365 Days of the Moon--August 14, 2014
Tycho's strange "railroad track" rays
Continuing yesterday's theme of crater rays, here we see Tycho's confusing ray system at near full moon. Tycho's young ray
system, thought to be only 108 million years old, splashes across half the face of the Moon. One rogue ray stretches as far
as Mare Serenitatis to the far northeast. In this view we see the ray structure is heaviest to the east, indicative that
Tycho was created by an asteroid strike arriving low from the west. The bright ray system is visible to the naked eye. A
binocular view of the rays at full Moon draw the eye straight to Tycho like a bulls eye.
However, Tycho's rays have some mysteries. We see several bright streamers radiating away from the crater, the "railroad tracks"
extending to the upper left and the single streamer to the lower left. Look closely...see the mystery? You would expect crater
rays to radiate from a central explosion point that created the parent crater. But these bright rays do not centrally converge
on Tycho. They are in fact tangential to Tycho's rim. What the heck?? I have no hard explanation for this.
This ray mystery led some respected mid-20th century lunar experts to think Tycho crater and its ray system were created by two
different events. My pet theory, open to correction if someone has an answer, is that Tycho was created by the impact of a
"rubble pile" asteroid. This is a class of asteroid that is not one solid body, but many big rocks weakly bound together by their
own gravity. As this rubble pile asteroid approached the Earth/Moon system 108 million years ago, our gravity broke it up into
multiple fragments, The fragments that hit the Moon first pushed out the offset rays, followed within seconds by the impact that
blasted out Tycho crater itself. The multiple impacts were spread over a 30 to 40 area, creating offset rays and a big crater.
Image taken with a Celestron 11 Edge HD, 2.5X Powermate, and Skyris 274M
Image and content Copyright Robert Reeves 2014
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