by Paul Gilster | Sep 23, 2009 | Sail Concepts |
It’s a long way from the back of an envelope to a deployed spacecraft, which is one reason why scientists write papers in journals and gather at conferences. Such venues are where ideas get shaken out, problems identified and solutions proposed. We sometimes talk about realistic technologies like solar sails as if all that remained were to build them, but as Roman Kezerashvili demonstrated at the recent conference in Aosta, there is a range of problems that we are only beginning to consider.
Kezerashvili (City University of New York), working with colleague Justin Vazquez-Poritz, has identified a significant area of concern for mission concepts that pass close by the Sun. Often called ‘Sundiver’ missions (a Gregory Benford coinage, if memory serves), these sails would be so constructed as to survive an extremely close solar pass. Perhaps protected behind an occulter until periherlion, the sail would then be unfurled to receive the full force of the Sun’s photons at extremely close range.
How close? No previous mission has ventured closer than 0.3 AU to the Sun. But Kezerashvili points to one recent study that showed deploying a sail at 0.1 AU could produce accelerations sufficient to reach 200 AU in 2.5 years, the Sun’s gravitational focus at 550 AU in 6.5 years, and the inner Oort Cloud at 2550 AU in thirty years.
Close passes work. We need highly reflective, low density sail materials that are extremely heat tolerant to withstand the conditions they will encounter, but there is no reason to think these are unattainable in the future. Kezerashvili believes that perihelion distances may be reduced as low as 0.05 AU – 0.1 AU as we develop the needed materials.
Image: From the recent Aosta conference, a snapshot taken in the Italian Alps. Left to right: Giovanni Vulpetti, Roman Kezerashvili, and Justin Vazquez-Poritz. Photograph courtesy of Roman Kezerashvili.
All of which is good news, but the problem that now emerges is one of navigation. Any time we venture so close to the Sun, we have to take account of General Relativity. The sail may be in close proximity to the Sun for only a short period of time, but this is also the period when the outward acceleration due to Solar radiation pressure is the greatest. The results of applying these calculations are stunning — our sail could be taken well off-course.
From the paper:
“…we consider a number of general relativistic effects on the escape trajectories of solar sails. For missions as far as 2,550 AU, these effects can deflect a sail by as much as one million kilometers. We distinguish between the effects of spacetime curvature and special relativistic kinematic effects. We also find that frame dragging due to the slow rotation of the Sun can deflect a solar sail by more than one thousand kilometers.”
For deep space purposes, this strikes me as the most significant result to come out of the Aosta sessions. Without the kind of trenchant analysis Kezerashvili and Vazques-Poritz offered up in two papers at the conference, a seemingly workable mission concept would have lacked a fundamental navigation solution. The duo examined as well more exotic factors such as the slowing of the passage of time near the Sun due to relativistic effects. An observer on Earth at 1 AU measures about 31 more seconds per year than an observer at 0.01 AU, leading to a redshift in the wavelength of sunlight whose effects on the optimum thickness of the sail turn out to be negligible.
Some relativistic effects are minor, then, but some are not. Indeed, we see the effects of General Relativity play out in terms of crusing velocity. Kezerashvili and Vazques-Poritz look at the motion of a sail from 0.01 AU outwards, one whose cruising velocity is 480 kilometers per second. With the effects of curved spacetime in mind, the radial component of its velocity turns out to be faster than what we would expect under a purely Newtonian approximation by about 1.65 meters per second. This is a difference, the authors note, that “…remains constant throughout most of the voyage and therefore has a cumulative effect.”
General Relativity, then, is a significant consideration in making a Sundiver mission a reality. Spacetime curvature can cause large deflections depending on our targets, but in any scenario, precision demands a full accounting of each of these variables. Not long ago we discussed the options for a fast mission to Haumea, an orbiter that was also discussed at Aosta. Obviously, the effects Kezerashvili and Vazques-Poritz studied would bear upon the navigational inputs for any sail mission to Haumea using a close solar pass.
