Prospects for Interstellar Travel

Be aware of Paul Titze’s continuing exegesis of John Mauldin’s book Prospects for Interstellar Travel (Univelt, 1992). I used Mauldin again and again as I developed my Centauri Dreams book, finding the dense and lengthy volume covered every conceivable aspect of interstellar flight as understood by current physics. But the book was published in a small press run and is hard to track down, although Amazon usually has a few copies from independent resellers available. Paul is doing the community a service by going through Mauldin chapter by chapter, highlighting the salient points with commentary.

A quote from an early chapter:

Relativity makes energy a serious problem through the limits imposed to prevent speeds greater than light. Relativity also offers tantalizing solutions: the slowing of time and Total Conversion of mass to energy. How closely propulsion might approach TC is explored in Chapter 4. One could hope to find a way to travel without the action-reaction rocket method–no exhaust, no acceleration, little travel time, no deadly beams, no titanic low-mass energy source–but these are still mostly dreams from sf. Thus far it is not surprising that “visitors” from other stars have not appeared recently nor left their garbage laying about. They also must contend with what their Einsteins discover about interstellar travel. If visitors were to arrive, one of the first facts we would want to know is “how did they do it?”

All of which, as Paul notes, impinges on the three goals once defined by the Breakthrough Propulsion Physics project:

• Mass: Discover new propulsion methods that eliminate (or dramatically reduce) the need for propellant.
• Speed: Discover how to circumvent existing limits (light-speed) to dramatically reduce transit times.
• Energy: Discover new energy methods to power these propulsion devices.

Mauldin’s treatment of other propulsion options, from solar sails and beamed propulsion to nuclear fusion and antimatter, is exhaustive even if dated, but there is much to engage the interest in later chapters on interstellar navigation, the building of colony ships, shielding options, starship subsystems, and the advantages of self-replicating probes. Science fiction writers will find enough fodder in Mauldin’s pages to justify the price, as will anyone serious about making the case for venturing beyond the Solar System. Paul Titze is doing us all a service by going through these pages sequentially and with thoughtful annotations.

SPESIF 2010 Approaches

The Space, Propulsion & Energy Sciences International Forum 2010 will be held beginning February 23 at the Kossiakoff Center, Applied Physics Lab, Johns Hopkins University. Aerospace engineer Glen Robertson moderates the sessions, which include NASA’s Les Johnson presenting “From Research to Flight: Surviving the TRL ‘Valley of Death’ for Robotic and Human Space Exploration,” and a panel on the first fifty years of the space age and prospects going forward moderated by Roger Launius, curator of the National Air and Space Museum. Robert Zimmerman, author of The Universe in a Mirror and other books, will speak at the conference’s banquet. More information available at the IASSPES site.

Looking Back at Life Elsewhere

In a lively new article, the Daily Mail takes a retrospective look at two events that tantalized us with the possibilities of finding extraterrestrial life. In fact, author Michael Brooks simply declares Gilbert Levin ‘the man who found life on Mars.’ Well, we thought so for a few days back in 1976, when an experiment on board the Viking Mars lander got a positive result, prompting Champagne, a party, and a jubilant phone call from Carl Sagan. But later experiments found no carbon in the Martian soil, the Champagne lost its bubbles and Sagan retracted his congratulations. These days Levin would like to see the mission results revisited, especially the possible malfunctioning of the carbon-detecting instrument, but we may have to wait for future probes to really understand what Viking did or didn’t find.

Which takes us back to August 15, 1977, when Jerry Ehman found a puzzling signal in data from a radio telescope in Ohio. The signal’s frequency looked promising — it came in at the 1420 MHz hydrogen line — and to this day Ehman says ‘I am still waiting for a definitive explanation that makes sense.’ From the Daily Mail’s article:

Ehman and his colleagues have explored every possibility: military transmissions, reflections of Earth signals off asteroids or satellites, natural emissions from stars, but nothing fits.

The strangest thing of all is that it came from a blank patch of sky. When Ehman and his colleagues looked at the exact location of the source, it turned out to be devoid of stars. Ehman’s only thought is that it could have been beamed from a spaceship travelling through the universe in search of some sign of life.

Not that he is totally convinced it really was aliens but he has never come up with a better explanation.

‘It had all the earmarks of being a signal from an intelligent civilisation,’ Ehman told me on the phone. ‘There it was, like it was saying, “Here I am – can you see me?”‘ But, he concedes, we may never have proof one way or the other.

Proof, of course, is what we need, but the WOW! signal still stands as perhaps our most interesting single SETI reception, one that could not be confirmed but impels many in the field to renewed commitment to the search. Brooks wonders whether we have been both extraordinarily lucky in possibly receiving a genuine signal of extraterrestrial life and amazingly careless in that we couldn’t follow it up or, for that matter, the elusive evidence of what happened on Mars. Good stories both, but the only practical thing is to go forward with new life detection methods for planetary surfaces as well as the depths of interstellar space.

