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New Constraints on the Pioneer Anomaly?

by Paul Gilster | Apr 4, 2006 | Outer Solar System | 1 Comment

That the Pioneer spacecraft have experienced some kind of anomalous acceleration is now well established. Just what the cause of that acceleration is remains an open question. But we do know that the anomaly appears as "...a constant and uniform acceleration directed towards the Sun...", as described in a paper called "What do the orbital motions of the outer planets of the Solar System tell us about the Pioneer anomaly?" The effect shows up in data from both spacecraft from the moment they passed the 20 AU mark on their journeys. The authors, Lorenzio Iorio and Giuseppe Giudice (Dipartimento di Progettazione e Gestione Industriale, Naples) note that recent work has not resolved the question of whether there is some internal factor aboard the spacecraft that is causing the anomaly, or whether its origin is external. In any case, the situation is intriguing enough that dedicated space missions to explore it have been proposed. This paper investigates whether there is an "...external,...

A Practical Mission to the Interstellar Medium

by Paul Gilster | Apr 3, 2006 | Interstellar Medium, Missions | 7 Comments

The first true interstellar mission may be on the drawing board right now. Yes, Voyager 1 has already crossed the termination shock 94 AU out and is still returning data, but we've never had a mission targeted from day one at interstellar space. Yet that region just beyond the influence of the Sun -- the Very Local Interstellar Medium -- is crucial; it will tell us much about the interface between the solar wind and deep space. Probing it will create new data on everything from gravitational waves to anomalous forces like those that may be acting on the Pioneer spacecraft, not to mention setting the stage for future missions. Now dubbed the Innovative Interstellar Explorer, the concept is for a robotic mission beyond the heliopause, and as refined through studies led by Ralph McNutt (Johns Hopkins University Applied Physics Lab) for NASA's Institute for Advanced Concepts, and now through continuing development as a NASA mission study, the IIE would take a 1000-kg payload on the first...

Short Takes for the Weekend

by Paul Gilster | Apr 1, 2006 | Astrobiology and SETI, Exoplanetary Science, Missions, Outer Solar System | 1 Comment

In which the hapless author tries to clear out his growing backlog of material. This may have to become a regular feature, since the amount of new information coming in about the extrasolar planet hunt alone would be enough to keep Centauri Dreams busy all day, not to mention continuing work on propulsion concepts from solar and magnetic sails to antimatter and ongoing discoveries relating to dark matter and energy. Herewith, then, a few shorter items compressed only for reasons of space and time, so to speak. On Transit Windows and Red Dwarfs The planet around GL 581, an M-class red dwarf discovered last September, is unusually interesting because of its low mass, roughly 17 times that of Earth. This is probably a Neptune-class world with some possibility of being observable through transits -- i.e., its orbit may cross its primary as seen from Earth, making it a candidate for the transitsearch.org collaboration. But the last transit window on March 28 was rendered useless by cloud...

The Case of the Disappearing Neutrinos

by Paul Gilster | Mar 31, 2006 | Antimatter | 6 Comments

Following up on yesterday's intriguing antimatter results at Fermilab, a neutrino study called the Main Injector Neutrino Oscillation Search (MINOS) is providing independent confirmation of a critical idea: neutrinos have mass. This is significant news because it helps to illuminate earlier experiments that suggested neutrinos oscillate between three different types, something that could occur only if they do have mass, and an effect that, given the sheer abundance of neutrinos in the universe, may provide clues to why antimatter has disappeared and how galaxies originally formed. Neutrinos are odd things indeed; they can pass through the entire Earth without interacting with matter. MINOS studies them by producing neutrinos at Fermilab using protons accelerated in a 4000 foot tunnel pointing toward a second detector some 450 miles away in Soudan, Minnesota. The neutrinos are measured first with a detector below the Fermilab site, with a second measurement being taken at a 6000-ton...

Clues About the ‘Antimatter Wars’

by Paul Gilster | Mar 30, 2006 | Antimatter | 0 Comments

With 700 physicists from 90 different institutions in 20 countries working on an experiment, you expect interesting results. And the DZero experiment at Fermi National Accelerator Laboratory is living up to the expectation. Scientists at Fermilab have been studying a subatomic particle known as the B_s meson (pronounced 'B sub s'). Their work suggests that this particle actually oscillates between matter and antimatter more than 17 trillion times per second. The data come from over 1 billion events at Fermilab's Tevatron particle accelerator, and more precise results are expected soon from a different Fermilab collaboration. And the more we learn, the better: exactly how particles turn into their own antiparticles, and with what frequency, is a major issue that could point to answers in an even bigger one, the balance between matter and antimatter in the universe. For if matter and antimatter appeared in equal numbers at the time of the Big Bang, their mutual annihilation should have...