The paper is R. Ya. Kezerashvili and J. F. Vazques-Poritz, “Escape Trajectories of Solar Sails and General Relativity,” (accepted for publication at Physics Letters B — preprint available). Orbital issues relating General Relativity to solar probes are discussed in the same authors’ “Solar Radiation Pressure and Deviations from Keplerian Orbits,” Physics Letters B 675 (2009), pp. 18-21 (abstract).
by Paul Gilster | Sep 22, 2009 | Astrobiology and SETI |
by James Benford
I first talked to Jim Benford back in 2003, discussing his work (wih brother Gregory) on microwave beam propulsion. He had already run experiments at the Jet Propulsion Laboratory demonstrating acceleration on a lightsail using these techniques, and was then hoping to run an experiment on The Planetary Society’s ill-fated Cosmos 1. The founder of Microwave Sciences, Benford’s earlier work at Physics International led to the development of the largest high power microwave experimental facility in the country. Along with continuing work on sail beamed propulsion concepts, the physicist has been actively studying questions of SETI and METI, musing on the kind of beacons we might find and the motivations for building them. Herewith some thoughts inspired by recent discussions in these pages.
We explored the motives for a civilization broadcasting to the galaxy at large (which I call Beacons, as they’re not targeted at specific stars) in one of the two papers we did last year, which was extensively described on this site. It will be published soon in the archived literature, as but for now it’s at:
Searching for Cost Optimized Interstellar Beacons, Gregory Benford, James Benford, Dominic Benford, http://arxiv.org/abs/0810.3966, and has been submitted to Astrobiology.
Through most of its history, SETI has assumed a high-minded search for other lifeforms. But other motives are possible. The categories of motivations as we described them:
What could motivate a Beacon builder? Here we can only reason from our own historical experience. Other possible high intelligences on Earth (whales, dolphins, chimpanzees) do not have significant tool use, so they do not build lasting monuments. Sending messages over millennia or more connects with our own cultures. Human history suggests (Benford G., 1999, Deep Time, Harper Collins, New York) that there are two major categories of long-term messages that finite, mortal beings send across vast distances and time scales:
Kilroy Was Here. These can be signatures verging on graffiti. Names chiseled into walls have survived from ancient times. More recently, we sent compact disks on interplanetary probes, often bearing people’s names and short messages that can endure for millennia.
High Church. These are designed for durability, to convey the culture’s highest achievements. The essential message is this was the best we did; remember it.
A society that is stable over thousands of years may invest resources in either of these paths. The human prospect has advanced enormously in only a few centuries; the lifespan in the advanced societies has risen by 50% in each of the last two centuries. Living longer, we contemplate longer legacies. Time capsules and ever-proliferating monuments testify to our urge to leave behind tributes or works in concrete ways (sometimes literally). The urge to propagate culture quite probably will be a universal aspect of intelligent, technological, mortal species (Minsky, Marvin, 1985, in Extraterrestrials: Science and Alien Intelligence (Edward Regis, Ed.), Cambridge University Press, also at http://web.media.mit.edu/~minsky/papers/AlienIntelligence.html).
Image: A Kardashev Type III civilization imagined. Would a culture able to tap the vast power of its entire galaxy engage in beacon building? What can we imagine about its motives? Art by Jon Lomberg.
Thinking broadly, high-power transmitters might be built for wide variety of goals other than two-way communication driven by curiosity. For example:
- The Funeral Pyre: A civilization near the end of its life announces its existence.
- Ozymandias: Here the motivation is sheer pride; the Beacon announces the existence of a high civilization, even though it may be extinct, and the Beacon tended by robots. This recalls the classic Percy Bysshe Shelly lines,
And on the pedestal these words appear:
‘My name is Ozymandias, King of Kings;
Look on my works, Ye Mighty, and despair!’
