NASA’s Curiosity rover has returned images showing evidence of an ancient, flowing stream on Mars after a close examination of two outcrops called “Hottah” and “Link”.
The rock outcrop shown below (named “Hottah” after Hottah Lake in Canada’s Northwest Territories) may look like broken up pavement, but it is actually exposed bedrock made up of smaller fragments cemented together.
This is what geologists call a “sedimentary conglomerate“. Scientists theorise that the bedrock was disrupted in the past (giving it the tilted angle) most likely through meteorite impacts.
The key evidence for the ancient stream comes from the size and rounded shape of the gravel in and around the bedrock.
Hottah has pieces of gravel embedded in it, called clasts (one of which is circled above), up to a couple inches in size and located within a matrix of sand-sized material. Some of the clasts are round in shape, leading to the conclusion they were transported by a vigorous flow of water.
The gravels in conglomerates at both outcrops range in size from a grain of sand to a golf ball. Some are angular, but many are rounded, and the similarity to pebbles found desposited in Earth’s streams and rivers is striking.
“The shapes tell you they were transported and the sizes tell you they couldn’t be transported by wind. They were transported by water flow,” said Curiosity science co-investigator Rebecca Williams of the Planetary Science Institute in Tucson, Arizona.
The finding site lies between the north rim of Gale Crater and the base of Mount Sharp, a mountain inside the crater which is Curiosity’s ultimate destination. Once there the rover will examine the sedimentary layers in the hope it will discover evidence of organic deposits, therefore confirming the past existance of life on Mars.
This is a truly exciting find!
Source: NASA MSL