Water supersaturation in the Martian atmosphere discovered

September 29, 2011, European Space Agency
Artist's impression of the Mars Express spacecraft in orbit. Image: ESA- Illustration by Medialab

(PhysOrg.com) -- New analysis of data sent back by the SPICAM spectrometer on board ESA's Mars Express spacecraft has revealed for the first time that the planet's atmosphere is supersaturated with water vapour. This surprising discovery has major implications for understanding the Martian water cycle and the historical evolution of the atmosphere.

Although numerous spacecraft have visited Mars over the past half a century, very few direct measurements of the vertical structure of the planet's atmosphere have been made. Since most of the spacecraft instruments have looked down at the surface, it has only been possible to infer the horizontal distribution of gases in the atmosphere, leaving the question of how water vapour is being mixed into the atmosphere almost unexplored.

This lack of direct measurements has meant that descriptions of the vertical distribution of water vapour – a key factor in the study of Mars' hydrological cycle – has generally been based upon global climate models.

This gap in the data has now been addressed by the SPICAM (Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars) imaging on .

The instrument can be used in occultation mode, when it studies light from the Sun that has passed through the planet's atmosphere just after sunrise or before sunset. The measurements can then be analysed to generate vertical concentration profiles for several atmospheric constituents, including water vapour.

Surprising new results, based on SPICAM data obtained during the northern spring and summer, indicate that the vertical distribution of water vapour in the is very different from previous assumptions.

Writing in this week's issue of the journal Science, an international team led by Luca Maltagliati of the Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS) in Guyancourt, France, describe SPICAM observations at infrared wavelengths that for the first time provide evidence for the existence of supersaturated water vapour on Mars.

Supersaturation 

The atmosphere of Mars holds 10 000 times less water vapour than that of Earth. However, water vapour is a very dynamic trace gas, and one of the most seasonally variable atmospheric constituents on Mars.

Under normal conditions on Earth, water vapour condenses around tiny dust or aerosol particles or salts when the atmospheric temperature drops below a certain "dew point". The atmosphere is then said to be "saturated", since it cannot hold any more moisture at that temperature and pressure. Any water vapour in excess of the "dew point" will normally condense to form droplets or icy crystals.

However, supersaturation may occur when some of the water vapour remains in the atmosphere, instead of condensing or freezing. When condensation nuclei (assumed to be dust aerosols on Mars) are too rare, condensation is impeded, leaving substantial amounts of excess vapour.

Water supersaturation in the Martian atmosphere discovered
Transport of water vapour in the Martian atmosphere. Image: ESA/AOES Medialab

Until now, it was generally assumed that such supersaturation cannot exist in the cold Martian atmosphere: any water vapour in excess of saturation was expected to be converted immediately into ice. However, the SPICAM data have revealed that supersaturation occurs frequently in the middle atmosphere – at altitudes of up to 50 km above the surface – during the aphelion season, the period when Mars is near its farthest point from the Sun.

Extremely high levels of supersaturation were found on , up to 10 times greater than those found on Earth. Clearly, there is much more water vapour in the upper Martian atmosphere than anyone ever imagined. It seems that previous models have greatly underestimated the quantities of water vapour at heights of 20–50 km, with as much as 10 to 100 times more water than expected at this altitude.

"The vertical distribution of water vapour is a key factor in the study of Mars' hydrological cycle, and the old paradigm that it is mainly controlled by saturation physics now needs to be revised," said Luca Maltagliati. "Our finding has major implications for understanding the planet's global climate and the transport of water from one hemisphere to the other."

"The data suggest that much more is being carried high enough in the atmosphere to be affected by photodissociation," added Franck Montmessin, also from LATMOS, who is the Principal Investigator for SPICAM and a co-author of the paper.

"Solar radiation can split the water molecules into oxygen and hydrogen atoms, which can then escape into space. This has implications for the rate at which has been lost from the planet and for the long-term evolution of the Martian surface and atmosphere."

The new paper analyses SPICAM data obtained when the Martian atmosphere is relatively dust-free. The absence of dust enables the instrument to measure the vertical profile to within 10 km of the planet's surface. The supersaturation levels are likely to plummet in the southern summer, when dust storms inject large amounts of aerosols into the , increasing the supply of condensation nuclei.

