by Paul Gilster | May 17, 2010 | Astrobiology and SETI |
Like astrobiology, SETI is a multi-disciplinary effort, one that pulls together our knowledge and speculation about everything from life’s origins to the development of planetary systems and the evolution of civilizations. It’s remarkable to remember that it was only fifty years ago that Frank Drake launched the enterprise by scanning a 400 kHz window for interstellar radio transmissions. Epsilon Eridani and Tau Ceti, his target stars, gave us no evidence of extraterrestrial life, but we’re continuing to refine the tools for detection.
The Allen Telescope Array is just one example of the radio telescope equipment being brought to bear. The Low Frequency Array (LOFAR) and the Square Kilometer Array (SKA) will offer new SETI options in a wide range of wavelengths. SKA will cover 70 MHz to 10 GHz, later extending up to 30 GHz, while LOFAR will survey the skies from 10 to 240 MHz. LOFAR is currently being built and will be the most sensitive radio observatory in the world until SKA comes online by 2017, with full operation by 2022.
So where does SETI stand at this juncture as we wait for the next generation of radio telescope equipment? That will be the subject of the Second IAA Symposium on Searching for Life Signatures, to be held from 6-8 October 2010 at the Kavli Royal Society International Centre (Chicheley Hall, Buckinghamshire, UK), which occurs immediately after a Royal Society meeting titled Towards a Scientific and Societal Agenda on Extra-Terrestrial Life, to be held at the same venue.
Image: The Lovell Telescope at Jodrell Bank Observatory. Credit: University of Manchester.
Anyone with a window for European travel this fall should consider the possibilities. The International Astronautical Congress takes place in Prague from 27 September to 1 October. Straight on to London (Chicheley Hall, a Georgian house surrounded by 75 acres of gardens and grounds, is 88 kilometers from the city) and you can attend both SETI sessions, staying either at Chicheley Hall itself or at a nearby hotel, but note that the earlier Royal Society meeting requires separate registration to reserve a place. In addition to the meetings, participants at the IAA session will have the chance to spend a day at the Jodrell Bank Observatory.
If you’re interested in participating, papers for the IAA Symposium are solicited on life and its evolution, exoplanetary science, habitability and life signatures, active and passive SETI, and the technological and societal aspects of finding extraterrestrial life and establishing contact. The Scientific Programme Committee, co-chaired by John Zarnecki, Martin Dominik, Claudio Maccone and Jean-Michel Contant, invites abstracts no longer than 400 words, to be sent by email to IAAsearchforlife@gmail.com. The deadline for receipt is 15 June, 2010.
by Paul Gilster | May 14, 2010 | Astrobiology and SETI |
Gliese 581 d seems to be emerging as the exoplanet to talk about in terms of possible life, at least for now. You’ll recall that the initial furor was all about Gl 581 c, but that world now looks to be more Venus-like than anything else, while Gl 581 d may just skirt the outer region of the habitable zone in this interesting system. Thus Dirk Schulze-Makuch’s contention at the recent astrobiology conference in Houston that this ‘super Earth,’ if it holds life, may have creatures on it that have adapted to the gravity of a planet at least seven times as massive as the Earth.
That would probably produce a population that tends to crawl rather than fly, said the Washington State researcher, and we can let our imaginations go to work on the possibilities. As to Gl 581 d itself, its orbit around this red dwarf may place it in the same relative position that Mars is to our Sun, but throw in volcanoes, a magnetic shield and a thick atmosphere with water oceans below and you could have the right astrobiological circumstances. I’m hoping readers will point me to science fictional treatments of higher-gravity settings a bit less extreme than Hal Clement’s Mesklin in the classic Mission of Gravity, where the local life-forms are 50-centimeter long intelligent beings in the shape of centipedes.
Image: Part of a John Schoenherr rendering of Mesklin from Hal Clement’s Mission of Gravity, from the cover of a 1960’s paperback. Could anyone capture the essence of a story better than the remarkable Schoenherr?
