by Paul Gilster | Aug 26, 2005 | Astrobiology and SETI
It’s hard to imagine water lasting for long on today’s Martian surface. But a team at NASA’s Ames Research Center has been studying gully sites that seem to indicate water outflows from what could be a subsurface aquifer. Indeed, the team’s computer simulations show that if liquid water did emerge from underground, it could create gullies about 500 meters long. “Our model indicates that these fluvially-carved gullies were formed in the low temperature and low pressure conditions of present-day Mars by the action of relatively pure liquid water,” said Jennifer Heldmann, principal author of the Ames study.
Take a look at the photograph, which shows the channel and debris apron of recent Martian gullies. The scale of the bar in the photo is 1 kilometer. If we are looking at the work of recent surface water, then it surely existed in a challenging environment. Given the temperature and air pressure at the surface, exposed Martian water should either boil or freeze almost immediately. But the way the gullies taper into small debris fields does suggest rapidly rushing water that froze or evaporated.
“In the Martian case, fluid well above the boiling point (which is a very low temperature at Mars’ low atmospheric pressure and air temperature) is suddenly exposed to the atmosphere,” said Heldmann. “The difference between the vapor and ambient pressures relative to the ambient pressure is large, and flash boiling can occur, leading to a violent loss of fluid.”
The Ames team will present its findings at the American Astronomical Society’s Division for Planetary Sciences annual meeting in Cambridge (UK) in early September. The study uses data from the Mars Orbiter Camera and other instrumentation aboard the Mars Global Surveyor spacecraft. But it also relies on studies of cold water saline springs in the Canadian high arctic, a polar desert that provides an analog to the Martian environment. Other analogs of Martian gullies have been studied in Iceland, with results pointing to water as the cause.
Centauri Dreams‘ take: A subsurface aquifer in the regions studied on Mars surely provides a prime landing site for future life-finding missions. But other explanations for gully formation are still in the running, ranging from calcium chloride brines to seasonal carbon dioxide outbursts and even snow melt. A thorough look at the alternatives is available on this page at the Planetary Science Research Discoveries site. An earlier article by Heldmann and colleagues is “Observations of martian gullies and constraints on potential formation mechanisms,” Icarus 168, No. 2 (2004), pp. 285-304.
by Paul Gilster | Aug 25, 2005 | Astrobiology and SETI, Culture and Society
How much do human cultures change over cosmically tiny time frames? Specifically, how alien would we find the Sumerian outlook on life if we could immerse ourselves in it today? How foreign would the world of pre-Columbian America appear to our touchy 21st Century ethics? Would we be comfortable, or capable of, adopting the cultural imperatives of either?
Now extend the question. Is it possible even within time frames of a few thousand years to imagine civilizations that are both stable over time while maintaining social goals like exploration and continual expansion? If the answer is questionable — and it is — then we can look at the Enrico Fermi paradox in another light. Perhaps the reason we haven’t found evidence of other technologies in our galaxy is that, while they are there, they are not expansionist over the periods of time needed to make themselves known to us.
Such are the musings of German physicist Claudius Gros (University of the Saarland), as developed in a recent issue of the Journal of the British Interplanetary Society. While working out a set of rate equations for the density of advanced civilizations, Gros points out that many scenarios for galactic expansion depend upon analogizing between what we see on Earth and what hypothetical alien societies might do. Thus we see lifeforms on Earth expanding until they have occupied every habitable niche. From this, we have taken for granted that this drive to expand would push mankind inevitably into the stars, fueling a colonizing wave that would engulf the galaxy.
But Gros notes that we are now seeing falling birth-rates in the industrialized world, and that we push intellectual and emotional reasons for expanding into space rather than the need to alleviate population pressure. “Our limited knowledge of the long-term dynamics of human, post-human and extra-solar advanced civilizations does not allow us presently to give a definitive answer to the question, whether humanity will ever produce social organizational forms stable over 103-106 years on a technically highly advanced level. And once it does, will this society be dedicated, at least partly, to long-term and peaceful expansion?”
Image: The galaxy NGC 3949, a spiral galaxy like the Milky Way. Are such vast cities of stars the home of long-lived cultures that lack any expansionist agenda? Credit: NASA, ESA, Hubble Heritage Team (STCcI/AURA).
Indeed, it could be argued that a stable social fabric over hundreds of millennia would preclude long periods of expansion, which might introduce social instabilities. This does not rule out, says Gros, the idea that advanced alien civilizations might undergo periods of expansion, but these may be limited in duration. Such civilizations might exist in great numbers without tripping over the Fermi paradox. The answer to ‘where are they’ would be ‘they are out there and living peaceably on their own turf.’ Gros again:
A finite density of expanding civilizations does not automatically imply an exponentially growing number of alien civilizations. To derive this result we did not need to postulate that all expanding civilizations cease expansion after a certain period. All we have done here is to drop the (ad hoc) assumption that the colonies of expanding civilizations automatically inherit all their characteristics.
Ad hoc assumptions are always a good thing to question when trying to deal with issues this intractable. The paper is Claudius Gros, “Expanding Advanced Civilizations in the Universe,” JBIS 58 (2005), pp. 108-110. Add it to the long list of papers flowing from a lunch table remark Fermi tossed off effortlessly some 55 years ago.
by Paul Gilster | Aug 24, 2005 | Outer Solar System
The New York Times offers a feature story (free registration required) on Caltech scientist Michael E. Brown, who used Palomar data to find 2003 UB313, the Kuiper Belt object thought to be larger than Pluto. Working with David Rabinowitz of Yale and Chad Trujillo of Hawaii’s Gemini Observatory, Brown is also behind the discovery of Quaoar and Sedna, substantial KBOs in their own right, but not of planetary dimension (although just what constitutes a planet is, inevitably, a focus of the article).
