Centauri Planets: Year-End Thoughts

The title of yesterday’s post — ‘The Odds on Centauri’ — would fit well with today’s musings. Alpha Centauri makes us ponder the odds not just in terms of interstellar bets and future space probes, but also in terms of the likelihood of life around these stars. And after all, 2008 saw significant work on this question, including the contributions of Philippe Thébault (Stockholm Observatory) and colleagues, whose studies of Centauri A and B show that while stable planetary orbits exist there, the odds on those planets forming in the first place are long.


Greg Laughlin (UC-Santa Cruz) isn’t necessarily daunted by this work (he explains why here), but the planet-hunter extraordinaire is realistic about life-bearing planets in this environment, and even more judicious about the possibility of a technological society making its home in the system. The question rises naturally out of recent publicity given the 20th Century Fox film The Day the Earth Stood Still, in which it was announced that the entire movie had been beamed in the direction of Alpha Centauri as a publicity stunt.

Image: Centauri A and B hanging over the horizon of Saturn. This Cassini image was captured captured from about 66 degrees above the ringplane and faces southward on Saturn. Ring shadows mask the planet’s northern latitudes at bottom. Credit: NASA/JPL/Space Science Institute.

The question: If somehow this transmission made it to Centauri, would there be anyone there to watch it? We’ll leave aside the issues that plague the original transmission, factors such as the fact that Alpha Centauri is barely above the horizon in Florida, and at the time of the transmission, according to Laughlin, “Alpha Cen (RA 14h:39m, DEC -60deg:50min) was below the horizon as viewed from 28 35 06N, 80 39 04W.” Forget that for a moment. Let’s just ask whether there might be, around one of the Centauri stars, a planet that could house a technological civilization.

Here’s what Laughlin came up with in a recent systemic post:

fp = Chance of a habitable planet orbiting Alpha Cen B = 0.6

fl = Chance that life evolved on that planet = 0.01

fi = Chance that life developed intelligence = 0.1

fr = Chance that intelligence understood Maxwell’s Equations = 0.01

fn = Chance that Maxwell’s Equations are currently understood on Alpha Cen Bb = 64,000 / 3×109 = 0.0000213.

This gives (fp)x(fl)x(fi)x(fr)x(fn) = one in eight billion, with Alpha Cen Ab kicking in an additional one in a trillion chance.

Of course, we’re plugging in most of these parameters without being able to do more than guess at their true value. Laughlin asked students in his classes, for example, to choose a value for fn based on their own estimate of how long a society will build radios. We also have to approximate values like fr, re an intelligent being’s capacity to understand Maxwell’s equations, and so on. There is not, in other words, a reason to abandon interest if you are one of those who hope for great things around Centauri, but it’s sobering to see that as things stand now, one in eight billion is a reasonable figure.

The exciting thing about our era of exoplanet discovery is that we learn game-changing things on a frequent basis. I, for one, would be delighted with the discovery of a small, rocky world around either of the major Centauri stars, one from which future study might extract spectroscopic evidence of life of whatever kind. But I’ll also be delighted at whatever we learn about planetary formation in the close binary environment, because that will help us understand how likely habitable planets may be around many stars. And if it turns out there is no one to watch The Day the Earth Stood Still wherever its stray signal may turn up, I can’t say that our hypothetical extraterrestrials will have missed much.

Addendum: Anyone who enjoyed the 1951 original of The Day the Earth Stood Still will want to read Brett Holman’s comments on the film in his superb Airminded blog. I particularly like his last line: “I do wonder just how credible a threat is a fleet of flying saucers flown by robots who can be pacified simply by speaking the words ‘Klaatu barada nikto’?”

The Odds on Centauri

My friend Tibor Pacher has taken our interstellar bet to a new level, publishing a lengthy letter on the subject in the current Spaceflight, a journal published by the British Interplanetary Society. Tibor, remember, had made a prediction I found outlandish: That “the first true interstellar mission, targeted at the closest star to the Sun or even farther, will be launched before or on 6 December 2025, and will be widely supported by the public.” I dissented, and we went public with the bet on the Long Bets site. Our funds are in the hands of the Long Now Foundation, with all proceeds going to good causes (details on the site).

