No Asteroid Strike on Mars

by | Jan 12, 2008 | | 10 Comments

The 36th Carnival of Space is up at Steinn Sigurðsson's Dynamics of Cats site. Standing out this week are the items flowing in from the American Astronomical Society meeting in Austin, which ran until Friday. The best place to get the overview is Universe Today, but both Random thoughts of an astro major and Bad Astronomy have tracked events closely. Also noteworthy this time around is the news that the asteroid strike on Mars is now effectively ruled out, the odds falling to one in 10,000. Image: 2007 WD5 from the University of Hawaii 2.2-meter telescope on Mauna Kea, Hawaii. The circled dot is the asteroid (click to enlarge; it's at dead center, in a green circle). Other dots are artifacts from cosmic rays. The stars are trailed because the telescope is tracking the asteroid as it moves among the stars. Credit: Tholen, Bernardi, Micheli with support from the National Science Foundation. Too bad, as the opportunities for close observation of such a hit would have taught us much...

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An Antimatter Cloud Around Galactic Center

by | Jan 11, 2008 | | 14 Comments

Although I had planned to push straight on to look at instrumentation for a true interstellar mission (using Mike Gruntman's landmark paper on the topic), I want to revise that schedule because of the recently announced antimatter news. We'll return to the instrumentation issue on Monday, including the tricky question of how a probe designed to reach 400 AU can make effective measurements given its speed (75 km/s in the best case scenario Gruntman looks at). Because that question just gets trickier as speeds ramp up, it's a major one for planning. But on to antimatter, a cloud of which has been known to exist around the galactic center since the 1970s, when balloon-based gamma-ray detectors first located it. Gamma rays are significant in terms of antimatter because electrons encountering positrons (their antimatter equivalent) annihilate each other, with their mass converted into high energy gamma rays. So the cloud's presence is well established. The question since its detection is...

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Building a True Interstellar Probe

by | Jan 10, 2008 | | 24 Comments

Imagine yourself aboard a spacecraft pushing into interstellar space. At what point would the Sun cease to be the brightest object in your sky? We're already looking at missions designed to study the local interstellar medium (LISM), with the goal of reaching anywhere from 300 to 400 AU, a region believed to be undisturbed by the Sun. From that range, the Sun still shows an apparent visual magnitude of -13.7, making it brighter than any other star we see from Earth (Sirius comes in at magnitude -1.46). So it's a long push. In fact, an early interstellar probe moving at 75 kilometers per second would have to travel six thousand years to reach the point where the Sun is no longer the brightest star. At 100,000 AU, which is 1.61 light years, our imaginary probe occupant would finally see a sky where the Sun was just another bright star. I get this information from a fascinating paper by Mike Gruntman (USC), who was kind enough to forward links not only to it but several other papers...

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Puzzling Short Gamma Ray Burst in Taurus

by | Jan 9, 2008 | | 1 Comment

Is the image at left an accurate depiction of what triggers at least some of the gamma-ray bursts we're now detecting? Or is it a model now in need of serious revision? We're looking at an artist's conception of the merger of two neutron stars, an event that produces gamma rays (note the jets emanating from the center). Such a scenario may be the cause of short gamma ray bursts (GRBs). But NASA's Swift satellite and the Gemini Observatory (Hawaii) have detected one such burst that takes us farther back in time than ever before, some 7.4 billion years. And therein lies a tale. GRB 070714B was detected last July 14, the second burst of the day (note the terminal B in the designation). Short bursts are those lasting less than three seconds, the most popular theory for their formation being neutron star merger and collapse into a black hole, with consequent ejection of energy. Such bursts are obviously tricky to study because their short duration calls for immediate follow-up with...

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Enceladus, Europa and Life

by | Jan 8, 2008 | | 14 Comments

Having looked at Titan and Europa yesterday, we can complete our outer planetary trifecta with a stop at Enceladus, lately of great interest as an active and possibly life-bearing moon. One hot spot detected there by Cassini is ejecting plumes of ice and vapor above the arid world in a cloud so fine that, according to William McKinnon (Washington University, St. Louis), the result is like a smoke made of ice, its particles about one-thousandth of a millimeter across. Enceladus is clearly a geologically active world, far from the inert desolation once expected. All of which makes the Saturnian moon intriguing in the extreme when you start wondering about the presence of water and the possibilities of life. But McKinnon is quick to dash that hope when asked bluntly whether there is evidence for a subterranean ocean: "I don't think so," McKinnon said. "The strongest piece of evidence against that is measurements made from Earth of the plume don't show any sodium. If the source of the...

