by Paul Gilster | Apr 10, 2008 | Exoplanetary Science |
Although the image below isn’t particularly striking, do focus in on it for a moment. You’re looking at what astronomers now consider the coldest brown dwarf yet to be found. Look just down from the top of the image and just left of center for the unusually red pinpoint. This is CFBDS J005910.83-011401.3, thankfully abbreviated CFBDS0059. A science fiction writer with brown dwarf credentials (Karl Schroeder is just the guy) could think of a more poetic name and set up a story around such a place.
Image: Three-color image of the star field in which the brown dwarf has been discovered. The brown dwarf is the very red object seen at the top left of the image. This image illustrates how very different is the color of this object compared to the other cold stars around. Image copyright Canada-France-Brown-Dwarf-Survey 2008.
As interesting stars go, CFBDS0059 isn’t all that far away, some forty light years. Massing between 15-30 Jupiter masses, it’s typical of brown dwarfs in at least one sense, not being able to sustain thermonuclear reactions. It’s also unusually like a giant planet, more so than other known classes of brown dwarfs, not only because of temperatures in the range of 350 degrees Celsius but also because of the presence of ammonia, hitherto undetected in brown dwarf near-infrared spectra.
By contrast, L dwarfs have temperatures in the range of 1200 to 2000 degrees Celsius, while the cooler T dwarfs (both of these are considered brown dwarf classes) come in at under 1200 Celsius. Are we looking at a new class of brown dwarfs in CFBDS0059? They would offer an unusual chance to fill in the gap between giant planets and stars. The most significant aspect of a find like this one is the chance to study a cold brown dwarf in relation to exoplanets we cannot directly observe. This ‘almost planet,’ not swamped by light from a parent star, may help us tune up our models for working with distant planetary atmospheres.
And other cool brown dwarfs fitting the proposed spectral class Y are likely to be found. The same team points to ULAS0034 as an example, and the paper on this work notes “We therefore expect to find another few similarly cool objects, and hopefully one significantly cooler…” The paper is Delorme et al., “CFBDS J005910.90-011401.3: reaching the T-Y Brown Dwarf transition?” accepted by Astronomy & Astrophysics and available online.
by Paul Gilster | Apr 9, 2008 | Sail Concepts |
Bear with me as I jump around wildly in this post, from Epsilon Eridani to happenings on our own Sun. The cause: Recent news about the solar wind from the Royal Astronomical Society’s meeting in Belfast that has me thinking about magnetic sails. The concept seems made to order for in-system propulsion. Instead of catching the momentum of solar photons with a large physical sail, try riding the flow of charged particles coming out of the Sun by using a magnetic sail generated aboard the vehicle. Velocities of several hundred kilometers per second seem feasible.
The thought of which reminded me to dig out a paper that Dana Andrews and Robert Zubrin presented at the 1990 Vision-21 symposium at NASA’s Lewis Research Center (now Glenn Research Center) in Cleveland. Andrews and Zubrin had written several papers on the concept, noting one way a magsail could operate. From the Vision-21 proceedings:
The magnetic sail, or Magsail, is a device which can be used to accelerate or decelerate a spacecraft by using a magnetic field to accelerate/deflect the plasma naturally found in the solar wind and interstellar medium. Its principle of operation is as follows: A loop of superconducting cable hundreds of kilometers in diameter is stored on a drum attached to a payload spacecraft. When the time comes for operation the cable is played out into space and a current is initiated in the loop. This current once initiated, will be maintained indefinitely in the superconductor without further power. The magnetic field created by the current will impart a hoop stress to the loop aiding the deployment and eventually forcing it to a rigid circular shape.
Other magsail concepts, like Robert Winglee’s M2P2 (Mini-Magnetospheric Plasma Propulsion) create a huge magnetic bubble around an interplanetary craft, an idea Winglee examined in two studies for NASA’s Institute for Advanced Concepts. But getting to the outer Solar System with magsails is one thing. Can we put the concept to work in interstellar missions? You wouldn’t think so, given the dispersion of the solar wind the further you move from the Sun, but Andrews and Zubrin realized that solar winds can be approached from two directions, one being the arrival of a starship at its destination, where braking becomes a critical function.
