by Paul Gilster | Sep 30, 2009 | Interstellar Medium |
Below you’ll see that I’m running Mike Brown’s sketch of the ‘new’ Solar System, one I originally ran with our discussion of Joel Poncy’s Haumea orbiter paper, which was presented at Aosta in July. The sketch is germane on a slightly different level today because as we look at how our views of the Solar System have changed over the years, we’ve learned how many factors come into play, including one Brown’s sketch doesn’t show. For surrounding the planets and nearer regions of the Kuiper Belt is the heliosphere, that bubble of solar wind materials whose magnetic effects help protect the inner system.
Image: Our view of the Solar System has gone from relatively straightforward to one of exceeding complexity. Credit: Mike Brown/Caltech.
Look at the heliosphere diagram below and you’ll see that while the eight planets are comfortably within it, our Pioneers and Voyagers are pushing toward or through the termination shock on their way to the heliopause. Galactic cosmic rays are shown pushing from deep space in toward the bow shock. Our new view of the Solar System must include the fact that the heliosphere does not extend to all of it. The Oort Cloud, that vast sphere of comets, is well outside it, and so would be those Kuiper Belt objects that wander too far from the Sun.
Image: Components of the heliosphere. Credit: NASA Ames.
How about a future mission to Sedna? Better be careful, because this odd object moves out to about 990 AU at aphelion. Our intrepid astronauts, having solved the propulsion problem, would now face galactic cosmic rays without the helpful shielding effects of the heliosphere. Galactic cosmic rays are subatomic particles — protons and some heavy nuclei — that have been accelerated to high velocity by supernova explosions. They’re enough of a problem on the interplanetary level, but become even more of one beyond the system.
All this comes to mind because we’re seeing an increase in cosmic ray intensities, some 19 percent higher than what we’ve seen in the last fifty years, according to Caltech’s Richard Mewaldt, who adds “The increase is significant, and it could mean we need to re-think how much radiation shielding astronauts take with them on deep-space missions.” This NASA news release points to three culprits: a flagging solar wind, a decline in the Sun’s interplanetary magnetic field, and a flattening of the heliospheric current sheet where the polarity of the Sun’s magnetic field changes from a plus to a minus.
We’re safe enough where we are, of course, because the Earth’s atmosphere has allowed life to weather far worse cosmic ray fluxes. But if Mewaldt is right, we may have experienced a low level of cosmic ray activity for most of the space era. “We may now be returning to levels typical of past centuries,” says the scientist, reminding us how much we have to learn about the factors that make space flight within and without the system a hazardous enterprise.
by Paul Gilster | Sep 29, 2009 | Exoplanetary Science |
I’m a great believer in getting the most out of older systems. The computer I do most of my work on is now eight years old. I have access to newer equipment, but I built this box with an eye toward longevity and I’m still happy with it. With the pace of technological change, it’s definitely gotten creaky despite additional memory, a new video card and various other upgrades. That means that Windows gets slower and slower on it, but then, I rarely use Windows, being an open source guy to the bone. Linux has always been my choice.
Now the nice thing about Linux is that, no matter which version I run (and I’ve run quite a few by now), I can get snappy performance out of this old box. The astronomical analogy isn’t too far to seek — these days we’re talking about building larger and larger Earth-based telescopes, and in fact have just inaugurated the Gran Telescopio Canarias on a 7,874-foot mountaintop in the Canary Islands, an instrument that has the largest segmented mirror — 10.4 meters — built so far for an optical-infrared telescope. All of which is great news, but consider how exoplanetary science also manages to pull good data out of much smaller, less heralded equipment.
Thus the June transit of HD 80606b, a gas giant of roughly Jupiter size some 200 light years away. About a dozen observatories went to work on the planet on the night of June 4, with a keen interest in tracking it because the previous transit, last February, had only been partially observed. The gas giant orbits once every 111 days and the transit is roughly twelve hours long, so astronomers adopted the tag-team approach to work on the event. Handing HD 80606b from Massachusetts to Florida (see below) to Indiana to Hawaii, various observatories captured some six hours of observations despite iffy weather along the route.
