by Paul Gilster | Dec 23, 2009 | Culture and Society |
by Larry Klaes
Long-time Centauri Dreams readers will know that Larry Klaes is a frequent critic of the portrayal of science in movies, and in particular of the ways Hollywood looks at aliens and our interactions with them. Larry has again been to the cinema, this time to see the new James Cameron release Avatar. He brings back a rich description of the film along with numerous insights on its potential for reaching the public.
When the United States was preparing to send the first humans to Earth’s largest natural satellite in the 1960s with Project Apollo, there were numerous scientists of the day who protested this effort. They felt that knowledge and even surface material could be gathered from the Moon far more cheaply and efficiently with automated probes than with astronauts.
On a technical and pragmatic level, those scientists were essentially correct. But as with many things in human society, the primary reasons for the existence of Apollo were about politics and power, specifically in this case to show up America’s chief Cold War rival, the Soviet Union, in the vast arena of space.
Most astronomers of the era eventually realized that if they wanted to learn a lot about the Moon and beyond, they had to jump on the relatively expensive and resource-intensive government-sponsored bandwagon or end up literally left behind in a cloud of smoke. Apollo may not have been the most efficient and productive way to reveal the ancient secrets of our nearest celestial neighbor, but it did work in the end.
This is how I have decided to approach the currently quite prominent existence of the new science fiction film Avatar by James Cameron in terms of educating the general public when it comes to the film’s themes of exobiology, exomoons, exoplanets, and human interaction on an interstellar scale.
Interstellar Ideas and the Public
Avatar is hardly the most efficient or inexpensive way to bring these major topics to a wide swath of society. However, just as the money, resources, and technology poured into Apollo brought hundreds of pounds of lunar rock and other invaluable space science data to Earth – as compared to the few ounces of lunar regolith retrieved by the three successful automated Soviet Luna craft during the 1970s – Cameron’s latest cinematic extravaganza will probably do more to make people aware and think about these literally universal ideas than dozens of books, articles, and documentaries on the same subject.
I and others may not agree with this, but the reality is that many people do get much of their “education” about the world and especially science from film and television, which is not obliged to be any more accurate and educational than it has to when their primary goal is to entertain in order to make a profit. So to dismiss Avatar out of hand because it may have a less than original plot and characters of limited depth is to dismiss as well a major opportunity to guide a public that may otherwise never bother to contemplate and confront the issues raised in this film.
Astronomers have detected over 400 alien worlds since 1995. Every day we come closer to finding the first Earth-type exoplanets and the first exomoons. When this happens, many consider it a given that various space agencies will begin to make serious efforts to reach those distant places in the galaxy, first to study them and then to send humans there in person to colonize. Just as other influential films have actually played a role in inspiring or deterring people from grand efforts, Avatar will probably be cited as either one of the catalysts for launching humanity to the stars or holding us back out of fear from alien unknowns or what we might do to others unlike us.
Cameron’s Work in Context
Let me first get some of the standard comments about Avatar out of the way: Yes, it is an impressive experience in terms of the 3-D effects making you feel like you are part of the film rather than the usual gimmick of objects flying at your face because they can. The effects do help to enhance the feel of being there in an alien place and in that respect Avatar is a cinematic landmark – assuming others have the means and the interest to follow in Cameron’s technological footsteps.
Many have compared the plot in Avatar to the great 1991 film Dances With Wolves and the 1995 Disney animated film Pocahontas. I would say that Avatar even more closely resembles a 1992 Australian animated film titled FernGully: The Last Rainforest, which has a plot about a human who is part of a major deforestation effort brought into the world of fairies who live in the forest and fear the destruction of their home. The deforestation is being conducted by giant yellow tree-cutting machines reminiscent of the ones tearing down the flora in Avatar. Personally I am ultimately more interested in the themes behind Avatar and its predecessors rather than who copied from whom, more of which will be discussed later.
