01 December, 2005

More probing

Typical, really; no sooner do I put up this post about how we're going to have to wait a bit before Mars Express starts searching for water, than ESA goes and announces that it's found some.

Well, maybe. What they have found is a buried impact crater beneath the surface of Chryse Planitia, a fairly flat area in the northern equatorial region of Mars (it's in the centre of the map here).

These data are from some of the very first observations made by the MARSIS radar, when it was still approaching close to the planet at night. The image below shows the results of two different passes, separated by about 50 km, over the same region in Chryse Planitia. Note that the vertical axis does not measure depth but time: it is measuring the delay between the radar pulse being sent out and reflected radio waves being recieved back at the source (so the further down the screen it is, the more time has elapsed).

When the radar pulse encounters a boundary between substances with different physical properties, some of its energy is reflected back up to the orbiter; these boundaries show up as bright finges on the plot above. The first reflector is obviously the surface (which reflects a lot of energy due to the large contrast between Martian air and Martian rock) but some energy is clearly making into the subsurface. In both plots you can see a number of curved reflectors; these could represent a series of impact basins, although they look a little to me like multiple reflections (where upward reflected energy bounces around between the buried reflector and the surface one or more times before escaping). There is no sign of this structure on the surface, so it has clearly been filled with rock debris since it formed.

What's causing the excitement is the horizontal reflecting horizon seen in the second profile (at about 25 microseconds, which is about 2km, below the surface). One possibility is that this represents the upper boundary of a layer of water- or ice-rich material filling in the bottom of the crater. It's not the only possibility, but it does make some sense: Chryse Planitia is a relatively low area at the bottom end of a number of outflow channels, including those from Valles Marineris, which show evidence of water erosion.

So, interesting, but not conclusive, perhaps. Still, it bodes well for the future. I like this quote from New Scientist:

The most exciting part of this experiment is simply "that it works", says MARSIS co-leader Jeff Plaut of NASA's Jet Propulsion Laboratory in Pasadena, California, US.

It seems that no-one was sure if this thing would actually work. Interesting how that only comes out now that they've seen it does...

30 November, 2005

Lava lake tectonics

Part of the duties of my new job is some lecturing on behalf of my supervisor (now boss, I suppose). I'm finding this a bit daunting, even if I have been given Powerpoint presentations for each lecture; this means at least I don't have to compile things from scratch, although it does take a while to remove all the instances of text zooming in with a swooshing sound (another crime against humanity perpetrated by Microsoft).

My first lecture started with a discussion of why we have tectonic plates, and I got to present a really cool example of a situation where similar processes are occurring over timescales much easier for us to grasp conceptually. All the pictures in this post come from a lava lake in the crater of Erte Arle volcano in Ethiopia. You get lots of the sorts of activity you’d associate with such an environment (such as fountain eruptions and bubbling molten lava), all occurring as the lava is heated from below and the hotter, less dense, material forces its way to the surface. However, what's even more interesting is that a lot of the time the surface of the lake is formed by a solid crust of cooled magma. Vigorous convection is still occurring beneath this crust, and in response to this the crust breaks up into a number of discrete slabs.

Sound familiar? The relationship between the lava crust and the convecting molten lava beneath it is precisely the same as that between the lithosphere and the asthenosphere - the convecting and non-convecting parts of the Earth's mantle. In both cases the boundary is controlled not by composition but by temperature - contact with the air has cooled the upper part of the lava lake so that it solidifies and begins to act rigidly; heat loss through the Earth's surface causes the same thing to happen to the upper 100 km or so of the mantle.

The internal strength of the lava 'plates' compared to the molten material beneath them causes them to move coherently over the surface of the crater, with little frictional drag at their base to slow them down, or dissipate any forces which are applied to them. In such a situation the forces exerted at the boundaries of the slabs become particularly important. Again, the same situation seems to apply for the tectonic plates on the Earth's surface, so it is no surprise that you can see analogues of different types of tectonic plate boundaries at the borders of the lava slabs. Here's a rift zone, where two slabs are moving apart:

The orange crack shows where lava is welling up to the surface of the lake. It cools and solidifies and is itself pushed away from the rift by yet more upwelling magma. Notice the symmetrical pattern of light and dark grey bands moving away from the crack - this is caused by slight variations in the composition of the upwelling magma over time (and is very reminiscent of the striped magnetic anomalies seen either side of a mid-ocean ridge).

