Expanded crater
Impact craters that expand due to subsurface ice sublimation.
Wikipedia / Wikimedia Commons
An expanded crater is a type of impact crater that forms when debris from a large impact creates small craters that subsequently lose their rims and increase in diameter. These features can be either primary or secondary impact craters. They are significant because they indicate the presence of abundant subsurface ice, particularly on Mars, and provide insights into where future colonists might find water ice.
- type
- Geological feature
- location
- Mars, especially Arcadia Planitia
- associated_primary_craters
- Gan, Domoni, unnamed 6 km crater
- estimated_ice_volume
- Variable; not a widely established canonical figure
- age_of_ice
- Tens of millions of years
- key_characteristic
- Loss of rim due to ice sublimation and collapse
Lore & Background
Expanded craters are not exclusively a subtype of secondary impact craters; they can also form from primary impacts. Large impacts eject debris that forms swarms of small secondary craters, but primary impacts can directly produce expanded craters as well. Studies of expanded craters have revealed locations where abundant ice may be present in the ground. These craters have lost their rims, possibly because the rim collapsed during expansion or lost its ice if composed of ice. Excess ice—ice beyond what fills pore spaces—is widespread in the Martian mid-latitudes, especially in Arcadia Planitia. In this region, many expanded craters likely form when impacts destabilize a subsurface layer of excess ice, which then sublimates. Sublimation converts ice directly from solid to gas. The impact breaks up the excess ice, increasing its surface area, which accelerates sublimation. After the ice disappears into the atmosphere, dry soil collapses, enlarging the crater diameter.
Reader's Guide
Expanded craters serve as a key indicator of subsurface ice on Mars. Because the region still contains abundant expanded craters, the areas between them likely hold substantial ice beneath the surface. If all the ice were gone, all expanded craters would also be gone. These craters are more frequent in the inner layer of double-layer ejecta craters, which are believed to form in ice-rich ground. Research published in 2015 mapped expanded craters in Arcadia Planitia and concluded the ice may be tens of millions of years old, based on the ages of four primary craters: Steinheim, Gan, Domoni, and an unnamed 6 km crater. Measurements and models indicate that at least 6000 km³ of ice remains preserved in non-cratered portions of Arcadia Planitia. Places on Mars displaying expanded craters may indicate where future colonists can find water ice.
Did You Know?
- Expanded craters have lost their rims, possibly due to collapse or loss of ice.
- The ice in Arcadia Planitia may be tens of millions of years old, based on the ages of four primary craters.
- Expanded craters can form from both primary and secondary impacts.
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