Meteorites Make a Big Splash on Mars: New Images of Secondary Craters by HiRISE
Written by Ian O'Neill
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…
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
Filed under: Astronomy
April 7th, 2008 at 1:04 am
My first impression forces me to ask the question; from which direction does the sun shine in this image? I ask that as the "craters" seem to have both a shadow and an area, towards the bottom right in the image, on each "crater" that seems to indicate an area that has been eroded by wind. The sort of erosion we normally see when the wind blows around a rock on the surface, not a crater beneath the surface. I therefore ask Are these instead, rocks on the surface?
April 7th, 2008 at 4:40 am
Great picture and explanation. How exciting it is to see the higher resolution evolve, almost on a daily basis. Thanks for keeping us up to date and simple enough for the masses to understand.
April 7th, 2008 at 5:19 am
There is a possible crater chain like this in northern Quebec.
http://www.ottawa.rasc.ca/articles/odale_chuck/earth_craters/possible_craters/index.html
http://www.ottawa.rasc.ca/articles/odale_chuck/earth_craters/possible_craters/04_crater_chain.jpg
Chuck O'Dale
April 7th, 2008 at 9:19 am
The "electric" guys are going to have a field day!
April 7th, 2008 at 12:28 pm
Chris, by doubling the size of the first photo I was able to see that the light comes mainly from the left. The shadows are shown irregular to the light due to dunes and chunks that are not regular with the craters. For example. the large, dark central crater broke out a chunk that tried to fall back in but didn't quite make it. It sits up bright and leaves a break line behind it at an odd angle. It also shows inside the main crater there where that odd chunk came from, and that, too, leaves odd shadow.
Hope this was some help somewhere!
April 7th, 2008 at 1:00 pm
AHA! By quadrupling the size of the second pic, I saw the angles of debris exhaust that lead right back to that "dark chip" at lower left edge of the pic. These "lines" are not great valleys, but just streaks in the dust and sand that lead back to the source of forceful impact that caused a strong wind across the surface. Bits of gravel and small rock left clearer lines, but they lead right back to that "chip" like clockwork. Very, very soon these lines will be erased by the regular winds, as they are small and just surface dust. But for now, we have the photo to keep and study. Again, Hope I am corrrect and helpful.
April 7th, 2008 at 11:06 pm
It looks like the craters are remnants of huge electric discharge impacts. It is an electric field day indeed (at least some time ago)!
April 9th, 2008 at 11:26 am
I think: what we see here is the impact site of a shower of meteors: A space rock of several hundred tons desintegrated as it entered the martian atmosphere, and the pieces smashed into Mars, producing the crater field.
Such fields of small craters are rather common. On Earth, similar crater fields can be found in Argentina, Australia, Danmark, and Poland.
Secondary craters cannot be created by ejectae from big impacts, because such impacts can´t create ejectae that are larger than pebbles.
To create a crater that is 30 m across, you need an energy of some 100 Gigajoules. A pebble can´t deliver that kinetic energy, and a larger body cannot survive the acceleration required to attain that kinetic energy.
Regards,
Günther
May 19th, 2008 at 8:46 am
jk im sorry
June 24th, 2008 at 2:16 pm
l seen this in a book