Brown on the terminology debate: “If people want to get rid of Pluto, I’m more than happy to get rid of Pluto and say this one isn’t a planet, either,” Dr. Brown said. “If culturally we would be willing to accept a scientific definition, that would be great… The only thing that would make me unhappy is if Pluto remained a planet, and this one was not one.”
Centauri Dreams‘ take: The simple solution is to declare anything Pluto-sized and up a planet, although it opens up the possibility that we will soon discover even more worlds that fit this definition. Nonetheless, de-throning Pluto from its planetary designation would be an even more arbitrary imposition that few in our society would accept. We may just have to get used to the fact that our Solar System is larger and far more varied than we thought.
by Paul Gilster | Aug 24, 2005 | Breakthrough Propulsion
Be aware of The Spaceward Foundation’s Elevator:2010 program, a challenge award offering a prize for the first laser-powered tether climbing demonstration that can meet specific criteria. A space elevator of the sort discussed in yesterday’s entry would send 20-ton elevator cars with about 900 cubic meters of space up a tether at 200 kilometers per hour, a cheap and safe way to reach geostationary orbit. The Spaceward Foundation intends to promote and test the technologies using a balloon-suspended tether several miles high.
The Foundation also offers a quick Space Elevator Primer with salient facts and comments about the concept, among them this thought on government inertia:
There is no doubt that the promise of the Space Elevator is mind boggling. And here lies the problem – it requires a paradigm shift. 100 years ago, people thought dirigibles were the only way to fly, and heavier-than-air flying machines were an odd-ball idea. Today, there is an almost unbreakable concept that you go to space with rockets, and there is a huge industry built around this concept. That’s a lot of inertia to overcome, and it requires both technical research and public pressure. We’re here to get the word out, to have as many people hooked on the Space Elevator concept as we can.
The Foundation’s time frame for a space elevator seems exaggerated, suggesting that fundamental problems will all be resolved by 2010, with an elevator in place by 2020. But the concept is worth pushing even if a resolution takes additional decades. The first Elevator:2010 competition will be held at the end of September in Mountain View, CA, with entries in climber technology and tether strength. Competitions thereafter are intended to be annual.
by Paul Gilster | Aug 23, 2005 | Missions
It was the Russian scientist Konstantin Tsiolkovsky who first proposed the idea of a space elevator — an incredibly strong cable stretching from the surface of the Earth to a point 100,000 kilometers in space. Along this track elevator cars would move, powered by electricity and whisking people and cargo into space at a tiny fraction of the cost of today’s chemical rockets. Tsiolkovsky was always ahead of his time, but the key drawback to the plan was that there was no cable material strong enough to support such loads.
Enter Sumio Iijima, who discovered carbon nanotubes in 1991. Long, cylindrical molecules whose walls are made of carbon atoms, nanotubes may turn out to be 100 times as strong as steel at one sixth the density. Carbon-nanotube composite fibers have been produced at kilometer lengths, but they’re not yet strong enough to provide space elevator capabilities. Nonetheless, ongoing work at places like Carbon Designs Inc. in Dallas may produce workable answers within the next few years.
When Bradley Carl Edwards (who is founder and president of Carbon Designs) started plugging numbers into the space elevator concept, he came up with a $10 billion price tag for a single elevator, with a second (using the now proven technologies of the first, and leveraging its capabilities) running perhaps $3 billion. In terms of getting into space, subsequent costs are dirt-cheap. Here’s Edwards, writing in IEEE Spectrum Online: “The estimated operational cost for the first elevator is several hundred dollars per kilogram to any Earth orbit, the moon, or Mars, a drop of two orders of magnitude over the cost of current launch technologies. With the completion of subsequent elevators, the cost would drop even further, to a few dollars per kilogram.”
Image: A European Space Agency view of a space elevator anchored to an offshore sea platform in the Pacific. Credit: Erkki Halkka/ESA.
These numbers seem exaggerated to me, but read the entire Edwards article here; it’s laden with details. The overall plan is this: the elevator cable would rise from its anchor on the equator, passing through the geostationary orbit at 36,000 kilometers and continuing for another 64,000 kilometers until reaching a 600 ton counterweight. With its center of gravity at the geostationary orbit mark, the entire structure would move with Earth’s rotation. 20 ton cars would move up and down its cable. They would contain passenger quarters like a cruise ship, with windows opening to extraordinary views as the cars ascended, reaching geostationary orbit in about eight days.
Centauri Dreams’ take: dropping the cost of reaching space opens up everything from asteroid mining to solar power collectors in orbit. The contrast to today’s half-billion dollar a launch Shuttle situation is obvious. Other ideas for cheap space access are out there, including Leik Myrabo’s marvelous lightcraft concept. What is clear is that the old model of enormous chemical rockets lifting ever larger payloads will no longer suffice. As we set about building a space-based infrastructure in the inner Solar System, we will be putting the technologies into place that will one day produce robotic missions to nearby stars. The space elevator concept may get us going; it is robust enough to deserve intense and continuing scrutiny.
For more, see Marc Boucher’s The Space Elevator Reference, a weblog devoted to the concept. Be aware, too, of Edwards’ book The Space Elevator: A Revolutionary Earth-to-Space Transportation System (2003). Arthur C. Clarke’s The Fountains of Paradise remains the outstanding fictional treatment.
