Seasonal changes can have a dramatic effect on how quickly Mars loses its water to space, a joint study between the Hubble Space Telescope and NASA's Mars Atmosphere and Volatile Evolution (MAVEN) mission has shown. Over 3 billion years ago, Mars was warm and wet, with large bodies of water on its surface and a thicker atmosphere. Today, however, Mars is desolate, cold and dry. So what happened to all the water? Plenty of Mars' water is still on the Red Planet. Vast reservoirs appear to be locked up deep underground at depths between 11.5 and 20 kilometres (7.1 and 12.4 miles). There's enough water inside Mars for a global equivalent layer (GEL), which essentially refers to how deep a planet-wide ocean it would create, between one and two kilometres (0.62 and 1.24 miles). Relatively small amounts of water-ice are also locked up in shallow permafrost and in Mars' polar ice caps. During the Martian summer, this ice can sublimate, dumping water vapour into the atmosphere. Most of that water vapour circulates from pole to pole, freezing out in the hemisphere in which it's winter, but some finds itself in the upper atmosphere, where solar ultraviolet light can break water molecules apart into their component atoms. The oxygen in water ends up oxidising materials on the surface or bonding with carbon to form carbon dioxide. Meanwhile, the hydrogen atoms can escape into space and get carried away with the solar wind.Based on MAVEN's previous observations, Mars has lost enough water to space to form a GEL tens to hundreds of metres deep. Combined with the huge amount of water recently found buried inside Mars, this implies the Red Planet was water-rich in its distant past. However, MAVEN, with the Hubble Space Telescope's help, has now shown that the rate of hydrogen loss is seasonal, with large increases in the escape rate at perihelion, which is Mars' closest point in its orbit around the Sun. This coincides with a strong upwelling of water vapour into the middle atmosphere, caused by seasonal heating. When at perihelion, Mars' southern hemisphere is tilted towards the Sun and the Red Planet is engulfed in its annual dust storm season - the airborne dust can contribute to atmospheric heating and water vapour content.<img src="https://cdn.magzter.com/1493279487/1727842947/articles/kXlKr971u1728456214345/1774141411.jpg" alt="image">"Scientists have found that Mars has an annual cycle that is much more dynamic than people expected 10 or 15 years ago," said John Clarke of the University of Boston. "The whole atmosphere is very turbulent, heating up and cooling down on short timescales, even down to hours. The atmosphere expands and contracts as the brightness of the Sun at Mars varies by 40 per cent over the course of a Martian year."These Hubble Space Telescope images compare the thickness of the Red Planet's atmosphere and its water loss at perihelion to aphelion

MARS LEAKS FASTER WHEN IT'S CLOSER TO THE SUN

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