The realm of Avatar is the moon Pandora, which circles a gas giant world named Polyphemus that in turn orbits the star Alpha Centauri A, among the closest of suns to Earth at just 4.3 light years, or about 25 trillion miles. Though in reality Jupiter-type exoplanets have not been detected in the Alpha Centauri system, which implies that such bodies may not exist, Avatar does help to make its audiences aware of the concept of moons as places for life to form and evolve, since most of the exoplanets found so far are giant worlds, many of them larger than Jupiter.
Thoughts on the Setting
As we have seen with our own Jovian planets since the days of the twin Voyager space probes, gas giant worlds do have retinues of large and dynamic moons, some of which may be homes for simple organisms. There is no reason not to think that alien gas giants might have exotic companions as well, though whether they would be like the residents of Pandora is much too early to say.
On the subject of living on the moon of a gas giant planet: Note how huge Polyphemus looms in the skies of Pandora as we are witness to throughout the film. It is certainly a very awe-inspiring and aesthetically pleasing image, enhancing the alienness of the moon and its inhabitants. However, I would think that being so close to a gas giant would cause all sorts of geological turmoil, which in turn would greatly upset the balance of life on Pandora, perhaps even to keep it from becoming complex.
To use a real-world example, note how the closest of Jupiter’s four Galilean moons, Io, is constantly pulled and churned about by the great mass of Jupiter and its fellow Galileans to the point where the moon is constantly spewing colorful sulfur across its uncratered surface. Despite the intense nature of Io’s environment, some scientists have speculated that the very geological processes that make Io such a violent place could bring about and support some kind of life, though probably nothing as complex as the creatures on Cameron’s alien moon.
An Exomoon’s Culture
Putting aside whether or not a tropical rainforest type ecology could evolve on a moon being so close to a gas giant planet, I had to wonder why the alien intelligence on Pandora, the Na’vi, did not seem to focus much attention on such an incredible sight as the planet Polyphemus, which seems to take up most of the sky over Pandora. Now granted I know the Na’vi are aliens, but since they also bear more than a slight resemblance to aboriginal peoples on our planet, I am surprised they didn’t focus at least some of their culture on the great world hanging over their heads.
Perhaps they did and the film chose not to explore that aspect of Na’vi society, but I found it strange that something like that would be ignored or treated casually. Certainly many human societies on Earth going back to prehistoric times paid a great deal of attention to the objects and events in the sky, as they were often crucial to the survival of those societies. Again, maybe the Na’vi did and Cameron chose not to focus on it, or their very close ties to the ecology of Pandora kept them looking downwards.
Larry’s review continues tomorrow with a look at the broader issues raised by the film and what it may say about our own aspirations in space.
by Paul Gilster | Dec 22, 2009 | Exoplanetary Science |
With much of the US east coast to the north of me digging out from the recent storm, I can only think how fortunate I am not to be trying to travel right now. The snow-clogged airports and snarled streets that are all over the news do have their effect on my thinking, though, which may be why I was reminded this morning of a much colder place, a certain Saturnian moon whose most recent image now offers yet more proof of the active hydrology going on there. Titan got a bit lost in the shuffle here late last week but I don’t want to ignore this compelling new image.
What we’re looking at is the flash of sunlight reflecting off one of Titan’s lakes. It’s not a huge surprise, given that we’ve identified lake-shaped basins that ought to have been ideal for liquid methane. But now that the Sun is directly illuminating the northern lakes as spring breaks out on that part of Titan, we can take advantage of conditions there to see things like this, taken with Cassini’s visual and infrared mapping spectrometer. It’s another confirmation that liquid exists in those basins.