The force pushing the slabs apart at this boundary will be transmitted to the opposite boundaries of the two slabs, where they will be pushed against their neighbours. In such a situation one plate is forced beneath the other, forming a 'subduction zone' (in the picture below, the lava slab is being pushed against the crater wall, but the principle remains the the same):

The best thing about this example, though, is that molten lava has a much lower viscosity than asthenospheric mantle, flowing at centimetres per second rather than centimetres per year. This means that you can see the equivalent of hundreds of millions of years of tectonic processes occurring in the space of a few hours. This movie (Quicktime) was created using time-lapse photography: as evening draws in, plates on the surface of the lava lake are created and die, move apart and push together. It's really cool. Watch it.

Probe update

Not as dodgy as it sounds, I promise!

  • Following a successful launch, ESA scientists have begun checking out the instruments on the Venus Express probe, by pointing them back at the Earth-Moon system and taking some pictures with the VIRTIS spectrometer. VIRTIS stands for 'Visible and Infrared Thermal Imaging Spectrometer' (it can apparently measure at ultraviolet wavelengths too but that would have mucked up the acronym...) and is designed to measure the composition of the lower atmosphere by measuring in spectral windows which are not blocked out by clouds in the upper atmosphere - according to this site you might also be able to make some surface measurements at near-infrared frequencies, which would be pretty cool.

    The probe is already 3.5 million kilometres away, so the data collected are not particularly ground-breaking, but they confirm that the instrument is in good shape for the real observations, starting when the probe enters Venus orbit in April next year, and are useful for calibration purposes.

  • The MARSIS radar on the Mars Express has now been operating for four months, as is summarised here. The orbiter has a highly eccentric orbit, and during most of the observation time so far the time of closest approach has been in the daytime. This means that the best measurements are being made when the upper atmosphere (ionosphere) is excited by solar radiation, making it more opaque to the lower radar frequencies required to penetrate the sub-surface. We're still getting lots of data about the structure of the Martian atmosphere and surface, but the real fun begins next month, when the closest approach will be at night; the search for underground water can then start in earnest. This delay in sub-surface measurements was not intentional, but a conseqeunce of the delay in deploying the radar booms last year. I'm glad the mission has been extended to compensate

  • Meanwhile, New Scientist reports that the Japanese Hayabusa probe, which managed to land on an asteroid and collect surface samples over the weekend (on the second attempt - on the first landing attempt last week the pellet gun designed to dislodge material from the surface of the asteroid failed to fire) is suffering from a thruster malfunction.
    Problems with the thrusters and control systems have plagued this mission from the start, so even if they get it working it's not clear if there's enough fuel to return the samples to Earth. Fingers crossed.

  • Finally, another in the seemingly non-ending stream of fabulous images from Cassini:

    This image of Enceladus is backlit by the Sun, and illuminates plumes of water vapour rising up from its south pole. The cause of this geological activity is not yet understood, but it's still pretty cool!

    A larger image can be found here,and an enhanced false colour image here.

28 November, 2005

Fission back in fashion?

The nuclear debate has reared its ugly head again, with Our Glorious Leader apparently 'convinced' (which sounds awfully familiar; does he never learn?) that we must turn to nuclear power to meet emissions targets and ensure energy security.

My views on the nuclear question are complex. I'm aware of the disadvantages, of course: the production of long-lived, highly radioactive waste products (and, more importantly, still no clue about how to provide safe long-term storage for them), the reliance on expensive technology which is difficult to maintain and dismantle, and the horrific consequences if something goes wrong. There are, however, potential benefits: the cuts in CO2 emissions resulting from less use of fossil fuels, and the reduced dependence on diminishing supplies of oil and gas, most of which comes from areas of questionable political stability (and that's before we stick our oar in). So the question is, do these benefits outweigh the risks?

When this first hit the news last week, I took what I thought to be a pragmatic 'lesser of two evils' line: it's not ideal, and in a perfect world we wouldn't touch nuclear fission with a barge pole, but given the likely gap between our energy use and that which is probably going to be supplied by renewables (in the near future at least), if we're serious about cutting greenhouse gas emissions then we might well have to consider it.

