What would be the best design for a submarine that could explore the deep and possibly life-bearing ocean beneath Europa’s ice? Carl Ross (University of Portsmouth, UK) has been pondering the matter, proposing a 3-meter long cylindrical vehicle made perhaps of a ceramic composite to offer the best combination of strength and buoyancy. And for getting through the ice itself? “It may be that we will require a nuclear pressurized water reactor on board the robot submarine to give us the necessary power and energy to achieve this.” Details to be found in A Submarine for Europa, recently published on Universe Today.
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If your sense of wonder could use the occasional jolt (and this can happen to us all), do check out the work of another Ross, Aaron by name. The film student has put together a terrific short (first noted here on The Discovery Enterprise) based on Arthur C. Clarke’s Rendezvous with Rama. Ross manages to capture in just a few minutes the mystery and majesty surrounding the arrival of a vast alien vessel in our Solar System. Music and special effects are equally provocative, and I’m stunned all over again at how the ability to ship video worldwide over the Net has energized and empowered such creative minds.
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We’ll be tracking our Voyagers for some time as they push out into the edge of the heliosphere and start to encounter interstellar space. But our first interstellar mission has a long way to go before it encounters another star. The next vaguely close pass for Voyager 1 will be when it drifts 1.7 light years by the unassuming AC+79 3888. And it will be another 358,000 years before Voyager 2 approaches Sirius. “Out there,” says Timothy Ferris, “our concepts of velocity become provincial.”
And I like the way he puts this: “The stars are moving, too, in gigantic orbits around the center of the Milky Way galaxy. Voyager, a toy boat on this dark sea, will not so much approach Sirius as watch it sail by, bobbing in its mighty wake.” Be sure to read Ferris’ whole New York Times article on the Voyagers and their golden discs. Few writers bring so poetic a voice to the space enterprise.
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Does Frank Drake think the SETI equation he made famous needs any revision? The question was put to him in this interview in Astrobiology Magazine. His answer:
No. I do get letters all the time suggesting we should add more factors, like the role of politicians. But all of that is a part of the already existing factors, so there’s been no need to change it. It’s held up well. The numbers may change, but not the equation itself. One rapidly changing factor in the equation is the typical number of planets in the habitable zone. Well, that number is changing all over the place, but that just reflects a healthy march of science towards the real truth.
That habitable zone question continues to bedevil us. Drake sees habitable zones as essentially infinite from a star because worlds with insulating layers — think Europa — may have suitable temperatures even at great distances from their parent star. Consider atmospheric habitats on each of the Solar System’s giant planets, where the insulating layer is gas and, if you choose your altitude carefully, the temperature is warm. Drake also throws in the greenhouse factor. Put Venus much farther from the Sun and its massive atmosphere could lead to liquid water on the surface. There are no easy calls on habitable zones, says Drake, and that complicates the equation’s results still further.
Hi Paul
Just a few thoughts on Drake’s “infinite habitable zone”. Moving Venus is a tricky one because we don’t know what its original water content was. While early models assumed the same water as Earth, current planet formation modelling reveals that not all terrestrial planets form the same. The level of volatiles is dependent on the “late veneer” of accreted material – if Venus received material from the inner Main Belt then it probably formed dry. Apparently the levels of Al26 in the original planetesimals varied significantly and some literally boiled away their volatiles.
The other complication is that water and carbon dioxide don’t make for a stable combination – the CO2 ends up dissolving and precipitating out as carbonate. Back in the 1940s spectroscopy revealed a lot of CO2 on Venus which to many indicated there was no water below the clouds else it would disappear into solution. Or else Venus had a planetary ocean and no land to help carbonate formation. Of course now we know differently, but the problem remains that carbon dioxide doesn’t stay put around oceans of water.
James Kasting and his colleagues have of course modified that somewhat by adjusting for the reduced chemical erosion as temperature declines. But that’s only stable until CO2 clouds start forming and it’s debatable whether a non-oxygen biosphere can sustain intelligence. Oxygen availability seems to have been the limiting factor that controlled the appearance time of metazoans, on this planet.
But there maybe other ways of making living things. I’m not convinced that there can’t be Life based on other solvents, gas phase chemistry or plasma crystals. But there may not be physical pathways based on such available for technological/industrial civilisation to arise and build radio-telescopes as SETI requires. Perhaps communicative ETIs require much more restrictive conditions than just Life or Mind require alone. Free-space life might make it to our Solar System, but such life may not be able to reach down to planetary surfaces – plasma creatures would find Earth’s atmosphere, gravity and magnetic fields a rather challenging environment.
Thus I think the only way SETI will ensure success is to actually go look instead of sitting back and listening.
I agree that habitable zones will depend on how wide the boundaries of life are.
Regarding the plans for the Europa submiarine, it reminds me of Jules Verne’s Nautilus, both concretely and conceptually. That’s probably what they should name the vessel if it is constructed.
On the scientific side, there are at least two important considerations. One is that the heat generated by the submarine or a drilling apparatus might heat-denature Europan lifeforms. The second is that it might shred them, as similar drills used to do with very fragile jellyfish-like terrestrial organisms.
Caveats asides, the prospect is immensely exciting — and this mission might help push the lifeform boundaries, and change our idea of what constitutes habitable zones.
Then again, Venus does have an enhanced deuterium/hydrogen ratio in its atmosphere, so clearly the planet has been losing hydrogen. If it is assumed that the original deuterium/hydrogen ratios of Earth and Venus were initially the same, you find that Venus has lost 99.9% of its hydrogen. Of course it is up for debate whether this initial hydrogen reservoir was in the form of water or a primordial hydrogen envelope.
Interesting coincidence. I just finished reading a book by Charles Sheffield (copyrighted 1992) called “Cold as Ice” whose main theme surrounds the possible discovery of life in the under-ice ocean of Europa using submarines. I’ve always enjoyed Charles’ writing, and his ability to tell good stories, with interesting characters, and a good basis on real science.
Frank, agreed about Cold As Ice. I read it a few years back — Sheffield is always interesting, and the science is solid. Nice to think there’s a bunch of his work I haven’t read yet.
Hi All
andy, Bullock & Grinspoon analysed the ratios and found that they could have been produced by comet infall and subsequent hydrogen escape. No primordial water needed.
“Cold as Ice” was a clever “Space Opera”. Interestingly for SETI Sheffield describes a Distributed Observation System which combines all the observing facilities across the Solar System to act as a gigantic imaging interferometer. In its trial run the DOS detects artificial structures in M31. I personally think that kind of system will be how we discover ETIs, unless SETA discovers mining scars or eroded old bases.
I’m still expecting a Bracewell probe to start chatting to us too.
Adam: regarding that, I have found the following references in ADS. Unfortunately they are all to papers with no arXiv version, so can only see the abstract.
Grinspoon (1987) Was Venus wet? Deuterium reconsidered – suggests comets as a water source rather than primordial ocean
Grinspoon & Lewis (1988) Cometary water on Venus – Implications of stochastic impacts – suggests comet impacts have effectively hidden early water history on Venus.
Grinspoon (1993) Implications of the high D/H ratio for the sources of water in Venus’ atmosphere – abstract says comets can’t be the source since the D/H ratio of source is too high, but might be from mantle outgassing.
Donahue (1999) New Analysis of Hydrogen and Deuterium Escape from Venus – suggests water may either be primordial or from a more recent outgassing.
Hmmm…