Image: Rosemary Hill Observatory in rural Levy County, Florida, in a shot from 1996 that shows Comet Hyakutake to the right of the dome, with the Pleiades and Venus on the left. Credit: Francisco Reyes/Rosemary Hill Observatory.
Thus an instrument like the 30-inch reflector at Rosemary Hill Observatory in Florida was able to play a key role in a string of observations that also included the 10-meter Keck I telescope in Hawaii. Useful observations, too, because HD 80806b’s orbit is an elongated ellipse whose cause is thought to be the pull of a companion star. According to this University of Florida news release, the recent observations have shown that the planet’s orbit is not aligned with the star’s rotation, evidence that this theory is correct. In any case, what a pleasure to be reminded that careful work can keep older equipment very much in the hunt.
Planet-hunter Greg Laughlin (UC-Santa Cruz) also commented on the collaboration, from which this:
This is just the sort of project that underscores the great value of ad-hoc collaborations. The Florida ingress observations, for example, were made using the University of Florida’s recently refurbished Rosemary Hill Observatory, 30 miles from Gainesville. The DeKalb observations, made by Indiana amateur Donn Starkey, produced reduced data that were among the best in the entire aggregate. Mount Laguna Observatory, run by San Diego State University, has generated many cutting-edge exoplanet observations, including critical photometry in the Fall 2007 HD 17156b campaign. The University of Hawaii 2.2m telescope turned out photometry with astonishing rms=0.00031 precision. And as the cherry on top, the simultaneous commandeering of not one but two major telescopes on Mauna Kea? It seems that perhaps someone has made a Faustian bargain.
The latest transit of HD 80606b was last Thursday morning. We’ll see what turned up.
by Paul Gilster | Sep 28, 2009 | Culture and Society |
Modeling a Space-Based Future
The submission deadline for the MiniSpaceWorld contest has, according to Tibor Pacher, been extended to November 1. Those with a yen to build scale models with a space theme should be considering the possibilities in the project, an exhibit showcasing everything from current rocket technology to basic principles of physics and astronomy, space travel as seen in science fiction and more. MiniSpaceWorld draws on the inspiration of the Miniatur Wunderland in Hamburg, which does for model railroads what Pacher hopes to do for space-themed modelers and educators.
Image: Tibor Pacher, who leads the MSW effort.
With the help of the Roland Eötvös Physical Society, the MSW design particulars are now being circulated to 1500 secondary school physics teachers in Hungary, which is the reason for the deadline extension. Full particulars can be found on the site, where I notice that the design contest award ceremony will be held in Budapest on December 5. The Hamburg railroad venue has shown, by drawing over five million visitors since its opening, that high quality modeling will have an audience. From model railroads to space may not be that big a leap.
Two Takes on Exotic Physics
Next Big Future recently hosted the Carnival of Space, always a good read, but I want to point you in particular to Brian Wang’s own posts on the Mach Effect and the work of James Woodward. Brian interviews physicist Paul March on his work on thruster applications growing out of these ideas in two posts that you can find here and here. At stake, March believes, is a drive that “…requires a certain minimum amount of local reaction mass to work with, which interacts with the mostly distant mass/energy in the universe via the ambient cosmological gravinertial field wave interactions.”
Interactions with the distant universe? To get to the heart of this, we have to go back to Ernst Mach, who explained inertia as being causally related to the most distant matter in the universe, an idea that is, needless to say, controversial. Einstein tried, but failed, to work the notion into his developing ideas of General Relativity, but the question of inertia’s origin remains tantalizingly elusive.
Image: James Woodward (California State University, Fullerton).
Woodward has been examining what he believes to be transient mass fluctuations in accelerated masses that could be explained in a Machian framework. It’s interesting stuff, and the subject of experimental work that is ongoing, although whether we are dealing with actual effects or ‘noise’ in the data is still unclear. Woodward’s own Web site gives his take on the matter. We also looked at Woodward’s work in our Frontiers of Propulsion Science book.
Interestingly, one reader (writing under the name Kurt9, familiar to Centauri Dreams regulars) noted on Brian’s site that Woodward’s notions seemed similar to John Cramer’s ideas on retro-causality, which are based on his transactional interpretation of quantum mechanics. March, in fielding the question, notes that Cramer’s concept is important because “… it provides a ready-made explanation of how inertial momenergy waves propagate to/from the mostly distant mass/energy in the universe in apparently zero local time.” We continue to await the results of Cramer’s lab work, a widely anticipated experiment that we’ve discussed often in these pages (an early post on the subject is here).
