Paul Gilster | Centauri Dreams

Interstellar Flight: The Dust Conundrum

by Paul Gilster | Feb 6, 2009 | Interstellar Medium | 11 Comments

It would be helpful if space were a bit more empty. A key problem facing an interstellar probe would be encounters with dust in the planetary system it leaves and, as it reaches cruising speed, dust impact in space between the stars. Although our Solar System seems to be in an unusually sparse pocket of space, the galaxy-wide distribution of hydrogen is roughly one atom per cubic centimeter. Dust -- bits of carbon, ice, iron compounds, and silicates -- is far rarer still, but enough of a factor to a ship moving at a significant fraction of the speed of light that the designers of the Project Daedalus craft built in a payload shield 32-meters in radius to protect their starship. Then again, much depends on your location. Have a look at the image below. It's an area called the Red Rectangle some 2300 light years from Earth in the constellation Monoceros. Although the center of the image seems to be a single star, it's actually the double star system HD 44179. The Red Rectangle is a...

Tightening the Asteroid Focus

by Paul Gilster | Feb 5, 2009 | Outer Solar System | 3 Comments

Asteroid (234) Barbara is an unusual object, a denizen of the main belt that may be a binary. The European Southern Observatory's Very Large Telescope Interferometer is able to piece together two bodies, with diameters of 37 and 21 kilometers respectively, separated by a bit over 20 kilometers. But as seen from Earth, the objects seem to overlap, so we don't know whether this is a true binary or an asteroid in the shape of a giant peanut. The former would be more interesting, for if we can calculate the orbits of these objects and combine them with diameter measurements, we'll learn about their density. This is why Sebastiano Ligori (INAF-Torino, Italy) calls Barbara "...a high priority target for further observations." Ligori is one of the researchers who used the combined light from two of the Very Large Telescope's 8.2-meter instruments to make these interferometric studies, creating a view as sharp as a single telescope whose diameter is as large as the separation between the...

COROT Finds a Small, Rocky World

by Paul Gilster | Feb 4, 2009 | Exoplanetary Science | 16 Comments

The COROT mission's 27-cm telescope has discovered the smallest exoplanet yet, with a diameter less than twice that of Earth. COROT-Exo-7b orbits a Sun-like star and highlights the ongoing space-based investigation into rocky worlds that is drawing ever closer to an Earth-mass object. This is the kind of work COROT was designed to do, flagging planetary transits across the face of a star from an orbital perch that allows long periods of uninterrupted observation and the chance to measure the size of the planets found. ESA's Malcolm Fridlund discusses the significance of the find: "This discovery is a very important step on the road to understanding the formation and evolution of our planet. For the first time, we have unambiguously detected a planet that is 'rocky' in the same sense as our own Earth. We now have to understand this object further to put it into context, and continue our search for smaller, more Earth-like objects with COROT." Finding a 'super-Earth' is one thing when...

New Angles on the Drake Equation

by Paul Gilster | Feb 3, 2009 | Astrobiology and SETI | 15 Comments

The Drake Equation in its various forms has been tormenting us for decades, raising the question of how to adjust variables that range from astronomical (the abundance of terrestrial planets) to biological (the probability of life's emergence) and even sociological (the average lifetime of a technological civilization). Wildly optimistic estimates of the number of technological civilizations in our galaxy are now giving way to more sober reflection. Now Reginald Smith (Bouchet-Franklin Institute, Rochester NY) offers up a new analysis looking at how likely radio contact is given a civilization's lifetime, and how widely that civilization's signals can be clearly received. The key question: What if there is a reasonable horizon for the detection of a signal from an extraterrestrial sender? Signals and Their Lifetime This is useful stuff, because contact depends not just upon the density of communicating civilizations (CC) but their average lifetime and the maximum detectable distance...

Interstellar Studies: Building the Base

by Paul Gilster | Feb 2, 2009 | Culture and Society | 9 Comments

With the Kepler mission scheduled for launch this spring, we should see increasing attention in the media on the detection of terrestrial-class exoplanets and speculations on possible life upon them. But it's easy to forget that Kepler has other important goals, taking estimates, for example, on the disposition of planets in multiple star systems, and studying the stars that have planets in orbit around them. Kepler will also be looking at planetary distribution, including 'hot Jupiters,' and examining their size, density and reflectivity. A Deep Space Challenge for Bloggers All of which is a tall order for a three and a half-year mission, but we can expect a successful run to result in an extended mission as Kepler keeps its gaze fixed on a region in space allowing it to monitor the brightness of more than 100,000 stars. Have a look at OrbitalHub's treatment of Kepler in the current Carnival of Space, where DJ runs through the mission parameters and examines the equipment. Looking...

