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Oxygen, Carbon Dioxide on Rhea

by Paul Gilster | Nov 30, 2010 | Outer Solar System | 11 Comments

Interesting chemistry on the surface of Saturn's moon Rhea seems a natural conclusion following the announcement of the discovery of oxygen in its evanescent atmosphere. And what a difference from Saturn's largest moon, Titan, whose atmosphere is not only thick, but packed with nitrogen and methane, with little trace of carbon dioxide or oxygen. Rhea's tenuous exosphere, which includes carbon dioxide, is so thin that its density of oxygen is about five trillion times lower than that of Earth's atmosphere. Even so, interesting things may happen on an icy surface in this scenario. I'm diverted as I write this -- pardon the digression, but this does come back to Rhea -- because I'm thinking about German friends who are fans of the wonderful 1960's television show Raumpatrouille (Space Patrol), which followed the adventures of the spaceship Orion some years before Star Trek ever appeared on German screens. First broadcast in 1966, Space Patrol went on to achieve true cult status in West...

Pulsar Navigation for Deep Space

by Paul Gilster | Nov 29, 2010 | Communications and Navigation | 6 Comments

We've seen some remarkable feats of celestial navigation lately, not the least of which has been the flyby of comet Hartley 2 by the EPOXI mission. But as we continue our push out into the Solar System, we're going to run into the natural limits of our navigation methods. The Deep Space Network can track a spacecraft from the ground and achieve the kind of phenomenal accuracy that can thread a Cassini probe through a gap in the rings of Saturn. But positional errors grow with distance, and can mount up to 4 kilometers per AU of distance from the Earth. To go beyond the Solar System, we'll need a method that works independently, without the need for ground station assistance. Pulsar navigation is one way around the problem. Imagine a spacecraft equipped with a radio telescope that can determine its position by analyzing the signals from distant pulsars. These super-dense remnants of stellar explosions emit a beam of electromagnetic radiation that is extremely regular, and as we've...

Astrobiology on the Cheap

by Paul Gilster | Nov 26, 2010 | Astrobiology and SETI | 8 Comments

Keeping space missions separate can be a difficult challenge when so many satellites are launched on a single rocket. Take O/OREOS (Organism/Organic Exposure to Orbital Stresses). The small satellite rode into space on an Air Force Minotaur IV rocket on the 19th, a launch we noted here in connection with the NanoSail-D solar sail demonstrator. For NanoSail-D was itself carried into space as part of the FASTSAT payload bus (Fast, Affordable Science and Technology Satellite), and FASTSAT and O/OREOS were subsumed under a mission called Space Test Program S26. Not to mention a number of other satellites from universities and industry that hitched a ride on the same booster. All of this produces not just confusion but acronym fatigue. Nonetheless, interesting science is in the works. O/OREOS is all about conducting astrobiology science experiments on the cheap using nanosatellites (CubeSats), helping scientists plan future experiments on how organic molecules are changed by exposure to...

A Cosmic Gravitational Wave Background?

by Paul Gilster | Nov 24, 2010 | Deep Sky Astronomy & Telescopes | 9 Comments

A gravitational wave is a ripple in spacetime, one that follows naturally from the theory of general relativity -- Einstein did, in fact, predict the existence of such waves back in 1916. Yet so far we have had nothing but an indirect detection in the form of the Hulse-Taylor binary (PSR B1913+16), a pulsar in a binary system that includes a second neutron star, the two orbiting around a common center of mass. The 1993 Nobel Prize in physics went to Richard Hulse and Joseph Hooton Taylor (Princeton University), who showed that the system's orbital decay corresponds with the loss of energy due to the kind of gravitational waves Einstein predicted. What we now need is a direct detection, but these waves have proven to be a tricky catch. Consider this: The distance between two spacecraft flying five million kilometers apart would be changed by about a picometer by the effects of gravitational waves. That's a distance 100 million times smaller than the width of a human hair, some...

