Tadpole on Mars


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Tadpole on Mars
Click for full image.

Cool image time! The image on the right, cropped and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on October 7, 2019, and shows a crater on the northern fringe of Arabia Terra, one of the largest transitional regions between the Martian northern lowlands and the southern highlands. It shows a crater with an inlet canyon that makes the entire crater resemble a wiggling tadpole.

This is certainly not first tadpole-resembling crater found on Mars. See for example this press release from February 2018, showing a tadpole crater with the tail being an outlet channel. In today’s image however the channel feeds the crater.

In fact, take a look at the full image. This crater apparently occurred right at the edge of a large mesa cliff, with this impact cutting into the cliff near its bottom. The canyon might have actually existed before the impact, with the crater merely obliterating the canyon’s outlet.

If you look along that escarpment to the east you can see similar southwest-to-northeast flows. One is a canyon flowing downhill through the escarpment, probably resembling what the first canyon might have once looked like before the impact. To the east of this is another tadpole crater. This second tadpole impact however took place on top of the mesa, so the channel flows out from the crater and then down off the mesa, the reverse of the tadpole crater above.

These flow features are consistent with the nature of this transitional zone, a region with many features suggesting it was once the shoreline of an intermittent ocean. That ocean, if it had existed, is long gone, though scattered across the Martian surface are geological ghost features like these that speak of its past existence.

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5 comments

  • Carl

    Why does the tadpole tail leave a shadow if it’s a canyon ?

  • Carl: The sun in the case of the main image is coming from the west and is about 51 degrees above the horizon when the picture was taken (info from the link). Thus shadows are cast on the western walls of the canyon. The shadows you see on the floor of the crater appear to be caused by a central ridgeline extending out into the canyon floor aligned with the canyon itself. I imagine that this is material that has, over time, flowed into the crater from out of the canyon, pushed by wind and avalanches.

    I hope that answers your question.

  • Jeff

    I agree with Carl. The cropped image does indeed look like a raised dome with a raised twisting appendage. As soon as I look at the full image though, the true relief unfolds.

  • Andi

    It’s a common optical illusion. If you look at the picture long enough, you can interpret it both ways

  • Jeff: This is intriguing, but not surprising. This illusion happens to everyone. Sometimes you simply have to turn the picture upside-down to get the shadows right. Sometimes you just have to train your mind to recognize where the sunlight is coming from.

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