Paul Gilster | Centauri Dreams

Surprise Find: Fragments of Fallen Asteroid

by Paul Gilster | Mar 26, 2009 | Asteroid and Comet Deflection | 5 Comments

Asteroid 2008 TC3 is surely a sign of progress. The eighty ton asteroid, which made a spectacle of itself upon entry into Earth's atmosphere on the morning of October 7, 2008, was the first space rock to have been observed before it collided with our planet. What we're hoping, of course, is that any future objects headed our way will be spotted early enough that, if their size warrants, they can be diverted or destroyed. It was thought that 2008 TC3 did a good job of destroying itself when it exploded some 37 kilometers above the Nubian desert, but two researchers recently traveled to the Sudan and, with help from students at the University of Khartoum, collected 280 pieces of asteroid over a 29-kilometer field. Peter Jenniskens (SETI Institute) calls the event "...an extraordinary opportunity, for the first time, to bring into the lab actual pieces of an asteroid we had seen in space." Jenniskens is lead author on the paper that now appears as the cover on the latest Nature. I...

Gravitational Waves: The Pulsar Connection

by Paul Gilster | Mar 25, 2009 | Deep Sky Astronomy & Telescopes | 21 Comments

I, for one, would like to be in on the detection of gravitational waves. They flow naturally from the theory of General Relativity and ought to be out there, but none have ever been directly detected. What might make finding them easier would be a spectacular event, such as the merger of a pulsar and a neutron star or a black hole, an event that should cause a huge emission of gamma rays in its final moments. Short-period binaries are the ticket -- find them and you have the chance to test General Relativity to high degrees of precision. Some 200,000 volunteers have already signed up for the EINSTEIN@Home project, which searches for gravitational waves from rapidly spinning neutron stars. The project is now looking for volunteers for its new search, one that will use home computers to analyze data gathered at the Arecibo Observatory in Puerto Rico in the hunt for binary radio pulsars. This is jazzy stuff, another opportunity, like SETI@Home and the Galaxy Zoo, for those of us with an...

How Much Is a Planet Worth?

by Paul Gilster | Mar 24, 2009 | Culture and Society, Sail Concepts | 7 Comments

The current Carnival of Space is up at OrbitalHub, with a lively take on habitable planets from Charles Magee's Lounge of the Lab Lemming. Magee, now a field geologist in central Australia, once operated a laboratory that analyzed crystalline and glassy solids -- 'everything from dead people to bits of the Moon,' as Charles puts it -- but he brings his analytical skills to bear this week on a much more theoretical problem: How much is a planet worth? Greg Laughlin (UC-Santa Cruz) has been kicking the question around on his systemic site, creating a prize for the first planet to reach a million dollars in value on his scale, with Earth setting the baseline at four quadrillion. Mars weighs in at a mere $13,988 on this scale, yet no known exoplanet even comes near that disappointing valuation. Magee has fun with Greg's equations and goes to work on Venus, focusing on its albedo. Assuming a terrestrial albedo (0.36), he quickly arrives at a Venusian temperature not dissimilar from the...

Life’s Left-Handed Secret

by Paul Gilster | Mar 23, 2009 | Astrobiology and SETI | 7 Comments

Twenty different amino acids go into making up the vast variety of proteins so essential to life. But why does life on Earth use only left-handed versions of amino acids to build them? After all, amino acids can be made in mirror images of each other. Jason Dworkin (NASA GSFC) notes the key issue. Mix left- and right-handed amino acids and "...life turns to something resembling scrambled eggs -- it's a mess. Since life doesn't work with a mixture of left-handed and right-handed amino acids, the mystery is: how did life decide -- what made life choose left-handed amino acids over right-handed ones?" Image: This artist's concept uses hands to illustrate the left and right-handed versions of the amino acid isovaline. Credit: NASA/Mary Pat Hrybyk-Keith. It's a question with ramifications for life elsewhere in the universe. Suppose the day comes when we finally get a robotic lander to Enceladus. The news flashes around the world: Life discovered on one of Saturn's moons! But is it truly...

Studying Habitable Planets with JWST

by Paul Gilster | Mar 21, 2009 | Exoplanetary Science | 9 Comments

Spotting transiting planets is what missions like CoRoT and Kepler are all about. The next step, getting a read on what's in the atmosphere of any transiting, terrestrial world, is going to be tricky. The biomarkers like ozone and methane, so crucial for determining whether there's life on a distant planet, are beyond the range of existing spacecraft. But the the next generation James Webb Space Telescope is also in the works, scheduled for launch in 2013. For nearby Earth-class worlds, JWST may be up to the task, at least for terrestrial planets that transit. In fact, if Alpha Centauri A turns out to have a transiting Earth-like planet (a major if!), it would take only a few transits to study the light filtering through its atmosphere to look for signs of life. Alpha Centauri is problematic in any case, but a recent study shows that the method -- breaking down the star's light during a transit to look for the characteristic markers -- could be extended to other stars, provided...