Two years before Vision-21, the two scientists had studied a potential one-way mission for a thousand ton payload to a star ten light years from Earth. Forget the magsail on the way out — the authors posited a lightsail pushed by a 1000 terawatt laser, initial acceleration limited by temperature constraints on the sail, and acceleration duration limited by the focusing capability of the laser optic system. The magsail would be deployed for deceleration into the target system, the total one-way trip time totaling 107 years.
But keeping interstellar journeys within a single human lifetime is obviously desirable. Fortunately, later work by Geoffrey Landis on dielectric sail materials allowed the authors to ramp up the acceleration. The 1990 paper posited a 5000 terawatt laser, which could reduce the travel time to 37 years when coupled with an improved magsail to reduce arrival times. Using a laser focusing mirror with a 50 kilometer aperture and a lightsail some 50 kilometers in diameter, Andrews and Zubrin figured 0.8 years for acceleration, 17.4 years coasting at roughly half the speed of light, and 18.8 years decelerating. The magsail is now 3100 kilometers in diameter versus 1000 in the earlier study, with deceleration times roughly half those found with the smaller sail.
Ten light years out gets you almost to Epsilon Eridani, assuming we find something there of interest. But let’s get back to our own Solar System. Before we can go magsailing even between planets, we need more information about how the solar wind operates. The work discussed at the Belfast meeting mentioned above pinpoints the source of the solar wind, using the UK-built Extreme Ultraviolet Imaging Spectrometer (EIS) aboard the Japanese Hinode spacecraft. The collision of magnetic fields from bright surface regions allows the requisite hot gases to flow out from the Sun. Says Louise Harra (UCL-Mullard Space Science Laboratory):
“It is fantastic to finally be able to pinpoint the source of the solar wind – it has been debated for many years and now we have the final piece of the jigsaw. In the future we want to be able to work out how the wind is transported through the solar system.”
Image: An X-ray image of the Sun made with the Hinode satellite on 20 February 2007. The insets show the flow of gas away from the bright region marked on the left. The blue image indicates material flowing towards us that will eventually make up the solar wind and the red image shows material flowing away from us back towards the surface of the Sun. Credit: L. Harra/JAXA/NASA/ESA.
This is the kind of jump we make when we study interstellar travel, from speculation about braking as we decelerate into another system to current research on our own star, work that is building the basis for what may one day become our first magsail deployments in space. Connecting the deeply speculative with the daily grind of ongoing research is what interstellar theorists are all about, the key being to keep the long-term goal in view even as we continue to build the necessary foundations.
The primary paper I’ve used for this discussion is Andrews and Zubrin, “Use of Magnetic Sails for Advanced Exploration Missions,” in the proceedings for Vision-21: Space Travel for the Next Millennium” (NASA Conference Publication 10059). Abstract here. The 1988 paper by the same authors is “Magnetic Sails and Interstellar Travel,” IAA Paper 88-553, presented at the 39th IAF Congress, Bangalore, India.
by Paul Gilster | Apr 8, 2008 | Culture and Society |
Centauri Dreams congratulates frequent correspondent Adam Crowl on the birth of his fifth child. Well done in Australia! Mother and eight pound, two-ounce boy are doing well. The newcomer will doubtless keep Adam busy, but not enough, let’s hope, to slow down his contributions here, or his continuing work on Crowlspace. If I still smoked, I’d light a cigar in honor of the event, but a nice Barossa Valley Shiraz I can manage…
by Paul Gilster | Apr 8, 2008 | Exoplanetary Science |
Keep your eye on a project in the Canary Islands called the New Earths Facility. Using a laser measuring device now being tuned up for the job, scientists intend to continue the hunt for terrestrial worlds with a greater than ever chance of success. Called an astro-comb, the device brings far greater precision to our existing Doppler techniques for finding exoplanets. In fact, early reports suggest it may increase the resolution of these methods by as much as one hundred times, making the detection of an Earth-like world in an orbit similar to ours feasible.
Now we’re getting into interesting territory indeed, not only in terms of planetary detections themselves but synergies with the ambitious Kepler mission, to be launched in 2009. Read on.
