by Paul Gilster | Feb 8, 2010 | Culture and Society |
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…
by Paul Gilster | Feb 6, 2010 | Missions |
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.
by Paul Gilster | Feb 5, 2010 | Outer Solar System |
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.
by Paul Gilster | Feb 4, 2010 | Exoplanetary Science |
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).
by Paul Gilster | Feb 3, 2010 | Outer Solar System |
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.