The Shape of ETI

What would any alien we heard from via SETI actually look like? New Scientist took a crack at this question in its January 23 issue (thanks to Gary Bennett for the tip), noting factors like its probably predatory instincts, or the fact that an extraterrestrial must be able to send and receive radio waves, laser beams or some other forms of communication. That seems to presuppose a basic technology and a social structure. From the article, quoting astrobiologist Dirk Schulze-Makuch :

So message-sending aliens will probably have some form of society. It need not be anything like human societies, however. “There are meta-intelligences in the societies of bees and termites. I can imagine something like a termite or ant colony that gets really intelligent,” says Schulze-Makuch. This does not tell us, however, whether they will be furry, scaly or slimy. Even on Earth, clever brains come in a wide variety of packages: dolphins and primates, parrots and crows, sea otters, honey badgers, octopuses and squid.

Yes, and what about convergent evolution? Do hearts and eyes and other features develop independently in different branches of life’s tree? We might then find aliens with recognizable eyes, and probably some kind of manipulating organs to work with their technology:

Putting it all together, the daring astrobiologist might be prepared to make a very small bet that SETI-type aliens will be social multicellular predators with eyes, sexes, and sticky-out bits of some sort. Unless, of course, the aliens were usurped by smart machines or decided to modify themselves using biotechnology. In that case, we might find tentacled monsters, pale skinny humanoids, shimmery beings of pure energy…

Every few weekends as we move toward the March 5 deadline for submission of abstracts to the next International Astronautical Congress, I’ll re-run this call for papers that I originally published in December. The Tau Zero Foundation hopes to energize discussion of FOCAL in the astronautical community and create a growing set of papers analyzing aspects of the mission from propulsion to communications, leading to a formal mission proposal. We hope anyone interested in furthering this work at the coming IAC in Prague will consider submitting a paper.

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.

Here’s something to consider re the recent Pluto news: The Hubble maps of the tiny world that were released yesterday show a resolution of roughly 300 miles per pixel. When New Horizons flies by Pluto/Charon in 2015, it will send images with a resolution of 300 feet per pixel. And we’ve been reminded once again that every time we look deeper into something hitherto unexplored, we’re likely to be surprised. The surprise in this case was the significant reddening of the dwarf planet and the time frame in which it occurred, a mere two years.

I thought the liveliest part of the teleconference on Pluto yesterday was Marc Buie’s response to what had appeared in his datasets. Buie (Southwest Research Institute) was looking at imagery collected by the Hubble Space Telescope from 2002 to 2003 and comparing it with the results of earlier ground-based observations, as well as with Hubble pictures taken in 1994. The dramatic reddening seems to have occurred between 2000 and 2002, even as the illuminated northern hemisphere continued to get brighter.

Asked about his reactions to the newer Hubble imagery, Buie was candid:

“The color change in such a short period had me scared, because it’s so hard to understand. I’ve been checking absolutely everything I can think of, wondering if I screwed this up somehow and got the wrong answer. If I did, I can’t find the mistake.”

Another key point: In the Hubble imagery, the color of Charon remains the same throughout, whereas the reddening of Pluto is pronounced. Have a look at the images below, which represent the most detailed view of Pluto taken to date:

Image: Hubble’s view isn’t sharp enough to see craters or mountains, if they exist on the surface, but Hubble reveals a complex-looking and variegated world with white, dark-orange, and charcoal-black terrain. The overall color is believed to be a result of ultraviolet radiation from the distant Sun breaking up methane that is present on Pluto’s surface, leaving behind a dark, molasses-colored, carbon-rich residue. The center disk (180 degrees) has a mysterious bright spot that is unusually rich in carbon monoxide frost. This region will be photographed in the highest possible detail when NASA’s New Horizons probe flies by Pluto in 2015. Credit: NASA, ESA and M. Buie (SwRI).

Buie noted that the images represent his best guess at the true color appearance of the dwarf planet. The reddening seems to be caused by ultraviolet radiation from the Sun, which breaks up the methane found on Pluto’s surface and leaves behind a dark red, carbon-rich residue. The surface we’re looking at is doubtless a consequence of seasonal changes, with ice melting on the sunlit pole and refreezing on the dark, southern pole. Pluto’s elliptical orbit contributes to a relatively quick transition between spring and polar summer in the northern hemisphere. Previous observations have shown the mass of Pluto’s atmosphere doubling in the period between 1988 and 2002, evidently because of the warming and melting of nitrogen ice. Even so, this much surface change in a short period is surprising.