But while I have enjoyed tweaking Tibor about the bet, it must be said that he has a solid motivation for going so far out on the speculative limb. The visionary founder of peregrinus interstellar, Tibor hopes to provoke discussion and keep people thinking. Along those lines, then, let’s look at his recent letter. One of the mission specs was a flight time of 2000 years or less to the star of choice. Assuming this is Proxima Centauri simply because of its, well, proximity, we arrive at a minimum average mission velocity of about 650 kilometers per second. That can be compared to Voyager 1’s 17.1 km/s to get an idea of the upgrade in velocity needed, but as we’ve noted in these pages before, the right kind of sail employing a Sun-diver maneuver might get at least close to that speed.

Useful data along the way? Tibor names the targets of opportunity: A craft traveling at 650 km/s gets out to the Kuiper Belt in about a year and reaches the heliosheath at 100 AU. Year two takes it out of the heliosphere entirely, while years five to ten are of note because they take us to the distance of the Sun’s gravitational focus, where Sol acts as a unique lens to magnify distant starlight. Recall that unlike optical lenses (where the light diverges after the focus), a gravitational lens has a focal line that extends to infinity. In other words, separations greater than 550 AU (where the gravitational lensing effect is first available) still offer unique observational possibilities.

Greg Matloff writes about this in his Deep Space Probes book (Springer/Praxis, 2000), noting that beyond 550 AU, the electromagnetic radiation from the occulted object under study is amplified by a factor of 108. And note this:

The ‘spot radius’ (distance from the centre line of the image at which the image intensity gain falls by a factor of 4) has been calculated…to be about 11 km for a Sun-spacecraft separation of 2,200 AU.

In other words, an outbound probe making lensing studies has a long observational run ahead of it. On the other hand, on a Proxima Centauri trajectory, what exactly will it be looking at? This is a rhetorical question, as I don’t know what is exactly on the opposite side of the Sun from this trajectory. Maybe one of our resident astronomers can fill me in.

Somewhere around year 20 of the Pacher probe’s mission it reaches the Oort Cloud, an area of obvious interest that may, in fact, extend halfway to the target star. We might also mention the Pioneer anomaly, for an outbound Proxima Centauri probe can obviously be studied in terms of anomalous acceleration along its route. Two thousand years after launch, the probe reaches the Proxima Centauri system, but for those who object that surely faster probes would have passed it along the way, I can only agree with Tibor that such a probe would get much done along its route before that happens, given a properly configured mission.

No, I won’t object to a 2000-year Centauri mission, powered perhaps by sail technology, on the grounds that it would quickly become obsolete. We don’t know what the future holds, and pushing the state of the art will teach us many things we would not otherwise have learned. Tibor and I have grounds for a bet, though, on the audacious idea that this mission might fly by December of 2025. If that occurs, I suspect advances in nanotechnology will be a large part of the story, but I will still be amazed if Tibor is the one to pop the Champagne cork when we meet seventeen years from now in Budapest to seal the deal.

Endurance Under the Ice

The Chicago Tribune offered up a Christmas day story on ENDURANCE, the NASA robot recently sent out for a shakedown mission in Lake Bonney, Antarctica. The lake is locked down under fifteen feet of ice, a place that could prefigure what we find under the ice on Europa. ENDURANCE stands for Environmentally Non-Disturbing Under-ice Robotic ANtarctiC Explorer, a vehicle created by Texas-based Stone Aerospace that is the successor to the Deep Phreatic Thermal Explorer (DEPTHX), which explored Mexican geothermal sinkholes in early 2007.


The Lake Bonney expedition is covering its story via blog entries accessible here, the most recent being a note from December 21, dealing with navigation in an environment rich in icebergs up against the face of a glacier. You may remember from an earlier story that ENDURANCE spent several days in the water at Lake Mendota, on the University of Wisconsin’s campus, last winter, with the new work pushing it into much harsher conditions. And history buffs will recall that Endurance was the name of Sir Ernest Shackleton’s ship, a vessel the Antarctic explorer had to abandon when it became abandoned in pack ice and crushed.