Explore further: A New Clue to the Hypothesis of Life on Mars

More information: "Evidence of Water Vapor in Excess of Saturation in the Atmosphere of Mars", by L. Maltagliati, F. Montmessin, A. Fedorova, O. Korablev, F. Forget, and J.-L. Bertaux, published in the 30 September 2011 issue of Science. www.sciencemag.org/content/333/6051/1868.abstract

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16 comments

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Isaacsname
4.7 / 5 (6) Sep 29, 2011
" This has implications for the rate at which water has been lost from the planet and for the long-term evolution of the Martian surface and atmosphere."

Or terraforming.

El_Nose
1 / 5 (3) Sep 29, 2011
terraforming ??? dude the palnet doesn't have a magnetosphere, solar wind has been stripping the atmosphere because of this lack. If this is terraforming - humans need to wake up , because that means some alien civ has the power to make our core stop rotating.

This is not terraforming
that_guy
5 / 5 (6) Sep 29, 2011
I remember when they detected a little snow at one of the landers a few years back.

I think this study lends evidence to the wetter models of martian past, rather than the 'drier' models that are coming out. If mars is still able to lose significant amounts (SIC) water through photodissociation, then that means that it likely had similarly more water to start with.

I'd like to point to el nose and isaac that

1. the photodissociative effect is rather slow, and would have negligable affect compared to terraforming over a few hundred or thousand years. If we had the ability to terraform mars, then we would also have the ability to maintain it.

2. The lack of a magnetosphere would have to be dealt with - likely thicker than Earth's, and tailored to help to block radiation from reaching the surface.

3. I'm not sure if Isaac meant good implications, but this has no significant terraforming implications compared to what we already knew.
Isaacsname
5 / 5 (1) Sep 29, 2011
What I meant is that it gives us a better idea of what the hydrologic cycles on Mars are like, which is only logically a small piece of the puzzle in regards to any possible terraforming in the future. If the loss due to photodissociation is significantly slow, wouldn't this just improve the chance at gradually altering the atmosphere ?
that_guy
5 / 5 (1) Sep 29, 2011
What I meant is that it gives us a better idea of what the hydrologic cycles on Mars are like, which is only logically a small piece of the puzzle in regards to any possible terraforming in the future. If the loss due to photodissociation is significantly slow, wouldn't this just improve the chance at gradually altering the atmosphere ?


Basically, the only new information was that there is a substantial amount of moisture in the air at times, under the current conditions. Everything else explained here, like the photodissociation rate and loss, is already relatively well known.

We are already well aware that terraforming would require us to massively change the hydrological cycle, atmosphere, etc. We have already known that over time periods that we would work at, that the loss of Oxygen, Hydrogen, etc. is insignificant over human lifetimes.
GSwift7
3.4 / 5 (5) Sep 30, 2011
You guys would probably love the books in the Mars trilogy by Kim Stanley Robinson. They are a little bit outdated now, but if you give them a read, you'll probably be amazed about how much he actually guessed right, but did not know for sure at the time.

One good idea he used was constructing human dwellings inside the lava tubes of Mars, to provide shelter from radiation. Another idea that I thought was clever was using a space-based mirror/lense to focus sunlight at the surface and vaporize rock as a method of thickening the atmosphere. It would still be poisonous air, but at least low pressure wouldn't be as much of a problem. As it stands now, humans would want to wear a hard suit with climate control, but no existing suit would work because they are too heavy for work on Mars. There's also too much gravity on Mars to use the hopping trick they used on the Moon, so a more flexible suit would also be needed. There are a ton of engineering barriers before humans can be martians.
that_guy
5 / 5 (1) Sep 30, 2011
@piroutte - Most of what you said has been covered or assumed already. I do however want to make some corrections to your line of thought.
1. The MS on earth primarily blocks cosmic rays/charged particles - It does very little to directly affect em radiation. The atmosphere primarily blocks the UV/EM radiation.
2. Venus has little or no MS, yet very little radiation reaches the surface...I have already touched on the fact that mars would need more atmosphere than earth...
3. Mars requires significantly less protection due to inverse square of distance.
4. Partial terraforming can be done at higher radiation with microbes that are hardier with more radiation.