Kuiper belt specialist Mike Brown (Caltech) pointed out at the teleconference that the changes on Pluto are more extreme than anything previously seen in the Solar System:

“We see Pluto in these images about as well as we see the Moon with the naked eye. Now imagine the Moon changing by that much in such a short period of time. If we look around the Solar System at the surfaces we can observe, we see changes to the ice caps of Earth and Mars and that’s about it. But Pluto offers up more dramatic changes than anything else. There’s a good reason for this: The Kuiper belt features objects in extreme orbits. Right now it’s in the spring of its year, but by 2108 it will be at its furthest from the Sun. Pluto in winter will be a colder place on which things will freeze out and re-condense.”

This second image gives an idea of the brightening found in the northern hemisphere:

Image: Two Hubble photo maps of the dwarf planet Pluto, as seen in 1994 and 2002-2003. The white areas are surface frost, and the dark areas are a carbon-rich residue caused by sunlight breaking up methane that is present on Pluto’s surface. A comparison of the maps shows that Pluto’s brightness has changed between 1994 and 2003. The northern pole is brighter and the southern hemisphere is darker. Summer is approaching Pluto’s north pole, and this may cause surface ices to melt and refreeze in the colder shadowed portion of the planet. Credit: NASA, ESA and M. Buie (SwRI).

Twelve orbits of Hubble were dedicated to Pluto between 2002 and 2003, using the ACS high resolution camera to make 16 images in each of two filters, one blue, one green, for a total of 384 images. Using dithering techniques and specially developed algorithms to reconstruct a higher-resolution image, the pictures are the result of intense processing requiring twenty computers operating continuously for four years. But they won’t retain pride of place as our best photos of Pluto for long. Buie intends to use Hubble’s Wide Field Camera 3 to make additional observations before New Horizons arrives. The more the better, for the current maps are already in use for planning the brief encounter.

When New Horizons does arrive, it will only have time to photograph one hemisphere in detail. The bright spot seen in the Hubble images, known to be rich in carbon monoxide frost, is a prime target for investigation. Doubtless further surprises await.

The papers are Buie, et al., “Pluto and Charon with the Hubble Space Telescope: I. Monitoring global change and improved surface propertices from light curves,” and Buie et al., “Pluto and Charon with the Hubble Space Telescope: I. Resolving changes on Pluto’s surface and a map for Charon.” Marc Buie’s page on Pluto at SwRI has links to both. They were released on February 4, the 104th birthday of Pluto discoverer Clyde Tombaugh.

What JPL’s Mark Swain calls ‘an absolutely brilliant way to characterize super-Earths’ has emerged from work performed with a small NASA infrared telescope, one that has allowed scientists to identify an organic molecule in the atmosphere of a distant gas giant. HD 189733b is an old friend by now, the subject of intensive studies with space-based telescopes that have revealed water vapor, methane and carbon dioxide in its atmosphere. In the new work, Swain’s team made a spectrographic detection of carbon dioxide and methane using a ground-based instrument and a new method to remove the effects of tracking errors and the variability induced by changes in the Earth’s atmosphere.

Image: To detect the chemicals in the atmospheres, astronomers measure light from the star system as its planet, which is lined up edge-on from our point of view, orbits around. The total light is measured (B in the chart at lower left), and then, when the planet disappears behind the star, the light of the star alone is measured (A). By subtracting A from B, you get light from just the planet. A breakdown of this light into its basic wavelength components is then plotted out to reveal the “fingerprints” of chemicals. These data, shown at upper right, are called a spectrum. The molecular drawings at lower right show the three molecules identified so far in the planet HD 189733b — water, carbon dioxide and methane. Credit: NASA/JPL-Caltech.

The gas giant in question orbits a K-class star in the constellation Vulpecula. And while the team didn’t tell us anything truly startling about HD 189733b, it was able to probe the emission spectrum between 2.0 and 2.4 μm as well as 3.1-4.1 μm, wavelengths where space-based telescopes lack capability. The result was the discovery of a bright infrared emission from methane on the day side of the planet that had not been anticipated.

In a paper in Nature, the authors speculate that activity in the planet’s upper atmosphere related to ultraviolet radiation from the parent star could be the cause of the emissions. But the team adds that more work is needed to be sure. While we await further studies, we can look forward to using the team’s new calibration techniques on larger ground-based instruments. Says Swain:

“The fact that we have used a relatively small, ground-based telescope is exciting because it implies that the largest telescopes on the ground, using this technique, may be able to characterize terrestrial exoplanet targets.”

Small indeed — the telescope is a 3-meter instrument located at NASA’s Infrared Telescope Facility at Mauna Kea, Hawaii that ranks 40th among ground-based telescopes. Couple the new methods with the continuing findings of our space-based observatories and the goal of studying the atmosphere of a planet that can support life seems just a little closer. Swain sees the technique being put to use in conjunction with the Hubble and Spitzer instruments and, eventually, the James Webb Space Telescope, to characterize the atmosphere of super-Earths, a category of planet whose numbers may swiftly grow via Kepler data.

