by Paul Gilster | Dec 8, 2007 | Culture and Society |
Ed Minchau offers up the latest Carnival of Space at his Robot Guy site. Centauri Dreams readers will want to look at Amanda Bauer’s presentation of an image taken by the Pluto-bound New Horizons spacecraft. It’s actually a composite showing Jupiter and a startlingly nearby Io. We’ve all seen Jupiter images, of course (thank you Voyager, Galileo, et al.), but take a look at this one to note the plume of the erupting Tvashtar volcano, a stunning reminder of how active this tortured little world continues to be.
Space Files has a nice overview of solar sail technologies beginning with Lou Friedman’s plans to develop Cosmos-2, a replacement for the lamented sail that perished in its launch attempt back in 2005. We still need to shake out this intriguing concept in space, and with NASA funding for sails in limbo, the private sector is the place to turn. Space Files gets into Japan’s recent experiments (useful as we learn how to deploy various sail configurations) and ESA’s GeoSail study. Getting this technology operational may become more of a priority for NASA, ESA and other agencies if Cosmos-2 can prove what sails can do.
Ed also links to Brian Wang’s survey of advanced propulsion systems. How does Brian keep up the pace at his advanced nanotechnology site? Not only is he a prolific writer but the wealth of images and links he produces can snare and hold my attention when I’m really supposed to be getting on with other work. I also want to point out his interesting piece on Franklin Chang-Diaz’ VASIMR (Variable Specific Impulse Magnetoplasma Rocket) engine concept, where he kicks around the idea of pairing the VASIMR drive with a proposed but evidently feasible portable nuclear reactor. No shortage of speculative fireworks here:
The total critical mass is from 600-1200 kg. The total mass for the nuclear reactor is probably under 100 tons and possibly in the 10-20 ton range. A nuclear powered Vasimr rocket would enable one way trips to Mars in 39 days and delivering 22 tons of payload. Vasimr engines can get up to 50,000 ISP which is 1100 times more fuel efficient than the Space Shuttle. The nuclear space vehicle would weigh about 600-1500 tons fully fulled. So it would take several launches using chemical rockets to put the pieces in orbit for assembly. A slightly scaled back system with one or two nuclear reactors would still enable trip to Mars for 70-100 day trips to Mars.
Finally, though not in this week’s Carnival, I want to note Universe Today‘s intriguing speculations on detecting plant life on distant exoplanets:
The question remains as to whether plants on distant worlds will use chlorophyll as their means of photosynthesizing light. Will the light they absorb be red, or a different color? Will the light they reflect be green or something completely bizarre, like magenta or bright blue? If they do use chlorophyll, their spectrum will be similar to that of our own planet. If not, their spectral signature may be rather different than that of Earth’s vegetation.
The discussion is keyed to work by Luc Arnold (CNRS Observatoire de Haute-Provence), who has been investigating whether the spectral analysis of light reflected off a planetary surface could tell us about the presence of vegetation there. How to take out the various noise factors — the composition of the atmosphere, the density of clouds, and so on — is all part of the puzzle. It will take a generation of space telescopes beyond even ESA’s Darwin (or whatever terrestrial planet finder technology NASA ultimately chooses to fund) to handle this job, but what a field day for exobiologists (and controversy) when it happens.
by Paul Gilster | Dec 7, 2007 | Astrobiology and SETI |
One thing I’m always asked when I talk about interstellar topics is how long it would take a spacecraft like Voyager to get to the nearest star. After explaining how far away Proxima Centauri and the slightly farther Centauri A and B really are, I tell the audience that Voyager, if headed in that direction, would be facing a travel time of over 70,000 years. That usually shifts the conversation considerably, because many people assume that if we can get to the outer planets, the nearest stars can’t be that far behind. If only it were so.