Icarus: Revisiting the Daedalus Starship

by Paul Gilster | Mar 19, 2009 | Missions | 65 Comments

by Kelvin Long Project Daedalus was the first thoroughly detailed study of an interstellar vehicle, producing a report that has become legendary among interstellar researchers. But Daedalus wasn't intended to be an end in itself. Tau Zero practitioner Kelvin Long here offers news of Project Icarus, a follow-up that will re-examine Daedalus in light of current technologies. A scientist in the plasma physics industry and an aerospace engineer, Long is assembling the team that will begin this work in 2010, following a 'Daedalus After 30 Years' symposium scheduled for September at the headquarters of the British Interplanetary Society. Can we improve Daedalus' propulsion systems, change its targets, modify its shielding? Numerous theoretical studies await. During the period 1973-1978 members of the British Interplanetary Society undertook a theoretical study of a flyby mission to Barnard's star, some 5.9 light years away. This was Project Daedalus, which remains the most detailed study...

Saturnian Transits (and a Memory)

by Paul Gilster | Mar 18, 2009 | Outer Solar System | 8 Comments

Every now and then a new space photo completely snares the attention. This one is a Hubble shot showing four of Saturn's moons moving in front of the planet. Note Titan at the top, while below it from left to right are Enceladus, Dione and (at extreme right) Mimas. To see the smaller moons, you'll want to click the image, which will take you to a zoomable view that captures these tiny satellites against the immensity behind them. Image: Saturn and four of its moons, as seen by Hubble's Wide Field Planetary Camera 2 on February 24, 2009, when Saturn was at a distance of roughly 1.25 billion kilometers from Earth. Hubble can see details as small as 300 km across on Saturn. The dark band running across the face of the planet slightly above the rings is the shadow of the rings cast on the planet. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA). The transit of the four moons is an unusual event because the rings only become tilted edge-on to Earth every fourteen to fifteen...

Prospects for Red Dwarf ‘Earths’

by Paul Gilster | Mar 17, 2009 | Exoplanetary Science | 20 Comments

Most stars in our region of the galaxy are low-mass M-dwarfs, making the investigation of their planetary systems quite interesting. If we learn that stars like these, which comprise over 70 percent of the galactic population, can be orbited by Earth-like planets, then the galaxy may be awash with such worlds. But some models have indicated that Earth-sized planets would be rare around these stars, working on the assumption that scaled-down versions of the Sun's protoplanetary disk would tend to produce only low-mass planets. Clearly, we need to know more about the masses of such inner disks, since available mass seems to be a key to the formation of habitable planets. Extrapolate the early nebula from our own Solar System to lower protoplanetary disk masses around M-dwarfs and the terrestrial worlds that form are no larger than Mars -- they're small, dry, worlds unlikely to develop life. Low-mass disks would seem to lead to low-mass planets. But what if those M-dwarf protoplanetary...

Interstellar Matters at UK Conference

by Paul Gilster | Mar 16, 2009 | Culture and Society | 4 Comments

Tau Zero practitioner Kelvin Long has organized an interstellar session at the forthcoming 2009 UK Space Conference, which will take place from April 1 to 4 at Charterhouse School, near Godalming Surrey. The overall conference looks to be an excellent one, with symposia on rocket technology, panels and presentations on astronomy and space science, much educational material for teachers and students, and the presentation of the Arthur Clarke Awards on the evening of the 4th. From our perspective, of course, it's good to see the Tau Zero logo up on the site's interstellar page, with links to all presentations. Long is a scientist in the plasma physics industry who will address inertial confinement fusion and antimatter-catalyzed fusion for space propulsion. You'll recall that inertial confinement was the propulsion system of choice for the Project Daedalus starship design created by members of the British Interplanetary Society. Antimatter-catalyzed fusion interests me in light of...

A New Tilt on SETI

by Paul Gilster | Mar 14, 2009 | Astrobiology and SETI | 6 Comments

The planets in our Solar System rotate around the Sun more or less in a plane (the ecliptic) that is tilted some sixty degrees with relation to the galactic disk. It's interesting to speculate that this could have ramifications in terms of the SETI hunt. Shmuel Nussinov (Tel Aviv University) considers the possibility that any extraterrestrial civilizations might try to contact us only after they had a fair idea we were here. And just as we are now trying, via Kepler and CoRoT, to track down small planets using the transit method, so too might extraterrestrials try to observe our transits, and having done so, to transmit a message. Targeting habitable planets should optimize chances for a successful reception. From our end, a prudent SETI strategy might then be to home in on the 'stripes' of the sky within which our system's planetary transits are detectable from other solar systems. As Nussinov writes: The thickness of the galactic disc in our neighborhood is ? 150 parsecs. With the...