The paper is Swain et al., “A ground-based near-infrared emission spectrum of the exoplanet HD 189733b,” Nature 463 (4 February 2010), pp. 637-639 (abstract).

Collisions between asteroids should be highly energetic affairs, with an average impact speed of close to 5 kilometers per second. We may be looking at the debris of a head-on collision between two asteroids in imagery provided by the Hubble Space Telescope. The object in question, originally thought to have been a comet, is P/2010 A2, discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) sky survey on January 6 of this year. The follow-up Hubble imagery dates from late January, and shows an unusual filamentary pattern near the nucleus.

Image: HST picture of the comet-like object called P/2010 A2. The object appears so unusual in ground-based telescopic images that discretionary time on Hubble was used to take a close-up look. This picture, from the January 29 observation, shows a bizarre X-pattern of filamentary structures near the point-like nucleus of the object and trailing streamers of dust. The inset picture shows a complex structure that suggests the object is not a comet but instead the product of a head-on collision between two asteroids. Credit: NASA, ESA, and D. Jewitt (UCLA).

No asteroid collision has been observed before, but the idea that the asteroid belt is continuously ground down by collisions is well established. Indeed, natural impacts of this kind are thought to supply the zodiacal cloud in our Solar System with its dust. When the image was taken, the object was 300 million kilometers from the Sun and 140 million kilometers from Earth. Taken by Hubble’s Wide Field Camera 3, the black and white image was made in visible light but uses a blue color map to bring out details.

The assumption is that the filaments consist of dust and gravel thrown out of the 140-meter nucleus. Another intriguing fact: The main nucleus of P/2010 A2 lies outside its own halo of dust, a configuration never seen before in a comet-like object.

“This is quite different from the smooth dust envelopes of normal comets,” says principal investigator David Jewitt of the University of California at Los Angeles. “The filaments are made of dust and gravel, presumably recently thrown out of the nucleus. Some are swept back by radiation pressure from sunlight to create straight dust streaks. Embedded in the filaments are co-moving blobs of dust that likely originate from tiny unseen parent bodies.”

Astronomers believe the lack of gas in the spectra of this object is consistent with a collision. We don’t seem to be looking at ices from a parent cometary body turning into vapor, but rather a shower of debris pushed by the pressure of sunlight into a comet-like tail. If P/2010 A2 is indeed the result of an asteroid collision, its orbit is consistent with its being a member of the Flora asteroid family, which was itself produced by collisional shattering. In fact, according to this NASA news release, one fragment of the collision that produced the Flora family may have been the impactor that struck the Earth 65 million years ago, possibly the cause of the mass extinction of the dinosaurs.

Suppose a civilization somewhere in the cosmos is approaching Kardashev type III status. In other words, it is already capable of using all the power resources of its star (4*10²⁶ W for a star like the Sun) and is on the way to exploiting the power of its galaxy (4*10³⁷ W). Imagine it expanding out of its galactic niche, turning stars in its stellar neighborhood into a series of Dyson spheres. If we were to observe such activity in a distant galaxy, we would presumably detect a growing void in visible light from the area of the galaxy where this activity was happening, and an upturn in the infrared. Call it a ‘Fermi bubble.’

That’s the term used by Richard Carrigan (Fermi National Accelerator Laboratory) in his latest work on what he calls ‘interstellar archaeology,’ the search for cosmic-scale artifacts like Dyson spheres or Kardashev civilizations. A Fermi bubble would grow as the civilization creating it diffused through space. Carrigan notes that, as Carl Sagan and others observed, the time to colonize an individual system is small compared to the travel time between stars. An expanding front of colonization might then move forward at a rate roughly comparable to the space travel velocity. A civilization could engulf its galaxy on a time scale comparable to the rotation period of the galaxy, and perhaps a good bit shorter.

Evidence for Artifacts?

You might think a galaxy like the M51 Whirlpool galaxy would be ideal for such study, but Carrigan says a rough qualitative estimate shows there are no unexplained ‘bubbles’ at the level of 5 percent of the M51 galactic area. The quest is tricky because spiral galaxy structure includes natural voids — even if a void in visible light with infrared enhancement were traced, it would be hard to regard it as anything other than natural. In fact, James Annis has suggested that elliptical galaxies , which exhibit little structure, might be a better place to look for Fermi bubbles than spiral galaxies. Whatever the case, we’ve moved a long way from conventional SETI, listening for intentional transmissions from other civilizations.

Image: M51, the Whirlpool Galaxy. A so-called ‘Fermi bubble’ might appear as a void in visible light here. NASA and The Hubble Heritage Team (STScI/AURA) Acknowledgment: N. Scoville (Caltech) and T. Rector (NOAO).