Titan: A Rainy Season Ahead?

by Paul Gilster | Jan 30, 2009 | Outer Solar System | 6 Comments

Rain seems to have been plentiful at Titan's south pole. A new analysis of Cassini imagery compares the region in recent times with what it was about a year earlier, noting new features in areas many scientists believe to be lakes of liquid hydrocarbons. Adding to the conjecture is the fact that extensive cloud systems covered the region during this period, evidence for a large rainstorm amid changing seasons. All this comes from the almost global surface map Cassini's Imaging Science Subsystem has been acquiring since April of 2004. Have a look at some of this imagery, and keep an eye in particular on Ontario Lacus, at the bottom of each image, noting the difference in brightness. Image (click to enlarge): The images on the left (unlabeled at top and labeled at bottom) were acquired July 3, 2004. Those on the right were taken June 6, 2005. In the 2005 images, new dark areas are visible and have been circled in the labeled version. The very bright features are clouds in the lower...

Beginnings of a Brown Dwarf Census

by Paul Gilster | Jan 29, 2009 | Deep Sky Astronomy & Telescopes | 6 Comments

Just how common are brown dwarfs? The answer is still up for debate, for stars like these (with masses less than 0.05 that of the Sun) are so small that they do not burn hydrogen, and as they age, they become more and more difficult to detect. But we'd like to know more, especially in understanding our local interstellar neighborhood. Red dwarfs are common throughout the galaxy, and we know that they can support planetary systems and even worlds in the habitable zone. Is it possible that brown dwarfs are even more numerous than red dwarfs? Asking questions like these takes us into what is known as the initial mass function (IMF), which involves the number of stars versus their masses at the time of their formation. The place to study the issue is a star forming region like the one shown in the image below. This Subaru Telescope composite shows the W3 Main region, about 6,000 light years away in the constellation Cassiopeia. A region like this is helpful because the majority of stars...

Most Accurate Exoplanet Image Yet

by Paul Gilster | Jan 28, 2009 | Exoplanetary Science | 11 Comments

I absolutely love the image below, so I decided to run it at full size although it doesn't quite fit the column width. You're looking at the result of recent work from the California & Carnegie Planet Search team, which used data from the Spitzer Space Telescope to produce what is probably the most accurate image yet of an exoplanet. It's not an actual photographic image, of course, but it's better than an artist's interpretation because it's based on highly realistic simulations. The planet in question is HD 80606b, which circles a star about 200 light years from Earth. This is a highly interesting place, some four times the mass of Jupiter and moving within a 111-day orbit around its star. What makes it stand out is the incredible eccentricity of its orbit. We're talking about a world that for most of its orbit is at distances that would be between Venus and Earth here in our system. But then it swoops in ever closer to its primary until it closes to within 0.03 AU, an encounter it...

A Crowded Inner System

by Paul Gilster | Jan 27, 2009 | Asteroid and Comet Deflection | 6 Comments

A small asteroid hitting the Earth's atmosphere is a spectacular phenomenon, but one likely to go unseen if the object has not been previously tracked. But that may be changing as we continue to install automated cameras across the planet. Take a look at this video of the object that exploded over Scandinavia on January 17. A Swedish camera recorded the event, which now goes worldwide over the Net thanks to the camera's owner, one Roger Svensson, and spaceweather.com. The January 17 incident was little more than a lightshow, startling for local wildlife but unnoticed by the sleeping nation beneath the brief glare. It does, however, remind us of the 1017 potentially hazardous asteroids (PHAs) now known to scientists. A PHA is an asteroid larger than 100 meters that may come closer than 0.05 AU to Earth. Prowling around the spaceweather.com site, I find twelve Earth-asteroid encounters this January alone, the closest being the 1.8 lunar distance passage of 2009 BD on January 25. Only...

A Science Fictional Take on Being There

by Paul Gilster | Jan 26, 2009 | Astrobiology and SETI | 19 Comments

If you're not a member of the Science Fiction and Fantasy Writers of America (still commonly known as the SFWA from the days before the 'fantasy' bit was added), you may not see the group's regular bulletin. That would be understandable, given that although it can be found on newsstands, the SFWA Bulletin now costs a solid $6.95 per copy. Nonetheless, keeping up with Robert Metzger's 'State of the Art' science column would keep me buying this journal even if it didn't come as part of my membership. Metzger, the author of the 2002 novel Picoverse and 2005's CUSP as well as a variety of short fiction in addition to his science writing (some of which is available online), speculates in his most recent column on a subject we've recently treated here. Would a species capable of star travel actually need to make the journey, given the advances in technology that would surely make it possible to learn more and more about exoplanets from its own star system? Metzger reviews current exoplanet...

