Fizzy water powered 'super' geysers on ancient Mars

2019-02-26 03:12:09

By David Shiga, Houston (Image: NASA/JPL/ASU) (Image: NASA/JPL/ASU) Huge fountains of carbonated water once erupted on Mars, hurling hailstones and mud several kilometres into the air, a team of scientists says. Geysers form in two ways on Earth. In some geysers, the water is blasted up into the air by steam escaping from underground, while in others, it is forced out by bubbles of carbon dioxide rushing to the surface. Both types can be spectacular; the Old Faithful geyser in Yellowstone National Park in Wyoming, US, for example, shoots scalding water about 45 metres into the air. Now, scientists say they have found signs of ancient geysers on Mars that would have dwarfed those in Yellowstone. Towering a couple of kilometres above the surface, Martian geysers rained hailstones and muddy water for several kilometres around. The geysers erupted when bubbles of carbon dioxide forced underground water up to the surface through cracks, say scientists led by Alistair Bargery of Lancaster University in the UK. “It’s like when you shake up a Coke bottle and all the fizz comes up,” team member Adam Neather told New Scientist. The evidence for this appears at two sites on Mars where cracks hundreds of kilometres long called Mangala Fossa and Cerberus Fossae stretch across the surface. Both cracks are the starting points for broad channels that appear to have carried huge quantities of water – between 10 and 100 times the flow of the Amazon River. At least some of this water seems to have erupted onto the surface in the form of enormous geysers. At Cerberus Fossae, water appears to have reached an area that is uphill from the crack and several kilometres away, based on the erosion of a slope there. A powerful geyser must have erupted from the crack to transport the water all that way, says team member Lionel Wilson. Near Mangala Fossa, muddy water from geysers apparently rained down onto the surface, creating mud flows. Later, when the water evaporated, only the sediment it carried would be left, forming ridged rock formations resembling the flows. Another possibility is that the sediment deposits are made of solidified lava, but the direction of the ridges appears to rule that out, Wilson says. When ridges form in lava flows, they are always perpendicular to the direction of flow, whereas the ridges in this case are parallel to it. Based on the distance of the deposits from the cracks, Neather says the geysers must have thrown material outwards by at least 4 kilometres. The team calculates that Martian geysers could throw material up to twice this distance. The secret to the power of the Martian geysers is that their source water seems to have come from very deep below the surface. The overlying rock at Mangala Fossa appears to have slumped downwards when underground water pockets emptied out, and the amount of this slumping suggests the water pockets lay about 3 to 4 kilometres below the surface. The pressure at such great depths means water would be able to hold large quantities of dissolved carbon dioxide, which may have come from underlying magma. Once a crack formed that connected the surface to the high-pressure water below, the water would have rushed upwards. The resulting drop in pressure would have had the same effect as opening a shaken soda can. Expanding bubbles of CO2 would have caused the muddy water to shoot out in geysers at more than 400 kilometres per hour. The geysers probably turned on very quickly and rose to great heights, helped along by the Red Planet’s weak gravity, which is just 38% as strong as Earth’s. “Maybe in a few minutes it grows to 1 to 2 kilometres,” Wilson told New Scientist. The fountains could have carried on spouting for a month or two, Wilson says, spewing massive amounts of muddy water onto the surface. Water at the periphery of the geyser would have quickly frozen in the -70 °C Martian air, pelting the ground as hailstones. Geologist John Dixon of the University of Arkansas in Fayetteville, US, agrees that the deposits could be the aftermath of a CO2 water fountain. “I think it’s definitely a viable hypothesis,” he told New Scientist. “It sure doesn’t look like any terrestrial lava flow that I’ve seen.” Geysers appear to have been active relatively recently on the 4.6-billion-year-old planet. Previous studies have estimated the channel connected to Cerberus Fossae to be less than 20 million years old. Neather presented the research last week at the Lunar and Planetary Science Conference in Houston, Texas,