Author: Adam

A Moistened Moon

The Moon is ‘wet’.

That’s the latest conclusion of a trio of observations by various spacecraft over a decade (here, here, here, here.) The question is: just how wet? Not very, but a whole lot more than we once thought. A thin layer of water molecules coats the whole surface of the Moon, at least part of the day, and more may well be found towards the Lunar poles. The colder the surface, the longer it sticks, and it’s very, very cold in the permanently shadowed polar craters – down to just 35 K… colder than Pluto! There, it’s hoped, the water has ‘stuck around’ for billennia and slowly accumulated to substantial amounts.

So, the Moon has water. And there are signs of more within the Moon, evidenced by hydrated minerals around new craters. That really throws that cat in amongst the pigeons, as current Moon-formation models have the Moon condensing largely from vaporised rock after Theia smacked into the Earth. Robin Canup, Moon-maker extraordinaire, commented that the current modelling doesn’t have enough resolution to really tell if bits of the collision that became the Moon were cool enough or not for water to be retained.

Science-fiction, of course, has featured underground water on the Moon for over 100 years – H.G.Wells mentions seas within the Moon in his “First Men in the Moon” and Herge has Tintin discover ice in a cave, are two famous examples. “Moon Zero Two” – a daft movie from 1970 – also mentioned, in passing, that the Moon Colony got its water from hydrated minerals underground. A silly movie for a lot of reasons, but it had some redeeming features, including a portable computer (!) which was quite a leap for 1970.

Digressions aside, what does it mean for the development of the Moon? Water – especially its hydrogen component – features heavily in a lot of industrial chemistry as well as sustaining life-as-we-know-it. A slew of processes become easier when there’s available water. But it’ll need to be heavily recycled because of the difficulty of gathering together significant amounts of moon-water. Learning to do that might teach us some useful tricks down here on Earth too.

From Waterworld to Dune…

Earth will one day be much like Titan. Lakes near the poles, occasional flash-flooding nearer to the equator, but otherwise a planet girt by dunes.

Usually the analogy between Earth and Titan goes the other way – Titan is a frozen pre-biotic Earth. And, in many ways, it is. But it’s also drying out as its liquid phase is destroyed by the Sun’s rays. Methane photolyses, makes haze and heavier organicky junk, tholins. What might have been a planetary ocean – though we don’t really know yet – is now remnant lakes huddling around the poles.

And, according to Jonathan Lunine, that’s where Earth’s headed inexorably as the Sun brightens over the aeons…

Titan as an analog of Earth’s past and future

…in about a billion years the stratospheric cold-trap will fail, water will rise into the ozone layer, and UV will bust it up into oxygen and hydrogen. Once there’s enough of it, then the hydrogen will start blowing away, carrying the oceans with it.

This, apparently, happened on Venus, but with some important differences. Firstly, Venus was hotter from the beginning, and so the loss began very early in its geophysical evolution. Secondly, Venus seems to have had less water than Earth and more carbon dioxide. Thus it may never have formed the immense carbonate beds that have locked up Earth’s CO2. Instead it dried too quickly to bury that particular by-product of its volcanism and eventually it became the dry, lead-melting furnace we know today.

Earth, instead of broiling, may become increasingly parched. Dunes of wind-blown sand may replace the vast current-formed dunes on the sea-floor, but water may find refuge nearer the poles, persisting for perhaps the whole of the Sun’s Main Sequence. As we’ve discussed here earlier a desert planet can avoid a runaway greenhouse state up to 1.7 times the current insolation – even more if the atmosphere thins out and the pressure spreading of carbon dioxide’s IR spectrum is reduced. The Sun will leave the Main Sequence at about 1.85 times its present insolation… close to what will drive Earth to uninhabitability.

Percival Lowell thought Mars was a desert planet, criss-crossed by canals carrying melt-water from the poles. The real Mars is too cold, but the far future Earth won’t be. Lowell measured Mars’ surface pressure to be 85 millibars – oddly enough that’s the end figure for a thinned out Earth atmosphere resistant to greenhouse runaway. And, like Lowell’s Mars, the remaining refuge for water will be the poles. If inhabited, that desert Earth might be watered across its deserts via deep canals, with narrow strips of vegetation staying close to the water supply. After losing its oceans to space, Earth’s deserts will be heavily oxidised by the oxygen from photolysis, becoming rust-red like Mars.

Lowell had the wrong planet, some 5.5 billion years early.