Meanwhile, the detection of a true Earth analog is probably not that far away, and when we do find it, what should we expect by way of living beings there? We won’t know for a long time, of course, but it’s worth noting that Simon Conway-Morris has long contended that certain body forms like eyes and wings keep showing up because they are ideal solutions for interacting with an environment like ours. It’s an argument that Charles Lineweaver (Australian National University) doesn’t buy into, as noted in this summary of the Houston conference from Astrobiology Magazine, where Lineweaver is cited on life’s unique evolutionary paths:
This theory of convergence, says Lineweaver, is flawed because it ignores the fact that life on Earth shares certain genes, and those genes are the foundation for what bodily forms can eventually develop. For instance, people often point to dolphin brain size as an instance of convergence with humans. Lineweaver says such a claim is ridiculous because it ignores the fact that 60 million years ago, humans and dolphins diverged from a common ancestor.
And will the life we eventually find be intelligent? Again, it will be a long time before we know, but I liked this ‘tweet’ from the same conference: “The word ‘intelligence’ is now so loaded it’s almost not useful. Better to say ‘species signaling apparatus.’ -C. Lineweaver”. Twitter skeptics should bear in mind how much a tiny message like that — sent by an attendee at a Lineweaver session at the conference — can turn a day’s writing in new directions.
You’ll find pocket summaries of some of the conference’s most interesting sessions in the Astrobiology Magazine feature, along with the predictions of Chris Impey (University of Arizona), who points to the future participation (if not driving influence) of private companies in the exploration of the outer Solar System. I’m not sure whether it was Impey or author Leslie Mullen who threw in the parting exhortation: ‘By 2060 – Voyage to Alpha Centauri!’ but I’m all for the idea, even if the realist in me thinks that voyage is about 250 years off. The beauty of the future, of course, is that our predictions are so often wrong, as I hope mine is.
by Paul Gilster | May 13, 2010 | Culture and Society |
I’ve heard of Dyson spheres and Dyson swarms, but what exactly are Dyson ‘dots’? As coined by Greg Matloff, C Bangs and Les Johnson in their book Paradise Regained, the term refers to a type of solar sail. These sails are not meant for moving things around the Solar System, but for reducing the amount of solar radiation hitting the Earth. The authors imagine large numbers of the Dyson dots placed near the L1 point, using the momentum from solar photons to maintain their position. Imagine thousands — maybe millions — of these sails equipped with sensors to receive the instructions of their builders, communicate with each other, and make changes in the configuration of the swarm.
Could you use a sail array like this to cool off the planet? From the book:
…using reasonable middle values for the parasol parameters — 80 percent reflectivity or albedo, mass 53 grams per square meter, positioned 2,100,000 kilometers from Earth — we would need almost 700,000 km2 of sunshade area to achieve a reduction of 0.25 percent in the solar constant, that is, some 37 million metric tons.
And let’s put this into perspective:
…bear in mind that the United States alone burns about one billion tonnes of coal every year. One supertanker of the many hauling petroleum around the world’s oceans weighs about half a million tons fully loaded; and 37 megatonnes is roughly just 3 days’ supply of crude oil… If each Dyson dot has an area of 10 km2, then our array, or school, would consist of 70,000 units.
Now back into an even deeper perspective, which is what Paradise Regained is all about. The authors advise us to look to extraterrestrial resources, to mine the heavens as a way of reducing the industrial footprint on Earth and restoring the planet’s ecological balance. Think space for resources, then, and realize that the 37 million tonnes referred to above amounts to the mass of a single, small stony-iron asteroid some 300 meters across, which is a class of rock so small that we’re only now starting to look for them.
Paradise Regained is a bracing study of what we might do in the near future to make life better, and that includes asteroid missions that could help us protect the Earth via methods like ‘gravity tractors’ and solar ‘parasols’ as well as missions to exploit their resources. In this context, the word ‘exploitation’ has less bite than it does on Earth, for resources in the Solar System are vast, and exist in an environment so deadly that there is little humans can do to degrade it. Moreover, a small asteroid 1 kilometer in diameter might contain 2 billion tons of iron ore, enough to meet the annual global demand for one year.
