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A big bright rock
mpc
post Sep 6 2014, 04:43 PM
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I stumbled over an interesting rock in Isidis Planitia. Or maybe it's not interesting, please decide yourself. I have been crawling around the area a little bit and haven't found an object that would be similar to this one. There are rocks of about the same size and also rocks of the same brightness but the combination of either quality in a single object stood out to me.

The place where it sits has been imaged by HiRISE twice: ESP_013924_1915 (2009) and ESP_037356_1915 (2014). Click the image below to see an animated GIF compiled from cutouts of either HiRISE image. The scale is 1.0 (28 cm/pixel) which makes the rock's diameter to be 7-8 m.

Attached Image


I also looked up CTX images of that place and found three: P13_006171_1921_XN_12N269W (2007), B11_013924_1915_XN_11N269W (2009) and D04_028706_1917_XN_11N269W (2012). Click the image below for an animated composition. The scale is 1.0 (5.5 m/pixel) which is just enough for the rock to be visible to CTX.

Attached Image


The rock can be clearly made out from the 2009 and 2012 images, but not from the 2007 image. Do you think that's because of different lighting conditions in 2007? Or was it not there yet? I was also wondering what the rock was made of to be this bright.

Thanks,
Michael
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djellison
post Sep 6 2014, 06:23 PM
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I think it's hard to make the case that the rock's definitely not there in the 2007 image. In-fact - I think it could be. That '07 image looks soft, perhaps a local or regional dust storm at the time - making it a tough call.

Be careful on the HiRISE resolution there - those images are map projected to 25cm/px - not the native res of the observation of 28cm/px

Can you provide a wider CTX view to call out the crater so we can find it perhaps in MGS MOC imagery or if we're lucky HRSC-SRC franes?
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Gerald
post Sep 6 2014, 07:45 PM
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The 2007 CTX shows less contrast at the location of the rock than the other two images.
This may make it difficult to distinguish the rock. Here a gif with a 2007 version with a contrast comparable to the 2012 image:
Attached Image

The brightness resolution of the 2007 image may just be too low to decide uniquely, whether the rock is visible.
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mpc
post Sep 6 2014, 09:16 PM
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If my math is right the location of the rock is 90.186E 11.317N (give or take 0.001). Attached is a wider CTX view of the area at 20% zoom.

Attached Image


AFAIK no MOC image exists of that place. There are a couple in the neighborhood, all taken before 2007, obviously. The one which is closest misses the spot by just a few hundreds of meters, unfortunately. I haven't checked HRSC, though.
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