In a picture of Phobos, it appears as if there are striations which circle it, and orthogonal striations which are reminiscent of topological maps. Are these digital photography effects or real? If they are real, what explanation do we have for them?

enter image description here

  • $\begingroup$ I suspect the OP is referring to the long, straight trails visible in many pictures, including on Phobo's Wikipedia page. IIRC, many people think these are evidence that the moon is beginning to be torn apart by tidal forces, but I'm not confident enough of this to post it as an answer. en.wikipedia.org/wiki/Phobos_(moon)#/media/… $\endgroup$
    – Bear
    Mar 3, 2017 at 14:21
  • $\begingroup$ This belongs to astronomy is'nt it ? $\endgroup$
    – Antzi
    May 29, 2017 at 2:34
  • $\begingroup$ @Antzi: No, planetary science is on-topic here. (It is probably also on-topic on Astronomy; that sort of overlap is totally fine.) In this case, the question is specifically about the sorts of sensors and sensor interpretation involved in Space Exploration, by means of actual probes. $\endgroup$ May 29, 2017 at 3:14
  • $\begingroup$ This is a great question, and great answers as well! I've modified the title just to make it more informative in future searches. $\endgroup$
    – uhoh
    Sep 5, 2018 at 3:55

2 Answers 2


Yes, they are real, not artifacts.

From the Mars Orbiter Camera website.

The rows of grooves and aligned pits on Phobos are related to, and were probably caused by, a large meteor impact that occurred on the side of Phobos that is not seen here. That large crater, Stickney, was named for the maiden name of the wife of the astronomer that discovered Phobos and the other martian satellite, Deimos, in 1877, Asaph Hall.

That crater was already visible in the Mariner 9 photos from December 1971.

On this 1998 picture (source http://www.msss.com/mars_images/moc/2003/05/16/) you can see the grooves radiate outward from Stickney:

enter image description here

  • $\begingroup$ There are pits along the grooves that some have speculated to be outgassing vents. So you could picture strata rubbing against each other, heating up volatiles which made their way out the cracks. $\endgroup$ Mar 7, 2017 at 3:13

As the closest someone with no academic experience can be to a Phobos expert...

Crater chains don't especially work, because you'd expect significantly more dispersion even if ejecta from Mars reaches Phobos in minutes.

Paths of rolling boulders matches surprisingly well https://www.hou.usra.edu/meetings/lpsc2017/pdf/2084.pdf http://www.planetary.brown.edu/pdfs/4150.pdf

but I find it hard to believe that every block would escape Phobos, and if you have enough ejecta return to bury boulders, you have enough to bury grooves.

Dust sifting into fractures is the most popular idea. The most common suggestion for fracture sources is tidal stresses, and that matches most grooves' orientations very well (source), the grooves on Phobos's leading edge don't really match. Other causes include outgassing vents and fractures caused by the Stickney impact (the latter becoming increasingly unlikely as Phobos increasingly looks like a reaccreted rubble pile).

Grooves have some different characteristics, so it's likely there's a combination of causes.

There's a region on Phobos's trailing edge without grooves. My personal theory as to why is that dust from Deimos is primarily deposited on Phobos's trailing edge. If the grooves are old enough, one would expect grooves there to be buried. (https://phobos-deimos.arc.nasa.gov/on-demand/, scroll to Horanyi)


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