A limestone karst in Chillagoe-Mungana Caves National Park, Queensland.
Karst topography is a landscape formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum.
It is characterized by underground drainage systems with sinkholes and caves.
It has also been documented for weathering-resistant rocks, such as quartzite, given the right conditions. Subterranean drainage may limit surface water with few to no rivers or lakes.
However, in regions where the dissolved bedrock is covered (perhaps by debris) or confined by one or more superimposed non-soluble rock strata, distinctive karst surface developments might be totally missing.
Photographic Image by NASA/JPL-Caltech/Univ. of Arizona
During a recent calibration exercise, NASA’s Mars Reconnaissance Orbiter captured a remarkable view of Earth and its moon from a distance of 127 million miles (205 million kilometers).
It’s so clear, you can even make out our planet’s continents.
To calibrate the HiRISE camera aboard the Mars Orbiter, NASA scientists needed to scan an object other than the Red Planet.
Seeing as Earth is right next door, that was an obvious choice.
The image is a combination of two separate exposures taken on November 20, 2016, and have been moderately adjusted to make both objects appear equally as bright (otherwise the Earth would have appeared too dark).
The combined view shows the correct positions and sizes of the two celestial bodies relative to each other.