A Workable Fusion Starship?

by Paul Gilster | Jan 23, 2009 | Advanced Rocketry | 44 Comments

by Adam Crowl In the market for a mammoth starship? Recently released work by Friedwardt Winterberg, discussed here by Adam Crowl, points to fast interplanetary travel and implies possibilities in the interstellar realm that are innovative and ingenious. Adam notes in an e-mail that Winterberg's drive has certain similarities to MagOrion, a system that in its earliest iteration combined a magnetic sail with small yield nuclear fission devices. Dana Andrews and Robert Zubrin first published that concept in 1997 and it has been evolving in the years since, but Winterberg's work takes the idea into the realm of what may be a truly workable fusion design. Read on as we follow up our earlier story on Winterberg with a much deeper look. Friedhardt Winterberg has worked on inertial confinement fusion since 1954 and was extensively involved in developing new fusion devices during the Cold War alongside bomb-makers like Edward Teller. Much of his non-fission triggering work was classified,...

Dark Matter and Galactic Origins

by Paul Gilster | Jan 22, 2009 | Deep Sky Astronomy & Telescopes, Exotic Physics | 3 Comments

Understanding how galaxies form is no easy matter, particularly when you factor in dark matter. Without a firm knowledge of what dark matter actually is, we're limited to discussing its perceived effects, something that researchers at Hebrew University of Jerusalem have coupled with computer simulations that change how we view the early universe. The large galaxies some three billion years after the Big Bang apparently didn't form from the merger of smaller disks of material, says this team. That earlier theory would have seen slow star formation as the various disks eventually came together. But the latest observations show that early galaxies created stars at a rapid rate. The new theory may explain why. It sees galaxies forming as the result of cold hydrogen flowing in narrow streams along the filaments of the so-called 'cosmic web' that defines the large scale structure of matter in the universe. These hydrogen streams would feed into the halos of dark matter that are believed to...

Detecting Alien Vegetation

by Paul Gilster | Jan 21, 2009 | Exoplanetary Science | 4 Comments

Could we find evidence of vegetation on distant exoplanets? The answer may be yes, according to recent work by Luc Arnold (Observatoire de Haute Provence) and team. If green vegetation on another planet is anything like what we have on Earth, then it will share a distinctive spectral signature called the Vegetation Red Edge, or VRE. The new paper creates climate simulations that explore whether planets with a distinctively different climate than modern Earth's could be so detected. Two earlier eras are useful here. The Last Glacial Maximum (LGM) occurred 21,000 years ago, with global temperatures on the order of 4 degrees Celsius colder than today, and a significantly lower sea level that produced more land surface. The Holocene, 6,000 years ago, is marked by a rising sea level amidst the de-glaciation occurring in the northern hemisphere. Perhaps the most striking contrast with today would be the Sahara, much more laden with vegetation than at any time since. Both provide a useful...

Earth-mass Exoplanets and Their Uses

by Paul Gilster | Jan 20, 2009 | Culture and Society, Exoplanetary Science, Sail Concepts | 19 Comments

What would it take to energize the public about interstellar flight? The answer seems obvious: Discover an Earth-type planet around another star. As happened with Gliese 581 c, once thought to be potentially habitable, the media would quickly focus on the question of how to get there. Interviewed by the BBC on that topic, I found myself explaining that a star over twenty light years away was an impossible target at our current level of technology, but the discussion quickly opened up into what we could do about that, and what methods might evolve to allow star travel. The point is to get people thinking not only about distances but methods. Right now we're still in the 'build a better rocket' mindset, one that doesn't comprehend the realities of adding more fuel just to push still more additional fuel. The equations are inexorable: Rockets can't do the job when we're talking about crossing light years, so we look for ways to leave the propellant at home. And because even fast solar...

The Earliest Stardust

by Paul Gilster | Jan 19, 2009 | Deep Sky Astronomy & Telescopes | 5 Comments

A familiar scenario from the early universe is getting a tune-up. It's long been believed that cosmic dust was first produced by supernovae, becoming the essential building block for the formation of planets. New work using the Spitzer Space Telescope suggests a second mechanism that complements the first. So-called 'carbon stars,' stars late in their lives and similar to red giants but containing more carbon than oxygen, may have played as significant a role as supernovae themselves. The work focused on the carbon star MAG 29, some 280,000 light years away in the Sculptor Dwarf galaxy. Says Albert Zijlstra (Jodrell Bank Centre for Astrophysics): "All the elements heavier than helium were made after the Big Bang in successive generations of stars. We came up with the idea of looking at nearby galaxies poor in heavier elements to get a close-up view of how stars live and die in conditions similar to those in the first galaxies." Image (click to enlarge): The star MAG 29, shown in...