Henry Hsieh on Main-Belt Comets

by Paul Gilster | Mar 29, 2006 | Missions, Outer Solar System | 3 Comments

Centauri Dreams recently discussed the discovery of so-called 'main-belt comets' -- icy objects found in asteroid-like orbits that apparently formed in the inner Solar System rather than on its outer edges. The work, performed by Henry Hsieh and David Jewitt (University of Hawaii) raises questions about the origins of Earth's water supply, which had been thought to have been delivered by cometary impacts on the primordial Earth. Could this water have, in fact, been delivered by main-belt comets, and could a mission to one of them yield the answer? A sharp-eyed reader wanted to know more: assuming we flew such a mission, how could we pin down the main-belt comets as the source, as opposed to the huge population of long-period comets with their highly elliptical orbits? Henry Hsieh was kind enough to respond: In recent years, the debate over the origin of the Earth's water has focused on the so-called D/H (deuterium to hydrogen) ratio of ocean water, comet water, and meteorite water...

Icy Moons and Their Oxygen

by Paul Gilster | Mar 28, 2006 | Outer Solar System | 0 Comments

Gas giant moons like Europa offer the tantalizing hint of life-sustaining conditions, with oxygen supplied by their abundant ices. But without sufficient heat, how is the oxygen to be coaxed from their frozen surfaces? So far, the explanation has been that high-energy particles bombarding such a moon's surface could help to release the gas, which would have already been molecularly bound with hydrogen. But a study at the Pacific Northwest National Laboratory suggests a different explanation. Simulating high-energy bombardment of a moon's surface, researchers there found that the process is much more complex. "We found that a simpler two-step could not account for our results," said PNNL staff scientist Greg Kimmel. "Our model is a four-step process." Here's how a PNNL news release explains what's going on: First, the energetic particle produces what is known as a common "reactive oxygen species" called a hydroxyl radical, or OH. Next, two OH molecules react to produce hydrogen...

‘Main-Belt Comets’ A Clue to Earth’s Water

by Paul Gilster | Mar 27, 2006 | Outer Solar System | 3 Comments

How did a newly formed Earth, supposedly hot and dry, wind up with oceans? Comets have been the leading candidate for the needed delivery mechanism, given their large ice content. But ice from the asteroid belt may make a better fit to Earth's water supply, and the discovery of a new class of comets there may mean that at least some objects in that part of the Solar System have ice at their surfaces. Asteroids and comets, in other words, may in some cases be more closely related than anyone realized. These conclusions come from work performed by University of Hawaii graduate student Henry Hsieh and professor David Jewitt, who have christened the newly discovered objects 'main-belt comets.' These are comets with asteroid-like orbits; they seem to have formed in the inner Solar System rather than in the frigid reaches of the Kuiper Belt or the Oort Cloud. The evidence? An object called asteroid 118401 is ejecting dust, just like a comet. And so is another mysterious comet known as...

A Potential Breakthrough in Quantum Gravity

by Paul Gilster | Mar 25, 2006 | Breakthrough Propulsion | 17 Comments

An effect that far exceeds what would be expected under Einstein's theory of General Relativity has been produced in a laboratory. The fact that the effect -- the gravitational equivalent of a magnetic field -- is one hundred million trillion times larger than what General Relativity predicts has raised the eyebrows of more than a few researchers. But Martin Tajmar (ARC Seibersdorf Research GmbH, Austria) says that three years and 250 experimental runs have gone into this work, and encourages other physicists to examine and verify it. If confirmed, the new findings could be a key result in the search for a quantum theory of gravity. We know that a moving electrical charge creates a magnetic field, and General Relativity assumes that a moving mass likewise generates a gravitomagnetic field, one that should, by the tenets of GR, be all but negligible. To test this, Tajmar and colleague Clovis de Matos (European Space Agency HQ, Paris) used a ring of superconducting material rotating...

Transit Window Soon to Open for GL 581

by Paul Gilster | Mar 24, 2006 | Exoplanetary Science | 0 Comments

If the goal is to find terrestrial planets around nearby stars, the transit method is our best bet. Sure, microlensing can deliver powerful results, and is fully capable, we believe, of finding a small, rocky world around a distant star. But microlensing as currently used is limited to stars that are tens of thousands of light years from Earth. In other words, find a terrestrial planet with microlensing and you can't do much by way of follow-up study. But transit methods are different. If a star's system of planets is oriented so that the planets cross in front of the star as seen from Earth, it is possible not only to find the planets but to do spectroscopic analysis and learn something of their composition. All that makes Transitsearch.org an exciting thing to be a part of. As discussed earlier in these pages, it's a cooperative project that gets amateur astronomers and smaller observatories into the transit hunt, supplying dates and times when transits are thought to occur. Greg...