Where else could we turn in the study of interstellar archaeology? Theoretically, synthetic or unnatural constituents in an exoplanet atmosphere could one day show us a sign of ETI. We’re already managing to study the atmospheres of particular gas giants, but thus far we lack the spectral sensitivity to clearly identify atmospheric signals of life or intelligence. A better bet might be stellar spectral signals, looking for example for signs of nuclear fission waste products that have been disposed of inside a star. More intriguing still is the idea of spectral modulation in stars nearing the end of their lives. Writes Carrigan:

…in the red giant phase Earth will most likely be swallowed as the sun expands. On the other hand if there was some possibility of life continuing the situation might engender a spirit of grand engineering and also an urge to communicate. In many cases the red giant environment generates varying maser signals. Modulation could emerge from dust clouds… moving and transforming in the spirit of weather systems on the Earth. (“Dust clouds” here is used to describe dust clumps around a star.) Modulation could also arise from linking the magnetic field from a Jupiter-scale planet and the stellar equivalent of the solar wind.

Dyson Spheres as Markers

As to those Dyson spheres, their use would greatly expand the useful area for activities for any culture that could build them, absorbing most or all visible light and re-radiating the energy of the star at lower temperatures. Various searches for infrared excesses around visible stars –hoping to target a partial Dyson sphere, perhaps a ring — have been attempted, but no candidates emerged from searches of several thousand stars. Even a pure Dyson sphere, completely surrounding its star, is a tricky catch because there are natural objects that mimic it, especially since dust clouds surround stars as they are born and as they die.

Carrigan used data from the IRAS spacecraft’s database of low resolution spectra, discarding objects that had been previously well categorized and narrowing the sample to sixteen sources that he calls ‘mildly interesting.’ The result:

Only three of these had relatively low spectral statistical fluctuations. All of the sixteen sources have some feature which clouds their identification as a Dyson sphere. In practice, most of the LRS candidates have higher temperatures and just don’t look much like the spectrum expected from a Dyson sphere. The search suggests that there are few if any even mildly interesting candidates within several hundred light years of Earth.

What can we do to sharpen the search for objects like Dyson spheres? Carrigan adds:

…a Dyson sphere does not require intent to communicate on the part of a civilization. The current detection reach is comparable to a SETI search. However there is a problem of confounding signatures from mimics such as carbon stars. Searches for potential Dyson spheres would be sharpened by developing more realistic pictures of construction scenarios including such factors as time to build and approaches to stability… Finally it would be interesting to consider how stellar evolution might stimulate the necessity of such large scale structures with a view to looking at candidate objects in the later stage of evolution along the main sequence.

A Parallel Track for SETI

When we contemplate the kind of structures or effects sought by the interstellar archaeologist, we acknowledge they demand technologies so far beyond our own that their construction seems all but miraculous. We can look for Dyson spheres, for example, but scarcely imagine how a culture could build at this scale. But these are limitations of our own state of development, and they don’t keep us from extrapolating to what civilizations far older than our own might be capable of developing.

Image: A Hubble Space Telescope view of the diverse collection of galaxies in the cluster Abell S0740, some 450 million light-years away in the direction of the constellation Centaurus. The giant elliptical looms large at the cluster’s center. Would we be able to detect signs of interstellar engineering in such an object? Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration.

As we supplement existing SETI searches with the search for interstellar artifacts, we have much to do to separate natural signatures from possible signs of intelligence, but engineering on a stellar or even galactic scale should be observable if our imaginations give us a serious hint of what to look for.

The paper is Carrigan, “Starry Messages: Searching for Signatures of Interstellar Archaeology” (preprint available). Highly recommended especially for its overview of current scholarship on the subject, including the fascinating work of James Annis and his search for Kardashev Type III civilizations. Note this on Annis’ work:

The distribution of galaxies on a plot of galactic optical brightness or luminosity versus the maximum rotation velocity or radius of the galaxy follows a fairly consistent pattern. Cases lying below the typical galactic trend line reflect visible light that has been absorbed and emitted somewhere else in the electromagnetic spectrum. Annis examined existing distributions for spiral and elliptic galaxies and looked for sources below the normal trend lines where more than 75% of the visible light would have been absorbed. No candidates were found in a sample of 137 galaxies. From this Annis inferred a very low probability of a Type III civilization appearing that would be found using this search methodology.

But Carrigan goes on to say:

With more recent information it is possible to extend the search to samples that are considerably larger and also more robust. It may be time to revisit this possibility. In particular with a sample ten to one hundred times larger one could examine the nature of a handful of outliers in more detail looking for any unique features such as a higher than normal infrared component. These outliers might be candidates for a radio SETI search.

Be aware as well of Martyn Fogg’s Planetary Engineering Bibliography, another useful source for sharpening our understanding of what future engineers might do.

