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Voyager Interstellar Mission in Jeopardy

by Paul Gilster | Mar 11, 2005 | Missions | 0 Comments

Nature is reporting that the two Voyager missions -- recently discussed here as our first active probes of the interstellar medium, if they live long enough to cross the heliospheric boundary -- may be terminated in October. The decision is not yet final, and there is always the hope that it will spur enough reaction among space scientists and others to force a reprieve. But if these missions end (along with six others, including Ulysses), the loss to science would be severe. Voyager 1 is the fastest man-made object, now leaving the Sun behind at over 17 kilometers per second, at a current distance of approximately 94 AU (14 billion kilometers from Earth). Voyager 2 is roughly 76 AU out. Both spacecraft should be able to continue transmitting until 2020 or later. At $4.2 million per year, the Voyager program catches NASA's eye as the agency ponders budgetary cutbacks. But to shut down two operational spacecraft as they approach the interstellar medium for the first time in history is...

Titan’s Complex Surface Analyzed

by Paul Gilster | Mar 10, 2005 | Outer Solar System | 0 Comments

The Cassini Imaging Team has published its first findings about Titan in the journal Nature. The complexity of Titan's surface and the extent to which it is continually modified draws the most attention. Where are the craters that should have pocked its surface over the past billion years? Thanks to Cassini/Huygens, some answers are beginning to emerge. Working with the last eight months of imagery from the orbiter, the team reports that thirty percent of the satellite's surface has now been mapped with resolutions high enough to pick out features as small as one to ten kilometers. From a press release from the Cassini Imaging Central Laboratory for Operations (CICLOPS): At this scale, what has been discovered are geologically young terrains with signs of tectonic resurfacing, erosion by liquid hydrocarbons, streaking of the surface materials by winds and only a few large circular features thought to be impact craters formed in the ice 'bedrock'. (The largest of these - a...

Speaking Up to Hans Bethe: An Appreciation

by Paul Gilster | Mar 9, 2005 | Culture and Society | 0 Comments

The death of Hans Bethe has been covered by the media worldwide, and William J. Broad's obituary in the New York Times seems among the most thorough and accurate of the accounts of his life. But to me, Bethe will always be seen through Richard Feynman's eyes, and I think Broad misses the point of the one Feynman anecdote he tells. Feynman first worked with Bethe at Los Alamos during the days of the Manhattan Project, and he recalls the physicist's openness to debate, and his focus on the issue at hand rather than personality. Here, Feynman has just arrived in Los Alamos, and work had just begun, as told in the wonderful Surely You're Joking, Mr. Feynman! (New York: W.W. Norton, 1984): "Every day I would study and read, study and read. It was a very hectic time. But I had some luck. All the big shots except for Hans Bethe happened to be away at the time, and what Bethe needed was someone to talk to, to push his ideas against. Well, he comes in to this little squirt in an office and...

Charting the Boundaries of the Heliosphere

by Paul Gilster | Mar 9, 2005 | Missions, Outer Solar System | 0 Comments

Has Voyager 1 left the heliosphere? The question is a reminder that the Voyagers are our first interstellar probes; they'll still be returning data when they move into the interstellar medium. The heliosphere is a kind of bubble created by the solar wind from the Sun, that stream of high-speed charged particles constantly blowing into space at roughly 400 kilometers per second. Observing how Voyager 1 makes the transition across the boundary of the heliosphere will provide our first in situ study of interstellar space. Some scientists believe that at roughly 90 AU from the Sun, Voyager 1 has already pushed up against the 'termination shock,' that region where the speed of the solar wind drops to subsonic levels. Now new data studied by French and Finnish researchers indicate that the shape of the heliosphere may be distorted, further complicating the question of just where the true interstellar medium begins. Rosine Lallement and colleagues used data collected by the Solar and...

Plasma in a Bubble

by Paul Gilster | Mar 8, 2005 | Advanced Rocketry | 0 Comments

Sonoluminescence -- the emission of light from bubbles in a liquid that has been excited by sound -- is a mystery. How does a sound wave put enough energy into such a small volume as to cause light to be emitted? The concentration of energy needed is something like a factor of one trillion, according to this Los Alamos National Laboratory introduction to the phenomenon. And not only that; the spectrum of the emitted light implies extremely high temperatures. Fusion, anyone? Well, not yet. But the slang term for sonoluminescence, 'star in a jar,' seems a little closer to reality now that the first direct measurements of the phenomenon are in. They show that the temperature inside a collapsing bubble can reach 20,000 degrees Kelvin, which is four times the temperature of the surface of the Sun. This work, by Ken Suslick and David Flannigan (University of Illinois at Urbana-Champaign), comes two years after controversial findings by an Oak Ridge National Laboratory team that found...

Toward an Active SETI

by Paul Gilster | Mar 7, 2005 | Astrobiology and SETI | 3 Comments

The search for extraterrestrial intelligence is, some would say, too passive -- it's pure listening, monitoring radio and, in some cases, optical wavelengths in hopes of intercepting either a message from another civilization or, perhaps, catching a snippet of its internal communications. But is there a place for an active SETI, one that is just as anxious to send a human message to the stars as to listen for the broadcasts of others? Not that there haven't been previous attempts to send signals, the most famous of which was the 1974 Arecibo message beamed in the direction of M13, a globular cluster in the constellation Hercules. The Hercules message, containing binary representations of the human form, the solar system, and other mathematical and chemical information, pushes us into the domain of long-term thinking, for it will take 25,000 years to reach its target (and, obviously, another 25,000 years for any reply). But M13 is also an interesting place to send a signal, for it is...