A Brown Dwarf in the Neighborhood

by Paul Gilster | Mar 23, 2006 | Exoplanetary Science | 0 Comments

How many brown dwarfs await discovery near the Sun? Nobody knows, but the most recent is an interesting object indeed. Found some 12.7 light years from Earth as a companion to the red star SCR 1845-6357, it is the third closest brown dwarf yet discovered. "If you think of the galaxy as being the size of Tucson," says Laird Close (University of Arizona), "it's kind of like finding someone living in the upstairs of your house that you didn't know about before." And that's not all that makes the new dwarf interesting. Its surface temperature of 750 degrees Celsius makes it a remarkably cool object, one of the lowest-temperature dwarfs ever found. SCR 1845-6357 is some ten times less massive than our Sun; it is located in the southern hemisphere constellation Pavo (the Peacock). The small size of this star is interesting because until now, no brown dwarfs had been found around stars with less than half the mass of the Sun. And what we can deduce about its companion is that the brown...

Seeding the Solar System with Life

by Paul Gilster | Mar 22, 2006 | Astrobiology and SETI | 2 Comments

For years now, we've had our eye on Mars rocks that are known to occasionally fall to Earth, blown off their planet of origin in some primeval impact. But recent computer modeling suggests that a reverse process may also occur: rocks from Earth, potentially carrying life, could reach environments as distant as Europa and Titan. The numbers are surprising. As presented by Brett Gladman (University of British Columbia, Vancouver) at the Lunar and Planetary Science Conference, from 30 to 100 objects from Earth would hit Europa after a period of 5 million years. Titan receives 20 hits. The question then becomes, can bacteria survive such a journey, given the violent heat and acceleration that would be involved in blasting them off the Earth? Relevant work at the conference suggests that they can. As summarized by Mark Peplow in a Nature.com article, scientists at the University of Florida (Gainesville) have fired marble-sized pellets into plates containing bacterial spores in water....

New Detector Boosts Laser Communications

by Paul Gilster | Mar 21, 2006 | Communications and Navigation | 0 Comments

Why is it so tricky to deliver large amounts of data from space? One key issue is frequency -- because the amount of data that can be transmitted varies with the square of the frequency, higher frequencies give you more bang for the buck. Moving the Deep Space Network from today's X-Band (between 8.40 and 8.45 GHz for deep space work and between 8.45 and 8.50 GHz for near-Earth operations) to the Ka-Band (31.80 to 32.30 GHz) will increase the network's capabilities by a factor of four or five. But the real goal is optical communications, where the far narrower signal carries a vastly increased amount of information. We need that kind of data-packing not only to get around spectrum-crowding as more and more spacecraft need to talk, but also to handle the high resolution imagery and video we'll want to see from future deep space missions. "It can take hours with the existing wireless radio frequency technology to get useful scientific information back from Mars to Earth. But an optical...

A River of Stars

by Paul Gilster | Mar 20, 2006 | Deep Sky Astronomy & Telescopes | 0 Comments

Centauri Dreams follows studies about dark matter with great interest, given the mysterious nature of the stuff and the fact that it apparently has so much to say about how galaxies form. One way to get a handle on dark matter is to study the positions and velocities of stars in the galaxies themselves, thus learning what forces must account for them and how unseen matter may be affecting where they travel. A new study in this vein has now uncovered a 'river' of stars of considerable size that arcs over the disk of the Milky Way. "We were blown away by just how long this thing is," says Carl Grillmair, an associate research scientist at the California Institute of Technology. "As one end of the stream clears the horizon this evening, the other will already be halfway up the sky." Image (click to enlarge): On an evening in early April, the new stream rises 45 degrees from the eastern horizon, passing just under the bowl of the Big Dipper. The North Star Polaris is at far left."...

Quantum Fluctuations and Inflation

by Paul Gilster | Mar 18, 2006 | Deep Sky Astronomy & Telescopes | 0 Comments

Inflation has always been hard to get one's thoughts around. If nothing can travel faster than light, then how can the universe itself have expanded from submicroscopic to astronomical size in mere moments? The solution -- that while nothing can move through space faster than light, space itself knows no such restriction -- is still unsatisfying, for we don't understand how inflation happens, or how it may still affect the accelerating expansion of today's universe. The best recent work on these matters has been done through analysis of data from the Wilkinson Microwave Anisotropy Probe (WMAP), using three years worth of observations of the cosmic background radiation. The temperature of that afterglow tells us much about the universe's age and how it developed, and WMAP can read such temperature fluctuations down to grades finer than a millionth of a degree. The new measurement gives us clues not only about that crucial first trillionth of a second, but also about how and when the...

