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https://www.livescience.com/65470-strange-martian-water-cycle.html
There's a hole in the Martian atmosphere that opens once every two years, venting the planet's limited water supply into space — and dumping the rest of the water at the planet's poles.
[...]On Earth, summer in the Northern Hemisphere and summer in the Southern Hemispheres are pretty similar. But that's not the case on Mars: Because the planet's orbit is much more eccentric than Earth's, it's significantly closer to the sun during its southern hemisphere summer (which happens once every two Earth years). So summers on that part of the planet are much warmer than summers in the Northern Hemisphere.
When that happens, according to the researchers' simulations, a window opens in Mars' middle atmosphere between 37 and 56 miles (60 and 90 kilometers) in altitude, allowing water vapor to pass through and escape into the upper atmosphere. At other times, the lack of sunlight shuts down Martian water cycles almost entirely.
https://doi.org/10.1029/2019GL082839 Dmitry S. Shaposhnikov, Alexander S. Medvedev, Alexander V. Rodin, Paul Hartogh. Seasonal Water “Pump” in the Atmosphere of Mars: Vertical Transport to the Thermosphere (pdf; paywalled)
(Score: 2) by JoeMerchant on Monday May 20 2019, @07:29PM
Hard to see how an influx of mostly water, even if hot from re-entry (and, how hot can the thin Martian atmosphere really heat a massive solid comet if it is deftly dropped by calculated orbit for a minimum heat before impact re-entry?) could net strip water from an atmosphere and surface so bereft of water in the first place. Is the implication that every meteor impact is stripping volatiles from the atmosphere, even if the meteor itself is comprised of mostly volatiles?
The ground impact will be hot, stuff will boil away, sure, but, again - shouldn't amount to a net loss, and the ambient global temperature means that the cloud that expands away from the impact crater will cool as it interacts with the thin, but present, atmosphere.
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