Weird Oblong Crater Deepens Mars Mystery
This amoeba-shaped depression on Mars, called Orcus Patera, has had planetary scientists scratching their heads for decades. Despite this sharp new image from the European Space Agency’s Mars Express spacecraft, the crater’s origin is a complete mystery.
Orcus Patera, discovered in 1965 by the Mariner 4 spacecraft, is located near Mars’ equator, between the volcanoes Elysium Mons and Olympus Mons. At 236 miles long, it would stretch from New York to Boston on Earth. Its rim rises over a mile above the surrounding plains, and its floor lies 1,300 to 1,900 feet below its surroundings.
But in spite of lying between two volcanoes and its designation as a patera — the name for deep, complex or irregularly shaped volcanic craters — scientists aren’t at all sure that Orcus Patera has a volcanic origin story. It could be a large impact crater that was originally round but later deformed by compressional forces. Or it could have formed after the erosion of aligned impact craters. 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, like a rock skipping on a pond.
The new images show that the crater’s rim is criss-crossed by rift-valley-like structures called graben, which are evidence for active tectonic forces in the area. Smaller graben are also visible inside the depression itself, suggesting that several tectonic events have stretched the ground. The depression also shows “wrinkle edges,” which indicate that the ground has been compressed as well as stretched. The dark shapes near the center of the depression were probably formed when dark material dug up by small impacts in the depression was blown around by the wind.
But these features all appeared after Orcus Patera was formed.
The oblong crater’s origin is still a mystery.
Story: Wired Science
That little dot in the lower center of the Sun?
The larger darker spot on the left side is a sunspot.
Auroras on Saturn: In this picture, the ring of green auroras might seem faint, but that curtain of light is shooting up about 600 miles from the cloud tops of Saturn’s south pole region.
Color details: Auroras are seen in bright green. Sunlight reflected off of Saturn’s rings and high-altitude haze are seen in bright blue. Heat emission from inside the interior is deep red.
Earth & Moon.
Taken from Mercury’s orbit by Messenger.
Ice lake on Mars
This is a giant patch of frozen water inside an unnamed impact crater on Mars. The existence of this water-ice patch on Mars makes life a more likely possibility and raises the prospect that past or present life will one day be detected.
The crater with ice disc is on the Vastitas Borealis, a broad plain that covers much of Mars’s far northern latitudes. The crater is 35 km wide, with a maximum depth of about 2 km. The image was taken by the High Resolution Stereo Camera on ESA’s Mars Express.
Scientists believe the water-ice is present all year round because the temperature and pressure are not sufficient to allow it to change states and vaporise into the atmosphere. It is not frozen carbon dioxide, because this type of ice had already disappeared from the north polar cap by the time this image was taken.
• Source: European Space Agency (Flickr)