When It Rains On Mars

It’s been raining in Brisbane this week, but does it rain on Mars? Is it raining on Mars right now?


Things on the Red Planet are a little different. Here’s some background.


Mars has around one third of Earth’s gravity, around one hundredth of Earth’s atmospheric pressure, and its atmosphere is almost entirely composed of carbon dioxide. So far we have not found any trace of water. There is ice at the poles, but it’s dry ice – frozen carbon dioxide.

That hasn’t always been the case. The various Mars probes, orbital surveyors and buggies that are still roaming about the terrain have not found any water, but they have found ample evidence that water existed on Mars in the past. There are plenty of geological features on Mars that are consistent with the movement of large bodies of water, and secondary rocks that have been observed that are almost certain to have formed inside ancient lakes. It seems certain that our smaller solar system neighbour had a Warm Wet past.

So where is all that water now?

Very early in its history, things on Mars may have been very similar to conditions on nascent Earth, but striking differences between the two planets led to major changes.

For a start, Mars lacked the powerful magnetic field that could shunt away the effects of the solar wind. Like our other neighbour Venus, which also lacks a strong magnetic field, that means that lighter molecules are knocked right out of its atmosphere. Carbon dioxide is more than twice as heavy as water. The molecular weight of CO2 is 44, while H2O is 18. That means a lighter grip on the molecule by Mars’ already lower gravity. So Mars’ early water has likely to have been irrevocably lost to space.

So it does not rain on Mars, we can be sure of that, but do we want it to?

I think the answer to that question should be a resounding “Yes!”

We live on a small, single planet in a vast, unwelcoming universe. Our planet-evolved bodies just don’t do too well in space. Even trying to orbit the planet in a tiny capsule a few kilometre above our heads is problematic. We have to take all our food and water. There is exposure to harsh radiation, and the threat of cold as heat radiates away into space. The lack of gravity itself is a major threat to our health. We just weren’t built for space, but that’s fine because we have Earth, right?

Well, there might have been an intelligent dinosaur that thought the same thing as it watched a 100 mile wide asteroid plunge into South America 65 million years ago, sending the Earth into a decades-long winter that saw most life die.

That was not the only mass extinction that Earth has experienced. There have been many. Life survived, sure, but every time it was knocked orders of magnitude back down the ladder of complexity. Sentience requires stability. Shelter.

If humanity wants to protect the precious flame of its civilisation, we need to look outward.

The astronomical programs looking to other solar systems are geared to finding Earth analogues. Other Earth-sized planets with similar gravity, with water, and that are the right distance from their suns for life. But its going to be a long, long time before we have the technology to cross the vast distances of space to these new places. Think about this – at the same velocity as the Voyager 1 probe it would take an astronaut 70,000 years just to get to our closest star, which is only 4 lightyears away.

So what do we do?

We can terraform. We take a planet like Mars and make it habitable for humans. We can thicken the atmosphere, releasing chemicals with high global warming potential that heat the atmosphere. We can add water and oxygen by diverting asteroids with these resources and crashing them into Mars’ surface. Maybe we could even do some genetic tampering to help the new crop of Mars humans cope with the lower gravity.

So when will it rain on Mars?

I hope it wont’ be too long, because when rains on Mars humanity will have taken its next, great step into the future, ensuring its survival.

Need Dry Ice? Try Mars.

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A new study on the Red Planet suggests that the sharply etched channels that crisscross its surface may have been cut by frozen CO2, rather than water.

The contention is that these gullies are very much active, and continue to form on Mars even now in cold weather. If that’s the case, than it is almost certainly ‘dry ice’ or frozen CO2 that is developing this geological feature.

Recent photographs captured by the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter, have enable a new look at the phenomenon, allowing researchers such as lead author Colin Dundas to examine the timing of gully formation over the last couple of years.


The conclusion was that the gully formation is occurring in winter, when the Martian atmosphere is condensing out as a solid. Unlike Earth, where the temperature and pressure conditions for the formation of dry ice does not occur in nature, on Mars they occur every winter, most notably in the form of a seasonal polar ice cap.

As many as 38 sites have now been identified as showing active gully formation. All at times when it would be too cold for liquid water to flow.

So if your heading out the Red Planet – don’t forget the Beer Cooler. The dry ice is free :).


Juggling Molecules on Mars

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Here is a little bit of Chemical Engineering in Space.

