Mars's mysterious elongated crater

Aug 27, 2010
Orcus Patera on Mars. Credits: ESA/DLR/FU Berlin (G. Neukum)

(PhysOrg.com) -- Orcus Patera is an enigmatic elliptical depression near Mars's equator, in the eastern hemisphere of the planet. Located between the volcanoes of Elysium Mons and Olympus Mons, its formation remains a mystery.

Often overlooked, this well-defined depression extends approximately 380 km by 140 km in a NNE-SSW direction. It has a rim that rises up to 1800 m above the surrounding plains, while the floor of the depression lies 400-600 m below the surroundings.

The term ‘patera’ is used for deep, complex or irregularly shaped craters such as the Hadriaca Patera and Tyrrhena Patera at the north-eastern margin of the Hellas impact basin. However, despite its name and the fact that it is positioned near volcanoes, the actual origin of Orcus Patera remains unclear

Aside from volcanism, there are a number of other possible origins. Orcus Patera may be a large and originally round , subsequently deformed by compressional forces. Alternatively, it could have formed after the erosion of aligned impact craters. 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, perhaps less than five degrees from the horizontal.

Credits: ESA/DLR/FU Berlin (G. Neukum)

The existence of at Orcus Patera is evident from the presence of the numerous ‘graben’, rift-valley-like structures that cut across its rim. Up to 2.5 km wide, these graben are oriented roughly east-west and are only visible on the rim and the nearby surroundings.

Within the Orcus Patera depression itself, the large graben are not visible, probably having been covered by later deposits. But smaller graben are present, indicating that several tectonic events have occurred in this region and also suggesting that multiple episodes of deposition have taken place.

The occurrence of ‘wrinkle ridges’ within the depression proves that not only extensional forces, as would be needed to create graben, but also compressive forces shaped this region. The dark shapes near the centre of the depression were probably formed by wind-driven processes, where dark material excavated by small impact events in the depression has been redistributed.

However, the presence of graben and wrinkle-ridges has no bearing on the origin of Orcus Patera, as both can be found all over . The true origin of Orcus Patera remains an enigma.

Explore further: Spaceship designer who helped send Gagarin into orbit dies at 92

Related Stories

Ancient caldera in Apollinaris Patera

Jun 09, 2006

These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express spacecraft, show the caldera of Apollinaris Patera, an ancient, 5-kilometer-high volcano northwest of Gusev Crater.

Pits and tectonic grabens in Phlegethon Catena

Feb 10, 2006

These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express spacecraft, show pits and tectonic 'grabens' in the Phlegethon Catena region of Mars.

Lava flows in Daedalia Planum

Oct 09, 2009

(PhysOrg.com) -- Mars Express imaged Daedalia Planum, a sparsely cratered, untextured plain on the Red Planet featuring solidified lava flows of varying ages.

Mars Photos: 3D Image of Solis Planum

Sep 12, 2004

These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, show part of a heavily eroded impact crater at Solis Planum, in the Thaumasia region of Mars. The images wer ...

Granicus and Tinjar Valles

Jul 28, 2006

The HRSC obtained these images during orbit 1383 at a ground resolution of approximately 23.7 metres per pixel. The images have been rotated 90 degrees counter-clockwise, so that North is to the left.

Recommended for you

Winter in the southern uplands of Mars

1 hour ago

Over billions of years, the southern uplands of Mars have been pockmarked by numerous impact features, which are often so closely packed that they overlap. One such feature is Hooke crater, shown in this ...

Five facts about NASA's ISS-RapidScat

1 hour ago

NASA's ISS-RapidScat mission will observe ocean wind speed and direction over most of the globe, bringing a new eye on tropical storms, hurricanes and typhoons. Here are five fast facts about the mission.

User comments : 6

Adjust slider to filter visible comments by rank

Display comments: newest first

Shootist
2.7 / 5 (6) Aug 27, 2010
Earth has one as well.

lat 70.0914
lon -159.430

It would be a mighty large "small" object to create a crater 380km x 140km.
Blicker
3.6 / 5 (5) Aug 27, 2010
The enigma for me is why most impact craters are round. I can only guess that so much energy is released that the craters are vaporized too rapidly for the impacting material to gouge out its direction; like a snapshot of a moving bullet with a super high speed camera looks motionless. That would suggest this crater was formed by a slower object as well as a shallow angle.
yyz
5 / 5 (3) Aug 27, 2010
A good view of this area is available using Google Mars or WWT Mars. The ESA release gives the coordinates as: 14deg N 177deg W. It's easy to spot the graben mentioned in the article on the left side of the crater, stopping at the rim. In one case, a very faint extension of a graben on the other side of the crater is visible! More images and info here: http://www.esa.in...subhead3
Caliban
3.7 / 5 (3) Aug 27, 2010
At the left side of the top image, you can see what appear to be crescent, or curved areas on opposite sides of the crater rim. My best guess is that this patera represents a String, or series of impacts, from a single, mutliple-impact event, later eroded and deformed tectonically.
Parsec
5 / 5 (3) Aug 27, 2010
The enigma for me is why most impact craters are round. I can only guess that so much energy is released that the craters are vaporized too rapidly for the impacting material to gouge out its direction; like a snapshot of a moving bullet with a super high speed camera looks motionless. That would suggest this crater was formed by a slower object as well as a shallow angle.


The analogy is sound. Consider what happens when a surface is impacted with a bullet. The bullet has to hit at a very shallow angle in order for the elongation of the entry wound. The relative velocities of most orbiting objects relative to each other are orders of magnitude more than of any bullet to a fixed surface.
kuro
5 / 5 (2) Aug 28, 2010
The enigma for me is why most impact craters are round.


when an object hits the surface, the kinetic energy it delivers causes a massive explosion. it is the effects of this explosion that create a crater many times larger than the size of the impacting object.

since the effects of the explosion - the heat and the shock wave - expand in about the same way in all directions, the resulting crater is more or less spherical.