by Paul Gilster | Jan 31, 2006 | Outer Solar System |
2003 UB313, the ’10th planet’ discovered by Michael Brown (California Institute of Technology), continues to fuel the debate over what constitutes a planet and where the division between planet and Kuiper Belt object should be. A new Hubble photograph shows the object to be slightly larger than Pluto, but nowhere near the 25 to 50 percent larger that Brown originally estimated.
But Brown was the first to state, early in the game, that we needed better data to get an accurate size estimate. And you can see why his original view made sense: if 2003 UB313 really is not much larger than Pluto, then it reflects over 90 percent of the light that hits it. What causes the additional brightness (Pluto, for example, reflects just 60 percent of incoming light) remains conjectural. But this must be an icy surface, and the distinctions between the new world and Pluto will continue to spur controversy.
Meanwhile, we have a new paper on another Kuiper Belt find, the object called 2003 EL61. The authors, who include David Rabinowitz (Yale Center for Astronomy and Astrophysics) and the aforementioned Brown, report on the detection of crystalline water ice on the surface. From the abstract: “The signature of crystalline water ice is clear and obvious in all data collected. Like the surface of many outer solar system bodies, the surface of 2003EL61 is rich in crystalline water ice, which is energetically less favored than amorphous water ice at cold temperatures, suggesting resurfacing processes may be taking place.”
The paper (submitted to the Astrophysical Journal) is “The Surface of 2003EL61 in the Near Infrared,” now available at the arXiv site.
And finally, a nice Plutonian note from the Lawrence Journal-World reminds us that Clyde Tombaugh will be honored this Saturday at the University of Kansas. January 4 would have been the KU alumnus’ 100th birthday. How fitting that the featured speaker will be Alan Stern, principal investigator for New Horizons, aboard which a portion of Tombaugh’s ashes now make their way to the world he discovered.
For more on Tombaugh, I lean toward David Levy’s ClydeTombaugh: Discoverer of Planet Pluto (Tucson: University of Arizona Press, 1991), but also check Margaret Wetterer’s Clyde Tombaugh and the Search for Planet X (Minneapolis: Carolrhoda Books, 1996).
by Paul Gilster | Jan 30, 2006 | Deep Sky Astronomy & Telescopes
As physicist Clifford Johnson notes in a Cosmic Variance post, Sunday the 29th was the anniversary of a powerfully symbolic event. As Johnson says: “On January 29th 1931, Edwin Hubble took Einstein up Mount Wilson to see the famous 100 inch telescope where Hubble had done at least two revolutionary things (with the aid of Henrietta Leavitt’s remarkable work on variable stars): (1) He demonstrated that the Milky Way Galaxy, where we live, is not the entire universe, but just one of many galaxies, and (2) He confirmed (ahem, not discovered) that the universe was expanding and (with Humason…who started out as the janitor at the observatory) quantified it in what we now call “Hubble’s Law”.
And don’t miss Johnson’s wonderful Walk Up Mount Wilson, complete with photographs, further background and the story of a wonderful morning hike. For a man who long resisted writing for a weblog (and for eloquent reasons), Johnson’s posts have become simply indispensable.
by Paul Gilster | Jan 30, 2006 | Advanced Rocketry |
It’s heartening to see that NASA has inked an agreement with a commercial firm to get its VASIMR (Variable Specific Impulse Magnetoplasma Rocket) technology into the private sector. Houston-based Ad Astra Rocket Company is actually located within the Johnson Space Center and, under the direction of president and CEO Franklin Chang-Diaz, focuses on the development of plasma rocket technologies. Its agreement with NASA should further work on a design widely thought to offer powerful advances over conventional chemical rockets.
Chang-Diaz is a veteran of seven Shuttle flights who retired from NASA last July to focus on the Ad Astra/VASIMR connection. The design, which he conceived back in 1979, uses magnetic fields to channel a plasma exhaust that would melt conventional rocket nozzles. An additional beauty of the concept is that both thrust and specific impulse can be varied during the course of a mission. Ad Astra compares this to the transmission in an automobile; the exhaust characteristics are varied while constant power is maintained, resulting in the shortest trip time with the highest payload for a given amount of fuel.
Plasma itself is a high-temperature ‘soup’ of charged particles that can be manipulated by a magnetic field. It’s fascinating to reflect that 99 percent of the visible universe — the Sun and other stars — is in a plasma state of some kind. And ponder this: the particles in plasmas capable of being created today move at velocities of 300,000 m/sec at temperatures comparable to those inside a star.
To create the plasma for VASIMR’s use, a propellant like hydrogen is injected into a system of magnetic cells, where it is first ionized and then heated by radio-frequency excitation before being exhausted out the back of the rocket by a magnetic nozzle. “The promise this system holds could dramatically reduce the travel time for interplanetary missions,” says Chang-Diaz, “cutting trip times to Mars by one half or better.” Another benefit: the engine’s residual magnetic field can theoretically provide shielding against radiation, while the variability of thrust and specific impulse offers a wide range of abort options.