From Dune to Waterworld: Part III

How does a water world stay wet when the Sun is too far away? We’ve looked at hydrogen/helium greenhouse effects – too much of a ‘good thing’ means the ocean is of super-critical steam not liquid water. But a planet without a Sun is a perfect candidate for a deep, dense atmosphere to keep its water wet. As James Kasting has pointed out, if it’s too cold then the hydrogen will condense and the atmosphere will collapse, so there has to be a decent heat-flow to keep the hydrogen gaseous, above about 33 K at the top of the atmosphere. Coincidentally that’s roughly Earth’s equilibrium temperature if we took away the Sun. But things were warmer in the past – the radioactive ‘glow’ of uranium, thorium & potassium-40 were about 6-10 times higher in the first half billion years of Earth’s youth. A planet unshackled from its Sun might keep such early warmth in and retain liquid water oceans, even in deep space, to this day.

But are there other heat sources? A low mass Brown Dwarf might burn deuterium for ~50 million years, then settle in to a slow decline as its heat is trickled away into space. Planets would form around such an object, but with a twist. Since the brown dwarf has a much lower mass & luminosity than the Sun its corresponding protoplanetary disk is smaller, denser and colder. Its planets form much closer to the parent body at Galilean moon style distances. This means inter-moon interactions & tidal forces become important, like the Galilean moons. Tidal energy powers extreme volcanism on Io and (probably) keeps an ocean warm beneath the ice of Europa – but the mutual interactions between the moons mean that their orbital eccentricity keeps getting “pumped up”, rather than dissipated away as heat once for all time.

With a heat source can Life form and persist on such worlds? We really don’t know, but some limitations do arise on what that Life might do in energetic terms. Animal life, as we know it, requires free oxygen at least at some point in the food-chain, but such doesn’t have to come from photosynthesis as we know it. Europa, for example, is an ocean encrusted in ice that is continually bombarded by high energy protons. This causes the dissociation of the ice and a slow build-up of oxygen trapped in it. With some kind of motion between surface and ocean, even via the slow burial of the ice by meteorite produced “regolith”, then there’s a supply of oxygen to the sea. Could it be sufficient to sustain animals? We won’t know until we go…

At the other end of the Solar System, where the Sun threatens runaway greenhouse effects, there are also unexpected prospects for Life. Present day Venus is very, very dry, but the deuterium-to-protium ratio in its clouds is much, much higher than the solar average, indicating the lighter hydrogen was lost to space. To achieve its present ratio there must have been a couple of hundred metres worth of water over the whole planet’s surface. Potentially more. As it was broken down by the Sun, oxygen would have accumulated before reacting with the surface rocks, potentially building up to high levels. Could hot, oxygenated oceans exist around planets of other stars to this day? With more water it’s possible that “ocean planets” could remain in a “wet greenhouse” state indefinitely, losing hydrogen to space, but with sufficient to remain wet for aeons. Such planets would be unimaginably hot from a terrestrial lifeforms point-of-view, but the potential of biology to adapt hasn’t been disproven. Some solvents, like foramide, have much higher temperature stability ranges than water, and thus may allow an alternative biochemistry.

Such wonders will remain theoretical to us if we remain in our star system. But do we need to launch probes to discover more, or is there an easier way? …Part IV

Classic Freeman Dyson papers online…

Freeman Dyson, for a Physicist without a PhD, has done some utterly cool and amazing things during his long career. One paper he wrote 41 years ago, based on his “Project Orion” experiences from 50 years ago, is this…

Interstellar Transport …watch out, as it’s an 18 Mb pdf. In the paper he introduces us to the fusion-bomb propelled starship, which is probably the best use of fusion bombs anyone has ever suggested. In the years since his design has served as a baseline for all further discussion, with newer versions merely tinkering with fusion ignition itself. Potentially a fusion-bomb starship can reach 0.1 c, thus making Alpha Centauri a 44 year one-way trip.

Another classic is his discussion of the very long term future of Life in the cosmos, albeit Life that has become very large “Black Cloud” style dispersed entities…

Time Without End

…he covers life into the mind-bogglingly remote period of 10^(10^76) years, which is an unimaginably large number, but not infinite. Yet even infinity might not be enough time to exhaust physical Life’s potential in his analysis. More recent cosmological speculation modifies his conclusions, but the certainty with which we can skein so far ahead is much less than often imagined.

