Paul Gilster | Centauri Dreams

Galactic Rims: News and a Reminiscence

by Paul Gilster | Jul 22, 2008 | Deep Sky Astronomy & Telescopes | 9 Comments

The image below is striking enough that I would have run it even without the interesting story it tells about the presence of organic materials in Messier 101. Viewed at infrared wavelengths and color-coded, the Pinwheel galaxy's spiral arms are visible, as is an outer zone, marked by a coral color, in which the organic molecules called polycyclic aromatic hydrocarbons disappear. These hydrocarbons are typically found in areas of star formation, with interesting implications for the appearance of life. So what does an organic-free zone tell us about the Pinwheel galaxy? "If you were going look for life in Messier 101, you would not want to look at its edges," said Karl Gordon of the Space Telescope Science Institute in Baltimore, Md. "The organics can't survive in these regions, most likely because of high amounts of harsh radiation." Image: The Pinwheel galaxy, otherwise known as Messier 101, sports bright reddish edges in this new infrared image from NASA's Spitzer Space Telescope....

Communicating with the Future

by Paul Gilster | Jul 21, 2008 | Culture and Society | 13 Comments

It dawned on me over the weekend that Centauri Dreams will soon enter its fifth year of operation, the anniversary being in mid-August. On Sunday I walked the neighborhood, musing over the changes the site has seen and thinking back to its inception. I realized that the actual germ of the idea goes back not to 2004 but to 1986. In those days I was, among other things, writing wine and restaurant reviews, and I found myself in Winston-Salem NC, where I had been sent to review some hot new bistro or other. That night in my hotel room I watched a news item on Voyager, which had just encountered Uranus, and reflected about human futures. The thinking went like this: Launched in 1977, the Voyagers could accomplish their prime mission easily within the lifetimes of those who sent them (their extended mission beyond the heliopause wasn't much discussed back then). But I began to imagine truly long-haul missions that would be brought home not by the people who sent them but by the next...

On Cycles of Exploration

by Paul Gilster | Jul 19, 2008 | Culture and Society | 6 Comments

The latest Carnival of Space is now available, with several items of particular interest to those of us fixated on deep space from the edge of the Solar System to nearby stars. Have a look, for example, at this take (from Astronomy at the CCSSC) on Makemake, a dwarf planet in the newly minted IAU sense, and also a plutoid, meaning a dwarf planet outside Neptune's orbit. Or try Starts with a Bang, where the speculation runs to placing human crews on long-haul starships using artificial incubators and frozen embryos, a subject we recently touched on in these pages. My attention was particularly drawn to Bruce Cordell's piece on How Great Explorations Really Work, in an intriguing site called 21st Century Waves. Here the idea is that great exploratory projects (think Apollo, for example) do not happen at random times, but tend to cluster around a 56-year energy cycle that coincides with major economic booms. My experience with the stock market tells me that when anyone identifies a...

EPOXI: Clues to Terrestrial Worlds

by Paul Gilster | Jul 18, 2008 | Exoplanetary Science | 9 Comments

You must see new video from EPOXI, whose effect can only be suggested by the photo montage below (click the link below for the movie). EPOXI is the combined extended mission of the Deep Impact spacecraft. As we discussed in an earlier story here, EPOXI turned its cameras on the Earth to view the moon transiting the planet's disk from a vantage point of 31 million miles. Think in terms of viewing the Earth the way we will eventually view terrestrial worlds around other stars. The idea is to build insights into how these worlds can be observed and characterized. Image: The moon crossing the Earth, as viewed by EPOXI. Video credit: Donald J. Lindler, Sigma Space Corporation/GSFC; EPOCh/DIXI Science Teams. Drake Deming (NASA GSFC), deputy principal investigator for EPOXI and leader of the extrasolar planet component of the mission (called EPOCh), points out how the information can be helpful: "Our video shows some specific features that are important for observations of Earth-like...

Red Dwarf Tides: Disrupting Life?

by Paul Gilster | Jul 17, 2008 | Exoplanetary Science | 8 Comments

It's easy to see why interest in planets around red dwarfs is growing. The low mass of such a star makes finding smaller planets feasible. It also produces orbits closer to the star, another aid to their detection. We know that planets can form near the habitable zone of such stars because we have the example of Gliese 581, where two planets orbit close to if not just within that region. But is a habitable planet always habitable? If not, what could make these conditions change? I'm looking at a paper that examines tidal effects, an important factor when dealing with M dwarfs. Planets in the habitable zone around these stars experience effects that can cause both their orbital distance and orbital eccentricity to decrease [see comments below re my original misstatement of the eccentricity change, now corrected]. The paper, by Rory Barnes (University of Arizona, Tucson), Sean Raymond (University of Colorado, Boulder) and team, examines an interesting parameter: The habitable lifetime....