Centauri Dreams‘ take: Using hydrogen as a fuel for VASIMR makes refueling along the route a viable option; hydrogen is going to be available at any destination reachable with this technology. The Mars mission that Chang-Diaz talks about could refuel on the surface of the planet, and hydrogen could also be used as a radiation shield during the long cruise. But for now the real story is the interface between NASA and Ad Astra, because getting advanced concepts into commercially viable frameworks is the key to serious progress.
by Paul Gilster | Jan 28, 2006 | Deep Sky Astronomy & Telescopes |
What would fling a star out of the galaxy at over 1 million miles per hour? Warren Brown (Harvard-Smithsonian Center for Astrophysics) and colleagues have some thoughts on that, based on their own and other studies in Europe that have so far identified five stellar exiles, a group now called ‘hypervelocity stars.’ “These stars literally are castaways,” says Brown. “They have been thrown out of their home galaxy and set adrift in an ocean of intergalactic space.”
Brown’s team went after galactic escapees in a targeted manner, using computer models that showed such stars would be forced into their current trajectories by interactions in the galactic core. The idea is this: a binary star swings too close to the black hole at the galaxy’s center. Its gravity tears the duo apart, in the process capturing one of the stars and ejecting the other one at high velocity.
Evidence exists not only in the exiled stars themselves but in the other half of the binary pairs that once contained them; the stars the exiles leave behind orbit the central black hole in just the kind of elongated, elliptical orbit that would be expected from the computer models. Brown’s team figures a star is ejected from the galaxy about once every 100,000 years, although our knowledge of the extreme conditions at the core still needs a great deal of refinement to understand the process.
And in a unique way, these curious objects are interstellar probes of their own. By studying them, we learn something about the structure of the Milky Way. Says Margaret Geller, co-author of the paper on this work, “During their lifetime, these stars travel across most of the Galaxy. If we could measure their motions across the sky, we could learn about the shape of the Milky Way and about the way the mysterious dark matter is distributed.”
The team’s study has been submitted to the Astrophysical Journal Letters as “A Successful Targeted Search for Hypervelocity Stars,” now available online at the arXiv site.
by Paul Gilster | Jan 27, 2006 | Astrobiology and SETI |
Robert Carrigan (Fermi National Accelerator Laboratory) drew quite a bit of attention last summer when he suggested that SETI signals could contain harmful information, perhaps created by a so-called ‘SETI hacker.’ Carrigan’s article has now appeared in Acta Astronautica, and it’s stuffed with beguiling ideas even if you find the premise unlikely.
“…will a SETI signal be altruistic, benign or malevolent?” Carrigan asks. “It would help to understand the motivations of a message before reading too much of it. Like Odysseus, we may have to stuff wax in the ears of our programmers and strap the chief astronomer to the receiving tower before she is allowed to listen to the song of the siren star.”
That’s fascinating stuff, recalling Fred Hoyle’s A for Andromeda and Carrigan’s own The Siren Stars, written with Nancy Carrigan and serialized in Analog in 1970. But this new paper is worth reading for reasons other than the hacker hypothesis; its author speculates widely on SETI itself. Ponder, for example, how the message carried by a SETI signal might vary depending on its originators. What information would an intelligent plant think to convey? A dog-like species would focus on scent and odor as more significant than the pictorial images so important to humans. And what would we make today of a signal carrying data only a quantum computer could decipher?
As to message size, look at today’s information equivalents. A desktop computer operating system is perhaps 1 gigabyte. Although the human genome contains three billion DNA base pairs, Carrigan estimates its effective information content at 0.05 gigabytes. An education through graduate school could be contained in 1-10 GB, while a lifetime of images stored once a minute might total 1000 GB.
Suppose we wanted to send the ultimate signal from Earth to the stars. Matthew Lesk speculated in 1997 that all the information in the world would require 12 exabytes of storage; Carrigan takes this further by adding profiles for all the world’s inhabitants, including their DNA information, bringing the total to 25 exabytes. The ultimate transmission might be one that includes DNA profiles not just for people but for all creatures and plants on the Earth.
Could a civilization attempt a transmission this comprehensive? If so, the signature of the signal would include short, bursty traffic to catch the attention, with long periods of electromagnetic transmission to carry the background data. Or would the message come in physical form? Carrigan notes that a 5mm sphere of DNA could store on the order of 25 exabytes of data. This seems an unlikely delivery mechanism, but the author argues that energy costs per bit for electromagnetic processes vs. delivery via what might be called ‘directed panspermia’ are similar for matter velocities on the order of .00001 of the speed of light. Future technologies, of course, could change this drastically.
But back to the paper’s central thesis: “The most important point is that large amounts of information can be transferred inexpensively at the speed of light even with current technologies. In addition, the message size can easily be so large that the underlying intent of the message would not be apparent.”
The paper, which belongs on the shelves of disks of anyone following the SETI search, is “Do potential SETI signals need to be decontaminated?” in Acta Astronautica 58 (2006), pp. 112-117. Carrigan’s own site contains earlier work on the theory.