Image: Physicist John Cramer in earlier days. A recent symposium honored his 75th birthday.
Cramer, by the way, investigated some of Woodward’s concepts in a study sponsored by NASA’s now defunct Breakthrough Propulsion Physics project. There are plenty of interesting links to follow in Brian’s two articles. Adam Crowl also discusses Woodward this week.
Let me also point you, while we’re talking about exotic physics, to Richard Oboussy’s interview with Jose Natario on his Interstellar Journey site. Natario has written two influential papers on warp drive. Quoting the physicist:
…I set up a fairly general model for a warp drive spacetime, which includes the Alcubierre model as a particular case. I showed that it is possible to have models where there is no overall contraction or expansion of space (although space does get severely distorted on the warp bubble wall). My hope was that one would then get less severe violations of the energy conditions, but that turned out not to be the case: one can easily prove that these models always violate the positivity of energy. I also showed that there are two other (in my view more serious) problems with the warp drive concept, namely the existence of horizons and infinite blueshift regions.
A major problem with current warp drive concepts: The warp ‘bubble wall’ is disconnected from the interior of the craft, making it impossible for crewmembers inside the vessel to control the wall. How to control something moving faster than light from inside the bubble itself, when your signals, traveling only at the speed of light, cannot reach the front of the bubble wall?
Image: Physicist Jose Natario (Instituto Superior Técnico, Lisbon).
No wonder Natario continues to call warp drive a ‘theoretical curiosity,’ but one that remains fascinating nonetheless. See Natario, “Warp Drive with Zero Expansion,” Classical and Quantum Gravity 19, no. 6 (March 21, 2002), pp. 1157-65.
Thorny Problems with Life Extension
Interstellar theorists are always looking for ways to reduce mission times enough that a scientist working on the project would live to see its completion. For Alpha Centauri, that means about ten percent of lightspeed, given the lengthy times assumed to develop and build the craft in the first place. But another way around the problem is to lengthen human lifespans to the point where a crew could survive a centuries-long mission, explore, and live to make the return.
Although we don’t often get into life extension issues here, it’s interesting that Athena Andreadis (University of Massachusetts) finds one current long-life motif to be all but pointless. Calorie reduction is said to make us live longer, but does it? Check this out, from her recent article in H+ Magazine:
All vitamins except B and C are lipid-soluble. If we don’t have enough fat, our body can’t absorb them. So the excess ends up in odd places where it may in fact be toxic — hence the orange carotenoid-induced tint that is a common telltale sign of many caloric restriction devotees. Furthermore, if we have inadequate body fat, not only are we infertile, infection-prone and slow to heal due to lack of necessary hormones and cholesterol; our homeostatic mechanisms (such as temperature regulation) also flag. And because caloric restriction forces the body to use up muscle protein and leaches bones of minerals, practitioners can end up with weakened hearts and bone fractures.
Image: Athena Andreadis examines a fundamental gene regulatory mechanism, alternative splicing, in her research.
Not only that, but because the brain runs on glucose, it starts releasing stress chemicals when it’s not getting what it needs, a problem that can induce hallucinations or false euphoria. Thus the history of shamans, desert prophets and others who have undertaken fasting as part of a quest for visions. And if you’re counting on red wine to keep you ticking now that you’ve learned you can eat again, Athena doesn’t think much of resveratrol as a life-extender:
…it doesn’t even extend life in mice — so the longer lives of the red-wine loving French result from other causes, almost certainly including their less sedentary habits and their universal and sane health coverage. That won’t stop ambitious entrepreneurs from setting up startups that test sirtuin activators and their ilk, but I predict they will be as effective as leptin and its relatives were for non-genetic obesity.