Image: This image shows the first flash of sunlight reflected off a lake on Saturn’s moon Titan. The glint off a mirror-like surface is known as a specular reflection. This kind of glint was detected by the visual and infrared mapping spectrometer (VIMS) on NASA’s Cassini spacecraft on July 8, 2009. It confirmed the presence of liquid in the moon’s northern hemisphere, where lakes are more numerous and larger than those in the southern hemisphere. Scientists using VIMS had confirmed the presence of liquid in Ontario Lacus, the largest lake in the southern hemisphere, in 2008. Credit: NASA/JPL/University of Arizona/DLR.
Bob Pappalardo, a Cassini project scientist based at JPL, conveys the power of the scene:
“This one image communicates so much about Titan — thick atmosphere, surface lakes and an otherworldliness. It’s an unsettling combination of strangeness yet similarity to Earth. This picture is one of Cassini’s iconic images.”
Iconic is right, and I suspect we’ll be seeing this image over and over again in future accounts of Cassini’s discoveries. While we had already identified liquid in Ontario Lacus, this specular reflection gives us a scene that is in some ways foreign, in other ways familiar. Katrin Stephan (DLR, Berlin), a member of Cassini’s visual and infrared mapping spectrometer team, recalls seeing the glint last July:
“I was instantly excited because the glint reminded me of an image of our own planet taken from orbit around Earth, showing a reflection of sunlight on an ocean. But we also had to do more work to make sure the glint we were seeing wasn’t lightning or an erupting volcano.”
That involved correlating the reflection with Titan’s geography, confirming that the glint came from the southern shoreline of Kraken Mare, which covers some 400,000 kilometers of the moon’s surface, an area larger than the Caspian Sea. The ongoing hydrological cycle brings liquid methane to the surface and shapes that surface just as water shapes the Earth.
The Titan ‘glint’ also reminds me of the work of Darren Williams (Penn State Erie) and Eric Gaidos (University of Hawaii), who have addressed the question of whether space-based instrumentation like a TPF-class telescope could pick up the glint of a ocean on a distant exoplanet. Let me quote again from one of the team’s papers: “…of all the extremely difficult measurements astronomers hope to make with a TPF-class telescope, time-series photometry and polarimetry that can lead to the identification of specular reflection from surface water might be the easiest.”
Maybe the Titan scene above is just the forerunner for an even more exotic detection down the road as we add to our space-based resources. The paper on that work is Williams and Gaidos, “Detecting the Glint of Starlight on the Oceans of Distant Planets,” Icarus Vol. 195, Issue 2 (June, 2008), pp. 927-937 (available in preprint form online). And consider an even more intriguing possibility, discussed a few years back by Peter McCullough (Space Telescope Science Institute) in a paper of his own:
…we propose to exploit the linear polarization generated by Rayleigh scattering in the planet’s atmosphere and specular re?ection (glint) from its ocean to study Earth-like extrasolar planets. In principle we can map the extrasolar planet’s continental boundaries by observing the glint from its oceans periodically varying as the rotation of the planet alternately places continents or water at the location on the sphere at which light from the star can be re?ected specularly to Earth.
If mapping the continents on planets around other stars doesn’t rouse your interest, you may not be paying attention! Of course, we may need to set up an observatory on the Moon to make this happen. The McCullough paper is “Observations of Extrasolar Planets Enabled by a Return to the Moon,” in Astrophysics Enabled by the Return to the Moon, M. Livio, Ed., Cambridge University Press, in press (preprint).
by Paul Gilster | Dec 21, 2009 | Exoplanetary Science |
What a welcome event the release of James Cameron’s new film Avatar must be for scientists working on the question of exomoons — satellites orbiting extrasolar planets. Imagine being a Lisa Kaltenegger (CfA) or David Kipping (University College London), hard at work exploring exomoon detection and possible habitability when a blockbuster film is released that posits a habitable moon around a gas giant. The film’s exomoon, called Pandora, fits a scenario that exomoon hunters tell us could exist, orbiting a giant planet in the habitable zone of its star, and it draws public attention as never before to exoplanet and exomoon detections.