A ‘Benchmark’ Brown Dwarf

by Paul Gilster | Nov 23, 2010 | Deep Sky Astronomy & Telescopes | 17 Comments

The WISE mission has received a lot of press in terms of discovering nearby brown dwarfs, but it's clear that finding low-temperature objects is a major investigation at many Earth-bound sites as well. That includes the UKIRT (United Kingdom Infrared Telescope) Deep Sky Survey's project to find the coolest objects in our galaxy, an effort that has paid off in the form of a unique binary system. One of the stars here is a cool, methane-rich T-dwarf, while the other is a white dwarf, the two low-mass stars orbiting each other though separated by a quarter of a light year. Understanding Brown Dwarf Atmospheres We need to put this find in context. In the absence of hydrogen fusion at the core, brown dwarfs depend upon gravitational contraction as their internal energy source. Cooling slowly over time as they shed their energies, brown dwarfs emit most of their radiation in the infrared, with spectra showing absorption bands of water, methane, carbon monoxide and other molecules in the...

Mission News: Sails, Nebulae, Comets

by Paul Gilster | Nov 22, 2010 | Sail Concepts | 1 Comment

NanoSail-D is now in space, following a successful launch on the 19th that involved eight satellites for university research programs and the US government. The sail experiment was carried aboard FASTSAT (the Fast Affordable Science and Technology Satellite) and is scheduled for release seven days after launch, with sail deployment three days later. We'll soon know how well the deployment of the sail -- a five second process -- proceeds, but how energizing to have another sail experiment in motion as we continue to shake out this technology. The NanoSail Twitter feed (@NanoSailD) is active and bears an uncanny resemblance to the amiable, chatty and often obscure IKAROS tweets from that mission's launch. Colorful Imagery from WISE Meanwhile, other missions continue to pop up with intriguing results, including WISE (Wide-field Infrared Survey Explorer), which has been surveying the sky at infrared wavelengths since January and is now on its NEOWISE mission, the extended sequence of...

Status Report on the Tau Zero Foundation

by Paul Gilster | Nov 19, 2010 | Tau Zero Foundation | 39 Comments

by Marc Millis A number of things have been happening recently with the Tau Zero Foundation, but most of them have been behind the scenes. Marc Millis, founding architect of the TZF and former head of NASA's Breakthrough Propulsion Physics project, now goes public with his thoughts on recent activities and where the Foundation is heading. To the fans and contributors of Tau Zero, thanks for your help and suggestions. It's time to talk about recent progress and next-steps. One major news item is that I took an early retirement from NASA, in February 2010, so that I could devote more time to Tau Zero. As much as I tried, I could not do both. I had to make the hard choice between following NASA or leaving that full-salary day-job to make advances via the more flexible Tau Zero Foundation. Now that I'm free of prior restrictions, we are restructuring how we operate and will be eventually shifting to a "Membership" format with regular newsletters. During the first week in November, I met...

A Red Giant Planet of Extragalactic Origin

by Paul Gilster | Nov 18, 2010 | Exoplanetary Science | 11 Comments

I can't begin today's entry, which deals with an unusual planet indeed, without first mentioning the passing of Allan Sandage, a man whose work I have admired for my entire adult life. A protegé of Edwin Hubble, Sandage would refine the latter's findings, re-examining Hubble's distance measurements to galaxies like Andromeda and helping us fine-tune our estimates of Hubble's Constant, a measure of the expansion of the universe. In fact, our current estimate, 71 kilometres per second per megaparsec, is only slight off Sandage's 1958 result. A final paper, on RR Lyrae variable stars, appeared as recently as June, one of 500 papers the astronomer wrote. Astronomy Now has a fine obituary of Sandage, who died at the age of 84. Looking Back from the Future Maybe it's the death of Sandage that has me in a retrospective mood as I tackle a most unusual exoplanet story. All morning I've been remembering a passage from H.G. Wells' The Time Machine in which the time traveler has found his...