Andreadis, noting that human lifespan has nearly tripled thanks to vaccines, antibiotics and other factors, doubts we will be able to extend it much further. Moderately overweight people are, according to recent studies, the longest-lived. Maybe propulsion scientists are our best bet after all, at least until we come up with an anti-aging technique that at present seems to be off the charts.
by Paul Gilster | Sep 25, 2009 | Exoplanetary Science |
Protoplanetary disks may not raise the same level of excitement that the discovery of new planets does, but to me, the idea of watching a planetary system form is awe-inspiring. I can’t help but wonder whether, going back about five billion years or so, astronomers around some distant star weren’t watching the early signs of planetary formation around our own star. Disks in their various stages give us a sense of the continuity of solar system development.
Continuity, that is, in the sense that stars seem to form planets as a matter of course. But we’re seeing yet more evidence this week that protoplanetary disks can vary markedly from star to star. Now comes news of the dust cloud around 51 Ophiuchi, which turns out to be not one but two distinct disks, an inner one with grains 10 micrometers and larger in diameter (based on infrared observations), and an outer one made up of primarily 0.1 micrometer grains.
Image: This graphic compares the inner and outer disk of the 51 Ophiuchi system to the location of the planets and asteroid belt of the Solar System. Credit: NASA/GSFC/Marc Kuchner and Francis Reddy.
The inner disk around this B-class star extends out to four AU and is considered one of the most compact such disks ever detected. The outer disk goes from seven AU out to about 1200 AU. In similar systems, inner and outer clouds are distinct, but 51 Ophiuchi, some 260 times more luminous than the Sun, offers up a change of pace. Here the disks seem to be connected, with the system having only a single belt of asteroids. Is this an infant system entering the late stages of planet building? Are terrestrial planets forming in the stellar haze?
Whatever the case, there is a lot of dust here. Christopher Stark (NASA GSFC) describes it this way:
“Our study shows that 51 Ophiuchi’s disk is more than 100,000 times denser than the zodiacal dust in the solar system. This suggests that the system is still relatively young, with many colliding bodies producing vast amounts of dust.”
Interesting work, and a study that takes advantage of the Keck Observatory’s interferometry capabilities to make high resolution measurements equal to a telescope as large as the distance between the primary mirrors involved, some 85 meters. The interferometer’s Nuller was then used to block direct starlight from the star, allowing the dust cloud to be measured to great precision. Observations from other instruments helped to fill out the picture.
We also got word this week of the unusual behavior of the disk around the young star LRLL 31, whose light has been seen to vary in as little time as a single week. One possibility here is the presence of a planet close to the star, which could be causing the planet-forming material to vary in thickness as it orbits the star.
James Muzerolle and team (Space Telescope Science Institute) are behind this one, having set about to study the IC 348 star-forming region in the constellation Perseus. These are young stars, about two to three million years old and some 1000 light years from Earth. Working with the Spitzer instrument, the team found changes to the light from the inner region of the system disk. Spitzer has shown that the disk has both an inner and an outer gap. Says Kevin Flaherty (UA, Tucson), “Transition disks are rare enough, so to see one with this type of variability is really exciting.”
Adds Elise Furlan (JPL):
“A companion in the gap of an almost edge-on disk would periodically change the height of the inner disk rim as it circles around the star: a higher rim would emit more light at shorter wavelengths because it is larger and hot, but at the same time, the high rim would shadow the cool material of the outer disk, causing a decrease in the longer-wavelength light. A low rim would do the opposite. This is exactly what we observe in our data.”
Image: An artist’s conception of LRLL 31. The data show that infrared light from the disk is changing over as little time as one week — a very unusual occurrence. In particular, light of different wavelengths seesawed back and forth, with short-wavelength light going up when long-wavelength light went down, and vice versa. According to astronomers, this change could be caused by a companion to the star (illustrated as a planet in this picture). As the companion spins around, its gravity would cause the wall of the inner disk to squeeze into a lump. This lump would also spin around the star, shadowing part of the outer disk. When the bright side of the lump is on the far side of the star, and facing Earth, more infrared light at shorter wavelengths should be observed (hotter material closer to the star emits shorter wavelengths of infrared light). In addition, the shadow of the lump should cause longer-wavelength infrared light from the outer disk to decrease. The opposite would be true when the lump is in front of the star and its bright side is hidden (shorter-wavelength light would go down, and longer-wavelength light up). This is precisely what Spitzer observed. Credit: NASA/JPL-Caltech/R. Hurt (SSC).