The Centauri stars are, of course, only the closest known (and who knows, perhaps there’s a brown dwarf a bit closer). Assume a space technology able to travel at close to the speed of light and you’re still dealing with travel times that amount to years, although time for the crew would be shorted according to those interesting Einsteinian effects that cause the crew of a vehicle traveling at 86 percent of lightspeed to experience half the elapsed time felt by those left behind. Getting to anything but the closest stars at such speeds is a long haul for any crew.
Seth Shostak talks about this issue in a recent essay, noting that 61 Cygni, the first star whose distance was correctly measured (in 1838, at the same time that Thomas Henderson was measuring the distance to the Centauri trio) is eleven light years away. To understand the distance, we play the analogy game: A ping-pong ball representing the Sun, placed in New York, would be matched by a smaller ball, representing 61 Cygni, sitting in Denver. We’re talking tens of trillions of miles.
Shostak’s point is to examine what he calls the ‘one percent’ rule. The Romans could hold an empire together as long as travel times to connect the empire were no longer than about one percent of the lifetime of the average centurion. Apply that to a space ’empire,’ even one moving at close to light speed, and you run into problems:
Even if we could move people around at nearly the speed of light, this “one percent rule” would still limit our ability to effectively intervene – our radius of control – to distances of less than a light-year, considerably short of the span to even the nearest star other than Sol. Consequently, the Galactic Federation is a fiction (as if you didn’t know). Despite being warned that Cardassian look-alikes were wreaking havoc and destruction in the galaxy’s Perseus Arm, you couldn’t react quickly enough to affect the outcome. And your conscripts would be worm feed long before they arrived on the front lines anyway.
Lively discussion, but what about communications? Information exchange usually takes place quickly, with our idea of maximum delay often limited to the amount of time it might take an overseas letter to arrive. That time is clearly shortening — we live in a world where a one-day delay in returning an e-mail can be perceived as mystifying, and the generation now being raised on iPods and iPhones, texting away at each other at whim, is unlikely to accept anything but instantaneous communications.
This may be useful, at least for those of us who worry about METI — the idea of sending messages to nearby solar systems rather than listening for signals from them. Do we as a civilization have the long-term approach needed, even if we decided such a thing were benign, to mount a continuing world-wide attempt to communicate with a civilization hundreds of light years away? The attempts made thus far have been sporadic. Will they become more than that?
Our cultural patterns argue against the idea, and although I am a champion of long-term approaches in most respects, in this case I defer to impatience. Because until we understand what we are doing and have an informed consensus on the matter, shouting to the cosmos could have implications we have yet to understand. Let’s put METI on hold.
A greatly enlarged public debate on METI is needed, one that incorporates a wide variety of disciplines, before further signals are sent. Meanwhile, that Great Silence that Fermi speculated about, and which we now seem to be encountering in our SETI searches, may simply imply that other cultures are much like ours, knowledgable about the distances involved and unwilling to make the generational commitment to a kind of communication that may never pay off. Shostak puts it this way: “…while the cosmos could easily be rife with intelligent life – the architecture of the universe, and not some Starfleet Prime Directive, has ensured precious little interference of one culture with another.” That may not be such a bad thing, at least until we have sound reasons for making our presence known in a cosmos we are only beginning to understand.
by Paul Gilster | Dec 6, 2007 | Exoplanetary Science |
With Hubble’s Space Telescope Imaging Spectrograph now out of commission, the study of exoplanetary atmospheres becomes a bit more problematic. But Seth Redfield (University of Texas at Austin) has now used a ground-based instrument to detect the atmosphere of a planet orbiting the star HD189733, some 63 light years away in the constellation Vulpecula. Discovered in 2004, this transiting world is about twenty percent more massive than Jupiter, orbiting its parent ten times closer than Mercury orbits our Sun.
Working from the ground is tricky but the odds go up when you observe more than a single transit. Redfield worked with eleven transits observed over the course of a year, using the Hobby-Eberly Telescope (HET) at McDonald Observatory in Austin. Studying the chemical composition of a distant atmosphere involves taking a spectrum during a transit and another when no transit is occurring. Working with the difference and comparing results over multiple transits helps you put together the atmospheric spectrum.
