One of the benefits of having a spacecraft in orbit around another planet for several years is the ability to make long-term observations and interpretations. The Mars Reconnaissance Orbiter has been orbiting Mars for over seven years now, and by studying before-and-after images from the High Resolution Imaging Science Experiment (HiRISE) camera, scientists have been able to estimate that the Red Planet gets womped by more than 200 small asteroids or bits of comets per year, forming craters at least 3.9 meters (12.8 feet) across.
“It’s exciting to find these new craters right after they form,” said Ingrid Daubar of the University of Arizona, Tucson, lead author of the paper published online this month by the journal Icarus. “It reminds you Mars is an active planet, and we can study processes that are happening today.”
Over the last decade, researchers have identified 248 new impact sites on parts of the Martian surface in the past decade from spacecraft images, determining when the craters appeared. The 200-per-year planetwide estimate is a calculation based on the number found in a systematic survey of a portion of the planet.
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The orbiters took pictures of the fresh craters at sites where before-and-after images by other cameras helped figure out when the impacts occurred. This combination provided a new way to make direct measurements of the impact rate on Mars. This will lead to better age estimates of recent features on Mars.
Daubar and co-authors calculated a rate for how frequently new craters at least 3.9 meters in diameter are excavated. The rate is equivalent to an average of one each year on each area of the Martian surface roughly the size of the U.S. state of Texas. Earlier estimates pegged the cratering rate at three to 10 times more craters per year. They were based on studies of craters on the moon and the ages of lunar rocks collected during NASA’s Apollo missions in the late 1960s and early 1970s.
“Mars now has the best-known current rate of cratering in the solar system,” said HiRISE Principal Investigator Alfred McEwen of the University of Arizona, a co-author on the paper.
These asteroids, or comet fragments, typically are no more than 3 to 6 feet (1 to 2 meters) in diameter. Space rocks too small to reach the ground on Earth cause craters on Mars because the Red Planet has a much thinner atmosphere.
For comparison, the meteor over Chelyabinsk, Russia, in February was about 10 times bigger than the objects that dug the fresh Martian craters.
HiRISE targeted places where dark spots had appeared during the time between images taken by the spacecraft’s Context Camera (CTX) or cameras on other orbiters. The new estimate of cratering rate is based on a portion of the 248 new craters detected. It comes from a systematic check of a dusty fraction of the planet with CTX since late 2006. The impacts disturb the dust, creating noticeable blast zones. In this part of the research, 44 fresh impact sites were identified.
Estimates of the rate at which new craters appear serve as scientists’ best yardstick for estimating the ages of exposed landscape surfaces on Mars and other worlds.
11 Replies to “Mars Gets Bombarded by 200 Small Asteroids and Comets Every Year”
Wouldt it be great to find a brand new crater near one of the rovers and take a cruise on over to see it? Surely they are thinking of this…
Since Mars is so near the asteroid belt, it is no surprise that it sweeps up a lot more rocks than other planets do.
Is there a roughly equal distribution of fresh impact craters across the surface, or are there areas that receive more than others?
Roughly equal. You would expect the dawn side to get somewhat more (as that is the direction of Mars’s orbital motion), but since Mars rotates daily, that gets spread out. By the same token, the polar regions might get a little less, but I would be surprised if that was more than about a factor of 2.
One thing you can do with these results is to use them to roughly date surfaces “by eye.” They imply that a 1 km by 1 km patch should receive 1 to 2 small impacts per million years. (Many of the HiRise images released in press releases are roughly 1 km x 1 km in size; you can find out the actual scale from the original image.) Look at the two larger images in this article. They each have a few dozen small impact craters, and, assuming they cover roughly 1 x 1 km, you can say just by looking at one that the surface there is probably between 10 and 100 million years old, or that sedimentation or erosion is enough to cover or erode such craters in that time. Surfaces without any small craters are geologically young (perhaps less than a million years for a 1×1 km image), surfaces covered with craters are geologically old (perhaps billions of years). Mars is unlike many places in the solar system in that you can find such a wide mixture of ages in different locations on the planet.
Thanks for that. We might be able to use this to date young features such as the water carved gullies. Could their age range be only a few thousand years or less?
I’m really hoping that the proposed plan to use one of the old NRO spysat telescopes as part of a new Mars orbiter works out. That would yield some incredible images of the surface of Mars.
Maybe better to use the old *.sat at Lagrange pts. as laser relay stations for Mars missions? Send the ASARS and other synthetic radar assets too! Think deep penetration radar…
The NRO gave NASA two (2!) of the telescopes, so let’s plant one at a Lagrange point and send the other to Mars along with the various radars. We could examine asteroids from Mars orbit for our later perusal, along with mapping Mars in incredible detail. Sigh, we can dream…
Hmm… So to further studies of asteroids and comets you might go to Mars, land near a fresh crater and collect samples?
Great article. Could we use MRO to even spot meteors before they hit and locate their impact crater in less than a day?
A remarkable report from MRO scientists a few years ago was the spotting of ice-filled craters in the northern plains that arose when meteor impacts uncovered shallow ice.
Such impacts of course would impart a great deal of heat. If we could spot them within a day of their being formed, we might even be able to see liquid water before it all evaporated off.
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