A Second Life for NanoSail-D

by Paul Gilster | Nov 17, 2010 | Sail Concepts | 6 Comments

I notice that the Planetary Society is doing some fundraising for its LightSail program, in this case looking for money to help build a spare for the LightSail craft. Lou Friedman puts it this way in a recent mailing: "We need to build a spare to insure our plans. It's the prudent move; much cheaper than purchasing insurance and building an entire new back-up craft, as long as we do it now, while the first spacecraft is being built." The cost of a back-up craft during this window is roughly $200,000. Some basics about LightSail-1: Its mylar sails are 4.5 microns thick, the thinnest ever made for spaceflight. When they deploy, they'll extend to cover 32 square meters, and the four sails should throw quite a reflection, acting like mirrors that would be visible from Earth and may appear brighter than any visible star or planet. The vehicle is to be formed from three CubeSat spacecraft, forming a 'bus' about the size of a shoebox that weighs about 4.5 kilograms. We've covered the...

Fermi Bubbles: Remnants of an Ancient Jet?

by Paul Gilster | Nov 16, 2010 | Deep Sky Astronomy & Telescopes | 3 Comments

Did the Milky Way once have a jet powered by matter falling into the supermassive black hole at galactic center? There is little evidence for an active jet today, but we do see jets like these in so-called 'active galaxies,' those that show higher than normal luminosity over much of the electromagnetic spectrum. Some jets in active galaxies can be thousands of light years long, evidently emerging from each face of the accretion disk around a central black hole in the so-called active galactic nucleus (AGN). And on a smaller level, we've found similar jets emerging from the accretion disks around neutron stars and stellar-mass black holes. Image: Streaming out from the center of the galaxy M87 like a cosmic searchlight is one of nature's most amazing phenomena, a black-hole-powered jet of electrons and other sub-atomic particles traveling at nearly the speed of light. In this Hubble telescope image, the blue jet contrasts with the yellow glow from the combined light of billions of...

A FOCAL Mission into the Oort Cloud

by Paul Gilster | Nov 15, 2010 | Missions | 29 Comments

After all this time, I'm still trying to wrap my head around the idea of massive objects in space as lenses, their distortion of spacetime offering the ability to see distant objects at huge magnification. On Friday we saw how the lensing effect caused by galactic clusters can be used to study dark energy. And consider the early results from the Herschel-ATLAS project, conducted by ESA's Herschel Space Observatory. Herschel is scanning large areas of the sky in far-infrared and sub-millimeter light. Many of its brightest sources turn out to be magnified by gravitational lenses, where light from a very distant object passes a galaxy much closer to the Earth, bending that light so that the image of the more distant galaxy is magnified and distorted. Because Herschel has only covered one-thirtieth of the entire Herschel-ATLAS survey area, it's likely that the project will uncover hundreds of gravitational lenses, offering astronomers the chance to probe galaxies in the early universe...

Gravitational Lensing Probes Dark Energy

by Paul Gilster | Nov 12, 2010 | Exotic Physics | 13 Comments

Abell 1689 is one of the most massive clusters of galaxies known, making it a superb venue for the study of dark matter. That's because the cluster, some 2.2 billion light years away, creates gravitational lensing that magnifies and distorts the light from galaxies far beyond it. Astronomers used Abell 1689 in 2008 to identify one of the youngest and brightest galaxies ever seen, a galaxy in existence a mere 700 million years after the beginning of the universe. That find, A1689-zD1, turned out to be ablaze with star formation in an era when stars were only beginning to emerge. New Hubble studies have now used Abell 1689 yet again to make some of the most detailed maps yet of dark matter. The idea is this: The cluster's gravitational lensing bends and amplifies the light of objects beyond it. The researchers, led by JPL's Dan Coe, go to work on the distorted images that result, figuring out the mass it would take to produce them. If the galaxies we see in the cluster were the sole...