Mapping a Galactic Transit System

by Paul Gilster | Mar 13, 2009 | Culture and Society | 10 Comments

I love the London Underground and have a great fondness for wandering about the city with a tube map stuck in my pocket. My wife and I last did this a few years back, making an early March trip in which we rented a Bloomsbury apartment for ten days and hopped all over the area, station to station, emerging for blustery walks to various historical sites (we were both, at one time, medievalists), then ducking into nearby restaurants for tea and warming up, talking about what we had seen and examining the map for our next stop. A map of the London Underground is a schematic diagram that has a beauty of its own, reducing a city beyond its topography to a sequence of formalized connections and zones. The fascination is in the abstraction of the familiar, rendering distance and space intelligible. Now look at what we might call a 'tube map' of the Milky Way, as produced by Samuel Arbesman, a postdoc at Harvard with an interest in computational sociology and, obviously, big maps. Click on...

How Many Stars in the Galaxy?

by Paul Gilster | Mar 12, 2009 | Deep Sky Astronomy & Telescopes | 39 Comments

We've often speculated here about how many stars exist in the Milky Way. Earlier estimates have ranged from one hundred billion up to four hundred billion, with a few wildcard guesses in the range of one trillion. The number is still, of course, inexact, but recent work has led to a serious misunderstanding of the subject. As reported in this earlier post, Harvard's Mark Reid and colleagues have discovered that the Milky Way is likely to be as massive as the Andromeda galaxy, which means that it could have the mass of three trillion stars like our own Sun. Does that mean that the Milky Way contains three trillion stars? Absolutely not. I'm seeing the three trillion star number popping up all over the Internet, and almost reported it that way here when I first encountered the work. The misunderstanding comes from making mistaken assumptions about galactic mass. Reid used the Very Long Baseline Array to examine regions of intense star formation across the galaxy, a study the scientist...

Rare Earth? Not Enough Data to Know

by Paul Gilster | Mar 11, 2009 | Astrobiology and SETI | 65 Comments

George Dvorsky takes on the 'rare earth' hypothesis in his Sentient Developments blog, calling it a 'delusion' and noting all the reasons why life in the galaxy is unlikely to be unusual. The post reminds me why the book that spawned all this was so significant. Rare Earth: Why Complex Life is Uncommon in the Universe (Copernicus, 2000) is Peter Ward and Donald Brownlee's take on our place in the cosmos, concluding that complex life is rare because an incredibly fortuitous chain of circumstances must arise for it to occur. Indeed, the authors argue that large parts of our galaxy are composed of what they call 'dead zones.' The argument is complex and looks at factors ranging from a planet's place in the galactic habitable zone (itself a controversial subject), its orbit around its own star, its size, its satellites, its magnetosphere, its plate tectonics, and more. I'm surprised to realize, looking through our archives here, that I haven't managed to do a complete review of Rare...

Browsing the Exoplanet Catalog

by Paul Gilster | Mar 10, 2009 | Exoplanetary Science | 13 Comments

We now have on the order of 335 confirmed exoplanets, with an ongoing race between the CoRoT and Kepler teams to find the first Earth analog in the habitable zone around another star. CoRoT's shorter observation cycles make finding a terrestrial world around a G-class star problematic -- the orbit would necessarily be on the order of a year, and the transit would then have to be confirmed with additional transits and whatever radial velocity observations could be mustered. But CoRoT just might find an Earth-class planet in the habitable zone of a K-class star, so we shouldn't assume Kepler is necessarily going to win the 'habitable Earth' race. I mentioned a few days back that the Planetary Society has unveiled its new Catalog of Exoplanets, a fine resource with the basics on detection methods and a glossary that complements a catalog filled with helpful orbital animations. If you want to get a quick read on a given exoplanet, take a look here. Some of these planets have gone beyond...

A Fine Intergalactic Haze

by Paul Gilster | Mar 9, 2009 | Deep Sky Astronomy & Telescopes | 12 Comments

Take a look at NGC 4565, a spiral galaxy seen edge-on. Spiral galaxies viewed at this angle often show dark dust lanes, the result of dust from dying stars mixing with interstellar gas. We've discussed the problem of interstellar dust in terms of objects moving at relativistic speeds between stars, but recent quasar studies are showing us that entire galaxies may expel dust to distances of several hundred thousand light years. In terms of the NGC 4565 image, that would be ten times farther than the visible edge of the galaxy. Image: Spiral galaxies seen edge-on often show dark lanes of interstellar dust blocking light from the galaxy's stars, as in this image of the galaxy NGC 4565. The dust is formed in the outer regions of dying stars, and it drifts off to mix with interstellar gas. Credit: Sloan Digital Sky Survey (SDSS-II). The astronomers who did this work talk of intergalactic space being filled with a haze of fine dust particles, a haze that can be examined by analyzing light...