The asteroid 16 Psyche may contain enough iron ore to take care of our needs for millions of years. Moreover, many asteroids contain nickel, cobalt, copper, platinum and gold. Thousands of Near-Earth Objects (NEOs) exist in the 100-meter range or bigger, providing an all but limitless pool of raw materials. Needless to say, the authors also throw into the mix the possibilities of tapping the Sun’s energy output — 3.86 X 1026 watts every second of every day. The infrastructure needs are huge, encompassing spacecraft, solar arrays, antennae, ground support equipment and more. Can we afford to build it?
…that all depends on the cost of energy and how much of a value we place on the environment. The cost of energy production is not as simple as dollars, euros or yen. What is the cost to the planet of the strip mining required for the coal we burn in our thousands of power plants? What is the payoff in reduced defense spending that will result from us not having to depend on the volatile Middle East for oil to generate electrical power? How much is it worth to eliminate the acid rain associated with the burning of fossil fuels? What benefits will we reap from a power system that produces no greenhouse gases? The authors contend that when the real societal costs are considered, as well as the real monetary cost from end to end, space-based solar power begins to look like a winner.
From mining to fusion, Paradise Regained covers the numerous options that space affords our species. As for the latter, helium-3 gets interesting because it’s a potential fusion fuel that, while rare on Earth, seems to be plentiful in the lunar regolith. If we can ever make fusion viable, a mixture of deuterium (heavy hydrogen) and helium-3 is a desirable fuel choice because it produces little residual radioactivity. Some estimates of helium-3 on the moon run to about a million tons, a potential solution to our energy needs for centuries.
Because it is stuffed with possibilities, it’s tempting to keep racing through this book popping out facts and prescient speculations, but I don’t want to ignore the moving, poetic side of it, reinforced by C Bangs’ lovely artwork, which harkens back to a pastoral world of the imagination even as it embeds itself in the cosmos. Thus the lovely Shakespeare quote from the introduction:
I know a bank where the wild thyme blows,
Where oxlips and the nodding violet grows;
Quite over-canopied with luscious woodbane,
With sweet musk-roses and with eglantine.
That’s from A Midsummer Night’s Dream, and it conjures up a vernal Earth we’d like to preserve even as we spread the benefits of technology and industry to the less advantaged. Myths of a ‘golden age’ are just that, reflecting a time-honored nostalgia for a past that never truly was, but there is a sense that we can ‘regain’ that dreamed of Earth by creating it for ourselves, using our technology wisely to offload industrial activities to nearby space. Buy two copies of this book and give one to your local school library. The ideas are spread out here in dazzling profusion, a chastening reminder to those who see no value in space exploration and believe such funds should be spent here on Earth. Here we learn that the space payoff may be huge, transforming our planet even as it feeds our dreams.
by Paul Gilster | May 12, 2010 | Deep Sky Astronomy & Telescopes |
We’d better get familiar with WHIM, the Warm-Hot Intergalactic Medium. According to some cosmologists, this sparse gas exists in the spaces between the galaxies, accounting for up to fifty percent of the normal matter found in today’s universe. That would explain a conundrum. By ‘normal matter,’ I mean baryons, the protons and electrons of the matter we deal with every day. It turns out that we can study distant gas clouds and galaxies well enough to form an estimate of the normal matter found in the early universe, and the problem is that the nearby universe, much older, shows only about half the amount of normal matter that we would expect to find.
Now researchers have used the Chandra X-ray Observatory and ESA’s XMM-Newton to detect a huge reservoir of interstellar gas apparently embedded in a large-scale structure known as the Sculptor Wall, some 400 million light years from Earth, providing strong support for the WHIM theory. We’re probably looking at material left over from the formation of galaxies, but studying it has been anything but easy, says Taotao Fang (UC-Irvine):
“Evidence for the WHIM is really difficult to find because this stuff is so diffuse and easy to see right through. This differs from many areas of astronomy where we struggle to see through obscuring material.”