We push deeper into the mysteries of brown dwarfs with the discovery of SDSS 1416+13B, an object orbiting another brown dwarf between fifteen and fifty light years from the Sun. The new dwarf, discovered in data collected by the United Kingdom Infrared Telescope (UKIRT) in Hawaii, is visible only in infrared light. Philip Lucas (University of Hertfordshire) cautions that there remains much we don’t know about the telescope’s latest find:

“This looks like being the fourth time in three years that the UKIRT has made a record breaking discovery of the coolest known brown dwarf, with an estimated temperature not far above 200 degrees Celsius. We have to be a bit careful about this one because its colors are so different than anything seen before that we don’t really understand it yet. Even if it turns out that the low temperature is not quite record breaking, the colors are so extreme that this object will keep a lot of physicists busy trying to explain it.”

Image: UKIRT UKIDSS near-infrared image of SDSS1416+13AB (left panel) and the Spitzer+UKIDSS mid-infrared image (right panel). Credit: JAC/UKIRT, Spitzer Space Telescope, University of Hertfordshire.

The work grew out of a dedicated brown dwarf search called the UKIRT Infrared Deep Sky Survey. The data showed an object far bluer at near infrared wavelengths than any brown dwarf observed before. Follow-up studies with the Japanese Subaru Telescope show that SDSS 1416+13B is a T dwarf, a type of brown dwarf with a methane-laden atmosphere. Further work at longer wavelengths via the Spitzer Space Telescope allowed a temperature estimate of 500 Kelvin (227 degrees Celsius). Ben Burningham (University of Hertfordshire), who made the discovery, notes where it fits in our current understanding of these objects:

“The fact that it is a binary companion to a warmer brown dwarf that also has an unusual spectrum is helping us to fill in some gaps in our understanding. It seems likely that both brown dwarfs are somewhat poor in heavy elements. This can be explained if they are very old, which also fits with the very low temperature of the faint companion.”

Interesting stuff. The team cautions that its parameters for this system are preliminary, but comes up with a possible separation of 45 to 135 AU for the binary pair. The system’s estimated age: 10 billion years. Take a look at the near-infrared spectrum from Subaru:

Image: Subaru near-infrared spectrum of SDSS1416+13B, taken with the IRCS spectrograph. The almost total absence of light at wavelengths between 1.7 and 2.5 microns reflects the low metal content and high gravity at the surface of the brown dwarf, and results in its very blue near-infrared color. These same physical properties enhance the brightness in the mid-infrared, and so the color flips to red when the near-infrared is compared with data from the Spitzer Space Telescope. Credit: Subaru Telescope (NAOJ), University of Hertfordshire.

Brown dwarfs become more and more intriguing, given their evidently high numbers and the possibility of one or more being found closer to us than the Centauri stars. The WISE mission should be able to find such an object, if it is there. In the meantime, sharpening our skills at observing these objects helps us chart the terrain between stars and gas giants. The paper is Burningham et al., “The discovery of a very cool binary system,” accepted for publication in Monthly Notices of the Royal Astronomical Society (preprint available).

The New Horizons probe to Pluto/Charon is approaching Uranus’ orbit, prompting the team’s Twitter poster to remember Challenger’s final crew in a tweet late yesterday. Challenger was lost on January 28, 1986, just as Voyager 2 reached Uranus, and thus we had the joy of a new planetary encounter mingling with grief for a fallen crew. I remember that day as vividly as anyone, I suppose. I was doing an intensive flight instruction seminar in Maryland, a weekend push that had me flying all day with students trying to improve their instrument landing skills. We were just headed out for another session when the news came, and a number of the pilots went to the closest TV to see for themselves.

We looked and shook our heads in disbelief. Then we got back into our respective cockpits and took off again, trying to keep those images out of our minds to focus on things like holding patterns and ADF approaches and staying out of a low icing layer over West Virginia that got more and more troublesome as the day went on. Grim memories because of their context. This morning also seems grim because of the recent death, evidently a suicide, of Andrew Lange, an astrophysicist at Caltech whose young career (he died at 52) was devoted to the microwave background that tells us so much about the early universe.

The investigation of the cosmos has always struck me as joyous and it’s troubling to examine it in the context of sudden death. But Lange’s contribution was immense. His Boomerang experiment, discussed in this New York Times feature, flew in 1998 over Antarctica. Boomerang stood for Balloon Observations of Millimetric Extragalactic Radiation and Geophysics. The balloon made a ten-day flight at 120,000 feet, detecting and mapping the microwave glow of the universe as it was when only 400,000 years old. The results suggested a flat universe, one that would keep expanding.