Space Voyaging a Century Out

by Paul Gilster | Mar 7, 2009 | Culture and Society | 25 Comments

A nice, tidy liftoff for Kepler, and like all night launches, well worth watching. The mission is generating a satisfying amount of attention in the press and a slew of news releases, from one of which which I'll quote Geoff Marcy: "In part, learning about other Earths -- the frequency of them, the environment on them, the stability of the environment on other Earths, their habitability over the eons -- is going to teach us about our own Earth, how fragile and special it might be. We learn a little bit about home, ironically, by studying the stars." And of course it's hard to argue with that, although the focus for most of us will only be tangentially here and most emphatically there -- just how many terrestrial worlds are out there, and how likely are the chances for their being in the habitable zone? Marcy gets preferential treatment here simply because, along with Paul Butler and a team of exoplanet hunters spread out over the globe, he has been involved in almost half of our...

Ceres: A Possible Source of Life?

by Paul Gilster | Mar 6, 2009 | Astrobiology and SETI, Outer Solar System | 25 Comments

The Kepler countdown proceeds and, naturally, will preoccupy many of us during the day. I won't try to keep up with the minutiae, as we're not set up to be a news site at that level of granularity. Go instead to the Kennedy Space Center's countdown page, where you'll find live video feeds, or the Kepler portal. You can track the Kepler feed on Twitter here, although it's been quiet all morning. The launch is scheduled for 10:49 EST (03:49 UTC) and the clock, as they say, is running. NASA TV should kick in about two hours before launch. If you want a Kepler diversion, try Astrobiology Magazine's story on Ceres as a possible source for life on Earth. What's not to like about yet another candidate for life in the outer Solar System? Even so, this one seems to be quite a stretch. The story focuses on a theory from Joop Houtkooper (University of Giessen), who sees the 'dwarf planet' (I think that's the right IAU terminology these days) as a potentially living world, a place a bit like...

Kepler, SETI and Ancient Probes

by Paul Gilster | Mar 5, 2009 | Astrobiology and SETI | 32 Comments

We've already speculated here that if the Kepler mission finds few Earth-like planets in the course of its investigations, the belief that life is rare will grow. But let's be optimists and speculate on the reverse: What if Kepler pulls in dozens, even hundreds, of Earth-sized planets in the habitable zones of their respective stars? In that case, the effort to push on to study the atmospheres of such planets would receive a major boost, aiding the drive to launch a terrestrial planet hunter with serious spectroscopic capabilities some time in the next decade. Budget problems? Let's fold Darwin and whatever Terrestrial Planet Finder design wins approval into the same package, and make this a joint NASA/ESA mission. Finding numerous Earth-like planets will be a driver, as will gradual economic recovery. Finding Many Earths The discovery of numerous 'Earths' would also galvanize public interest in interstellar flight, which offers a useful educational opportunity. Even the short-lived...

New Life in an Ancient Lake?

by Paul Gilster | Mar 4, 2009 | Astrobiology and SETI | 5 Comments

If we're looking for pristine environments for life, Antarctica offers much. More than 150 subglacial lakes have been discovered beneath the ice sheet, isolated from the surface for long periods and possibly home to species that have never before been observed. From November 2007 to February 2008, a subglacial lake named Lake Ellsworth was studied by a four-person team that used seismic and radar surveys to map the lake's depth and take other measurements that made clear its potential for exploration. Their blog is archived here, and it makes for good reading. Image: A DeHavilland Dash-7 flying near the British Antarctic Survey research station at Rothera. The station is 1630 kilometers southeast of Punta Arenas, Chile, and served as a staging area for the Lake Ellsworth studies of 2007-2008. Credit: Natural Environment Research Council. Europa, anyone? Well, there are certain resemblances. If the thickness of the ice on Europa is still controversial, we know for a fact that Lake...

Temperature Inversion on Pluto

by Paul Gilster | Mar 3, 2009 | Outer Solar System | 14 Comments

With an atmospheric pressure one hundred thousand times less than that on Earth, Pluto becomes an even more intriguing object than usual when it moves closer to the Sun in its 248-year orbit. This period, occurring now, causes the temperature of the surface to increase, and that causes what had been frozen nitrogen (with trace amounts of methane and, probably, carbon dioxide) to sublimate into gas. Studying these matters with ESO's Very Large Telescope, astronomers have now found unexpectedly large amounts of methane in that atmosphere. Image: Artist's impression of how the surface of Pluto might look, according to one of the two models that a team of astronomers has developed to account for the observed properties of Pluto's atmosphere. The image shows patches of pure methane on the surface. At the distance of Pluto, the Sun appears about 1000 times fainter than on Earth. Credit: ESO/L Calçada. A second discovery: The atmosphere of the distant ice world is some forty degrees Celsius...

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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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