Hartley 2: Primordial Dry Ice

by Paul Gilster | Nov 11, 2010 | Outer Solar System | 9 Comments

Keep an eye on the EPOXI site at the University of Maryland. New images from the Hartley 2 comet encounter are coming in, some of them truly breathtaking, as is the one at left. The jets clearly visible in the image can be linked with distinct areas on the surface of the comet, the first time we've ever seen a comet with this degree of clarity. Image by image, the tiny comet is yielding its secrets. We now learn that spectral analysis of the material coming from the cometary jets shows it to be primarily carbon dioxide, along with dust and ice particles. Image: This enhanced image, one of the closest taken of comet Hartley 2 by NASA's EPOXI mission, shows jets and where they originate from the surface. There are jets outgassing from the sunward side, the night side, and along the terminator -- the line between the two sides. The image was taken by EPOXI's Medium-Resolution Instrument on Nov. 4, 2010. The sun is to the right. Credit: NASA/JPL-Caltech/UMD. Jessica Sunshine (University...

WISE: First Ultra-cool Brown Dwarf

by Paul Gilster | Nov 10, 2010 | Deep Sky Astronomy & Telescopes | 32 Comments

"To a man with a hammer, everything looks like a nail," said Mark Twain, one take on which is that the way we see problems shapes how we see solutions. That fact can be either confining or liberating depending on how open we are to examining our preconceptions, but in the case of Amy Mainzer (JPL), it leads to a natural way to describe a failed star. Mainzer, who is deputy project scientist on the Wide-field Infrared Survey Explorer mission (WISE), is an amateur jewelry-maker. For her, it's easy to look at the image below and see gems. "The brown dwarfs," says Mainzer, "jump out at you like big, fat, green emeralds." And that emerald below, dead center in the image, is hard to miss. Image: The green dot in the middle of this image might look like an emerald amidst glittering diamonds, but it is actually a dim star belonging to a class called brown dwarfs. This particular object, named "WISEPC J045853.90+643451.9" after its location in the sky, is the first ultra-cool brown dwarf...

The Poetry of SETI

by Paul Gilster | Nov 9, 2010 | Astrobiology and SETI | 5 Comments

Stephen Baxter's "Turing's Apples," which originally ran in a collection called Eclipse Two (2008), is an intriguing take on SETI and the problem of extracting meaningful information from a signal. It's a bit reminiscent of Fred Hoyle's A for Andromeda (1962) in that the SETI signal received on Earth contains instructions for building something that may or may not pose a threat to our species. Sorting out the issue involves discussion of information theory and Shannon entropy analysis. Say again? Best to handle this by quoting from the story. In this scene, the protagonist's brother, who is obsessed with the signal his team has received from the direction of the Eagle Nebula and, ultimately, the galactic center, is explaining how information is being extracted from it. Shannon entropy analysis looks for relationships between signal elements. The brother goes on: "You work out conditional probabilities: Given pairs of elements, how likely is it that you'll see U following Q? Then you...

Of Comets and Deep Space Aspirations

by Paul Gilster | Nov 8, 2010 | Outer Solar System | 11 Comments

The Hartley 2 flyby was an outstanding event, and the only thing I regret about my recent travels was that I was unable to follow the action as the images first streamed in. By now, sights like the one at left have made their way all over the Net, so I won't dwell on them other than to say that if you haven't seen the short video clip of the EPOXI flyby, you should definitely give it a look. You're getting the view from a spacecraft that closed to 700 kilometers or so of the surface, during an encounter taking place at a speed of 12.3 kilometers per second. Image: Comet Hartley 2 can be seen in glorious detail in this image from NASA's EPOXI mission. It was taken as the spacecraft flew by around 6:59 a.m. PDT (9:59 a.m. EDT), from a distance of about 700 kilometers (435 miles). Jets can be seen streaming out of the nucleus. Image credit: NASA/JPL-Caltech/UMD. I'll go along with EPOXI principal investigator Michael A'Hearn's description of the comet's "stark, majestic beauty."...