Interesting exomoon scenarios beyond gas giants are also possible, as this image shows. We’re learning that we can detect exomoons using tools like transit time duration measurements, and there are other methods, too, like microlensing and distortions of the Rossiter-McLaughlin effect. A paper from Kipping that we examined here recently makes the case that a Kepler-like instrument could detect exomoons around gas giants in the habitable zone down to 0.2 Earth masses — that would yield 25,000 stars, for example, in Kepler’s field of view that could undergo screening for such moons.
Image: This artist’s conception shows a hypothetical ringed super-Earth as viewed from one of its moons. Both super-Earth and moon are habitable and contain liquid water. Credit: David A. Aguilar, CfA.
What Lisa Kaltenegger asks in her new paper is whether we could make any definitive statements about the habitability of such worlds. And it turns out the answer is yes, assuming we’re using the right equipment (a 6.5-meter instrument, like the James Webb Space Telescope, would be required). And assuming that the exomoon in question is close to maximum separation, in which case an exomoon transit across its star (as seen from Earth) is comparable to the transit of a planet of the same size, provided that the projected semimajor axis is larger than the stellar radius. The transits of planet and exomoon, in other words, need to be separate events so that we can make the necessary measurements to characterize the exomoon.
From the paper:
Habitable-zone exomoons may be detected in the near future with missions like Kepler and could be orbiting their planet at a distance that allows for spatially separate transit events. In that case transmission spectroscopy of Earth-like exomoons is a unique potential tool to screen them for habitability in the near future. Spatially separating the exomoons from their parent planet improves their detectability because their absorption signature are about two orders of magnitude lower than the absorption features of an EGP [extrasolar giant planet] spectra.
We learn here that low-mass M-class dwarfs are the easiest stars to work with because of the favorable contrast of star to planet. In fact, Kaltenegger’s work shows that in the best case scenario, atmospheric H20, CO2 and O3 features in the infrared could be detected in one year for transiting habitable exomoons around M5 to M9 stars at a distance of up to 10 parsecs. Note that nearby M-dwarfs are ideal for this investigation because their habitable zones are close to the star, increasing transit probability and transit frequency.
M-dwarf exomoons have another advantage in the issue of habitability. We’ve long debated whether a planet in the habitable zone of such a star would be capable of hosting life considering that it would probably be tidally locked to its star, one side constantly baked by sunlight, the other in constant darkness. Whatever the answer (and tidal lock may not be a show-stopper for life on such worlds), an exomoon around a gas giant in this scenario, says Kaltenegger, would be tidally locked not to the star but to the planet, and would therefore have regular night-day cycles, just like Earth.
Cameron’s film depicts a habitable exomoon in the Alpha Centauri system, specifically around Centauri A. If such a moon were to exist around Centauri A, a 6.5-meter instrument like the JWST would indeed be able to characterize it, and quickly. Kaltenegger notes:
“You would only need a handful of transits to find water, oxygen, carbon dioxide, and methane on an Earth-like moon such as Pandora.”
In fact, under idealized observing conditions, a single transit observation of an Earth-like body around Centauri A would potentially allow screening for habitability. We know from earlier work that gas giants are unlikely around Centauri A or B — we would have probably found them by now — but we can’t rule out Earth-class planets. The person to turn to on such matters is Debra Fischer (Yale), whose ongoing work examining the Centauri stars for planets may soon yield answers to such questions. Fischer was recently quoted in Popular Mechanics in an article discussing the accuracy of the Avatar movie. Here’s a snippet from the article discussing Fischer’s radial-velocity work at the Cerro Tololo Inter-American Observatory (CTIO) in Chile.
This “wobble technique” has already ruled out the presence of Jupiter- or Saturn-scale exoplanets (like Polyphemus) around the Alpha Centauri stars. But “there’s a very good chance,” Fischer says, that planets with masses near that of Earth’s could grace this star system. “There’s still so much we don’t understand about planet formation around single stars,” Fischer says — let alone triple-star systems like Alpha Centauri. So in terms of what may be out there, “it’s almost an open slate.”