Detecting Life in Enceladus’ Plume

by Paul Gilster | Jul 16, 2008 | Outer Solar System | 2 Comments

Now in press at Astrobiology is a look at the possibilities of life on Enceladus that holds out hope for detecting biomarkers with data gathered during a Cassini flyby. That's an exciting possibility, depending as it does not on an orbiter or lander mission from an indefinite future but on equipment we've currently got in Saturn space. And the Enceladus picture remains fascinating because of the possibility that some microbial systems on Earth that operate far beneath the surface may offer examples of how life could evolve on a cold and distant moon of Saturn. We've already found a dozen icy particle jets coming out of Enceladus' south polar regions, all pumping material into a plume that extends for thousands of kilometers. A 2005 Cassini flyby revealed, among other things, water vapor, methane and simple organic compounds, even as other Cassini instrumentation showed the moon's south polar region to be anomalously warm. If there is liquid water under the south polar region, could...

Planetary Prospects Around Proxima

by Paul Gilster | Jul 15, 2008 | Exoplanetary Science | 9 Comments

We've been paying a lot of attention to Centauri A and B in the past two years, but what about Proxima Centauri? After all, this is the closest star to our Sun, a fifth of a light year out from the two major Centauri stars, and free of the close binary problem. You would think this small red dwarf would rank higher on our list of astrobiologically interesting places, but until recently, that red dwarf status has been an encumbrance. It has been only within the last eleven years that the presumed tidal locking of planets in the habitable zone of such stars has been found not to be a necessary deterrent to the formation of a stable climate. Today, M dwarf interest grows. There's at least the chance of a workable ecosystem around such a star, assuming flare activity (common to these stars) might act more as an evolutionary stimulus than a deterrent to life. Moreover, the long lifetimes granted to M dwarfs mean that stable environments could exist for many billions -- perhaps hundreds of...

A Discouraging Outlook for Centauri A Planets

by Paul Gilster | Jul 14, 2008 | Exoplanetary Science | 15 Comments

The news about planetary prospects around the Centauri stars has been positive enough lately that a paper suggesting otherwise introduces a rather jarring note (to me, at least). After all, we've detected more than forty extrasolar planets in multiple systems, a significant percentage of all detected exoplanets, and while most of these are in systems where the stars are widely spaced, there are planets around stars like Gliese 86 or Gamma Cephei where the separations are in the range of a Centauri-like 20 AU. Moreover, key studies have shown that planetary orbits in the habitable zone of the Centauri stars are viable. But what Philippen Thébault (Stockholm Observatory), Francesco Marzari (University of Padova) and Hans Scholl (Observatoire de la Côte d'Azur) bring to the table is a different question. Never mind that planetary orbits may be stable -- how likely are planets to form in these settings in the first place? It turns out that the last stage of planet formation has been...

Exploring Titan via Blimp

by Paul Gilster | Jul 12, 2008 | Outer Solar System | 9 Comments

The latest Carnival of Space is now available at the Space Disco site, where Dave Mosher has put together a helpful slideshow of entries handsomely illustrated and linked to the originals. With seven new blogs coming online at Discovery Space, we'll doubtless be seeing contributions from many of these fine writers, people such as Ray Villard, Chris Lintott and Mosher himself. I'm particularly looking forward to Jennifer Ouellette's Twisted Physics blog, which this week offers a backgrounder on tachyons. In terms of our usual beat, deep space from the outer planets into interstellar space, I'll send you to David S.F. Portree's Altair VI site, where the author has gone to considerable trouble to present the results of a study by Science Applications, Inc. (SAI) on the possibilities of futuristic missions to Titan. This material was originally presented in 1983 at a NASA workshop and offers a view of what should still be a viable game plan: To seed the clouds of Titan with floating...

Creating Binary Asteroids

by Paul Gilster | Jul 11, 2008 | Asteroid and Comet Deflection | 3 Comments

Photons streaming outward from the Sun can impart momentum, which is how a solar sail works. But even more subtle effects produced by the warming of irregular objects may have visible results. A new study of asteroid moons and how they form invokes the tongue-twister known as the Yarkovsky, O'Keefe, Radzievskii, Paddack effect, mercifully shortened to 'YORP effect' by those who study it. A body warmed by the Sun gives off infrared radiation, which carries momentum as well as heat. An asteroid's spin can thus be speeded or slowed by sunlight. Add plenty of time and things get interesting. Start with the kind of asteroid that is little more than a pile of rocky rubble held together by gravity, then spin that rubble pile up slowly over a period of millions of years and eventually material will be slung off from the asteroid's equator. Colliding materials of this nature can eventually coalesce into the satellite we see orbiting its parent, says Patrick Michel (Cote d'Azur Observatory,...