Remembering Steve Ostro

by Paul Gilster | Jan 17, 2009 | Asteroid and Comet Deflection | 4 Comments

By Larry Klaes It was while I was working on our recent story on Near Earth Objects that Larry Klaes' obituary for Steve Ostro arrived, a serendipitous event given Ostro's landmark work in identifying planetoids and especially those that come perilously close to us. Ostro's death last December came at a time of increasing public understanding of the threat posed by these objects. Yet the JPL radar astronomer, who used Arecibo's facilities to such good effect, worked with tools that are now in danger of losing their funding, a commentary on how flexible our priorities can be even on issues of planetary survival. Ostro's voice in Arecibo's defense will be deeply missed. Steven J. Ostro, a major player in radar astronomy who was both an alumnus and teacher at Cornell University, passed away on December 15 from pneumonia brought on by a long bout with cancer. He was 62 years old. Ostro received his Master's Degree in engineering physics from Cornell in 1974. Ostro then went to the...

Interstellar Missions from the Living Room

by Paul Gilster | Jan 16, 2009 | Culture and Society, Exotic Physics | 20 Comments

Seth Shostak and I independently hit upon the same topic yesterday, Seth in his regular venue on Space.com and I with a Centauri Dreams post that asked how advances in observational technology might replace actual interstellar travel. Seth's take is somewhat different from mine, arguing as he does that while we'll spread through the Solar System, we'll likely explore the galaxy from home. I, on the other hand, argue that at least a small number of humans will find the means to make the long journey, but perhaps not in ways we often imagine. Changing How We See Things I return to the topic to get some of Seth's observations into play here. For the point of both articles was that we're making remarkable advances in how we see things, advances that are far more striking than what we've managed in propulsion. Thus it took seven decades to go from the V-1 moving at one mile per second to New Horizons, which moves toward Pluto/Charon at ten miles per second. A factor of ten increase in...

The ‘Why’ of Interstellar Flight

by Paul Gilster | Jan 15, 2009 | Culture and Society, Exoplanetary Science | 15 Comments

From the standpoint of pure research, one of the arguments for not going to nearby stars is that by the time we develop the needed technologies, we'll have no need to make the journey. After all, we'll soon be able to learn vast amounts about nearby worlds from space-based telescopes, not to mention planned Earth-side instruments like the European Extremely Large Telescope, a 42-meter powerhouse 100 more sensitive than the best of today's optical telescopes. Putting observatories on the far side of the Moon is another way we'll see deeper than ever before. Extend space research out fifty years, a hundred, and you have to reckon with capabilities we can only dream about today. Webster Cash (University of Colorado) has been championing one Sun-shade design (there are others) that in its fullest deployment could give us views of an exoplanet as if we were no more than a hundred kilometers away. Or consider the fusion of new propulsion technologies with space-based observatories that can...

Mapping the Solar System’s Edge

by Paul Gilster | Jan 14, 2009 | Interstellar Medium, Sail Concepts | 3 Comments

Riding the solar wind with some kind of magnetic sail is one path into the outer Solar System, but before we can develop an operational technology around the idea, we have to learn much more about how the solar wind works. This stream of charged particles flows outward from the Sun at great speed -- up to well over 400 kilometers per second -- creating the 'bubble' in the interstellar medium known as the heliosphere, within which our Solar System exists. Understanding how that wind interacts with the true interstellar space that lies beyond will give us a better idea of its properties and those of the boundary region at system's edge. Image: The Solar System in context, placed within the heliosphere created by the solar wind. Credit: Southwest Research Institute. IBEX (Interstellar Boundary Explorer) is a space mission that may tell us more as it examines the edge of the heliosphere. Tuned up after two months of commissioning, the spacecraft is now gathering data, mapping the...

The Numbers on NEOs

by Paul Gilster | Jan 13, 2009 | Asteroid and Comet Deflection | 7 Comments

The Spaceguard program, originally mandated by Congress in the 1990s, is in the business of detecting, tracking and cataloging near-Earth objects (NEOs). Spaceguard's goal has always been as ambitious as it is crucial: To locate ninety percent or more of the objects that approach the Earth and are more than one kilometer in diameter. So how is Spaceguard doing? According to Stephen M. Larson (University of Arizona), who manages the Catalina Sky Survey, "We're about 85 percent there." But even when we reach 100 percent, the story is far from over. An object just a third of a kilometer in diameter would explode with an energy more than twenty times that of the largest thermonuclear bomb. NASA received another mandate in 2005 to identify near-Earth asteroids and comets down to 140 meters in diameter, still large enough to destroy a city. And even though impacts like these seem to occur only once every several thousand years, no one can say when the next potential strike could happen....

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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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