More Dyson material is available online here and there throughout the Web, a select few at this webpage…

Dyson at Wisdom Portal

…which is a testimony to his appeal across ideologies. Infectious optimism.

From Dune to Waterworld: Part II

Fire and Ice, Venus and Mars, are just beyond the limits of the Habitable Zone in our solar system. How might worlds turn out differently, on the Outer Fringe….

Good question. People have noted before now that Mars and Venus seem to be in the wrong places – if Mars was in Venus’ orbit and Venus in Mars’ then they both might be habitable. Or at least able to have liquid water on their surfaces.

Would they? Venus has about 1000 tons of carbon dioxide sitting on every square metre of its terrain, much like an ocean worth of the stuff. If the planet cooled to its effective temperature, 235 K (-38oC), then the CO2 would become unstable against condensation. Its liquid range is between ~-79oC and 31oC at ~5 and 74 bars respectively. Thus it really would form an ocean if the planet was cool enough as Raymond Pierrehumbert points out…

Atmospheric collapse on Venus-like planets orbiting M-dwarfs

…thus the inspiration for this piece. Venus is, technically, an Ocean Planet already with an ocean of supercritical CO2 below the 74 bar pressure line and some enzymes will work quite happily in supercritical CO2. A cooler Venus, with a deep CO2 ocean, could conceivably host some form of life, albeit without the lipid bilayer cell walls terrestrial life employs, as they require polar solvents to form. Carbon dioxide is definitely non-polar.

What of oceans more like our own? A real Ocean Planet will probably form a Snowball beyond a certain distance from its Sun without some super-strength Greenhouse gases. Why so? The trick is to do with the albedo feedback mechanism – basically what happens is that a bit of snow forms sea-ice increasing the planet’s reflectivity (albedo), thus reducing the amount of heat reaching the sea, thus forming more sea-ice… and before you know it the whole sea is locked in ice right down to the equator. It happened to Earth several times during the late Proterozoic and would happen on any Earth-ish planet just a bit further out from the Sun. Without serious greenhouse gases that is.

Carbon dioxide isn’t bad, but it forms high albedo clouds of ice crystals when the planet is creeping out to ~1.3-1.4 AU. If such clouds covered a planet 100% then they’d be a fantastic greenhouse heat-trapping layer – Pierrehumbert’s early work on them gave Mars a toasty 25oC surface even when the Sun was at 70% of its current luminosity. Problem is they probably can’t give total coverage, thus reflecting away more than they can trap.

Methane is a better gas at trapping heat, but it has a limitation: the anti-Greenhouse effect. This is Titan’s problem – a world-girdling high-altitude haze layer of ‘polymerised’ methane by-products which stops the light/heat from getting to the ground. Simulation work by James Kasting et.al. shows that the haze kicks in when the CO2/CH4 concentration ratio approaches unity.

Ammonia is even better at trapping heat, but just doesn’t last under the UV bombardment from a G2 star. A cooler star, with a lower UV output, would allow the stuff to survive, but into red-dwarf territory there’s too much UV/x-rays from flares, at least around younger red-dwarfs.

So what to do? Surprisingly a decent greenhouse can be achieved with hydrogen/helium…

Ocean-bearing planets near the ice line: How far does the water’s edge go?

…in fact with more than 200 bar of H/He the surface is too hot for liquid water at all. The planet just doesn’t cool enough. So how do you get it cool enough?

Take away the Sun… Part III

We’re All Africans

African tribe populated rest of the world – Telegraph.

Simple really. We were all Africans some 60,000 years ago, then a tribe got a bit of wanderlust and left. More probably a corridor opened up along the coasts and we spread out. In Europe we encountered Homo neanderthalensis, in Java we met Asian Homo erectus and on Flores, the Hobbits Homo floresiensis. Did we kill them? Trade with them? Give them flu? Or out-compete them for a common resource? By c.30-25,000 years ago it was just Homo sapiens and the Hobbits… are they still around like old Indonesia legends say? Or was the eruption on Flores c. 12,000 bp their Waterloo?

Theory of Brown Dwarfs and their kin

[astro-ph/0006383] Theory of Low-Mass Stars and Substellar Objects.

Excellent paper on Brown dwarfs with model figures on radius, temperature and luminosity, plus different spectral band strengths, for a number of ages of the model brown dwarfs. In otherwords a major resource for a whole range of papers that have followed in the 9 years since.

