Picture This: Evidence of liquid water on Mars

Salt streaks offer hints that water flows on Mars today

Mars water

Salt deposits show up as dark-bluish streaks in this image. They are seen falling down into a Martian canyon known as Coprates Chasma. The salt was left behind by seasonal water flows, a new study suggests.

JPL-Caltech/NASA, University of Arizona

New data suggest that during parts of the year, water flows on Mars. Studies have found evidence that this Red Planet once had plenty of water — and that surface moisture or ice might still remain. But there was no evidence of actual flowing water. Until now.

And even now, that evidence is still indirect.

For some time, scientists have witnessed seasonal dark streaks. They appear etched onto some slopes of the Martian surface. They form each year during the Martian summer, then disappear as winter approaches. A new study has now analyzed light spectra at four of these streak sites. Scientists used a spectrometer (Spek-TROM-eh-tur). It analyzes light reflected off of the Martian surface to gauge the minerals present. The instrument is flying aboard the Mars Reconnaissance Orbiter, a satellite.

Those seasonal dark streaks are hydrated salts. Or that’s the conclusion of a new report. The compounds appear to be magnesium perchlorate, magnesium chlorate and sodium perchlorate. Each salt is a type that normally needs liquid water to form. So scientists believe liquid water must be flowing down the slopes. Along the way, it appears to be depositing the salty residues.

The salt trails show up only in warm seasons. Rising temperatures probably drive water to the surface, the scientists say. Still unclear is the source of that water. It could be buried ice, underground pools or something else. The new report appeared online September 28 in Nature Geoscience.

Power Words

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magnesium   A silvery and rather hard metallic element having the atomic number 12. It is the most lightweight of the structural metals and is about as electrically conductive as aluminum.

Mars The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.

perchlorate This naturally occurring chemical is a potentially cancer-causing component of certain jet fuels, explosives and fertilizers. In animals, this pollutant can perturb levels of thyroid hormones.

planet A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and it must have cleared other objects out of the way in its orbital neighborhood. The solar system consists of eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

salt    A compound made by combining an acid with a base (in a reaction that also creates water).

satellite    A moon orbiting a planet or a vehicle or other manufactured object that orbits some celestial body in space.

sodium A soft, silvery metallic element that will interact explosively when added to water. It is also a basic building block of table salt (a molecule of which consists of one atom of sodium and one atom of chlorine: NaCl).

spectrometer An instrument used by chemists to measure and report the wavelengths of light that it observes. The collection of data using this instrument, a process is known as spectrometry, can help identify the elements or molecules present in an unknown sample.

spectrum (plural: spectra) A range of related things that appear in some order. (in light and energy) The range of electromagnetic radiation types; they span from gamma rays to X rays, ultraviolet light, visible light, infrared energy, microwaves and radio waves.

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