Pit craters are found on solid bodies throughout our Solar System, including Earth, Venus, the Moon, and Mars. These craters, which are not formed by impacts, may be signs of underground lava tubes, which are created when the top of a stream of molten rock solidifies and the lava inside escapes, leaving a hollow tube of rock If part of the roof of the tube is unsupported, parts of it can fall, making a hole or pit along the path of the lava tube.
This image shows pit craters on Mars, running north-south and east-west, and likely following a lava tube not land. Credit: NASA/JPL-Caltech/UArizona
On Mars, pit craters are typically bowl-shaped and usually occur in flat, featureless terrain, and planetary scientists can tell a pit crater from an impact crater because pit craters typically have no rims raised or ejected, as impact craters do. most of them can be easily identified by their lack of raised rims or ejecta, which would be present if an impact had created the crater.
But the Mars Reconnaissance Orbiter and other previous missions orbiting the red planet have identified more than 100 pit craters around the Tharsis region of Mars that have unusual features compared to other pit craters.
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Called atypical pit craters (APCs), they generally have sharp, distinct rims, vertical walls, or overhangs that extend to their floors. They are usually cylindrical or bell-shaped, and their surface diameters can be one-third larger than typical pit craters. They can range between 50 and 350 meters in diameter.
The Tharsis region is the large volcanic plateau near the equator in the western hemisphere of Mars that is home to the largest volcanoes in the Solar System, and scientists think that the abundance of APC in this region comes from underground tubes that can cross. among the giant volcanoes of Mars.
An atypical pit crater near Elysium Mons. Credit: NASA/JPL-Caltech/UArizona
But now MRO has found several APCs in another volcanic region that is older than Tharsis. The atypical pit craters shown here are located near the Elysium Mons volcano, which is the third largest mountain on Mars and is located in the Martian eastern hemisphere.
MRO scientists are excited to find these older APCs, as they believe they “should reveal erosional features and possibly whether they are old or formed more recently. HiRISE has targeted many APCs on Tharsis, but scientists they say these are the first to be suggested on older grounds.
The area around Elysium Mons has many craters on its surface, and while some were likely formed by meteorite impacts, many show no ejection pattern. Also, many are aligned in linear patterns that are radial to the summit caldera, so planetary scientists believe they likely formed by collapse when lava retreated from below the surface, rather than by impact of meteorites
As we discussed in a recent article, these pit craters create entrances to underground lava tubes. On the Moon, they could provide thermally stable habitats as well as safe protection from cosmic rays, solar radiation and micrometeorites for future human explorers.
Further reading: HiRISE Image of the Day: APC near Elysium MonsPaper: Atypical pit craters on Mars: New insights from THEMIS, CTX and HiRISE observationsNASA: Pit craters and giant volcanoes
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