March 25, 2014
A Snake with Two Heads
image by Harald Paleske, Germany
About 85 years ago Rümker was described as a ruined crater, and 25 years later as a plateau. It isn't a crater of any sort, but it is indeed an elevated area. I wouldn't call it a plateau though, for the top isn't flat. Rümker is a pile of domes, ably studied by the Geologic Lunar Research group. Harald's image is remarkable in showing Rümker's shadow stretching to the terminator. The image also shows three different rilles - do you see them all?
At top right is the strange, deeply incised, unnamed rille near the crater Sharp. According to measurements on the LRO QuickMap it is about 700 m deep - amazingly deep for a rille. At bottom right is the just visible twisted rille that seems to start at a curved depression near where the mare runs into the ejecta from the Sinus Iridum impact. The Sharp Rille, well shown at top, right of center, is the third rille here. And if you look closely you can see a named rille - the Mairan Rille - just north and west of the twisted one. You many say, this makes four rilles, not three - and you would be officially right, for Mairan and Sharp are different names. But if you follow the Sharp rille south using 125 m resolution on the LRO QuickMap (with the new big shadows layer) you can trace a continuous rille from the beginning of the Sharp Rille to the beginning of the Mairan Rille. This is a snake with two heads. So which way did the lava flow? Which is the real vent? Once again using the QuickMap elevation tool you will discover that both ends of the combined rille are at about -2300 m elevation and both gently slope down to -2600 m. In other words both ends are high, and lava from their vents would flow 300 m downhill to their middle, but then would have to flow 300 m UPHILL to reach the other end? What do you think explains this?
3.03.2014. 225mm Unigraph (solar telescope), SR 445m, green filter, exp. time 1/15sec., stack 250/4000frames, seeing good.
21st Century Atlas chart 20.
Yesterday's LPOD: An 19th Century Marvel
Tomorrow's LPOD: The Little Things Also Count