Image: The dotted line shows the planet’s orbit around the star HD189733. The planet orbits the star once every 2.2 Earth days, crossing the face of the star well below its equator. The small circles indicate the planet’s location during each of Seth Redfield’s more than 200 HET observations over the course of one Earth year. The red circles indicate observations during transit; the rest of the circles denote out-of-transit observations. Credit: S. Redfield/T. Jones/McDonald Obs.
None of which is easy. The light blocked out by the planet amounts to only 2.5 percent of the star’s total light as seen from Earth, and Redfield figures another 0.3 percent for the planetary atmosphere. But gradually the pieces of the puzzle come together. Redfield says this about his method:
“Each time the planet passes in front of the star, the planet blocks some of the star’s light. If the planet has no atmosphere, it will block the same amount of light at all wavelengths. However, if the planet has an atmosphere, gases in its atmosphere will absorb some additional light.”
Which gets interesting indeed when you look at the planet at wavelengths corresponding to specific transitions of the sodium atom. The presence of sodium means that the planet absorbs more starlight at those wavelengths, making the planet appear larger by about six percent than at other wavelengths. With sodium now detected, the search can move to other atmospheric constituents. Hundreds of observations went into this result, along with the necessary task of filtering contamination to the data from Earth’s atmosphere.
So precise was the work that the transmission spectrum achieved from this distant transit via ground methods was higher in resolution than previous Hubble work on exoplanetary atmospheres. Honing this technique will get us into even more interesting territory as we start extending our methods to planets more amenable to life. It will also give us a head start as we wait for the next generation of space-based observatories to provide data at higher levels of precision.
The paper is Redfield, Endl et al., “Sodium Absorption From the Exoplanetary Atmosphere of HD189733b Detected in the Optical Transmission Spectrum,” accepted for publication in Astrophysical Journal Letters (abstract).
by Paul Gilster | Dec 6, 2007 | Administrative
It’s been a long night. A bug in one of our security software plugins caused all users to run into problems when trying to post messages. Sorry about this! I think I’ve finally resolved the matter and you should find things back to normal. If you tried to post and were unable to get site access, please try again, and thanks for your patience.
by Paul Gilster | Dec 5, 2007 | Astrobiology and SETI |
By Larry Klaes
Larry Klaes’ look at the Allen Telescope Array reminds us of the power of philanthropy at getting serious projects funded. It’s a topic we’ll be re-visiting as the Tau Zero Foundation comes online early in the coming year. I’m reminded also of the One Laptop Per Child project, which is seeing private donations for these educational tools supplanting government shortfalls in some developing countries. Properly targeted, the philanthropic dollar is a powerful thing, and think of the results if the ATA finds a genuine signal!
Cornell astronomer and science popularizer Carl Sagan left quite a legacy in a number of science fields, including and especially those which were considered to be somewhat fringe at one time.
One prime example of his support of a science field that was not universally accepted in earlier eras was SETI, the Search for Extraterrestrial Intelligence. At a time when many astronomers did not seriously consider the possibility of other beings existing beyond Earth and relegated aliens to UFO and science fiction tales, Sagan promoted and participated in some of the first scientific searches and contact efforts for extraterrestrial life.
One of the latest results of Sagan’s efforts in SETI was recently dedicated in a remote region of northern California. Called the Allen Telescope Array (ATA) after its most prominent benefactor, Microsoft co-founder Paul Allen, the installation can look to Sagan as an inspiration. Seattle billionaire Allen cited a conversation with the Cornell astronomer in 1995 as the catalyst that prompted him to donate $25 million to construct the most advanced SETI project yet built.