The incredible trek to the Antarctic coast that followed, and the ensuing journey to South Georgia, have become the stuff of legend, a fate that may well await the robotic ENDURANCE’s successors when they tackle environments like Europa and who knows what other subterranean bodies of water in the Solar System. For now, the current ENDURANCE is performing flawlessly at the end of its fiber-optic tether, “…determining its own routes underwater, evading obstructions and returning by dead reckoning to the team of relieved scientists,” in the words of the Tribune.

Image: ENDURANCE, an underwater explorer that may presage remarkable expeditions to come. Credit: Stone Aerospace.

And this is interesting:

As it hovers under the ice, the robot spools out a series of instruments every few minutes that measure water temperature and dissolved materials as well as taking pictures of the ice above and the dark lake floor below. Days after it began, the robot found what looked like an outcrop of lichen-covered rocks—microbial colonies that researchers said were unlike any others known to exist in the lake.

“There’s some things in these images that I’ve never seen before,” said investigator Peter Doran of UIC [University of Illinois at Chicago].

Oh for the chance to try out a matured successor to ENDURANCE off-world! That, of course, will be a long-time coming, but developing the key technologies now is another step in the right direction. Lake Bonney, we now learn, turns out to be an ancient salt lake trapped under fresh water and ice, a reminder that we have much to learn about our own planet as we shake out these new tools. Autonomy is the ticket, of course, and ENDURANCE is already proving that it can choose its own routes, avoid obstacles, and work its way back to the scientists who dispatched it under some of the most extreme conditions on Earth.

Addendum: You can also track this story via Shilpa Gulati’s blog; Shilpa is a member of the ENDURANCE team now on the ice.

Carnival Notes: Fusion and Dark Energy

Is nuclear fusion easier to exploit in space than on Earth? Surprisingly, harnessing the power that drives the Sun may be a simpler challenge in propulsion terms than creating clean, safe power supplies for our planet. So says Brian Wang, whose NextBigFuture site speculates on fusion development (and, I should add, also hosts this week’s Carnival of Space). Wang, who has been following fusion development for years, notes key differences between space and planet-side technologies, one of them being that dealing with stray neutrons is easier when you can vent them directly to space, rather than developing reactor materials that can both exploit their energy and ensure maximum safety.

We know that a fusion power plant on Earth must operate for many years, working with steady state fusion that affords low maintenance and maximum reliability. Space, however, offers a different set of goals, with duty cycles in months before major overhauls, and the possibility of interesting pulsed fusion options as well. In terms of creating a clean, high vacuum, space is obviously a simpler environment than a planetary surface. Brian’s conclusion: Generating propulsion is a lesser challenge than producing electricity, while other non-electric uses of fusion, such as creating relatively inexpensive PET isotopes for use in cancer diagnosis, are equally promising offshoots of the search for fusion power.

Also of note in this week’s carnival is Dave Mosher’s post on dark energy, which offers up links to Discovery News stories covering the topic in some detail, with discussion of how dark energy is studied, where the research is headed, and why it has drawn its share of skeptics. It’s a useful package, one highlighted by James Williams’ quick video overview of the question and the ever-reliable Ray Villard’s look at the ultimate fate of the cosmos. For still more on dark energy, have a look at the video below, put together by Alexey Vikhlinin of the Smithsonian Astrophysical Observatory, describing the latest results in this new and compelling science.

The monastic plainchant in the background is a nice touch. And why not — we’re talking about principles that have shaped the growth of matter in the cosmos at the largest scales and over immense periods of time. A certain sense of awe is both welcome and inescapable.

BBC Audio: Dyson and Clarke


Will life spread out from Earth to flourish in the cosmos? Freeman Dyson has always supported the idea, and with great persuasiveness. BBC Four has created an archive of interviews on its Web site, among which is a clip of Dyson discussing life’s variety and the imperative of broadening its range. The theoretical physicist, who played an important role in the development of the ‘atomic spaceship’ concept called Project Orion, doesn’t believe man’s role is simply to send the occasional astronaut out in what he calls ‘a metal can’ to look out a window.