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Meanwhile, Around the Outer Planets…

by | Jan 7, 2008 | | 15 Comments

The outer planets turn out to be far livelier places than we ever expected in those distant pre-Voyager days. Io set the tone, but look at all the activity we've found from Enceladus to Triton, and now we've got continuing Cassini revelations as well as new interpretations of what the Galileo probe found around Jupiter. Some of this is striking indeed, as witness a paper called to my attention by Larry Klaes and Adam Crowl discussing what may be happening on Europa in terms of energy. The apparent presence of that sub-ice ocean on Europa has made it of great interest for astrobiology. The problem has been the availability of energy. Christopher Chyba (Princeton University), working with Kevin Hand (Princeton) and Robert Carlson (Caltech) have used data from Galileo's Near-Infrared Mapping Spectrometer to determine that the Jovian moon could maintain an oxidized ocean. I should have the full text of this one shortly (right now I'm working solely from the abstract), but the gist of the...

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Notes & Queries 1/5/08

by | Jan 5, 2008 | | 4 Comments

Studying people on Earth is one way to learn how long-duration space missions may affect the human body. The Human Test Subject Facility at the Johnson Space Center is looking for test subjects in a series of 'bed rest' studies that will be conducted over the next ten years. A head-down tilt bed is used, with extended periods in which the participants stay in bed with their body tilted slightly downward (a minus six degrees incline). The longest stretch involves 90 days lying in bed, hard to imagine, but those interested in volunteering for these compensated studies should have a look at the Human Test Subject Facility background page. ------- Both of Saturn's poles -- and not just the southern one -- seem to be home to a set of hot cyclonic vortices. That's a bit of a surprise given the earlier belief that sunlit conditions contributed to the south pole hot spot. But the north pole has been out of sunlight since 1995. Just what are these apparently long-lasting vortices? Leigh...

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Suggestive Red Dust in Protoplanetary Disk

by | Jan 4, 2008 | | 39 Comments

Another youthful star makes the news today, the eight million year old HR 4796A in Centaurus, some 220 light years from Earth. As we saw yesterday, we have much to learn about how planets form around young stars. This one hasn't yielded a planet, but its dust disk, discovered in 1991, seems to derive from a planetary system in formation, the evident product of collisions between small bodies called planetesimals. The latest work on HR 4796A draws on observations made by the Near-Infrared Multi-Object Spectrometer aboard the Hubble Space Telescope. The spectra that John Debes and Alycia Weinberger (Carnegie Institution, Washington) studied in visible and infrared light scattered by the star's disk look red and imply the existence of the large organic carbon molecules called tholins. These are organic aerosols, complex molecules that, on Titan at any rate, remain suspended in the atmosphere and may contain chemical precursors to life. Image: Red and near infrared wavelengths from the...

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Musings on a Youthful Planet

by | Jan 3, 2008 | | 11 Comments

People seem to be getting younger all the time. I'm told this is a common perception as you get older. In any case, it wasn't so long ago that I met the son of an acquaintance at an informal gathering. He looked to me to be about fourteen years old, but something warned me not to assume this. I said "What do you do? Are you in school?" His reply: "No, I've got my own dental practice downtown." I don't know how old you have to be to become a dentist, but I do know it's a lot older than fourteen! Exoplanets and the stars they circle, on the other hand, seem to be mostly of a certain age, the denizens of relatively mature systems. Which is why TW Hydrae is so interesting. It's an infant in stellar terms, at eight to ten million years old only a fraction of the Sun's age. Like other stars in its age group, it is surrounded by a circumstellar disk of gas and dust, the sort of place where planets can form. And indeed, what seems to be the youngest planet yet detected has now been located...

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San Marino: Assessing Active SETI’s Risk

by | Jan 2, 2008 | | 31 Comments

Our recent discussions of active SETI, otherwise known as METI (Messaging to Extraterrestrial Intelligence), highlighted many of the key issues involved while demonstrating just how controversial the topic has become. But is there a way to look at METI experiments more objectively? The San Marino Scale has been widely suggested as a method for assessing the risks we incur with deliberate transmissions from the Earth to other stars. Introduced by Iván Almár in 2005, the Scale is a work in progress that draws on the model of the Richter Scale, which quantifies the severity of earthquakes. The IAA SETI Permanent Study Group continues to work on it, hoping to measure "...the potential exposure of employing electromagnetic communications technology to announce Earth's presence to our cosmic companions, or replying to a successful SETI detection." More on the background of the Scale here. Hungarian theorist Tibor Pacher has been calling my attention to the San Marino Scale for some time,...

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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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