Then I read this op-ed by Magnus Linklater in The Times, which is mainly based on the work of Jan Willem Storm van Leeuwen and Philip Bartlett Smith. Unfortunately, I can't find any of their stuff on-line as a primary source, but their biographies (pdf) indicate that you can't just write them off has raving eco-hippies; they have both spent large parts of their careers involved with the nuclear industry.

According to Linklater:

What they have done is look at the entire life cycle of a nuclear power station, from the mining of the uranium to the storage of the resulting nuclear waste. Their conclusions make grim reading for any nuclear advocate.

They say that at the present rate of use, worldwide supplies of rich uranium ore will soon become exhausted, perhaps within the next decade. Nuclear power stations of the future will have to reply on second-grade ore, which requires huge amounts of conventional energy to refine it. For each tonne of poor-quality uranium, some 5,000 tonnes of granite that contains it will have to be mined, milled and then disposed of. This could rise to 10,000 tonnes if the quality deteriorates further. At some point, and it could happen soon, the nuclear industry will be emitting as much carbon dioxide from mining and treating its ore as it saves from the 'clean'” power it produces thanks to nuclear fission.

And that's before you've even considered the enrichment stage, where you separate U-238 from the non-fissile U-235, which also requires energy. We will of course meet this point even sooner if a new generation of reactors increases the global appetite for enriched uranium; after which the CO2 emissions 'saved' by nuclear electricity generation will be insufficient to offset that used to produce the fuel for it. Worse still, as demand for uranium ore increases, where will it all come from?

Not friendly Canada, which produces most of it at present, but places like Kazakhstan, hardly the most stable of democracies. So much for 'secure'” sources of energy. We would find ourselves out of the oil-producing frying pan, right in the middle of the ore-manufacturing fire.

Hmmm...suddenly I'm not so sure about that cost-benefit ratio. Especially when you consider that electricity generation as a whole only accounts for about a quarter of the total UK energy usage - getting on for 50% of the fossil fuels we burn are presently consumed by transport and domestic gas (The DTI provides some only slightly impenetrable figures here). Switching some gas-power stations off and replacing them with nuclear isn't going to affect those sectors at all.

So, could nuclear be an intermediate option in a long-term strategy - buying us time to switch over to more sustainable energy sources and usage? Possibly, but building nuclear power stations is a long and drawn out process (even the optimistic projections of proponents seem to reckon if we started right now it would be at least 10 years before we could add new nuclear capacity to the National Grid. And the cost will be fearsome. I wonder what you could do if you invested those billions in renewables (still scandalously cash-starved despite the high-minded rhetoric)? Or used it to every house in Britain loft insulation and solar heating systems?

I won't deny I have environmental sympathies, but I'm willing to be convinced that nuclear has a role in providing for our future energy needs. But I do have severe doubts which I'd like to be addressed. In detail. Unfortunately, if you'll forgive my cynicism, I have a feeling that this 'debate' which is currently being called for might well consist of 'this is right, anyone who disagrees is out of touch with the issues'. Don't know where I could have got that idea from...

04 October, 2005

If you're a Dan Brown fan...

...and haven't read Deception Point, LOOK AWAY NOW!

I got this book for my birthday. I can't claim to be the greatest fan of Dan Brown; I read The Da Vinci Code to see what all the fuss was about, but had no real inclination to sample more of his ouvre. However, I've spent the past few evenings skimming through it, and I can't say that my opinion of his authorship has been heightened by the experience. I can appreciate that he's very clever at weaving together a narrative which hits the buttons for the X-Files generation, but I find his writing style a little annoying. The fact that most of the characters are a little underdeveloped (or sketchy and cliched if you're feeling bitchy) and prone to exposition-speak ("you mean that this document proves that the conspiracy reaches all the way to the White House?") is almost a given in this genre; but in addition Mr. Brown feels the need to give the make and model, and often the development history, of any piece of equipment that is mentioned, and this is truly irritating.

But this is not why I write. Some of the controversy around The Da Vinci Code (and the cause of the Catholic Church's righteous indignation) hinged around its claims to authenticity - that is was more than an imaginative thriller, but had a certain basis in fact. As an author, in fact, Dan Brown seems to take great pains to provide the appearance of authenticity (which is probably the reason for the aforementioned overdescription of equipment). Not that this appearance neccesarily means anything, of course, if some of the scholarly reaction to The Da Vinci Code is anything to go by.