Nothing beside remains. Round the decay
of that colossal wreck, boundless and bare,
The lone and level sands stretch far away.
- Help! Quite possibly societies that plan over time scales ~1000 years will foresee physical problems and wish to discover if others have surmounted them. An example is a civilization whose star is warming (as ours is), which may wish to move their planet outward with gravitational tugs. Many others are possible.
- Leakage Radiation: These are unintentional, much like objects left accidentally in ancient sites and uncovered long after. They do carry messages, even if inadvertent: technological fingerprints. These can be not merely radio and television broadcasts radiating isotropically, which are weak, but deep space radar and beaming of energy over solar system distances. This includes “industrial” spaceship launchers, beam-driven sails, “planetary defense” radars scanning for killer asteroids, and cosmic power beaming driving interstellar starships with beams of lasers, millimeter or microwaves. There are many ideas about such uses already in the literature (Benford, G. and Benford, J., 2006, “Power Beaming Concepts for Future Deep Space Exploration,” JBIS 59, pp. 104-107).
- Believe and Join Us: Religion may be a galactic commonplace; after all, it is here. Seeking converts is common, too, and electromagnetic preaching fits a frequent meme.
The point is that there can be many motives, with two-way communication only one of them. The METI signals we’ve sent from Earth are detectable for only very short distances on the scale of the galaxy, typically a light year. Therefore, higher powers and larger antenna areas are required for serious Beacons.
All SETI search strategies must assume something about the beacon builder. Our other paper of last year (Benford, J., Benford, G., & Benford, D., 2009, “Messaging with Cost Optimized Interstellar Beacons”, arxiv.org/abs/0810.3966, submitted to Astrobiology) made the argument that whatever the motivations, the driver in building METI transmitters on such scales will be economics.
While cultural passions can set goals, economics determines how they get done. Many long-term spectacular projects, such as the pyramids of Egypt, lasted only a century or two and then met economic limits. The Taj Mahal so taxed its province that the second, black Taj was never built. The grand cathedrals of medieval Europe suffered cost constraints and, to avoid swamping local economies, so took several centuries of large effort. Passion is temporary, while costs constrain long-term projects.
So, we should look at cost as the limiting factor that will tell us things about what we should be looking for in SETI searches.
by Paul Gilster | Sep 21, 2009 | Astrobiology and SETI |
by Jon Lomberg
It seems fitting that we should be in the midst of a three-part series on SETI and METI issues. As Larry Klaes reminded me in a recent comment, September 19th was the fiftieth anniversary of the paper that began the modern SETI era, Morrison and Cocconi’s “Searching for Interstellar Communications” (available here). Artist, lecturer and polymath Jon Lomberg now adds his own take on the discussion. Pay particular attention to the question of signal duration — would a METI signal be continuous or intermittent? Much rides on the answer.
Lomberg is a familiar figure to Centauri Dreams readers. Creator of the Galaxy Garden (Kona, Hawaii), Jon is an astronomical artist working in many media whose work is known throughout the space community and beyond. Viewers of COSMOS will know that he was chief artist on that project, serving as Carl Sagan’s principal artistic collaborator for many years. His splendid work on CONTACT, where he storyboarded many of the film’s astronomical animations, showed what could be achieved in film with an adherence to scientific fact and solid conjecture.
Jon designed the cover for the Voyager Interstellar Record, the human artifact now pushing its way into true interstellar space. In other words, this is a man with experience at creating messages designed to reach out across vast gulfs of space and species. Here Jon adds to our discussion of SETI and METI with a look at what an interstellar beacon might be, and what it might be designed to do.
Let’s step back from the consideration of methods of transmission and the relative virtues of radio,optical, etc. The physics of these are well understood, so naturally it is the domain of search space that is easiest to study and manipulate. We can choose what kind of transmitters and receivers we will use. The only real progress in SETI has been the improvement of the sensitivity and bandwidth of the receivers. No doubt we will soon have the ability to monitor MOST of the radio/microwave spectrum at once. But perhaps that will not solve our problem of finding beacons.