On the Speculative Edge

by Paul Gilster | Jul 10, 2008 | Exotic Physics | 143 Comments

The continuing activity on the Practical Positronic Rocket threads has made it clear that we need a place for speculations that do not flow out of particular posts. What we're aiming at down the road is to implement discussion software that will make such threads easy to follow and contribute to, but for now we're dealing with weblog software that is not optimized for the task. Hence this thread, which is open to rational theorizing about interstellar issues in comments that do not reflect content found in the posts elsewhere on the site. If your idea is 'blue sky' and not related to a particular post, this is the place to put it.

A Scarcity of Gas Giants?

by Paul Gilster | Jul 10, 2008 | Exoplanetary Science | 11 Comments

We'd all like to think our Solar System is a run-of-the-mill place, filled with the kind of planets, including our own, likely to be found around other stars. But maybe it's not so ordinary after all. For recent work suggests that stars like the Sun aren't all that likely to form planets the size of Jupiter or larger. So while small, rocky worlds may or may not be common -- we're still finding the answer to that one -- the combination of rocky worlds and gas giants we take for granted may actually be distinctive. Once again I'm reminded how many conjectures go into our projections of habitable worlds. Here's one possibility: Without a large gas giant in the outer solar system to act as a gravitational shield for the inner system, planets in the habitable zone of a star might be so pelted by space debris that life would be unlikely to form on them. So it's conceivable that any findings about the scarcity of gas giants are a blow to our astrobiological hopes around other stars. At...

Tau Zero Foundation

by Paul Gilster | Jul 8, 2008 | Tau Zero Foundation | 51 Comments

by Marc G. Millis Marc Millis, former head of NASA's Breakthrough Propulsion Physics program and founding architect of the Tau Zero Foundation, now gives us a look at the Foundation's current status and his thoughts on where it's going. To those who have been waiting for the Tau Zero Foundation to begin in earnest, your patience is greatly appreciated. We are definitely making progress and this article describes that status. Sneak preview For the readers of Centauri Dreams, the URL at the end of this article takes you to a sneak preview of our public website. Although the site is far from done (many corrections and additions still needed) enough content is there to give you an idea of what we're delivering. Donations can now be accepted via the "support us" page (hint, hint). Yes, even modest donations speed up progress. We are, after all, still an all-volunteer effort, setting this up in addition to our day-jobs. Stages of Implementation Initially a network of volunteers, the Tau...

The Ethics of Interstellar Journeying

by Paul Gilster | Jul 7, 2008 | Culture and Society | 47 Comments

We usually picture the far future in terms of the most exotic possibilities. And why not: Getting to the stars with warp drive or wormhole makes the entire galaxy accessible. But while we work toward such goals, a raft of technologies continue to develop that can get us to another star with currently understood physics. Imagine, for example, a starship pushed to ten percent of lightspeed by a powerful laser array, a tiny vessel enabled by nanotechnology to carry a cargo of human genetic material. I played around with the concept years ago in a story called "Until Anna Changed," which dealt with a colony around another star whose inhabitants had all been raised upon arrival by their starship's crew, beings called Adepts who were manifestations of artificial intelligence. The Adepts were to move on to another star when the colony was mature enough to survive, but the story looked at what happened to a particular colonist when his own Adept unexpectedly returned. The dynamics of growth...

Comet Mission Zeroes in on Asteroid

by Paul Gilster | Jul 5, 2008 | Outer Solar System | 2 Comments

Much can be learned from a close look at an asteroid, as the European Space Agency's Rosetta spacecraft will demonstrate this September. For one thing, interactions between the solar wind and the asteroid can deepen our knowledge both of the object and the forces that act upon it. For another, studying what's around the asteroid can be useful, especially now that we know some asteroids have even smaller asteroid 'moons.' But Rosetta's September target, asteroid (2867) Steins, is an interesting case in and of itself. E-type asteroids, which this one is, are relatively common in regions closer to the Sun but uncommon within the main belt itself. They're typically small and show a high albedo, reflecting more light from the Sun than the average asteroid. Moreover, while they're apparently made of silicates and basalts, their composition is only poorly understood. Thus the choice of (2867) Steins as a target within a larger mission plan that culminates in 2014 at comet 67/P...