So much of what we come into contact with is made of four elements – carbon, hydrogen, oxygen and nitrogen – the main elements of living systems. Add phosphorous and sulphur and you have what comprises 98% of all living systems.

The chemistry for juggling these four atoms – C, H, O, N – has been around for a long time.

Engineers and scientists have been confident enough in the chemistry and the various ways of manipulating them to propose various sets of reactions for use in gathering resources out in the vast reaches of space, as part of human exploration. This is part of a wider field of study called In Situ Resource Utilisation (ISRU), which has formed a key part of plans to explore other part of the solar system, particularly Mars, for the better part of two decades.

In the Mars Direct concept Robert Zubrin proposed using the well known Sabatier reaction:

CO2 + 4H2 => CH4 + 2 H2O

To react hydrogen with the Martian atmosphere to produce methane and water – very useful things to have on the red planet. The methane would be stored and kept for use as rocket fuel.

Methane and oxygen are a handy combination. In terms of chemical rocket propellant candidates, the Specific Impulse (Isp) of Methane and Oxygen at 3700 m/s is second only to Hydrogen and Oxygen at 4500 m/s (to convert to seconds of impulse multiply by 0.102).

Meanwhile the water from the Sabatier reaction would be split via very familiar electrolysis reaction:

2 H2O => 2H2 + O2

The idea was that only the hydrogen would need to be transported to the Red Plant. H2 weighs a lot less than CH4, freeing up space and payload for the 6 months transit to Mars.

Various test rigs were constructed on Earth, using analogues of the Martian atmosphere, which has been well characteristed since Viking. Mars has a lot of CO2 – more than 95% of the atmosphere – and a nice analogue of the Martion atmosphere right down to the low pressure could be similated for the rig. The CO2 is initially absorbed onto zeolite (an ever popular sorbent) under conditions simulating the Martian night. During the Martian ‘day’ the CO2 desorbs and passes into the Sabatier reaction vessel with the H2, which is heated to 300C. Reaction then occurs in the presence of the right catalyst (in this case pebbles of ruthenium on alumina). The water from the reaction is condensed out and passed to the electrolysis unit.

Still awake?

OK. Not surprisingly scientists and engineers planning Mars missions were concerned about overly complex systems forming such major part of a critical path.
Current plans for ISRU on Mars revolve around direct dissociation of the Martian atmosphere i.e.

2 CO2 => 2 CO + O2

[BTW if you could pull off this reaction at room temperature on Earth you would be an instant billionaire]

The current Mars Design Reference Mission proposes the production of oxygen on Mars through direct dissociation. Methane will be transported directly from Earth, with the ascent vehicle still using the tasty combination of methane and oxygen in its rocket engines.

So how is the CO2 pulled apart? There are many contenders, all of which uses a lot of energy. On Mars that energy is currently planned to be delivered by a 30 kW fission power system.

The front-runner for CO2 dissociation is thermal decomposition, followed by isolation of the O2 using a zirconia electrolytic membrane at high temperatures.

This system was developed for its first flight demonstration as the Oxygen Generator Subsystem (OGS) on the defunct Mars Surveyor Lander, which would have been launched in 2001 (but was cancelled following a string of Mars mission failures – Mars Climate Orbiter (1999), Mars Polar Lander (1999), Deep Space 2 Probes 2 (1999). That was a bad year. ).

The OGS was to demonstrate the production of oxygen from the Martian atmosphere using the zirconia solid-oxide oxygen generator hardware. This unit was designed to electrolyze CO2 at 750C (1382 F). The Yttria Stabilized zirconia material – once a voltage is applied across it – acts as a oxygen pump allowing the O2 to pass through it and be collected. The plan was to run the unit about ten times on the surface.

As I mentioned there were various contenders for the process. Such as molten carbonate cells, which operate around 550C with platinum electrodes immersed in a bulk reservoir of molten carbonate. Personally, the engineer in me shudders at the thought of trying to manage any sort of molten system that remotely.

The final system for CO2 decomposition used on Mars is probably still a work in progress. It will be interesting to see what develops there.

The fact is the initially proposed Sabatier reactions did not produce enough O2 to react with the methane, so some form of CO2 splitting process was still required.
So there are some things we can do to juggle molecules when we get to Mars.

Is everyone out there looking forward to getting to the Red Planet and grappling with what we find there?