Weird Crater on Mars is a Mystery

by Nancy Atkinson on August 27, 2010

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Orcus Patera is an enigmatic elliptical depression. Credits: ESA/DLR/FU Berlin (G. Neukum

This is one of the strangest looking craters ever found on Mars, and this platypus-tail-shaped depression, called Orcus Patera, is an enigma. The term ‘patera’ is used for complex or irregularly shaped volcanic craters, but planetary scientists aren’t sure if this landform is volcanic in origin. Orcus Patera lies between the volcanoes of Elysium Mons and Olympus Mons, but its formation remains a mystery. This is the latest image of the object, taken by ESA’s Mars Express.

It could be an impact crater that originally was round, but then subsequently deformed by compressional forces. Or, it could have formed from two craters next to each where the adjoining rims eroded. However, the most likely explanation is that it was made in an oblique impact, when a small body struck the surface at a very shallow angle.

Relief image of Orcus Patera. Credit: ESA/DLR/FU Berlin (G. Neukum)

It is 380 km long by by 140 km wide, and has a rim that rises up to 1,800 meters above the surrounding plains, while the floor of the depression lies 400–600 m below the surroundings. The floor of the depression is unusually smooth.

The image above was created using a Digital Terrain Model (DTM) obtained from the High Resolution Stereo Camera on ESA’s Mars Express spacecraft. Elevation data from the DTM are color-coded: purple indicates the lowest-lying regions, and beige the higher elevations. The scale is in meters.

Source: ESA


Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

Spoodle58 August 28, 2010 at 4:27 AM

@ Emilio
I would like to see the topography beneath the surface fill also.
We have a radar instrument in Mars orbit, SHARAD on the MRO.
Lets get it there.

Messenger August 28, 2010 at 6:57 AM

The lake bed hypothesis doesn’t explain the surrounding ridge. But crater chains, which explain the ridges and shape, don’t leave smooth floors. It must be combination of events over time.

Start with a crater chain. Assume the event allowed magma to initially smooth over the crater floor, then allow water to flow in over time, cutting the access channels we see and further smoothing the lake bed as silt is deposited.

AndyInv August 28, 2010 at 7:07 AM

Love the ‘platypus’ description Nancy! It looks almost like a glancing blow, and fairly recent, judging by the lack of fresh cratering within. Mars Express continues to delight.

HelloBozos August 28, 2010 at 9:30 AM

Looks like it impacted,rolled,impacted,rolled,Impacted Hard!! an split Mars Crust an finaily Slid to stop an exploded probly like are moons Tyco creator but with alot more inward motion

RUF August 28, 2010 at 11:09 AM

Looks like a shalow-angle inpact in mud.

Dori August 28, 2010 at 12:07 PM

I’m about as amateur as you can be in this field, but I wonder if it could have been an impact into the side of a small volcano, or at least a hotspot on the side of a long slope.

Molecular August 28, 2010 at 12:57 PM

Looks like an angled impact that skidded forward as it burrowed deeper into the surface.

Torbjorn Larsson OM August 28, 2010 at 1:15 PM

I’m going to vote for a heavily modified crater chain again, so it will edge closer to a win. :-)

Really, the oblique angle impact needs a case picture. To be even slightly elliptic an impact, that typically expands ~ 20 times for a high speed impactor and so naturally swamps the impact ellipticity, would need to be ~ 80-90 degrees. That explains the commonality of round impact craters and the scarcity of even slightly elliptic.

It's a face plant.

I’ll buy that: it could be a face plant after hearing about Hoagland’s “face on Mars”.

Aqua August 28, 2010 at 2:18 PM

The terraces on either side can be ‘cruised’@:

Impact scenario: An object, perhaps a piece of Demos or Phobos(?), for eons orbits Mars. Aerobraking events during particularly energetic planetary dust storms lowers this object’s orbit. The gravitational stresses eventually shatter object into a cohesive flying mass of smaller objects composed of silica, carbon, water ice, heavy water ice and frozen gases. As the lead object enters the Martian atmosphere it generates a plasma shock wave in front of it. Behind it a hot ion tail heats up some of the following pieces to fusion temperatures. A sword of hot plasma crashes into the surface and melts its way through to a magma reservoir/chamber below. Pressure from molten magma in the nearby volcano’s pushes molten magma back through the fractured units and slowly fills the cratered depression into a pond like surface.

Addendum: Doesn’t that look like a great place to put a spaceport!

Aqua August 28, 2010 at 2:24 PM

I wonder if there’s residual or other geothermal heat to be tapped?

Aqua August 28, 2010 at 2:38 PM

I’d like to see what the mag. field looks like at Orcus Patera!

Jon Hanford August 29, 2010 at 3:23 AM

Seems there is a lot of speculation as to the origins of Orcus Patera (and that makes for good reading) so I add the following:

What if this feature is the final resting place of an earlier Martian moon? Possibly a small body snatched from the asteroid belt into an unstable, decaying orbit similar to Phobos. Or maybe it was a companion body to Phobos or Deimos that that was destroyed when Mars captured them aeons ago. We now know binary asteroids are not that uncommon. Pure speculation……..and food for thought.

“Absolut Mars”

Would give a whole new meaning to the phrase “plowed under” :D

Jon Hanford August 29, 2010 at 3:41 AM


Seems that you had a similar idea (I missed it before I posted mine).

My initial impression was a modified crater chain and that seems somewhat favored in comments here. Of course, for Dick Hoagland, this may be the landing strip for alien craft from the Phobos mothership. :)

RUF August 29, 2010 at 12:26 PM

Anyone else feel that the surface was wet, or mud-like? It can be a real thick mud, and doesn’t have to be a soaking wet surface.

Spacerider August 30, 2010 at 5:18 AM

I had a closer look at the image and have you guys seen the blue patch in crater thats almost in the middle of the the main “wierd crater” ? Looks like water ? Interesting. Its a stand out anyway. Can someone explain that?

Aqua August 30, 2010 at 6:17 AM

@RUF – Yeah… recently newly formed craters at Mars equator showed signs of pure water ice! It may be that there is a frozen ocean of water below much of Mars’ surface… The impact of a cloud of hot plasma as I posited above might then melt an elongated trench? Conversely, a closely spaced meteor chain would do the same?

Have you noticed that MANY of the craters we see on Mars look as though a rocky object smashed into mud? The patterns of ejecta surrounding indicate tsunami like waves through a viscous slurry! KER SPLAT!

jimhenson August 31, 2010 at 3:36 PM

It obviously is geologic activity within the planet and not a meteorite impact, because it is located between two volcanic craters. The expansive rock outcrop have a smooth texture to them that only finely crystalline molten rocks would have after cooling. this implies a basaltic lava composition flow that filled a lower elevation basin when the volcanoes erupted.

a good guy September 10, 2010 at 7:09 AM

I’m surprised no one else noticed this: it’s a giant footprint!

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