The finding was consistent with the theory of inflation, an incredible expansion of the universe in its earliest moments. The Times story quotes Marc Kamionkowski (Caltech) as saying, “Boomerang was just crystal clear; it was the shot heard around the world.” The findings were backed by the Maxima experiment, which Lange had a hand in, and the Cosmic Anisotropy Telescope. They were later confirmed by the Wilkinson Microwave Anisotropy Probe (WMAP). The 1998 finding of the universe’s accelerating expansion fits the Boomerang results nicely — if there was not enough matter in the universe to make it flat, we now learned there was certainly enough energy.

It could be said, then (and Michael Turner at the University of Chicago makes this case) that Lange’s Boomerang team were the first to demonstrate that the geometry of the universe is flat. He went on to work on detectors for continuing the study of the cosmic microwave background. What forces drove his own life to its early end we can only leave to conjecture, but it’s one of life’s redemptive elements, as Challenger reminded us, as Columbia reminded us, that while death can turn exhilaration into stunned silence, it cannot still the resurgence of spirit that hands over the work to new volunteers who will bring new missions home. Requiescat in pace.

It was in 1900 that mathematician David Hilbert created a list of the most significant unsolved problems for mathematics at a conference in Paris. The list would eventually be fleshed out to reach a total of 23 problems. Hilbert’s Paris talk, “The Problem of Mathematics,” began this way:

Who among us would not be happy to lift the veil behind which is hidden the future; to gaze at the coming developments of our science and at the secrets of its development in the centuries to come? What will be the ends toward which the spirit of future generations of mathematicians will tend? What methods, what new facts will the new century reveal in the vast and rich field of mathematical thought?

The Wikipedia entry on Hilbert notes that the 23 problems, fewer than half of which were presented at the meeting, have gone on to be discussed throughout the following century, with some remaining unresolved to this day. I look at Hilbert’s introduction and think about how apropos the idea of gazing at ‘coming developments of our science’ is to what we do here. Maria Spiropulu, a senior scientist at CERN near Geneva, used Hilbert when talking to the New York Times‘ Dennis Overbye about a weekend conference that recently concluded in Los Angeles. The Physics of the Universe Summit had a grand title, and Spiropulu hoped to use it to “…set out the questions for the next nine decades.”

Now, of course, we have the Large Hadron Collider, which offers the chance to create conditions similar to those existing in the earliest moments of the universe. The trick is in making sense out of what it may show us. Lisa Randall (Harvard) pointed to Galileo’s maxim that physics progresses more when working on small problems than talking about large ones, which could be taken as a way of saying that no matter how elegant a theory may be, it often runs into problems when we get into the details. Supersymmetry, for example, could explain things like dark matter, but Randall points out that no supersymmetric effects have turned up yet as deviations in the Standard Model of physics. Randall believes they should have.

Overbye’s article on the Summit lays out its interesting methodology:

Organized into “duels” of world views, round tables and “diatribes and polemics,” the conference was billed as a place where the physicists could let down their hair about what might come, avoid “groupthink” and “be daring (even at the expense of being wrong),” according to Dr. Spiropulu’s e-mailed instructions. “Tell us what is bugging you and what is inspiring you,” she added.

Adding to the air of looseness, the participants were housed in a Hollywood hotel known long ago as the ‘Riot Hyatt,’ for the antics of rock stars who stayed there.

The eclectic cast included Larry Page, a co-founder of Google, who was handing out new Google phones to his friends; Elon Musk, the PayPal electric-car entrepreneur, who hosted the first day of the meeting at his SpaceX factory, where he is building rockets to ferry supplies and, perhaps, astronauts to the space station; and the filmmaker Jesse Dylan, who showed a new film about the collider. One afternoon, the magician David Blaine was sitting around the SpaceX cafeteria doing card tricks for the physicists.

Wish I were a friend of Page’s — I could use a Nexus One! This is a lively bunch and ideas must have been flying. Gordon Kane (University of Michigan) opined that the Large Hadron Collider would indeed discover supersymmetry but offered no explanations that would point to a theory of dark energy. One big question at a time. Overbye quotes Lawrence Krauss (Arizona State) on the matter of theories and their application, and this, too, is entertaining:

“We get the notions they are right because we keep talking about them,” he said. Not only are most theories wrong, he said, but most data are also wrong — at first — subject to glaring uncertainties. The recent history of physics, he said, is full of promising discoveries that disappeared because they could not be repeated.

Physics can take us from optimism to pessimism in a heartbeat. Are we on the verge of discovering a true ‘theory of everything?’ Or are we likely to be more confounded with each new assault on the secrets of the universe? We haven’t a clue how to explain dark energy, and dark matter remains undetected. For that matter, as Overbye notes, we’ve assumed that dark matter is a kind of particle. What if, instead, it is an ‘entire spectrum of dark behaviors’? Are there forces as well as particles on what these physicists are calling the ‘dark side’?