Canada: The Case for a Prehistoric Impact

by Paul Gilster | Jul 4, 2008 | Asteroid and Comet Deflection | 5 Comments

As America celebrates its Independence Day, I'm thinking not only of the fireworks in store for tonight but also those that may have lit up northern Canada almost 13,000 years ago. The case for an asteroid or comet impact there has been strengthened by work in Ohio and Indiana that examines an unusual fact: Gold, diamonds and silver found in the region owe their origins to the diamond fields of Canada. Did glaciers bring these deposits, which evidently arrived in the same period as the supposed impact, much further south? Or is geophysicist Allen West correct in flagging them as the signs of an ancient catastrophe? Ken Tankersley, an anthropologist at the University of Cincinnati, doubted West's notion and opted for the glacier theory until his recent work on the deposits. Says Tankersley: "My smoking gun to disprove (West) was going to be the gold, silver and diamonds. But what I didn't know at that point was a conclusion he had reached that he had not yet made public -- that the...

An Eclipsing Confirmation of Einstein

by Paul Gilster | Jul 3, 2008 | Exotic Physics | 5 Comments

Putting the General Theory of Relativity to the test gives us a chance to look once again at Einstein's understanding of gravity to see how it conforms with reality. We know the theory is incomplete because it doesn't tell us what happens to gravity at the subatomic level. But on the macro-scale of the larger universe, General Relativity is again confirmed in new work involving an unusual pair of neutron stars. The work, performed by an international team using the Jodrell Bank telescope in Cheshire and the Green Bank instrument in West Virginia, examined two pulsars that orbit each other, the only known case out of some 1700 identified pulsars where two are found in such a configuration. Emitting beams of radio waves, the two stars offer another observational opportunity -- their orbital plane lines up nearly with their line of sight to Earth. The result: An eclipsing signal as one pulsar moves behind the ionized gas surrounding the other. The fortuitious lineup makes possible an...

A Poetic View of the System’s Edge

by Paul Gilster | Jul 2, 2008 | Interstellar Medium | 2 Comments

My wife is the most gifted poet I know. I often marvel at her ability to see things with new eyes, to take experiences we have shared and look at them with such a fresh and uncluttered view that the events are transformed and new meaning extracted from them. All of which came to mind this morning in a far different context as I pondered how good science does much the same thing. A case in point in this 'poetry of science' is offered by a view of the edge of the Solar System made not with photons but with neutral atoms, in data gathered by the twin STEREO spacecraft. It's a new kind of astronomy that draws on a different way of looking at the unexplored frontiers of the heliosphere. Our Voyager spacecraft, of course, are in this region, so we're getting new data all the time, but from an optical perspective, the outer heliosphere is invisible. This is where the solar wind -- that stream of charged particles moving outward from the Sun -- reaches the limits of the Sun's influence, a...

NanoSail-D: Solar Sail Deployment Planned

by Paul Gilster | Jul 1, 2008 | Sail Concepts | 11 Comments

Solar sail development has surely been a frustrating thing for Sandy Montgomery, who knows that what stands in the way of pushing this technology into space isn't the need for scientific breakthroughs but adequate funding. Montgomery's team at Marshall Space Flight Center has been examining the potential of solar sails for a long time, and is well aware that leaving the propellant behind is a way to get more payload to your destination with considerably less overhead all around. And solar sails, which can ride the momentum imparted by photons from the Sun, are the ideal way to study 'propellantless' propulsion with near-term technologies. What a pleasure to see the launch window approaching for a solar sail deployment experiment in space, led by Montgomery's team and counterparts at NASA Ames. NanoSail-D is to be launched aboard a Space Exploration Technologies (SpaceX) Falcon rocket some time at the end of July or the beginning of August. Montgomery calls it the "...first fully...

100th Anniversary of a Cosmic Warning

by Paul Gilster | Jun 30, 2008 | Asteroid and Comet Deflection | 11 Comments

By Larry Klaes "Suddenly in the north sky… the sky was split in two, and high above the forest the whole northern part of the sky appeared covered with fire… At that moment there was a bang in the sky and a mighty crash… The crash was followed by a noise like stones falling from the sky, or of guns firing. The earth trembled." So wrote a witness -- fully forty miles away from the event -- of the Tunguska impact of 1908, whose 100th anniversary is today. As Larry Klaes notes, small bodies still undetected by astronomers could pose the threat of another Tunguska, making the hunt for Earth-crossing objects a matter of high importance not just for science but planetary security. Across the many billions of miles of space that our Solar System occupies in its small piece of the vaster Milky Way galaxy, the most numerous members of our celestial neighborhood by far are the comets, planetoids, and meteoroids. Although much smaller than the Sun, the major planets, and...

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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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