An open slate indeed. And certainly the question of habitable exomoons around nearby M-dwarfs remains open as well. The paper is Kaltenegger, “Characterizing Habitable Exo-Moons,” available online. Also see David Kipping’s new paper “Pathways Towards Habitable Moons,” (available online), from the “Pathways towards Habitable Planets” Symposium in September, which includes this interesting statement that confirms Kaltenegger’s optimism on characterizing habitable exomoons:
For the case of a system within 10pc and a 0.2 M? habitable exomoon, we predict that molecular species could be found using transmission spectroscopy with JWST after the binning of ?30 transit events.
by Paul Gilster | Dec 18, 2009 | Missions |
The Tau Zero Foundation is announcing a call for papers related to the FOCAL mission. The venue: The 61st International Astronautical Congress in Prague, which convenes on the 27th of September, 2010 and runs to October 1. Specifically, we are looking for papers for session D4.2, “Interstellar Precursor Missions,” whose focus is “…missions that significantly expand science — using existing and emerging power and propulsion technologies.”
Long-time Centauri Dreams readers are well aware of Claudio Maccone’s FOCAL concept, a mission to the Sun’s gravitational lens at 550 AU and beyond. FOCAL would make possible studies of astronomical objects at unprecedented magnifications. The electromagnetic radiation from an object occulted by the Sun at 550 AU (i.e., on the other side of the Sun from the spacecraft), would be amplified by 108. Moreover, whereas with an optical lens light diverges after the focus, light focused by the Sun’s gravitational lens stays fixed along the focal axis. Every point along the straight trajectory beyond 550 AU remains a focal point for any vehicle we put on this trajectory.
Imagine, then, two possible FOCAL mission targets. The first option would be to launch the probe toward the heliopause in the place where it is closest to the Sun, the direction of the incoming interstellar wind. This would allow useful studies of the heliosphere itself, but the deeper goal would be to reach 763 AU, the place where the cosmic microwave background will be focused by the Sun’s gravitational lens upon the spacecraft. As Maccone has shown, detecting lower frequencies pushes the focus further from the Sun — the focal distance, in other words, changes as a result of frequency.
We’ve learned how valuable information about the CMB is to cosmologists. Now imagine the result of examining the CMB with the vast magnifications possible through a FOCAL probe. But a second choice is also available. FOCAL could be optimized for close study of the Alpha Centauri stars, especially if current efforts pay off and we do find interesting planets around Centauri A or B. Centauri demands a different kind of mission because it is far from the ecliptic. The flight path is problematic because the Centauri stars are so close, requiring ion propulsion to achieve the necessary spiral trajectory.
Addendum: So many readers have mentioned Dr. Maccone’s recent SETI Institute lecture that I want to go ahead and link to it now, although I was planning a separate piece on it next week. When I met with Claudio recently in Austin, he was getting ready to leave for the West Coast to make this presentation before concluding his US trip and heading back to Italy. What a pleasure it was to talk to him at leisure about FOCAL.
But all of these are matters that now need to be taken to the next step at the International Astronautical Congress, where they will gain further visibility in the scientific and industrial community. Papers are solicited on the propulsion problem — is a solar sail optimal? Nuclear-electric? Perhaps VASIMR? We also hope for submissions on the scientific return from a FOCAL mission, on telecommunications technologies, on computing requirements, and perhaps on the social and cultural value of a concept that would take human technologies further from the Sun than any previous missions.
Image: The FOCAL mission as currently envisioned by Claudio Maccone. The image is taken from the cover of his book Deep Space Flight and Communications: Exploiting the Sun as a Gravitational Lens (Springer/Praxis, 2009), and shows two 12-meter antennae operating through a tether which is gradually released, allowing a field of view much larger than that offered by a single antenna. Credit: Claudio Maccone/Springer.
