratering history of the Moon, and of the whole solar system, was such that most of the craters formed long ago when there was a lot of debris still floating around from the formation of the solar system,” he said. “Then, all these craters formed, and then maybe there were lava flows that covered them up. So, [if] you have lava flows on top of craters, the lava flows must be younger than the craters.”
There are also craters on top of other craters. Obviously, the top craters must be newer than those below them. Without actually going to the Moon, Dr. Filippenko said, it’s possible to tell the relative ages of the Moon’s features by seeing what lies on top of what.
“But to determine absolute ages, you actually have to get samples of these rocks and figure out their actual age,” he said. “The way that’s usually done is through radioactive dating. If you get Moon rocks and measure the relative amounts of the parent nucleus and the daughter products, you can figure out how long those parent nuclei have been decaying.
“By figuring out how much of the different parent nuclei and daughter products there are, you can figure out how long this rock has existed since it was last molten.”