What are the ideal properties of an interstellar beacon from a human perspective, whether sending or listening?
- It should be as easy as possible to detect.
- It should transmit/receive using technology we possess.
- It should be detectable from the planet’s surface. as well as from instruments in space.
- It should be sent in as many wavelengths possible (radio, microwave, IR, optical, x and gamma)
- It should be as loud/bright as possible.
- It should be beamed directly toward us.
- It should be uninterrupted, constantly repeating some pattern.
- If there is an interval of silence between repetitions, it should be short.
(defining short and long in the context is a topic for another post. For the sake of argument let’s say a duty cycle of one hour is short. A duty cycle longer than 1 day is long)
The most significant limiting factor of all METI done so far, as well as most attempted SETI strategies, is the “haystack” of duration (how long a beacon signal lasts) and the duty cycle (how often is it repeated). Even if we were so amazingly lucky as to reach a planet of radio-smart ETs , the chances of any of our METI transmissions being detected is small because the signals only last a short time and are not repeated. (Indeed, acquiring the signal a second time is the filter through which any possible messages must pass. All the various WOW signals we have heard have not).
Image: Thinking about how a METI signal might be sent may cause us to re-evaluate our methods as we search for extraterrestrial intelligence. Artwork by Jon Lomberg.
Larry Klaes points out that sending uninterrupted powerful beacons is expensive. I would add to that annoying. Tests of tsunami sirens here in Hawaii are necessary but annoying, so they happen in my neighborhood only at 11:45 a.m.on the first Monday of each month. We want the tests and we want the test alarm to be very loud, but not happen too often.
A loud isotropic SETI beacon may temporarily inconvenience somebody doing something else in the society sending the beacon. Shielded, directed beacons are less problematic locally, but also impossible to detect if you are not in the beam. So short, powerful all-directional beacons on many wavelengths may be a better fit for societies living near their own beacon transmitters. Make a really loud noise only intermittently, but one very easy to spot for the time it is on the air, whatever instrumentation you are using to listen.
Duration and power seem inversely related: the briefer the transmission, the cheaper the energy. Is it better to have a very powerful beacon at the expense of length of transmission? A brief, very powerful burst could be detectable at much larger distances than a weaker one that lasts longer.
Duty cycle is the key variable. How long does a sender wait to charge up the capacitor (or whatever) before transmitting again? How often will the neighbors tolerate it? In my opinion, senders will likely opt for briefer and stronger beacons, because they are much easier to detect and reach many more potential targets while minimizing local inconvenience. Beacons must therefore be repeated– but at what interval?
Unless we can devise strategies that allow continuous monitoring of targets (or send repeated METI beacons ourselves) we could be looking in the right place at the right frequency– when they are off the air. Very strong, brief bursts simultaneously in many known wavelengths and “Z-waves” (Sagan’s generic term for methods we don’t know about yet) would reach the greatest diversity of searchers. Senders really interested in finding others would cast their net as widely on the EM spectrum as possible.
Uninterrupted continuity of observation is the strategy that is most likely to detect intermittent but powerful beacons. A new SETI strategy would use arrays of low-cost, small receivers to look in many selected “special” directions: nearby exoplanets, sunlike stars, galactic center/anticenter axis, etc. By passing off to receivers worldwide we sustain continuous searching without a lapse. Perhaps such a search could be piggybacked on home satellite dishes, like seti@home.
The reason I am unconcerned about any risk with current METI is that the very brief transmissions sent only once are probably too short to be detected, and in any case impossible for recipients to confirm with a second observation.