Image: Physicist Freeman Dyson, whose thoughts on life’s spread into the cosmos can be found in the BBC archives. Credit: Dartmouth College.

On the contrary, says Dyson in his interview, humans may have a shepherding role in building a permanent presence in space. Instead of ships full of scientists or colony vessels establishing a new human foothold, Dyson would argue that we humans are representative of a far larger pattern, the spread of living things in all their variety. Our major role is to assist. We’re talking here about migrating whole ecologies, but not as forced transplants on other worlds so much as adaptations that, over the eons, will assume their own unique identities:

If you look at the natural world, you see that everywhere life has gone, it brings tremendous variety. The natural world is beautiful just because there is such a tremendous variety of living creatures — trees, plants, butterflies, birds. And I think the same thing will happen in the universe at large. The universe will just be a far more beautiful and interesting place when life has taken it over.

Note the implication that life has not yet taken the universe over, perhaps a comment on the likelihood of success for our SETI efforts, if not an answer to the Fermi question. Dyson goes on:

Life will spread and diversify everywhere the same way it has on Earth. Life just has this ability to adapt itself to all sorts of different environments, and I don’t think it will stop at one planet, when you see the whole universe waiting there. That’s the reason I believe we shall go out there and take our plants and animals with us.

It’s a bold view and not one that fits readily within the constraints of governmental space programs. But where does it start? Although space settlements near Earth might seem to be the answer, Dyson told his BBC Four interviewer that he had no use for the kind of habitats envisioned by Gerard O’Neill, finding them far too bureaucratic. Instead, he opts for ‘little bands of adventurers’ going out, working at their own risk and with agendas set by themselves. The Mayflower’s voyage across the Atlantic is an analog to what he sees happening in space:

There’s a tremendous amount of stuff already floating around in orbit just waiting to be salvaged by anyone who’s brave enough to go and do it. There’s a lot of stuff on the Moon which is lying there. That’s the way the Mayflower people worked. They didn’t build the Mayflower; they rented it. I imagine we’ll do the same thing. We will certainly make us of whatever the government provides, and that kind of stuff can usually be had very cheap.


As always, Dyson is energizing, and you’ll want to check the BBC Four archive to hear these bits (thanks to Teleread for the tip on this), at the same time wondering, as I do, why interviews like these aren’t offered in their entirety there. But do poke around. Arthur C. Clarke also has some audio clips, including his recollections of Stanley Kubrick’s first contacts with him re 2001: A Space Odyssey. Clarke says he received a letter from Kubrick ‘out of the blue,’ saying he wanted to do the ‘proverbial good science fiction movie, and did I have any ideas.’ At the time, interestingly enough, Clarke not only didn’t know Kubrick, but had never heard of him.

Image: Arthur C. Clarke at work. Credit: Billye Cutchen.

We brainstormed, developing all sorts of ideas, and when we had a fairly clear concept of what we wanted to do, Stanley said ‘write the novel and I’ll derive the screenplay from it.’…There was feedback in both directions, because I would write part of the novel and he would write the screenplay, and I would read the screenplay and feed it back into the novel. Later on, when he was actually filming, I was still feeding things from the film back into the novel. Because the novel didn’t come out until well after the film.

The later novel 2010: Odyssey Two would be developed through an entirely different method. Clarke acknowledges that he had to write 2001: A Space Odyssey with film in mind, creating scenes that he could visualize on screen, but 2010 was written as simply the best novel he could create, and ‘if anyone wants to film it, good luck to them.’ I loved both films, but in many ways still find 2010 the more interesting, a view few of my friends share. In any case, give Clarke a listen, and be aware that in this BBC interview archive, you’ll also find Werner Heisenberg, not to mention literary figures of distinction from Graham Greene to Iris Murdoch, and a host of actors, musicians and philosophers.