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White veins of Mars: Curiosity hits 'a jackpot' in quest for wetter past

Curiosity rover has found mineral-filled fissures in the rocks of Gale Crater on Mars. Together with other evidence, the minerals suggest that the rocks were once 'saturated with water.'

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Yellowknife Bay, a portion of a larger feature the team dubbed Glenelg, is the lowest, hence oldest, formation the rover has explored. It hosts a number of clues that point to a watery past. [Editor's note: The original version of this paragraph gave an incorrect relative age for the Yellowknife Bay formation.]

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  • Using the equivalent of a geologist's magnifying glass on the end of the the robotic arm, researchers identified a wide variety of rock textures. These range "from conglomerate to sandstone to siltstone" and all "are sedimentary rocks, meaning that other rocks had to be broken down into fragments and transported elsewhere," says Aileen Yingst, a researcher with the Planetary Science Institute in Tucson and deputy principle investigator for the robotic hand lens, known as MAHLI. How were they transported? Many of the fragments are too big to have traveled on the Martian wind, suggesting water.
  • A layered, rock outcrop the team has named the Shaler Unit indicates a stream flowed through the area, shifting small sediment dunes on the stream bed in ways that formed the layers.
  • The composition of the white minerals in rock veins is consistent with calcium sulfate, plus a fair bit of hydrogen. The relatively high levels of hydrogen suggest the minerals precipitated out of water flowing through the fissures.

The mineral-filled fissures looked similar to those found in rocks in the Sahara, says Nicolas Mangold, a researcher with the Laboratoire de Planétologie et Géodynamique de Nantes in France and a member of the Curiosity rover's ChemCam team. Those desert veins were formed when water circulated through the cracks.

Given the conditions under which calcium sulfate forms on Earth, he suggests the veins on Mars formed at low to moderate temperatures.

The estimate hints at why the team is excited not just to have found evidence of water, but water that bears the raw material for precipitation of minerals. Like sedimentary rocks, minerals are made of bits and pieces from somewhere else – in this case from ions released from rock somewhere else as water flowed over or through it. And different minerals precipitate out at different temperatures, yielding some information about the environment at the time the minerals formed.

As Curiosity explores Yellowknife Bay, it will undergo its last test – using a drill at the end of its arm to extract the first drill samples. Those samples will be used to clean the delivery system the drill uses to transfer the samples to a pair of chemistry labs inside Curiosity's chassis. Once the cleaning ends, the drill will provide samples to the labs for analysis.

Researchers have selected a rock named for the late John Klein, Curiosity's former deputy project manager, who passed away in 2011. Drilling should begin within the next two weeks.

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