Long-lived civilizations will be patient civilizations. They will expect searchers to be patient as well. A patient search is not one constantly changing targets. It is choosing your direction of search and settling in to listen constantly until you hear something. Until we do that, it is premature to speak of any “silence in Heaven.”
by Paul Gilster | Sep 18, 2009 | Astrobiology and SETI |
?by Larry Klaes
About a decade ago while attending a SETI conference, I was listening to a researcher give a talk about detecting messages from other galaxies such as the giant elliptical galaxy Messier 87 and the immense Virgo galactic cluster it resides in. Since M87 is about 60 million light years from the Milky Way, I later asked him why would someone send a message that they could not hope to get a reply to for 120 million years at the least.
His reply was rather vague and dissatisfying to me. It was along the lines of they would do it for the sake of being able to sending such a message across such a vast distance and time. I was left with the impression he did not fully think out why any intelligence would send messages across millions of light years of intergalactic space with even less hope of a reply than our token METI (Messaging ExtraTerrestrial Intelligence) effort with Messier 13 in 1974 via Arecibo, for which we will need to wait 50,000 years for the quickest reply from there if ever.
Image: Messier 13, a globular cluster containing roughly one million stars in the halo of the Milky Way. It lies in the constellation Hercules, 25,000 light years from the Sun. Credit: Robert Lupton, Sloan Digital Sky Survey).
The SETI researcher seemed focused on the mechanics of how such a message would be done, which is good in itself of course, but not the why of it, which for me is the entire key of whether such transmissions will ever take place or not. Setting aside funding and resources for a moment, no serious science project is going to happen unless you give those in control of such things a reason for doing so that is agreeable to them.
Look at the Apollo manned lunar project conducted by the United States in the 1960s. If it were not for the underlying major goal of the two main Cold War nations trying to best each other via space, it is more than likely we would still be talking about sending humans to the Moon some day in the future. Just look at how we haven’t left LEO in person since late 1972 because of changes in the geopolitical climate.
Later on at the same conference I talked with some other SETI scientists about a METI type of idea that had intrigued me since I read author James Gunn’s 1972 SF novel The Listeners, where a civilization circling the star Capella sends humanity all its knowledge because its sun is going to explode and they know they cannot escape it otherwise (at the very end of the novel, it is revealed that a similar broadcast is also on its way to Earth from the region of the Crab Nebula, the remnants of the famous supernova of 1054 CE).
This made sense to me, as a sophisticated culture would not want to die off in vain and disappear completely from existence. They also would have nothing to fear or lose from signaling the rest of the galaxy about themselves. Not only would they remain alive in their records and the memories of others, but perhaps their knowledge might even enlighten and enrich their neighbors. And they wouldn’t be around if the recipients weren’t friendly in any event.
Image: Even a description of DNA could be sent to the stars. Art by Jon Lomberg (from the collection of Frank Drake).
I brought up this idea to these SETI folks, who surprisingly dismissed it out of hand. Maybe some things have changed in the last ten years, but I got the distinct impression that at least some of those who work in SETI thought that aliens would contact us purely for the good of increasing scientific knowledge. Or as I said above, the focus from these researchers seemed to be on the methods of interstellar (and intergalactic) signaling, not the potential range of reasons behind it, which is no small factor here.
Maybe there are such enlightened and altruistic societies out there with only those pure motives in mind. Certainly I am taking educated guesses here as much as anyone else from this planet. But just as Apollo happened mainly to showcase international and ideological might with science taking a backseat despite how NASA presented things, I am willing to bet that any alien species, even an insane one, will be conducting such a major undertaking as a sustained METI effort with more than one motive in mind. Certainly these motivations will include improving the various situations for the signalers.
Thus my desire to focus on delving into *why* any race of beings might want to conduct METI, especially one designed to last for many years and cover much of the galaxy, which would make sense if you don’t know who your neighbors are and you want to make sure to hit as many potential targets as possible. As a bonus for humanity, figuring out why an intelligence might want to signal us will help narrow our search in that very big celestial haystack out there, saving our SETI projects money, time, and resources in the process.