The illustration below is an artist’s impression of the Sculptor Wall, which stretches tens of millions of light years and contains not only thousands of galaxies but also a large reservoir of WHIM, according to theoretical simulations. To study it, the researchers looked at an active galactic nucleus (AGN) at X-ray wavelengths that lies on a line of sight to the Sculptor Wall but is two billion light-years away, behind it from our vantage point. The black hole is generating massive amounts of X-rays, allowing their absorption by the WHIM to be studied as they make their way to Earth.
Image: This artist’s illustration shows a close-up view of the Sculptor Wall, which is comprised of galaxies along with the warm-hot intergalactic medium (WHIM). Scientists used Chandra and XMM-Newton to detect the WHIM in this structure by examining the X-ray light from a distant quasar, which is represented in the spectrum (inset). This discovery is the strongest evidence yet that the “missing matter” in the nearby Universe is located in an enormous web of hot, diffuse gas. Credit: NASA/CXC/M.Weiss; Spectrum: NASA/CXC/Univ. of California Irvine/T. Fang et al.
What turns up in the data is the absorption of X-rays by oxygen atoms in the WHIM, consistent with the distance of the Sculptor Wall and also consistent with predictions of the temperature and density of the WHIM. The implication is that the WHIM will also be found in other large-scale structures, with confidence in the theory growing because these observations, as opposed to earlier claimed detections, were made with two different X-ray telescopes. With the distance of the Sculptor Wall known, the statistical significance of the absorption detection is much higher than in earlier blind searches that observed AGN in random directions.
It’s important to stress that the ‘missing matter’ is not ‘dark matter,’ which is under such intense investigation because of its role in the dynamics of galaxies and galactic clusters. The current studies tell us nothing new about dark matter but do help us track down normal matter that is found in the WHIM at extremely low density, equivalent to about six protons per cubic meter, significantly less dense than the interstellar medium between stars in our galaxy. The interstellar medium contains about a million hydrogen atoms per cubic meter.
Indeed, says Fang, “Evidence for the WHIM has even been much harder to find than evidence for dark matter, which is invisible and can only be detected indirectly.” The paper is Fang et al., “Confirmation of X-Ray Absorption by Warm-Hot Intergalactic Medium in the Sculptor Wall,” Astrophysical Journal Vol. 714, Number 2 (10 May 2010), pp. 1715-1724 (abstract / preprint).
by Paul Gilster | May 11, 2010 | Exoplanetary Science |
Recent work from the Lick-Carnegie team has found that the M-dwarf HIP 57050 is orbited by a Saturn-mass world with an orbital period of 41.4 days. What catches the eye about this exoplanet is its temperature, some 230 kelvin or -43 degrees Celsius, warm enough to place it in the habitable zone of the star. Based on our knowledge of the gas giants in our own Solar System, it’s a natural supposition that this is a world with moons, and if so, their location in the habitable zone draws inevitable comparisons with fictional worlds like Pandora.
M-dwarf Habitable Zones
So what do we know about M-dwarfs that can help us with this system? For one thing, they’re exciting objects for radial velocity studies because of their low mass, making the signature of an orbiting planet more readily apparent than with larger stars. We also know that their low temperatures move their habitable zones in much closer to the star than in our system, ranging from 0.1 to 0.2 AU, corresponding to an orbital period of between 20 and 50 days. Finally, M-dwarfs are either less likely to have readily detectable planets, or the planets they do have are small enough compared to the planets of G-class stars like the Sun to make them more difficult to find.
As to the position of HIP 57050 b within the habitable zone, the verdict, based on 9.9 years of observations, seems clear. From the paper:
If we assume that the inner boundary of the habitable zone (HZ) of the Sun is at 0.95 AU (Kasting et al. 1993), and its outer boundary is at a distance between 1.37 AU and 2.4 AU, depending on the chosen atmospheric circulation model (Forget & Pierrehumbert 1997; Mischna et al. 2000), then by direct comparison, the inner boundary of the HZ of HIP 57050 would be at a distance of 0.115 AU, and its outer boundary would be between 0.163 AU and 0.293 AU. From Table 3, the perihelion and aphelion distances of HIP 57050 b are at 0.112 AU and 0.215 AU respectively, suggesting that this planet spends the majority of its orbital motion in the HZ of its host star.