The preliminary program for the Prague IAC has already been posted. The deadline for submitting abstracts to the Congress is 5 March 2010. Let me quote from the IAC documentation on what the criteria for selection will be:
Paper selection
Submitted abstracts will be evaluated by the Session Chairs on the basis of technical quality. Any relevance to the Congress main theme of ‘Space for human benefit and exploration’ will be considered as an advantage.
The criteria for the selection will be defined according to the following specifications:
* Abstracts should specify: purpose, methodology, results and conclusions.
* Abstracts should indicate that substantive technical and/or programmatic content is included
* Abstracts should clearly indicate that the material is new and original; explain why and how.
* Prospective authors should certify that the paper was not presented at a previous meeting and that financing and attendance of an author at the respective IAC at Prague to present the paper is assured.
Full information about the meeting and the submission process is available through the official Call for Papers & Registration of Interest.
by Paul Gilster | Dec 17, 2009 | Outer Solar System |
The Hubble Space Telescope is capable of extraordinary things, but a 35th magnitude object is beyond its capabilities. In fact, 35th magnitude is 100 times dimmer than what the instrument can see directly. But an ingenious investigation using Hubble’s Fine Guidance Sensors (FGS) has turned up the smallest Kuiper Belt Object yet found. Not surprisingly, the method involves an occultation, in which the object discovered passed in front of a background star and revealed itself through the tiny signature of the event.
Imagine tracking down something that is only 975 meters across but almost seven billion kilometers from the Sun (a solid 45 AU). By comparison, the smallest Kuiper Belt Object previously seen in reflected light is about fifty times larger. Hilke Schlichting (Caltech) and team took advantage of 4.5 years of FGS data to make the find. The Fine Guidance Sensors provide navigational information to Hubble’s attitude control systems by looking at specific stars for pointing. And they’re good enough to pick up a brief occultation.
Image: This is an artist’s impression of a one-half-mile-diameter Kuiper Belt Object (KBO) that was detected by NASA’s Hubble Space Telescope. The icy relic from the early solar system is too small for Hubble to photograph. The object was detected when it passed in front of a background star, temporarily disrupting the starlight. Credit: NASA, ESA, and G. Bacon (STScI).
The find points to the value of archival data, reminding us that the discoveries we make upfront with many of our instruments are bulked up years later by painstaking analysis of vast datasets. In this case, Schlichting’s team analyzed FGS observations of 50,000 stars from some 12,000 hours of Hubble observing time along a strip of sky within twenty degrees of the ecliptic, where most KBOs are likely to be found.
Only one occultation, a 0.3-second event, came out of this work, but it was enough to tease out the tiny KBO. The duration of the occultation made it possible to estimate the distance of the object, while the amount of dimming offered up a rough calculation of its size. As we have much more FGS data covering the full range of Hubble’s operations since its 1990 launch, the possibility of finding more KBOs will keep the project going.
And what can this KBO tell us? We’re seeing that the Kuiper Belt is most likely in a state of ‘collisional evolution,’ with debris colliding over the course of the Solar System’s existence to grind KBOs into ever smaller pieces. That’s deduced by the presence of only one occultation in these data, which indicates there are fewer sub-kilometer sized KBOs than would be expected from the population of larger KBOs with radii exceeding 50 kilometers. As we are learning with debris disks around other stars, continuing collisions would produce this result.
Note, too, the relevance of this story to our recent discussion of using Kepler or similar space missions to detect Oort Cloud objects. Here again the occultation of background stars and the application of statistical analysis to the data is the method that fleshes out our view of the outer system.
It’s no surprise, then, to see that one of the co-authors of the paper on this work is Caltech’s Eran Ofek, who along with Ehud Nakar advanced the idea of looking for Oort Cloud occultations. The paper is Schlichting et al., “A single sub-kilometre Kuiper belt object from a stellar occultation in archival data,” Nature 462 (17 December 2009), pp. 895-897 (abstract).
