Astronomy Picture of the Day 10-28-02

NASA ^ | 10-28-02 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2002 October 28

Earth's Richat Structure
Credit: Landsat 7, USGS, NASA

Explanation: What on Earth is that? The Richat Structure in the Sahara Desert of Mauritania is easily visible from space because it is nearly 50 kilometers across. Once thought to be an impact crater, the Richat Structure's flat middle and lack of shock-altered rock indicates otherwise. The possibility that the Richat Structure was formed by a volcanic eruption also seems improbable because of the lack of a dome of igneous or volcanic rock. Rather, the layered sedimentary rock of the Richat structure is now thought by many to have been caused by uplifted rock sculpted by erosion. The above image was captured last year by the orbiting Landsat 7 satellite. Why the Richat Structure is nearly circular remains a mystery.

[petuniasevan]

Astronomy Fun Fact:

Here's proof that one has to be careful in any interpretation of what we see, whether it be on Earth or in a distant galaxy. Wouldn't you think "impact crater" if you saw this type of structure on Mars, for instance?

50 kilometers is about 30 miles.

[petuniasevan]

[farmfriend]

That is a cool picture.

[firewalk]

Thanks for the ping & good morning

[sistergoldenhair]

Thanks for the ping.

[headsonpikes]

Wonderful image!

[RightWhale]

Very strange feature.

[Graewoulf]

Looks like the structure above a salt dome. Any maps of this structure showing dips?

[petuniasevan]

I can't find any topo map of the structure.

Here's what a NASA page had to say:

"Initially interpreted as a meteorite impact structure because of its high degree of circularity, it is now thought to be merely a symmetrical uplift (circular anticline) that has been laid bare by erosion. Paleozoic quartzites form the resistant beds outlining the structure. The reason for the high degree of circularity is not clear."

http://eob.gsfc.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=2124