Studying the Doppler shift of distant starlight has already achieved a remarkable precision, capable of finding planets down to about five Earth masses in orbits as far from the star as Mercury. But the farther we get from the star, the trickier these observations become. The same is true for planetary size. Larger worlds are much easier to find, making finding planets as small as the Earth in an orbit similar to our own a challenge. The astro-comb ought to make a difference.
Image: CfA astronomers are developing a new device that may be the first to spot Earth-like planets, like the hypothetical world with two moons shown in this artist’s concept. The “astro-comb” uses a laser to provide an ultrasensitive way of measuring a distant star’s wobbling motion, which is induced by an orbiting planet. Credit: David A. Aguilar (CfA).
Pulses of laser light linked to an atomic clock create a standard against which the astro-comb can measure the incoming starlight. The technology is based on so-called ‘laser combs’ that have been in use for creating precision clocks. Such a comb creates spikes of laser light evenly spaced in wavelength — hence the comb metaphor — that can be projected into a spectrograph. Ronald Walsworth (Smithsonian Astrophysical Observatory) added a filtering device to the laser comb that spreads the ‘teeth’ of the comb to make the technology workable for astrophysics.
If the device proves out, numerous applications should be possible beyond the planet hunt. The paper on this work, for example, talks about measuring the decelerating expansion of the early universe (as opposed to what is now believed to be the renewed acceleration of same in a much later era). But planets, Earth-like ones at that, are what inevitably come to mind, taking pride of place in the paper on this work:
Beyond our ?rst demonstration, astro-combs should enable many observations that have previously been considered technically unachievable. One example is the search for a 1-Earth-mass planet in an Earth-like orbit around a Sun-like star, which requires a sensitivity of 5 cm s?1 and stability on at least a 1-year timescale.
Deploying an astro-comb at the William Herschel Observatory in the Canaries should boost the powers of the spectrograph to be located there under the auspices of the Harvard Origins of Life Initiative and the Geneva Observatory to the point where that instrument can find Earth-like planets. Known as the HARPS-NEF (High-Accuracy Radial-velocity Planet Searcher of the New Earths Facility) spectrograph, the instrument is similar to the HARPS spectrograph in Chile.
Interestingly, the Canaries facility, its instrumentation augmented by an astro-comb, offers useful support to the upcoming Kepler mission. Kepler will go after planetary transits, looking at 100,000 solar-type dwarf stars in a single field of view for four years. Kepler’s problem: The space-based observatory will be able to detect Earth-sized planets but unable to measure their mass because of the tiny Doppler values they generate. Current models for terrestrial planets suggest that the combination of mass and radius information will help us tell the difference between rocky planets and water worlds.
HARPS-NEF, especially as boosted by the astro-comb, should help make this possible. A prototype astro-comb will be tested this summer at the Mount Hopkins Observatory in Arizona, with improvements feeding into the Canaries project. The paper is Chih-Hao Li et al., “A laser frequency comb that enables radial velocity measurements with a precision of 1 cm s-1,” Nature 452 (3 April 2008), pp. 610-612 (available online).
by Paul Gilster | Apr 7, 2008 | Asteroid and Comet Deflection |
Impacts from space debris are much in the news again. The death of Arthur C. Clarke plays a role in at least some of the interest, the New York Times reprinting an op-ed piece the writer did for that paper back in 1994. This was not long after Shoemaker-Levy demonstrated what a cometary impact might do even to a massive gas giant, getting people thinking about the options if we discovered an asteroid or comet heading our way. They might also have been reminded of Rendezvous with Rama.
Clarke had discussed asteroid impacts in the early pages of the 1973 novel, setting up Project Spaceguard as a defense mechanism — a 1992 NASA workshop report on near-Earth object detection honored Clarke by being named the Spaceguard Survey. In the op-ed, Clarke made it clear what he thought the stakes were:
In view of the number of collisions that have taken place in this century alone — most notably, a comet or asteroid that exploded in 1908 in Siberia with the force of 20 hydrogen bombs — there is a very good case for a global survey of the possible danger, particularly as the shared cost among nations would be negligible compared to most national defense budgets. (Incidentally, historians might also be advised to undertake some surveying. Just as the numerous meteor-impact craters on Earth were never found until we started looking for them, so there may have been disasters in history that have been misinterpreted. Sodom and Gomorrah have a good claim to be meteorite casualties; how many others are there?)
