A weird lunar lava field

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Weird terrain at Ina on the Moon

Cool image time! The image on the right, reduced and rotated 180 degrees to post here, comes from a recent release for Lunar Reconnaissance Orbiter (LRO). It shows a flow of lava that partly covers an older terrain.

Some scientists propose that Ina formed as very young (less than 100 million years) volcanic eruptions because only a few larger impact craters (>20 m) have formed on its surface. Others believe it is quite ancient (3.5 billion years), possessing highly unusual physical properties that stifle the formation of normal impact craters. At least everybody agrees it was formed as basalt was erupted to the surface! But how and when Ina formed remains open.

Ina’s morphology is so unusual that it is easy to see inverted topography – that is, craters appear as bubbles rather than bowls! Think of Ina as a cast iron frying pan with freshly poured pancake batter; the wiggly textured material is the frying pan and the bulbous smoother mounds are the batter.

The image to the right has been rotated 180 degrees so that my mind at least can see it with the craters as bowls and the uplifted smooth lava as uplifted. If this doesn’t work for you, click on the link and look at the original image.

While some scientists think the lava flows are recent, no one knows at present the origins of the rougher terrain that the lava has partly obscured.



  • BSJ

    Number 99 on the Lunar 100 observation list. Quite challenging to observe with amateur telescopes!

  • Localfluff

    I mostly see bowls instead of craters. And it’s irritatingly hard to switch it around. Does it really help to rotate the image? I’ll try that next time.

  • BSJ

    Yes, It’s best to have the shadow of an object towards the bottom of the image, towards yourself.

    That’s what your brain is looking for.

    If you look closely at a shaded relief map, that shows terrain features, the shadows will be down to the lower right. As if illuminated from the upper left.

    “using a southern light source can cause multistable perception illusions, in which the topography appears inverted.”


  • mpthompson

    I wonder if the rough surface that lacks obvious craters is a brittle crust that meteorites simply punch through to be embedded in the softer and older material beneath.

    Think of it like this. A BB shot at smooth sand will leave a crater-like impression, but if there is a sheet of paper placed on top of the sand, the BB will leave a small a small hole in the paper and be absorbed by the sand without leaving much of a crater under the paper. The paper prevents the large displacement of ejected material that forms the crater.

    Just an idea that something similar may be at play here. Perhaps what appears to be small craters in overlying surface may actually be much deeper holes.

  • Localfluff

    @mpthompson That’s a cool idea! The hollow Moon. Maybe one can match them with exit craters on the far side :-D

  • Alex Andrite

    The link to the LROC site is very rewarding. Thanks.
    I have copied and sent the LROC site to teacher friends. Great project material there !

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