In Deception Point it is my turf that is being trodden upon (in a broad sense anyway), because the focus of the story is a meteorite, discovered in the Artic by NASA, which contains fossils. The main characters of this story are non-NASA people who have been called in to verify this apparent discovery of alien life. Cue smug palaeontologist, talking about one of these supposed alien fossils:

"The most impressive characteristic of this organism is that it fits perfectly into our Darwinian system of taxonomy and classification."

a fact which is apparently support for 'panspermia', the theory that earth was seeded with life from space.

Erm... No.

To be fair, Mr. Brown describes the concept of panspermia rightly enough, but makes a complete dog's breakfast of the implications if it were true. In such a case, then we might expect life on other planets to have a similar underlying biochemistry. And possibly insect-like life could have developed, 'like' being the key word because the resemblance would be, at best, superficial. Such creatures might share generic features with Earth insects, like segmented bodies, multiple appendages, or a hard carapace acting as attachment point for muscles, but looking closer you would find that they were built completely differently (a bit like the way bird and bat wings look similar but have entirely different underlying structure). This is because even if it was derived from the same basic source, the evolutionary history of life on another planet would be dependent on a complex interplay between mutation and environment which would never exactly duplicate what has occurred on Earth. Therefore, the discovery of organisms that fit into Earth taxonomy in a "meteorite" would scream "fake!" to any competent biologist or geologist, which as it turns out, it is (a fact which is revealed on the back cover of my copy, so I feel few qualms about revealing here), although our intrepid top scientists need to go through a lot of technobabble before they are convinced of this.

Should I care? The fact that I get so worked up about scientific inaccuracies in works of fiction causes certain friends of mine take me to task for being a bit anorak-esque. But so often, you find scientific concepts being mangled beyond all recognition when it would work just as well if they got it right. I find that annoying, and it can hardly help combat the scientific cluelessness of the general public. This sloppiness is especially unforgivable when the authors make claims about the painstaking research behind their novels. Not in the right areas, clearly. Admittedly, the plot of Deception Point would have to be retooled a bit to make it work and be scientifically accurate, but it could be done. It might even make it a bit more readable.

29 September, 2005

Endings and beginnings

Yesterday was my 27th birthday. I am quite introspective at the best of times, and this time of year usually triggers even more wallowing in questions of the "Where have I got to, where am I going, and is this where I should be?" variety. A further contributing factor this year is the fact that on Monday, I also submitted my PhD thesis. Therefore, as well as giving me not one, but two, convenient justifications for demanding free beer from my friends, this week also marks the end of an era. So it's only natural that I look back and ask: what have I learnt from my PhD?

  • Don't do any lab work in the month before your funding runs out. It's far better to wallow in ignorance than to uncover data which forces you to completely rewrite your thesis. Believe me.

  • When your supervisor asks you to help with something, 'help with' is invariably a synonym for 'do without any further input from me'.

  • You'll always bump into your supervisor on your coffee breaks or when you're leaving the building at 3:30, but never when you're working feverishly and leaving the building at midnight.

  • The fact that you don't pay taxes will earn you the eternal scorn of all your friends with proper jobs, even though they still take home three times as much money as you.

  • Erm...

Seriously, although I have spent almost four years doing research, and have even had a couple of papers published (with more on the way), I'm still not entirely convinced I understand how the whole scientific endeavour really works. Which is unfortunate, because that was the whole point of my doing a PhD in the first place (although the fact that I got to spend a serious amount of time doing fieldwork in New Zealand may well also have contributed to my choice...). At the end of my degree, I knew I wanted a career with some sort of scientific spin, but I couldn't really find anything that really appealed. I liked the idea of doing research, but was unsure whether I was cut out for the academic life.

And right now, I find myself in exactly the same position. I've enjoyed the research, but in many ways my PhD has felt like an extended undergraduate dissertation; lots of time working on my own, and not really feeling part of the research community in my department, let alone in the world at large. So how am I supposed to assess what working in it is like? Or maybe that is what it's like...

Either way, it seems I have a bit more time to answer these questions. Although I now have a few ideas about what else I might want to do, they have yet to bear fruit, so next week I find myself starting a new job working for my PhD supervisor. Nothing like a bit of continuity, I suppose. And I do get my weekends back.