Image: The Evpatoria radio telescope in the Crimea, from which several METI signals have been sent to the stars.
The following is a short list of ideas I have created to consolidate my thoughts on why an alien intelligence would conduct their own METI program. It is certainly not meant to be complete and other ideas are welcome.
1. An ETI signal is intercepted by humanity by mistake. This would be an ETI message aimed our way by accident that was intended for someone else. Obviously, this one could come from anywhere at any time.
2. A “stunt” message, just like certain groups of humans have been doing lately by broadcasting Beatles songs, Doritos advertisements, and personal messages towards nearby star systems. I would even put the possibility of a practical joke in here, as some aliens may be as big a bunch of wiseasses as we are. Note how often humor is left out of the equation when considering the motives and behaviors of other intelligences. Why can’t they laugh about the absurd as much as we do? It may be not only a sign of intelligence but also a survival mechanism in this often bizarre and frequently dangerous Universe.
These messages could come from just about anywhere, but they have the serious drawback of being of very short duration. Only recently have we started more than a handful of consistent SETI programs, and even they are limited to a few electromagnetic realms and often with numerous gaps in data gathering time.
3. A deliberate “ping” to get our attention to open up a dialogue and information exchange. This can range from sheer scientific curiosity to the need for something they don’t have but we do (Nachos?). They may also be doing this for darker motives, from seeing who is out there to convert, conquer, colonize, or outright destroy. After all, if one species can colonize the whole Milky Way galaxy in just a few million years as has been asserted, others may find that to be a very legitimate threat to their existence and want to stop such a problem in advance.
I would like to think that 400 billion star systems across 100,000 light years of space should be room and resources for lots of beings – but when did logic ever play into certain motives when it comes to survival?
I have always always been a bit skeptical of the idea pushed by Carl Sagan about advanced intelligences broadcasting the equivalent of the Encyclopedia Galactica around the Cosmos to anyone who might want it. No one in their right mind goes around sharing every detail and secret of their lives with unknown and unpredictable strangers, so why would even an advanced species want to share their knowledge and power with potential rivals? Plus as SF author David Brin has pointed out, information unique to us may be our one bargaining chip with alien societies and we would not want to give it away for free.
4. A flood of information from a society that knows it is going to be destroyed not only as a species but their knowledge and works, too (see above). Having little to lose or fear from their information being used against them, these ETI send us and others all that they know to preserve themselves at least in data form.
This is one legit reason for SETI to aim its instruments at novae, supernovae, hypernovae, and GRBs, along with red giants, white dwarfs, pulsars, and even black holes. Supernovae are also important to check out for signals from non-threatened ETI who might use them as natural cosmic beacons.
5. Really advanced beings might signal us to say things like “Hey, we’re the big guys on the block – don’t even think about messing with us” to “We need your solar system for our latest Dyson Shell Galactic Mind Expansion Project, thanks ever so much” to “Hey, Charlie, we found some more vermin over here – get the Raid!” These guys might be found around the galactic core, in globular clusters, around black holes, or way out in the very cold fringes of the galactic edge.
To be honest I think we will have a better chance of finding them by their infrared signatures or astroengineering structures, as I don’t know if such beings would ever bother talking to us, but obviously I could be wrong. They might message us just because they know they can and cannot be harmed by us. People have been known to poke a stick in an ant colony just to see how the little insects will react.
Of course, G class stars with exoplanets where the Jovian-type worlds are not orbiting their suns in a matter of mere days and could therefore have Earthlike worlds (or habitable exomoons orbiting any Jupiter-type exoplanets) are potentially good bets too. And we might have beings exploring or colonizing all kinds of other star systems such as red dwarfs, but whether they would be doing METI as well is another matter.
Image: The Arecibo radio observatory in Puerto Rico. It was during the dedication of this facility that a message toward the globular cluster M13 was sent. Credit: SETI Institute.