An Eclipsing Brown Dwarf Binary

by Paul Gilster | Mar 17, 2006 | Deep Sky Astronomy & Telescopes, Exoplanetary Science | 0 Comments

Making accurate measurements of distant binary objects isn't easy, but it helps when the two targets are edge-on as seen from Earth. That sets up an eclipsing binary, and in the case of a newly discovered duo of brown dwarfs in the Orion Nebula, provides helpful information. We now know that the the larger of the two brown dwarfs is 55 times the mass of Jupiter, while the smaller is 35 times larger (with a 10 percent margin of error in the calculation). Such measurements help firm up theoretical models of brown dwarf formation and composition. Image: An artist's conception of a pair of eclipsing brown dwarfs. Credit: NASA, ESA, and A. Feild (STScI). "This binary pair is a ˜Rosetta stone' that will help unlock many of the mysteries regarding brown dwarfs," says Keivan Stassun, assistant professor of astronomy at Vanderbilt University, who led the team of astronomers who made the new observations. "We understand how stars form in the crudest sense: They are formed when clouds of dust...

Andrew Gould on the Science of Microlensing

by Paul Gilster | Mar 16, 2006 | Exoplanetary Science | 3 Comments

A recent query about how astronomers work out the mass and radius of planets found through microlensing -- such as the so-called 'super-Earth' recently discovered 9000 light years from our Sun -- prompted Centauri Dreams to query one of the principals in that discovery. Andrew Gould, leader of the MicroFUN collaboration and professor of astronomy at Ohio State University, was kind enough to clarify how this fascinating science proceeds. Herewith his response: We obtain a planet-star mass ratio from a fit to the light curve. This parameter (q) is a standard output from fits to microlensing curves generated by binary lenses (two point masses, e.g., star and planet). Now, for low-magnification microlensing events, such as OGLE-2005-BLG-390Lb (which was announced by the PLANET team in January), it is generally possible to estimate the mass just by looking at the light curve. And in those cases it can be explained easily to the non-expert (although PLANET did not do this in their...

An Early Surprise from Stardust

by Paul Gilster | Mar 15, 2006 | Outer Solar System | 3 Comments

There seems to be an emerging maxim in deep space studies: every new mission will overturn at least one enshrined assumption Thus the early Stardust results, studying the cometary debris from Wild 2. Because comets come out of the outer dark in their long arc toward the inner system, one would expect them to be made of materials that were born in cold temperatures. But Stardust has brought us cometary dust that's packed with minerals formed at high temperatures. What a fascinating set of challenges now face the Stardust researchers. They've found olivine in the Wild 2 materials; it's a compound of iron, magnesium and various other things (the Stardust sample is primarily magnesium). Most astronomers believe that olivine crystals are formed from glass that has undergone heating near stars. So how crystals of olivine can show up in the Wild 2 samples bears scrutiny -- after all, Wild 2 is thought to have formed well beyond the orbit of Neptune. And olivine isn't the only oddity about...

An Icy ‘Super-Earth’

by Paul Gilster | Mar 14, 2006 | Exoplanetary Science | 5 Comments

9000 light years away, a planet thirteen times as massive as the Earth orbits a star half the size of the Sun. At -330 degrees Fahrenheit, the newly discovered planet is one of the coldest worlds ever discovered. And its placement within its solar system is interesting indeed, for the icy object occupies an area where, in our system, the asteroid belt holds sway. "We've never seen a system like this before," said Andrew Gould (Ohio State University, and leader of the MicroFUN collaboration, "because we've never had the means to find them." MicroFUN (MicroLensing Follow-Up Network) is exoplanetary hunting via gravitational microlensing. A star crosses in front of a far more distant one as seen from Earth. The gravity of the intervening object bends light rays from the more distant star and magnifies the image, operating much like a lens. From our observational standpoint, the image of the star brightens as the 'lensing' star crosses in front of it, then fades as the lens moves further...

The Color of Pluto’s Moons

by Paul Gilster | Mar 13, 2006 | Exoplanetary Science | 2 Comments

We have interesting exoplanetary news coming up in tomorrow's post, but until then let's talk about Pluto, and the latest Hubble findings about this intriguing system. The two recently found moons are now seen via Hubble imagery to have the same color as Charon, meaning that all three Plutonian satellites are roughly the same shade as Earth's moon. That's an interesting finding, because it suggests that all three moons were formed in the same event. It's also interesting given the reddish hue of Pluto itself, about which we'll learn more in the years leading to the New Horizons encounter in 2015. Image: The new HST/ACS observations made on March 2nd reveal that all three of Pluto's satellites are neutrally colored, unlike reddish Pluto itself. Pluto's reddish color is believed to be due to reddening agents created by the effects of sunlight acting on its nitrogen and methane surface ices. Charon's surface is known to consist primarily of water ice; the similar color of P1 and P2 may...

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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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