Monoliths of Mars

I personally hope that one of our many probes to the planets will turn up an anomaly that can’t be explained as a natural formation. The weird thing in Saturn’s rings, the white spot of Venus and rectangular craters on the Moon are pretty odd, but not overly compelling – the scale is too vast or our resolution is too poor. Yet the Monoliths of Mars (and Phobos) are kind of cool…

Triad of Monoliths on Mars

Buzz Aldrin discusses the Phobos Monolith

…I think Buzz is pretty sure the Phobos ‘object’ is just a boulder BUT that’s not the point. Doesn’t matter how good our resolution gets, we just won’t know what these things are until we can go look for ourselves… and that’s reason enough to get to the planets! Because we don’t know/can’t know what we’ll find in person.

And I think getting there is getting easier all the time. We don’t need nukes necessarily either. Ultra-light photovoltaic arrays are being developed which can supply in-space electrical power at 10 kWe/kg. RTGs struggle to get 10-20 W/kg and solid-core nuclear reactors struggle to get ~0.1-0.5 kWe/kg, so those space-rated ultra-light PVs are a step ahead. We just need a decent rocket to attach them too, and as I have discussed here a few posts ago VASIMR is the right rocket for the job.

But there’s another point in favour of such systems IMHO… they provide a LOT of power even when you’re not flying between the planets. Megawatts of power on Phobos can power space refuelling systems, extracting water from the rocks and electrolysing it for LH2/LOX propellant. Then a Mars lander can be fuelled AT Mars, so we don’t have to cart the stuff all the way from Earth (and watch 20% boil-off en route.) A Mars lander can then land on FULL rocket thrust after a bit of aerobraking and NOT stack like just about every other landing scenario yet studied.

Down from the Trees NOT Up from the Ground

Humans are the only habitually bipedal apes on the ground. However their ancestors and close kin show signs of adaptations to bipedalism going right back to a certain ape from 20 million years ago, Morotopithecus, as illuminated for us by Dr. Aaron Filler in his book The Upright Ape. One niggling contraindication to this theory is the presence of knuckle-walking in gorillas and chimps, our closest living relatives with whom we share a Last Common Ancestor. However the specific adaptations for knuckle-walking don’t appear in any of our fossil ancestors and now a new study has produced evidence that the adaptations in gorillas and chimps are distinct and likely to have evolved independently…

Upright Gait May Have Roots in the Trees

Bipedal humans came down from the trees, not up from the ground

Eureka-Alert on the new study

…so one particular objection to Filler’s theory has been removed. But is he right? And why did one particular line of arboreal bipeds walk on two-feet on the ground instead of knuckle-walking like their close kin?

Nukes to LEO

The old Delta Clipper concept was a very cool outcome from the old SDIO, but NASA and its cronies killed it, either through false promises of “something better” (remember “VentureStar”?) or neglect. However not everyone has forgotten DC-X’s potential and Eric Davies has even proposed an upgrade to nuclear…

Nuclear DC-X

… not a pure NTR but an LOX Augmented NTR (LANTR) to have sufficient thrust-to-mass to get into orbit. According to the sources behind the original study (a 2004 review by Eric Davis) NTRs have been operated without any radionuclides entering the exhaust stream, so it should be “safe” within the atmosphere. Aside from prompt X-ray and neutron radiation from an operating reactor, that is, neither of which is lasting. We surround launching chemical rockets with a necessary danger zone and an NTR would be no different. Probably not even significantly larger either since the thing wouldn’t explode as mightily as an Ares V or a Shuttle in the worst case scenario. Plus a reactor core designed to run at 3000 K and 100 ATM is going to be a tough mofo to start with.

The proposed NTR is a centrifuged particle bed reactor, based on the “Timberwind” system studied by the SDIO. That, of course, made the Greens and NoNukers shit kittens when originally proposed, but I suspect the political mood is more receptive now to nuke-power than it has ever been, especially if people see more civilian action and more noises about nuclear disarmament. Lobbing Solar Power Satellite components to orbit 100 tons at a time should make an LANTR attractive to any right thinking Green – like yours truly – because the overall fossil fuel cost is reduced significantly.

Once enough installed beamed-power is available to launch Leik Myrabo’s Lightships then the LANTR can be moved permanently off-world, where it really should be. But until then it’s one solution we should examine while trying to reduce the cost to LEO.

Hat-tip to Brian Wang for spotting this one… Nuclear DC-X