This from the news today:
however:
So where did it all go?
Some of it may have gone underground, some is bound up in hydrated minerals or frozen in the polar icecaps, and the rest probably evaporated into space over hundreds of millions of years.
The “V” lizard-people stole the oceans…
Expanding on what Q.E.D. said, most of the water was probably dissociated into hydrogen and oxygen by ultraviolet light. The hydrogen would easily escape into space in Mars’ light gravity, and the oxygen would partially combine with rocks and partially escape. The rest of the water is most likely locked up in the soil as permafrost.
The same place as the oceans on Earth did millions of years ago. They literally evaporated into space. With Mars’ weaker gravity, it took even less time despite the chill.
“Hey FtG, whadda call those big wet things all over the planet?” Umm, those are recent oceans. Earth’s oceans are constantly being renewed by vulcanism (and possibly by comets<- big debate). Mars hasn’t had much vulcanism in recent years.
However, that left Mars very salty and salt deposits on the surface bind up lots of free water whenever they can. Salt pans in the middle of the driest deserts still have quite a bit of water in them.
So there is still a heckuva lot of water on Mars. Just very, very salty.
Mars lost most of its magnetic field about 4 billion years ago. Without a magnetic field to divert the solar wind, ions (such as UV ionized water) are efficiently stripped from the upper martian atmosphere: The Solar Wind at Mars
Are UV photons sufficiently energetic to dissociate water molecules? I’m fairly certain they aren’t.
Thanks everyone for your responses. Apparently there is not complete agreement as to where the water went .
Squink thanks for the very interesting and largely non-technical link giving a description for people who, like me are complete ingnoramuses on this subject.
I was particularly interested in this statement:
Is this a widely held view amongst those knowledgeable in that area? As a corollary of that statement, are any attempts to terraform Mars also doomed?
Furthermore: are there are any theories as to why the Martian magnetosphere stopped working (beyond the immediate causes listed in the article)?
ftg At what rate does vulcanism replace earth’s water? Do you know of any sites where I can find out more about this?
It’s possible that I’m wrong here, but I’ve seen this stated in quite a few different science articles over the years. Maybe only the near x-ray ones can…this paper mentions that “Water vapor photolysis in the lower atmosphere produces H” on page 9. It doesn’t say what frequency of light is needed though.
It goes on to explain that this process is slow and probably only accounts for about enough water loss to cover Mars with 2.5 meters of water over the lifetime of the planet. Seems the biggest factors are Mars’ low initial supply, and low gravity allowing what it did have to escape during meteor bombardments.
I might as well post this essay here, although I see Thaumaturge has posted a link to Catling’s article, which was my main source; I am primarily interested in the chances of retreival of the Martian water and terraforming our neighboring world, and the announcement of the recent evidence for water on Mars encouranges my belief that a water-rich Mars could be possible.
Mars formed from the material in the solar nebula and reached its present size by 4.6 billion years ago (gigayears ago; Gya) ; the amount of water on the early planet is unknown, but there are two main options; either Mars had a similar amount of primeval water to the Earth, or it may have had somewhat less; much of the early waterin this region had become bound into bodies known as planetary embryos, and if Mars encountered fewer of these objects it may have started out significantly drier.
The evidence from Spirit and Opportunity seems to indicate that water was relatively plentiful in the early period, so we now have to consider where this water has gone.
The first age of Martian history, from 4.6 Gya to 3.8 Gya has been labelled the Noachian period; the atmosphere, mostly CO2 and nitrogen was perhaps six times as thick as that on Earth today. Liquid water was possible in these conditions, despite the fact that the early Sun was as much as 30% less bright. So there may have been seas, and there are many water-associated features in Noachian period terrain. The core of Mars was still hot enough for a magnetic field at that time, so the effects of solar wind and hard UV on the atmosphere were lessened.
However there were many impacts during the Noachian; 200+ craters larger than 5km per million km^2; this was one reason for atmosphere (and water) loss- impact erosion.
Because of Mars’ lower gravity, the effect of large impacts was to expel volatiles into outer space; the fraction that exceeded escape velocity never returned. (This will have to be accounted for in any terraforming project which involves volatiles crash-landing on Mars- if the impacts are too energetic, the volatiles will escape to a greater or lesser extent).
A second mechanism for Martian atmosphere loss was hydrodynamic escape; the early planet still contained a lot of the primeval hydrogen from the solar nebula; this will have been expelled by volcanic outgassing as it rose through the semimolten interior; a lot of hydrogen in the atmosphere would make it less dense, so the whole atmosphere would swell, and gases of all kinds would be driven off at the top of the swollen atmosphere; another way of looking at it is that hydrogen quickly boils off, but drags some of the other atmospheric components with it.
By the end of the Noachian, when impacts became less frequent and the magnetic field disappeared as the core cooled down, the atmosphere was down from 6 atmospheres to 0.06 atmospheres; liquid water would no longer have been possible.
Now the magnetic field had gone, the solar wind could rip away at the top of the atmosphere; this very variable effect is sometimes known as sputtering.
Additionally the hard UV from the early Sun (although the sun was less bright, it was smaller and hotter- so more UV) could strip water in the atmosphere into oxygen and hydrogen by photolysis; the hydrogen would escape, dragging other gases with it; the oxygen would combine readily with the rocks of Mars, forming sulphates, haematite, perhaps carbonates.
By these processes, impact erosion, hydrodynamic loss, sputtering and photolysis, the atmosphere of Mars eventually reached its current level of 0.006 x Earth’s. However the water loss will have been drastically reduced once the atmosphere was no longer thick enough to produce a greenhouse effect; when it got too cold the water will have turned to ice, which is much less volatile. In fact is is quite possible that much of Mars’ water is still there; as ice it would be incorporated into the rock as part of the solid matrix, or far underground as liquid water; the surface is freeze dried, and evidently very salty, though chorine seems to be scarce- the salts are mostly sulphates… but the loss of water to surface sinks seems to have been a major mechanism of water loss from the surface. One estimate says that half of the water left at the end of the Noachian is still there.
In other words, much of the water may still be there, buried deeply. During the later Martian periods, the Hesperian and Amazonian, it seems that combinations of orbital cycles and axial tilt have periodically brought liquid water to the surface; it may be possible to achieve this by artificial means, particularly using positive feedback mechanisms, and bring Martian water to the surface again.
The H-O bond enthalpy is about 460 kJ/mol, which works out to a photon wavelength of about 250nm, in the UV.