China's Mars rover discovers evidence of liquid water on the Red Planet
With an Earth-like climate and an ocean flowing across its surface, was once a very different place to the dry, barren world it is today. What has remained a mystery, however, is where all this water went, with scientists believing most of it likely became trapped in the planet's outer layer, or crust. This led to the widespread belief that it currently only exists in solid form in rocks and as a gas in water vapour, but an exciting new discovery suggests there is also a liquid variation, too. The breakthrough is important because China's Zhurong rover, which landed on the Red Planet in 2021, detected evidence of this liquid water on sand dunes at low latitudes, i.e. towards the equator and away from its poles. Scientists say the liquid water forms when salts in the dunes cause frost to melt at low temperatures. However, it is likely to remain in this state for only a short length of time, as Mars is too cold for water to stay liquid on the surface. Last year an international team of , while in 2009 it was detected on a leg of the Mars Phoenix Lander in the planet's arctic region. Scientists analysing that discovery said that based The reason this is key is because surface temperatures are relatively warmer nearer the equator, meaning conditions are more suitable for life than those closer to the planet's poles. 'This is important for understanding the evolutionary history of the Martian climate, looking for a habitable environment, and providing key clues for the future search for life,' said He and his team used data obtained by the Zhurong rover's Navigation and Terrain Camera (NaTeCam), Multispectral Camera (MSCam), and its Mars Surface Composition Detector (MarSCoDe). This allowed them to study the surface features and material compositions of dunes in the rover's landing area. Their analysis revealed that the surface layer of the dune was rich in hydrated sulfates, hydrated silica, iron oxide minerals and possibly chlorides. 'According to the measured meteorological data by Zhurong and other Mars rovers, we inferred that these dune surface characteristics were related to the involvement of liquid saline water formed by the subsequent melting of frost/snow falling on the salt-containing dune surfaces when cooling occurs,' said Professor QIN. The researchers proposed a scenario for how this liquid water comes about. Unlike Earth, the obliquity (or tilt) of Mars changes substantially on timescales of hundreds of thousands to millions of years. At today's 25-degree tilt on Mars' rotational axis, ice is present in relatively modest quantities at the north and south poles. However, research has shown that ice builds up near the equator when Mars is tilting more, while the poles grow larger at very low obliquities. The authors of the new study theorise that low latitudes cool during the Red Planet's large obliquity, like it is currently, which leads to frost and snow that solidifies dunes and leaves traces of saline water. That's despite very low pressure and water vapour content making it difficult for liquid water to sustainably exist on the planet today. It is for this reason that experts had believed that water could only exist in solid or gaseous forms. Until now, no evidence had shown the presence of liquid water at low latitudes on Mars, which is why the breakthrough is potentially exciting. It suggests there are certain conditions where liquid water can emerge in some parts of present-day Mars. Of course, past studies have already shown that the Red Planet could have held enough water to cover its entire surface in a layer measuring between 330ft (100m) and half a mile (1km) deep. This was more than four billion years ago, when Mars was warmer and wetter and possibly had a thicker atmosphere. However, when this disappeared the planet's climate changed dramatically and gave rise to a world hostile to life, which we see today. The new discovery will add hope to the work of NASA's Perseverance rover, which is currently searching an ancient crater lake for signs of past life. It is collecting samples which are due to be returned to Earth for analysis in the 2030s. The new study has been published in .