So Terraforming is in no way out of the question, although it will not come any time soon given the amount of work and technology needed.

You're describing the steps we would take currently to colonize mars, instead of terraforming, which is far down the line.
HealingMindN
not rated yet Sep 30, 2011
Either Quaid started the reactor - or - that vapor has always been there, just like the flora. They just happen to be more noticeable now.
that_guy
5 / 5 (1) Sep 30, 2011
High energy EM radiation tends to be hard to harvest, due to the energy it imparts to individual atoms. It can break apart molecules (Photodissociative affect). Photosynthesis is a molecule based chemical reaction. If the molecule is broken at random spots when it absorbs a photon, that makes it difficult to use reliably. That's why hard UV/x-rays/gamma rays are so bad to life.

It is impractical to harvest energy from those photons. In addition, life on earth is adapted to absorb energy from the soft uv and upper infrared spectrum. You would need to engineer a new biological mechanism from scratch to go above that.

I do agree that we'll want to adapt life to conditions on mars, but first we'll want to hurl some comets/etc to mars, to help adapt it to our view of life. The terraforming is essentially to make it easier for us to exist on it easily after all.
tysoncable
5 / 5 (1) Oct 01, 2011
@pirouette. life on mars? are you serious? if you have evidence of it then you're holding a piece of evidence that the rest of the world has been waiting for since time immortal. can you elaborate on what you mean exactly.

Nanobanano
1 / 5 (2) Oct 01, 2011
That_Guy:

True Terraforming is too expensive and too inefficient with any remotely proposed technology.

Water and air SHOULD be imported to the planet via use of comets, however, you don't need enough to make an earth-like atmosphere for the entire planet. You just need enough to use in fully contained, sealed habitats.

If figure Mars could support a couple hundred million humans, and a complete biosphere, and an "American" standard of living by the time it was fully developed.

Probably the biggest near-term obstacle to colonization is that nobody knows anything about the viable resources on Mars in terms of construction and mining. There is no wood, obviously, so we're talking complete reliance on metals for all construction.

Just prospecting for resources might take decades or centuries, unless you had automated, self assembling robots to help in the process. Look how long it took humans to find and use resources on earth...thousands and thousands of years...
Humpty
1 / 5 (2) Oct 03, 2011
We could send a ship to the core of Marrs and drop some nukes around it to restart it spinning.
Torbjorn_Larsson_OM
5 / 5 (2) Oct 03, 2011
"the palnet doesn't have a magnetosphere, solar wind has been stripping the atmosphere because of this lack."

["Atmospheric escape", Wikipedia:] "The relative importance of each loss process is a function of planet mass, atmosphere composition, and distance from a star. A common erroneous belief is that the primary non-thermal escape mechanism is atmospheric stripping by a solar wind in the absence of a magnetosphere. [...] Recent models indicate that stripping by solar wind accounts for less than 1/3 of total non-thermal loss processes.[2]"

In other words, this idea is (rather new) folk physics. But there was never any clear evidence of the importance of the magnetic field, just untested hypotheses.
yyz
5 / 5 (1) Oct 03, 2011
@Torbjorn[OM],

Hi, I post as JonHanford over at UT and look forward to your erudite posts there (...and now here)! ;-)

Thanks for the elucidation of the (new) role of magnetospheres in retaining planetary atmospheres. I see a lot of misunderstanding of it's role in such matters, such as the one you quoted.

that_guy
1 / 5 (1) Oct 03, 2011
@nanobanano

I mostly agree. Terraforming of any kind will definitely be a long and difficult process. Initial terraforming activities would almost definitely be partial or contained.
kaasinees
1.2 / 5 (6) Oct 05, 2011
The big question if there was liquid water in Mars past. And if so what happened to it? There is argumentation about the marks on Mars surface, could also have been created by lava. I think its likely that there was liquid water though. But as we look at it now i believe Titan has a higher chance of hosting Life than mars in the present.

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