Looks like its likely a piece of space junk that got embedded like a knife.
If Mars had more atmosphere, it would have burned up on the way in.
I agree, a result of impact, but possibly more likely to be ejecta from a distance.
Red Planet’s Ancient Equator Located
Scientific American (online) | April 20, 2005 | Sarah Graham
Posted on 04/24/2005 8:18:25 PM PDT by SunkenCiv
http://www.freerepublic.com/focus/chat/1390424/posts
Did A Giant Impact Create The Two Faces Of Mars?
New Scientist | 3-15-2007 | David Shiga
Posted on 03/15/2007 2:14:24 PM PDT by blam
http://www.freerepublic.com/focus/news/1801508/posts
New Theory: Catastrophe Created Mars’ Moons
space.com | 29 Jul 03 | Leonard David
Posted on 07/29/2003 8:56:47 AM PDT by RightWhale
http://www.freerepublic.com/focus/news/954539/posts
Deep Hole Found on Mars
Space.com on Yahoo | 6/6/07 | Leonard Davis
Posted on 06/06/2007 12:13:11 PM PDT by NormsRevenge
http://www.freerepublic.com/focus/f-chat/1845949/posts
The Yardangs of Mars
Geological Society (UK) | July 24, 2004 | staff
Posted on 01/01/2005 11:18:55 AM PST by SunkenCiv
http://www.freerepublic.com/focus/chat/1312117/posts
-and for fun-
Barsoom, the Face, Structures on Mars
Our Tiny Little Minds | Past, Present, Future | various
Posted on 05/16/2006 9:00:11 AM PDT by SunkenCiv
http://www.freerepublic.com/focus/bloggers/1633114/posts