HIP 57050b has an orbital eccentricity of 0.31, but this may not be a major issue for any interesting moons around the planet:
Although the planet makes small excursions outside the HZ, due to the response time of the atmosphere-ocean sysem (Williams & Pollard 2002; Jones et al. 2006), and the effect of CO2 cloud circulations (Selsis et al. 2007; Forget & Pierrehumbert 1997; Mischna et al. 2000), the times of these excursions are small compared to the time that is necessary for a significant change in the temperature of the planet to occur. In other words, the planet could hardly be more squarely in the HZ and will most likely maintain its habitable status even when its orbit is temporarily outside of this region.
A Problematic Habitat
Could a habitable moon exist here? Theoretically so, but the paper goes on to note that in our Solar System, on the order of 0.02% of the mass of the gas giants is found in their moons. Run the numbers and you wind up with a moon that is about 2 percent of Earth’s mass, or 1/5th the mass of Mars. That doesn’t sound particularly promising, but in an article in Scientific American, Darren Williams (Penn State) points out that larger moons could form on their own and be captured by a massive planet’s gravity.
We may be looking at that situation in our own system in Neptune’s moon Triton, which possibly arrived where it is today by being captured by Neptune, with a binary object pairing with Triton being ejected in the process. Williams, who has simulated the situation on objects as massive as the Earth, says that an Earth-size moon could form around a gas giant this way, with a secondary object the size of Mars being lost along the way. So while we’re a long way from discovering a moon around HIP 57050 b, we do at least have a world in the habitable zone of its star and the possibility of objects around it that are astrobiologically interesting.
But while this system continues to yield its secrets, don’t be surprised if we get the actual detection of an exomoon in the near future. CoRoT 9 b transits its star on June 17, and researchers will be using the Spitzer Space Telescope to look for evidence of rings or moons. And if this planet fails us, it’s also possible that the Kepler space telescope will be able to flag the presence of moons around some of the planets it finds.
Alpha Centauri Seven Years Too Late
Check the Scientific American article for good links to recent work, including studies by Lisa Kaltenegger (Harvard University) showing that the James Webb Space Telescope may be able not just to detect exomoons but to study their atmospheres. It’s interesting, too, to hear Sara Seager (MIT) talk about exoplanetary moons in light of recent films:
But if astronomers manage to turn up an extrasolar moon in the coming years, even a habitable one like those of sci-fi lore, some aspects of Pandora will remain firmly fictional. “What’s interesting is Avatar is out of date by about seven years,” Seager says. Astronomers have looked for the presence of giant planets in the habitable zone of Alpha Centauri, the nearby star system that is home to Pandora in the film, and have not found one. That’s not to say that Alpha Centauri doesn’t have a habitable world of some kind—it would just have to be a planet like our own, rather than a moon. “If they had called me or someone else in exoplanet astronomy,” Seager says, “we would have advised them to just put an Earth there.”
M-dwarfs and the Metallicity Connection
All the exomoon speculation is fascinating in its own right, but a major finding of the Lick-Carnegie paper is that the strong correlation between metallicity and expected planets — giant planets should be more likely with increasing metallicity of the host star and increasing stellar mass — may hold up with M-dwarfs despite earlier doubts. In fact, HIP 57050 has twice the metallicity of our own Sun, making it among the highest metallicity stars in our neighborhood. Indeed, “…planet-bearing M-dwarfs do appear to be systematically metal-rich, suggesting that there is no breakdown of the planet-metallicity correlation as one progresses into the red dwarf regime.”
The paper is Haghighipour et al., “The Lick-Carnegie Exoplanet Survey: A Saturn-Mass Planet in the Habitable Zone of the Nearby M4V Star HIP 57050,” Astrophysical Journal Volume 715, Number 1 (20 May 2010), pp. 271-276. Abstract and preprint available.