Fascinating stuff, and we’ll know more as astronomers follow up with ground-based telescopes. The paper on LRLL 31 will run in the Astrophysical Journal Letters; for now, a news release is available. The paper on the Keck work is Stark et al., “51 Ophiuchus: A Possible Beta Pictoris Analog Measured with the Keck Interferometer Nuller,” Astrophysical Journal 703 (2009), pp. 1188-1197 (abstract). A preprint is available.
by Paul Gilster | Sep 24, 2009 | Outer Solar System |
My first glimpse of Ganymede ran like this:
Three dead men walked across the face of hell. Their feet groped past frozen rock, now and then they stumbled in the wan light, and always they heard the thin, bitter mumble of wind and felt the cold gnawing at their flesh. Around them there was death, naked stone reaching for a cruel sky of stars, a lean, poisonous whirl of snow which was not snow, that whipped about them and then lay still to crunch under their tread. Jupiter was low in the south, a great shield which glowed amber.
That’s not today’s Ganymede, but a mid-1950’s version as seen in Poul Anderson’s The Snows of Ganymede (Ace Books, as part of an Ace Double that included Anderson’s War of the Wing Men, otherwise known as “The Man Who Counts”). I bought this off a newsstand in St. Louis and remember reading it while waiting for a sandwich to arrive at a lunch counter just off Clayton Rd. I would have been something like nine years old.
That memory made the recent news about mapping Ganymede irresistible. It’s not the place Anderson imagined, but then just count how many other surprises we’ve had from our deep space probes. Voyager and Galileo data have come together to hand us a view of Ganymede that tells us where our imaginations strayed, but as we saw in the rest of the Jovian moon system, Ganymede was hardly the first place that didn’t fit what we expected. Think of that billiard-ball smooth face of Europa, and the startling volcanoes of Io.
What we have here is the first global geological map of Ganymede, the largest satellite in the Solar System (it’s larger than Titan, and for that matter, the planet Mercury). This is a world 5262 kilometers in diameter, the only satellite known to have a magnetosphere. The map displays geological features that help us understand how the moon has evolved over the years, not only internally but also through interactions with other Galilean satellites and in terms of objects striking its surface.
The team, led by Wes Patterson (Johns Hopkins University Applied Physics Laboratory) combined low-resolution photos from Voyager with high-resolution Galileo imagery to create what we see below:
Image: (top) A global mosaic of Jupiter’s moon Ganymede, constructed from the best images collected during flybys of the Voyager 1, Voyager 2, and Galileo spacecraft.
(bottom) A few layers of the geologic map of Ganymede, showing the boundaries between light terrain (white) and dark terrain (brown), and the massive number of tectonic features in the light terrain (black lines). The map is being used to analyze stress fields that could have been responsible for ripping apart the surface of Ganymede in the past (red arrows). Credit: Wes Patterson/JHUAPL.
Here’s Patterson on the significance of this result:
By mapping the entirety of Ganymede’s surface, we can more accurately address scientific questions regarding the formation and evolution of this truly unique moon. Work done using the map by collaborator Geoff Collins at Wheaton College, for instance, has shown that vast swaths of grooved terrain covering the surface of the satellite formed in a specific sequence. The details of this sequence tell us something about the forces that must have been necessary to form those swaths.
If we do get to the Europa Jupiter System Mission, now in the conceptualizing and planning stage at NASA and ESA, we’ll be looking at a Ganymede orbiter as well as one around Europa. This early geological map will clearly be of use in that scenario, helping scientists characterize the moon in detail. The work was presented at the European Planetary Science Congress in Potsdam on the 16th.
So now we have the third completed map of a Moon, the first two being our own Moon and the second Callisto. As to The Snows of Ganymede, it’s well worth a read even today, at least for those of us who love most of Anderson’s work, unraveling as it does political intrigue and mystery on the distant Moon. It’s also hard to find, appearing (to my knowledge) only in the Ace venue and in an earlier issue of Startling Stories (Winter, 1955). Worth seeking out if you happen to be in a used bookstore, that rapidly disappearing artifact of an earlier time.