No answers here, but plenty of questions, in keeping with Dr. Spiropulu’s wish to emulate Hilbert. As a series of investigative doors wide open to the 21st Century, the topics discussed here lead to both exhilaration and confusion. We’ve seen much the same thing occurring in the exoplanet hunt, where we hardly thought we’d find anything as outrageous as planets orbiting a pulsar, or ‘hot Jupiters’ existing breathtakingly close to their stars. The trick seems to be to build the tools that let us push farther and deeper into nature, without prejudging what we will find. ‘Prepare to be surprised’ is as good a motto for today as any.

As I’m just finishing up Richard Holmes’ The Age of Wonder (Pantheon, 2009), the Royal Society had been on my mind even before the two-day conference on SETI that concluded yesterday made the news. If you haven’t read the Holmes book, by all means do so. It’s a fascinating study of the development of science and the imagination in the late 18th Century and into the Romantic era, with cameos by the likes of Shelley and Keats and in-depth discussions of everyone from Pacific voyager Joseph Banks to the chemist Humphry Davy. It’s a cliché to say I couldn’t put the book down, but this one fully deserves the compliment.

With the Royal Society now in its 350th year, a conference steeped in SETI and questions of astrobiology seems made to order as we track the data from our far-flung space observatories. I wanted to mention that Paul Davies’ public lecture at the conference, called “The Eerie Silence: Are We Alone in the Universe,” will be made available at the Royal Society video archive within a week or so. Davies (Arizona State), a physicist and popular science writer, argued at the conference that we should look here on Earth to see whether life has appeared on our planet more than once. A ’shadow biosphere,’ one representing forms of life entirely different from our own, might be present in isolated ecological niches.

Addendum: The Davies talk is now available here.

Davies is thinking of places like the dry valleys of Antarctica, or lakes saturated with salt, or volcanic vents. It’s an idea we’ve examined here before, and one you can follow up on in Davies’ article “Are Aliens Among Us?”, which ran in late 2007 in Scientific American Vol. 297, No. 6, pp. 36-43 and is available online. Davies’ book The Eerie Silence: Renewing Our Search for Alien Intelligence, is to be published by Houghton Mifflin Harcourt in April.

Pondering Davies’ ideas, London’s Times Online notes that a US Geological Survey team led by Felisa Wolfe-Simon is investigating places like Mono Lake in California, where arsenic contamination might support life-forms that use arsenic the same way other life-forms use phosphorus. Not everyone agrees, of course, and the article quotes Colin Pilinger, leader of the Beagle 2 Mars landing attempt, as saying that looking for arsenic-based life is ‘wildly science fiction,’ and ‘you’d be off your trolley’ to look for it.

I wish I could have been at this conference to have heard Pilinger’s own talk, not to mention Alfred Harrison’s. The latter, from the University of California at Davis, took on the huge question of how humans would react to the reception of a signal confirming the existence of extraterrestrial intelligence. Here’s his response to the Times:

“It is easy to imagine scenarios resulting in widespread psychological disintegration and social chaos. But historical prototypes, reactions to false alarms and survey results suggest that the predominant response to the discovery of a microwave transmission from light years away is likely to be equanimity, perhaps even delight.”

And the Guardian’s coverage of the conference looks at the parallel some people make with the famous 1938 ‘War of the Worlds’ broadcast of Orson Welles, which caused some in the radio audience to panic at the thought of an invasion from Mars. Harrison dismisses the idea:

“The public reaction was overstated. Most people who thought the broadcast was real took sensible actions to protect themselves,” Harrison said. “Surveys suggest most people think they will be fine, but they worry about others freaking out.”

I’m not sure which surveys Harrison is referring to, but one that supports him was presented as far back as 1996 at the OSETI II conference in San Jose (CA), where Miguel Sabadell and Fernando Salamero (University of Zaragoza, Spain) demonstrated that there was widespread public interest in extraterrestrial contact. Asked whether contact with ETI would be good for mankind, an overwhelming 79 percent answered Yes, and 77 percent agreed that if we receive a SETI signal, we should answer.

Also supporting Harrison were the results of a 2002 Roper poll that concluded:

“Most Americans appear comfortable with and even excited about the thought of the discovery of extraterrestrial life. Three-quarters of the public claim they are at least somewhat psychologically prepared for the discovery of extraterrestrial life, and nearly half are very prepared.”

This story in Nature News looks at Simon Conway Morris’ contribution to the conference. Morris, a paleontologist at Cambridge, points to examples of convergent evolution in Earth’s biological history to make the case for there being a limited number of ways to organize a sensorium or a society. The lives of intelligent aliens could, in other words, be every bit as violent as the lives of beings on Earth. Whatever the case, Martin Dominik (University of St. Andrews, UK) notes that no government has plans for what to do if intelligent life is confirmed elsewhere in the universe. One hope for the conference is that it will persuade policy makers to take the matter into consideration as the numerous imponderables of such contact are examined.