Mars’ surface was probably not ever warm and wet long enough to support life, a new study published today in Nature concludes. But underground on the Red Planet might be a different story. By taking a look at several years of data from orbiting spacecraft and examining more than 350 sites on Mars, a team of researchers determined that Martian environments with abundant liquid water on the surface existed only in short episodes. But liquid and likely warm water more likely lasted for longer periods of time below the surface, and this would have been occurring at about the same time that life was developing on Earth.
“If surface habitats were short-term, that doesn’t mean we should be glum about prospects for life on Mars, but it says something about what type of environment we might want to look in,” said Bethany Ehlmann from Caltech and JPL, who is the lead author of the study. “The most stable Mars habitats over long durations appear to have been in the subsurface. On Earth, underground geothermal environments have active ecosystems.”
And so, the best place to look for signs of past life on Mars may be underground.
The researchers’ findings seem to indicate that Mars’ surface was almost always cold and dry, and any appearances of water – and the salts they left behind – occurred during geologically brief periods. This is certainly not the first time research has suggested brief periods of water flowing on Mars, or that underground water may have persisted, but the news study does help to provide a better picture of the history of water on Mars and even if it could possibly be there today.
Clays are crucial to understanding past water on Mars, as they form only when water is around long enough to change the chemical structure of rocks into clay, and different types of clay minerals result from different types of wet conditions.
In 2005, clay minerals were discovered in many regions of Mars by the OMEGA spectrometer on the ESA’s Mars Express. This finding seemed to indicate the planet was once warm and wet. But there’s a problem with Mars’ atmosphere – it is not thick enough now for water to be retained on Mars’ surface, and there is not scientific consensus that it was ever thick enough in the past to have allowed water to remain on the surface.
But this new study supports an alternative hypothesis that warm water persisted under Mars surface and many erosional features seen by the orbiting spacecraft were carved during brief periods when liquid water was stable at the surface.
“The types of clay minerals that formed in the shallow subsurface are all over Mars,” said John Mustard, professor at Brown University in Providence, R.I. Mustard a co-author of the study. “The types that formed on the surface are found at very limited locations and are quite rare.”
During the past five years, researchers used OMEGA and NASA’s Compact Reconnaissance Imaging Spectrometer, or CRISM, instrument on the Mars Reconnaissance Orbiter to identify clay minerals at thousands of locations on Mars. Clay minerals that form with small amounts of water usually retain the same chemical elements as those found in the original volcanic rocks later altered by the water.
The study interprets this to be the case for most terrains on Mars with iron and magnesium clays. In contrast, surface environments with higher ratios of water to rock can alter rocks further. Soluble elements are carried off by water, and different aluminum-rich clays form.
Another clue is detection of a mineral called prehnite. It forms at temperatures above about 400 degrees Fahrenheit (about 200 degrees Celsius). These temperatures are typical of underground hydrothermal environments rather than surface waters.
Two upcoming missions will help decipher the water clues left behind on Mars. The Curiosity rover, or the Mars Science Laboratory will be heading towards Gale Crater, to investigate a large, layered hill that contain clay and sulfate minerals. Curiosity is scheduled to launch later this month.
These new findings also have implications for how Mars’ atmosphere may have evolved over time, and the Mars Atmosphere and Volatile Evolution Mission, or MAVEN, in development for a 2013 launch, may provide evidence for or against this new interpretation of the Red Planet’s environmental history. This new study predicts MAVEN findings will beconsistent with the atmosphere not having been thick enough to provide warm, wet surface conditions for a prolonged period.