SETI programs have traditionally been sporadic both in terms of funding and their search parameters, going back to 1960 when former Cornell astronomer Frank Drake began the first modern effort, named Ozma, using a large radio telescope to monitor just two nearby stars — Tau Ceti and Epsilon Eridani — over a four-month period. By the early 1990s, SETI programs in the United States were in jeopardy when NASA pulled its support for the effort. Fortunately for the field, private efforts such as the SETI Institute and the SETI League picked up where the government left off, though they too often suffered from limited telescope resources.
First conceived by Frank Drake, the ATA is a revolution for both SETI and radio astronomy in general. Dedicated both to SETI projects and galactic astronomy, the array offers a sense of focus. The SETI Institute will no longer have to vie for time with other projects using various large radio telescopes around the world. The 42 twenty-foot wide dishes currently in operation will be expanded to 350 in the coming years. Not only will the ATA do wonders for astronomy using relatively inexpensive off-the-shelf technology, but it will also serve as a test bed for much larger radio astronomy projects utilizing collections of many telescopes functioning as a single unit, such as the Square Kilometer Array (SKA), planned for construction in the next decade.
Other notable features about the ATA include its ability to scan large areas of the sky rapidly. The array will be able to simultaneously scan numerous star systems and monitor over forty million radio channels. The modern technology of the ATA also allows it to filter out effectively the many sources of artificial noise from human civilization, a major bane to radio SETI, while searching for the alien ones.
The first SETI effort for the ATA will be to scan the center of our Milky Way galaxy, where billions of stars reside, for several months. The cluster of radio telescopes will then begin a more detailed assignment, examining approximately one million nearby star systems. This will be a thousand fold increase over all previous SETI efforts going back to Ozma. This number does not include the few brief explorations of some neighboring galaxies, which hold hundreds of billions of suns. Several such studies were conducted by Sagan and Drake themselves.
The previous effort by the SETI Institute, called Project Phoenix, looked at fewer than 800 star systems for only a few weeks each year from 1995 to 2004, borrowing telescope time first from the Parkes Radio Observatory in Australia and then the Cornell-run Arecibo Radio Observatory on the island of Puerto Rico. Living in a galaxy with 400 billion stars, it is easy to see why SETI researchers are excited about the ATA.
Images: Views of the Allen Telescope Array. Credit: ATA.
Some scientists doubt that even the capabilities of the ATA will be able to detect alien civilizations in the galaxy. Aside from those who say the Milky Way is either barren of any life besides that on Earth or that few aliens are more developed than bacteria, some question whether advanced ETI would use the relatively primitive method of radio to transmit messages into deep space.
One alternative to interstellar communications is through the optical portion of the electromagnetic spectrum, specifically with lasers. A powerful laser beam could contain far more information than a radio message, including video images, which may certainly facilitate understanding between two very different cultures. Others advocate sending physical messages between the stars, something like the metal plaques and records on the Pioneer and Voyager space probes, respectively.
Some scientists declare that we are looking for the ‘wrong’ kind of aliens in the wrong kind of places, namely biological beings not too dissimilar from humans living on Earthlike planets circling yellow dwarf stars. Milan ?irkovi? and Robert Bradbury contend that beings that survive their cultural adolescence will become what Hugo de Garis calls artilects, vast machine intelligences far beyond our level of intellect. These artilects may prefer to exist in the dark outer regions of the Milky Way, huddled around suns inside massive Dyson Shells, where the much colder temperatures allow them to function better. Such highly advanced minds housed in such truly alien ‘bodies’ may help to explain why we have yet to detect any ETI or why no obvious messages have come our way.
Whatever the situation may be or the types of ETI that may exist in the Universe, one thing is certain: If we do not search for them, we will likely never find them, or they us. The Allen Telescope Array is a major new step in improving our chances to find what is or is not out there. What we learn from this exploration into the unknown will have a profound effect on our species and society.
For more information on the ATA, check out the ATA section on the SETI Institute Web site.