In Search of the Mad Rocketeer

by Paul Gilster | Mar 5, 2005 | Culture and Society | 0 Comments

It seems fitting that the crater named Parsons is on the Moon's dark side. It's named after John W. Parsons, a youthful rocket builder who joined Texan Frank Malina in the early experiments that would lead to the creation of the Jet Propulsion Laboratory. Parsons, Malina and a childhood friend named Ed Forman patched together equipment from junkyards and at one point tried to script a movie about going to the Moon, hoping that selling it to Hollywood would fund their idea of launching a rocket to Earth's upper atmosphere. The three formed the Rocket Research Group at the Guggenheim Aeronautical Laboratory at Caltech, where Theodore von Kármán, the Laboratory's director, gave them lab space and campus equipment to pursue their dreams. This was back in the 1930's, when the group's rocket motors were being tested at the Arroyo Seco near Pasadena. Around that time, Chinese graduate student Tsien Hsue-shen (who would go on to become the father of Chinese rocketry) joined the team,...

Tiny Star Complicates Search for Exoplanets

by Paul Gilster | Mar 4, 2005 | Exoplanetary Science | 1 Comment

Can a star look like a planet? Evidently so, to judge from observations of the star OGLE-TR-122. Astronomers working at the European Southern Observatory's Paranal Observatory in Chile have discovered that the star experiences a drop in brightness every 7 days 6 hours and 27 minutes, a strong indication (when combined with radial velocity measurements) that a low-mass star is regularly moving in front of its larger companion as seen from Earth. Measuring radial velocity allows scientists to discriminate between stars and planets as the cause of the brightness variations. The OGLE (Optical Gravitational Lensing Experiment) survey has been studying changes in the brightness of stars that could be caused by the transit of such unseen companions. And this one, christened OGLE-TR-122b, turns out to be a rarity indeed. It adds up to one-eleventh of the Sun's mass, making it the smallest known star, only 16 percent larger than Jupiter though 96 times as massive as that planet. "This result...

Hunting for Planets Around Epsilon Eridani

by Paul Gilster | Mar 3, 2005 | Deep Sky Astronomy & Telescopes, Exoplanetary Science | 0 Comments

The image below is Epsilon Eridani, some 10.5 light years from Earth, as seen in the infrared by the Spitzer Space Telescope. We have evidence of the existence of at least one planet around the star, orbiting at 3.4 AU, but subsequent attempts to detect other planets have thus far failed. However, a debris disk, detected at radio frequencies, is known to exist, and it provides evidence of other planets based on perturbations in the dust and rocks of the disk itself. Epsilon Eridani is a comparatively young star (730 million years old), and so provides a useful case study of a solar system in formation. The Spitzer photograph comes courtesy of Massimo Marengo, who heads a team that is using the Spitzer instrument to detect Epsilon Eridani's unseen companions. In this ongoing study, working especially with Spitzer's Infrared Array Camera (IRAC), the team has developed methods of light subtraction that can suppress most of the light from the central star, allowing the detection of...

Of Brown Dwarfs and Habitable Worlds

by Paul Gilster | Mar 2, 2005 | Exoplanetary Science | 0 Comments

A story in a recent issue of New Scientist covers the possibility of planets around brown dwarfs, focusing on the work of Kevin Luhman of the Harvard-Smithsonian Center for Astrophysics. Centauri Dreams looked at this study in a previous posting, but writer Hazel Muir adds a further comment on habitability around such worlds based on Luhman's work: It is conceivable that such planets, if they form, could be habitable. The surface temperature of the mini brown dwarf is 2300 kelvin, so a planet 1.5 to 7 million kilometres away could host liquid water. Planets very close to a brown dwarf would be scorched at first, but would become hospitable as the star cooled. Brown dwarfs take a long time to cool, so the planet could remain habitable long enough for life to evolve. Another thought, from Andrew Collier Cameron at the University of St. Andrews in the UK, who is quoted in the article: brown dwarfs might be useful hunting grounds for exoplanets, given the faintness of the brown dwarf...

Kurt Gödel and the Spacetime Continuum

by Paul Gilster | Mar 2, 2005 | Culture and Society | 0 Comments

Be aware of Time Bandits, an article by Jim Holt in the March 2 New Yorker, which studies the relationship between Albert Einstein and mathematician Kurt Gödel, now best known for his incompleteness theorems. The first of these, as Holt writes, "...demonstrates that no logical system can capture all the truths of mathematics." Here's a sample from this fascinating piece, discussing what happened when Gödel took on the relationship of space and time: What Gödel found was the possibility of a hitherto unimaginable kind of universe. The equations of general relativity can be solved in a variety of ways. Each solution is, in effect, a model of how the universe might be. Einstein, who believed on philosophical grounds that the universe was eternal and unchanging, had tinkered with his equations so that they would yield such a model—a move he later called "my greatest blunder." Another physicist (a Jesuit priest, as it happens) found a solution corresponding to an expanding universe...

Testing Laser Communications Around Mars

by Paul Gilster | Mar 1, 2005 | Communications and Navigation | 0 Comments

Building the first interplanetary laser link, a project known as the Mars Laser Communications Demonstration, will be one of the topics discussed at an upcoming conference in Anaheim. The gathering targets the latest developments in optical technologies from key players in the industry, but it's the use of lasers for space communications that catches Centauri Dreams' eye. As we go deeper and deeper into the Solar System and beyond, we'll need these technologies to allow for effective data return. Ponder this: because radio signals fall off in intensity with the square of their distance, a spacecraft twice as far from Earth sends a signal with four times less strength. The 23-watt signal of Voyager has spread to a beam width 1000 times the diameter of Earth by the time it reaches us. The Jet Propulsion Laboratory's James Lesh says that makes the Voyager signal twenty billion times less powerful than what it takes to run a digital wristwatch. Move to Alpha Centauri and the dropoff...

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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