Interesting in light of a clay tablet discovered in the ruins of Nineveh by Austen Henry Layard some 150 years ago. Itself more than 2500 years old, the tablet is apparently a copy made by an Assyrian scribe of a much older tablet. Showing drawings of constellations amidst cuneiform symbols, it is being put forth as evidence of a large fireball passing over Mesopotamia and observed by Sumerian astronomers. Alan Bond (Reaction Engines Ltd.) and Mark Hempsell (Bristol University) argue in a new book that the tablet records events in the sky on June 29, 3123 BC.
If Bond and Hempsell are right, the trajectory of a large object traveling across Pisces can be made out, consistent with an impact near the town of Köfels in the Austrian Alps. Tens of thousands might have died in the impact of this object, thought to be over a kilometer in diameter. A low incoming angle of six degrees would explain the lack of a crater at Köfels, the asteroid striking a mountain eleven kilometers from the village and exploding.
A fireball would have resulted, but no crater. The area is known to have endured a massive landslide some 500 meters thick and five kilometers in diameter, but the lack of a crater had puzzled previous scientists. Puzzled them enough, in fact, that many geologists think no impact was involved. Even more questionable is Bond and Hempsell’s suggestion that energy from the fireball traveled as a back plume out over the Mediterannean, re-entering the atmosphere in ways consistent with the destruction of the very Sodom and Gomorrah Clarke cites. Says Hempsell:
“The ground heating, though very short, would be enough to ignite any flammable material, including human hair and clothes. It is probable more people died under the plume than in the Alps due to the impact blast.”
This is a fascinating theory and I’m all for examining the historical record for possible references to asteroid impacts, but the interpretation of cuneiform tablets is exceedingly difficult work subject to numerous different and competing analyses. Let’s wait to see what specialists in the area have to say about this particular interpretation. NASA’s David Morrison also notes that we should at least look for computer modeling to demonstrate the possibility of the back plume wreaking destruction in the Sinai, an idea he says ‘sounds pretty incredible.’
Although dubious, I’d like to see this story work out for more than just scientific reasons. After all, Alan Bond’s name should be familiar to Centauri Dreams readers. Along with his rocketry work at Rolls Royce and later fusion studies for the UK Atomic Energy Authority, Bond was the lead author of the Project Daedalus final report. I defer to no one in my admiration for the work of the British Interplanetary Society on the first full-fledged engineering study of a starship, a battered photocopy of which sits about eight feet away from me, laden with annotations.
Considerably less questionable than Köfels is new evidence of the largest meteorite ever known to have struck Britain, falling some 1.2 billion years ago near the town of Ullapool. Those of us who travel often in Scotland can attest to the beauty of Ullapool and environs today, but 1.2 billion years ago ejecta from this strike were apparently scattered over an area at least fifty kilometers across. Here’s a bit of the confirmatory evidence, presented by Ken Amor (Oxford University):
“Chemical testing of the rocks found the characteristic signature of meteoritic material, which has high levels of the key element iridium, normally only found in low concentrations in surface rocks on Earth. We found more evidence when we examined the rocks under a microscope; tell-tale microscopic parallel fractures that also imply a meteorite strike.”
Image: Artist’s impression of a large meteorite hitting the Earth. The crater from the strike at Ullapool was quickly buried in sandstone, preserving evidence of the impact. How many other craters from large meteorites or even asteroids remain to be discovered? Credit: © MIKE AGLIOLO/SCIENCE PHOTO LIBRA.
The paper here is Amor et al., “A Precambrian proximal ejecta blanket from Scotland,” Geology Vol. 36, Issue 4 (April 2008), pp. 303-306 (abstract). The book on the possible strike at Köfels is Bond and Hempsell, A Sumerian Observation of the Köfels’ Impact Event (Alcin Academics, 2008). Whether or not the latter is borne out by subsequent research, it’s good to see the subject of Earth impacts continuing to make headway in the popular press, perhaps evidence that the need for planetary defense planning in the Arthur C. Clarke mode hasn’t been entirely lost on editors busy with more short-term projects.