Beyond Hartley 2: EPOXI’s Hunt for Exoplanets

by Paul Gilster | Nov 4, 2010 | Exoplanetary Science | 1 Comment

I had hoped to be able to cover the Hartley 2 flyby today, but I'm traveling on Tau Zero business and have to write this entry early. Instead, I'll at least keep the EPOXI mission focus by talking about the other half of this unique venture, an investigation of exoplanet systems. We can always talk about what the Hartley 2 encounter produced next week, but not before, as the schedule is crowded and I doubt I'll be able to get an entry posted here at all on Friday. Remember that the Deep Impact spacecraft that visited Tempel 1 in 2005 is now on an adventuresome extended mission called EPOXI (although the spacecraft, confusingly enough, still retains the original 'Deep Impact' name). The spacecraft was reawakened in the fall of 2007 and directed to a flyby of the Earth for a gravitational assist that would put it into a heliocentric orbit for the Hartley 2 encounter. On the cruise portion of that journey, the extrasolar component of the mission kicked in. EPOCh (Extrasolar Planet...

Closing on Hartley 2

by Paul Gilster | Nov 3, 2010 | Outer Solar System | 3 Comments

With NASA's EPOXI mission closing on comet Hartley 2 at 12.5 kilometers per second, be aware that live coverage of the close encounter will begin at 1330 UTC (0930 EDT) on Nov. 4 from mission control at the Jet Propulsion Laboratory. NASA TV streaming video will be available, and you should also be able to watch the action on a JPL Ustream channel. Finally, NASA's Eyes on the Solar System Web tool, a 3-D environment for Solar System exploration, is available for viewing a real-time animation of the cometary flyby on your PC. EPOXI is a great instance of re-purposing a spacecraft to extract maximum value. This is the Deep Impact vehicle that gave us such a spectacular view of the impactor smash-up on comet Tempel 1 back in the summer of 2005. Under the name EPOXI, the mission has pressed ahead with two separate objectives, the first being EPOCh, or Extrasolar Planet Observation and Characterization, which has involved a number of nearby stars known to have transiting exoplanets. The...

Millis: Thoughts on the ‘100-Year Starship’

by Paul Gilster | Nov 2, 2010 | Missions | 19 Comments

by Marc Millis When Pete Worden (NASA Ames) spoke to the Long Now Foundation recently, he surely didn't realize how much confusion his announcement of a '100-Year Starship' study would create. The news coverage has been all over the map and frequently incorrect, ranging from intimations of a coverup (Fox News) to mistaken linkages between the study and competely unrelated talk about one-way missions to Mars (the Telegraph and many other papers). What's really going on in this collaboration between NASA and DARPA? Marc Millis has some thoughts on that based on his own talks with the principals. Millis, former head of NASA's Breakthrough Propulsion Physics project and founding architect of the Tau Zero Foundation, here puts some of the myths to rest and explains where the 100-Year Starship fits into our future. If you have not yet heard, there's been a bit of news flurry over the announcement that DARPA is funding NASA Ames to the tune of $1M for a one-year study for a "100-Year...

Enchanted with the Outer System

by Paul Gilster | Nov 1, 2010 | Outer Solar System | 13 Comments

It's staggering how much our view of the Solar System has changed over the past few decades. The system I grew up with seemed a stable place. The planets were in well-defined orbits out to Pluto and, even if it were always possible another might be found, it surely couldn't pose any great surprise in that great emptiness that was the outer system. But today we routinely track trans-Neptunian objects with diameters over 500 kilometers -- about 50 of these have now been found, and some 122 TNOs at least 300 kilometers in diameter. We know about well over a thousand objects in that ring of early system debris called the Kuiper Belt. It's an increasingly messy place, this outer Solar System, and it has its own terminology. We have centaurs and plutinos, resonance objects, cubewanos, scattered disk objects (SDOs), Neptune trojans, damocloids, apollos and, perhaps, inner Oort cloud objects. Nope, this isn't the Solar System I grew up with, and every new discovery adds to the enchantment....

Charter

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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