Meteorites Make a Big Splash on Mars: New Images of Secondary Craters by HiRISE

by Ian O'Neill on April 6, 2008

A few irregularly shaped craters from secondary, low energy impacts on the Mars surface (NASA)
They look like pockmarks caused by shrapnel from a huge explosion. Actually they are surface features on Mars as seen by the High Resolution Imaging Science Experiment (HiRISE) on board the Mars Reconnaissance Orbiter (MRO). But what are they? They’re not potholes formed by geological processes, they’re not openings to ancient lava tubes, they are impact craters… but not like any impact crater you’ve seen before…

The whole range of secondary impact craters in Chryse Planitia (NASA)

Most meteorite impact craters are roughly circular. If they are fairly new, ejected debris will be obvious emanating from the impact site. However, recent images by the HiRISE instrument appear to show tiny impact craters, in a swarm, each looking like they have been chiselled roughly out of the Martian regolith (pictured left).

The area of the image covers roughly 0.5×1.5 kilometres (25cm/pixel; features down 85cm can be resolved) of a large outflow channel in the Chryse Planitia region. The craters are actually secondary impact craters caused by large chunks of Martian rock being thrown up into the air after an energetic impact from a meteorite. To give an idea of size, the largest craters are about 40 meters across, a little smaller than an Olympic-sized swimming pool. It is not clear where the primary impact crater is in relation to the debris craters in the full-resolution image.

There appears to be dark material inside these small craters, possibly from the debris digging into layered deposits of different minerals just below the surface. Ripples of sand and dust are also evident. As these small craters are quite shallow, they will fill up and level out with wind-blown material quickly, so these secondary craters are fairly young when compared with geological timescales.

Source: HiRISE mission site

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Hello! My name is Ian O'Neill and I've been writing for the Universe Today since December 2007. I am a solar physics doctor, but my space interests are wide-ranging. Since becoming a science writer I have been drawn to the more extreme astrophysics concepts (like black hole dynamics), high energy physics (getting excited about the LHC!) and general space colonization efforts. I am also heavily involved with the Mars Homestead project (run by the Mars Foundation), an international organization to advance our settlement concepts on Mars. I also run my own space physics blog: Astroengine.com, be sure to check it out!

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