Now there have been a number of legitimate METI projects over the years emanating from Earth that were not just stunts. A list of these efforts may be found at the Wikipedia entry on Active SETI. While these information messages were put together with some thought and planning and were sent out using powerful radio telescopes, they still suffer from being relatively brief in duration and therefore have limited chances of being picked up by unsuspecting (and hypothetical) alien species.
As one example, the Arecibo Message of 1974 to Messier 13 was just three minutes long. What are the odds that even if there are a fair number of suitable ETI living in that globular star cluster 25,000 years from now that even one of them will just happen to detect that transmission as it zips along? Not even the “covert” 20-minute METI effort by Joe Davis of MIT in the early 1980s has much better odds of being detected in the Milky Way. More recent METI broadcasts have all been narrowly focused and capable of being received by relatively few stars.
The shortness of these METI efforts is why I left them off the list but wanted to mention them just the same. ETI could be doing similar such broadcasts, but the odds of our detecting them with our current SETI programs are slim. Thus our chances lie with the sustained METI programs, which as has been pointed out already, may have some very interesting reasons behind their existence.
?
by Paul Gilster | Sep 17, 2009 | Outer Solar System |
I’m sure there are people who can keep things straight in the shifting world of planetary definitions, but given the fact that I’m still not used to Pluto’s demotion, I have to look twice before I write anything on the subject. After checking, then, I confirm that Haumea, the interesting outer system object recently considered as the target of a fast orbiter mission (see this earlier post, and its sequel), is called a ‘dwarf planet.’ Orbiting in the Kuiper Belt, Haumea joins Eris, Pluto and Makemake in this category, the fourth largest dwarf planet now known in the Kuiper Belt. Dwarf planet Ceres is a main-belt asteroid, and thus not, like the others, a KBO as well.
Image: Composite image of computer model frames showing Haumea’s red spot as the dwarf planet rotates. Credit: P. Lacerda .
What’s special about Haumea? Its shape, for one thing. The distant world rotates in 3.9 hours, faster than any other large object in the Solar System. That spin seems to account for Haumea’s unusual ellipsoidal shape, which is itself thought to be the result of an ancient impact. Whatever the case, the ellipsoid measures 2000 kilometers by 1600 by 1000 kilometers, balancing gravitational and rotational accelerations.
And now we have new information: Haumea has a spot. The findings were presented by Pedro Lacerda at the European Planetary Science Congress in Potsdam on Wednesday. Lacerda (Queen’s University Belfast) has this to say about the find:
“Our very first measurements of Haumea told us there was a spot on the surface. The two brightness maxima and the two minima of the light curve are not exactly equal, as would be expected from a uniform surface. This indicates the presence of a dark spot on the otherwise bright surface. But Haumea’s light curve has told us more and it was only when we got the infrared data that were we able to begin to understand what the spot might be.”
Further observations planned for 2010 on ESO’s Very Large Telescope should tell us more. Haumea is thought to be covered in water ice, based on spectroscopic observations, but its density (2.5 times that of water) implies that its interior is rocky. The spot is evidently an area richer in minerals and organic compounds than its surroundings. One possibility is that the spot is the scar of an impact, one that left traces of the impactor on the surface of Haumea, possibly mixing with materials from within the dwarf planet. Changes in brightness flagged this area, which is redder in visible light and bluer at infrared wavelengths. I’m thinking the light curve of Haumea must be a thorny thing to untangle, given the speed of rotation and oddball shape.
Two papers cover this discovery. The first is Lacerda et al., “High Precision Photometry of Extreme KBO 2003 EL61,” Astronomical Journal Vol. 135 (May 2008), pp. 1749-1756 (abstract). The second is Lacerda et al., “Time-Resolved Near-Infrared Photometry of Extreme Kuiper Belt Object Haumea,” Astronomical Journal Vol. 137 (February 2009), pp. 3404-3413 (abstract). Look here for links to full text, and also for an interesting animation of these findings.
