Scientists have long debated whether liquid water was abundant on ancient Mars. Warm conditions make it much more likely life would have developed independently on the surface of ancient Mars. Now a new comparison of Mars with similar depositions on Earth lends weight to the idea that early Mars had one or more long periods dominated by rainstorms and flowing water, with the water later freezing.
Professor Briony Horgan, of Purdue University, said: “We know there were periods when the surface of Mars was frozen; we know there were periods when water flowed freely.
We know there were periods when the surface of Mars was frozen; we know there were periods when water flowed freely
“But we don’t know exactly when these periods were, and how long they lasted.
“We have never sent unmanned missions to areas of Mars which can show us these earliest rocks, so we need to use Earth-bound science to understand the geochemistry of what may have happened there.”
Previous studies of weathering in radically different climate conditions such as the Oregon Cascades and Iceland illustrate how climate affects pattern of mineral deposition, like that seen on Mars.
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On Earth, silica deposition is found in glaciers which are characteristic of melting water.
And scientists can identify similar silica deposits in younger areas on Mars, while also seeing older areas similar to deep soils from warm climates on Earth.
This leads space scientists to believe there was a general slow trend from warm to cold, with periods of thawing and freezing on Mars between three to four billion years ago.
Professor Horgan added: “If this is so, it is important in the search for possible life on Mars.
“We know that the building blocks of life on Earth developed very soon after the Earth’s formation, and that flowing water is essential for life’s development.
“So evidence that we had early, flowing water on Mars, will increase the chances that simple life may have developed at around the same time as it did on Earth.
“We hope that the Mars 2020 mission will be able to look more closely at these minerals, and begin to answer exactly what conditions existed when Mars was still young.”
Analysis of the surface geology of Mars supports a trend from a warm to a cold climate, however, the climate models don not support this, due to the limited heat arriving from a young Sun.
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Professor Horgan added: “If our findings are correct, then we need to keep working on the Mars climate models, possibly to include some chemical or geological, or other process which might have warmed the young planet,” said Horgan.
The researchers compared Earth data to Martian minerals detected using the NASA CRISM spectrometer, currently orbiting Mars, which remotely identifies surface chemicals where water once existed.
NASA also took data from the Mars Curiosity Rover.
Professor Horgan is a co-investigator on the Mars 2020 mission, due to be launched in July 2020 and will explore the Jezero Crater in February 2021.
Professor Scott McLennan, Stony Brook University – not involved in the study – said: “What is especially exciting about this work is that it used well understood Earth based geological processes from regions that are good analogs for Mars.
“The results not only make sense from the perspective of developing climate evolution models for Mars but also demonstrated a possible mechanism for forming the most interesting and perplexing and non-crystalline components that have been found in all of the samples analysed so far by the NASA Curiosity rover.”
Ancient valley networks and lake deposits on Mars are clear evidence liquid water was once abundant on the surface, but whether the climate was warm and wet or cold and icy is poorly understood.
However, the mineralogical record of Mars may provide new constraints on the paleoclimate.
NASA news: Early Mars likely had one or more long periods dominated by rainstorms
A series of studies using samples from Mars analog terrains on Earth have been used to better understand the effects of climate on weathering mineralogy.
Weathering in alpine glacial settings of the Oregon Cascades is driven by frequent melt, and water and sediments have low residence times in the glacial system.
Abundant alteration products in proglacial terrains include silica coatings on bedrock and poorly crystalline silicates in glacial sediments.
Analysis from sediments at cold-based margins of the Antarctic ice sheet also show poorly crystalline silicates, consistent with weathering by transient melt.
In contrast, sediments from warm-based zones show enrichments in crystalline clay minerals, thought to be caused by longer residence times under the ice sheet.