by Paul Gilster | Jul 21, 2007 | Culture and Society |
Those who have toiled in the vineyards of literary studies may recognize the allusion in my title to Notes & Queries, a journal collecting short pieces on a variety of research topics. Back in grad school I was forever looking up odds and ends in its pages related to the Anglo-Saxon alliterative line. A far cry from the Kuiper Belt and extrasolar debris disks!
But I need the occasional short feature here that, like Notes & Queries, collects things I want to highlight, each interesting, I hope, and useful to the interstellar-minded.
- The indefatigable Brian Wang offers a lengthy piece on External Pulsed Plasma Propulsion and nuclear rockets in general. Have a look to see a NASA study from 2000 and its design principles for EPPP, which uses thrust from plasma waves in ways reminiscent of Project Orion. The post also studies the old NERVA designs and offers numerous links for follow-ups. “We just have to have the courage to become a truly interplanetary civilization,” Brian argues in tones that Centauri Dreams readers will admire. But is nuclear the best way forward? Plenty of food for thought here.
- John Cramer’s time experiment has occupied us before, and I won’t re-summarize that work other than to say that it focuses on what Einstein called ‘spooky action at a distance,’ the strange and seemingly connected behavior of entangled particles that have been separated (for more, see this older Centauri Dreams article). Can Cramer demonstrate an effect that seems to occur before its cause? The latest news, from Alan Boyle’s site, is that Cramer’s research fund has reached $40,000, from foundations and private donors. Just returned from Brookhaven National Laboratory, he aims to conclude the experiment by the end of September. On the other hand, maybe we’ll hear about it earlier if he succeeds?
- Galaxiki is a virtual galaxy based on the Web 2.0 wiki concept, currently housing over a million stars and solar systems that can be explored. Since each system represents a single page on the wiki, site members can edit the pages to create a fictional galactic history for each. Because beings in different systems meet each other, writers have to work to keep their story-lines consistent (which should become a larger and larger challenge). The free Galaxiki may prove addictive to those who need the occasional break from peer-reviewed papers and have an empire to build.
- I get less opportunity to read weblogs than I would like, but the various ‘carnivals’ keep me alerted to good postings. The 12th Carnival of Space is now available, this one hosted by Music of the Spheres. Stories range from the remarkable Galaxy Zoo project to a pilgrimage to the 100-inch telescope at Mount Wilson (this is where Edwin Hubble did so much to explain the nature of galaxies and the expansion of the universe). Similarly, Philosophia Naturalis is now up with its 12th iteration, looking at dark matter candidates, the history of the moon’s orbit and the implications of high-redshift galaxies for the epoch of reionization.
A final weekend thought: You may see some odd changes today and tomorrow as I examine new plugins and consider theme modifications to the site. Consider this a weekend of experimentation at this end, but the tests shouldn’t prove obtrusive and Monday should be business as usual.
by Paul Gilster | Jul 20, 2007 | Outer Solar System |
As if New Horizons didn’t already have its work cut out for it, now we have the possibility of seeing a frigid geyser going off on Pluto’s companion Charon when the probe arrives in 2015. The process is called cryovolcanism, the movement of liquid water onto the surface where it freezes into ice crystals. New high-resolution spectra obtained at the Gemini Observatory (Mauna Kea) show ammonia hydrates and water crystals spread patch-like across the surface of the distant world.
The suggestion is that liquid water mixed with ammonia is pushing out from deep within Charon, leading to an interesting conclusion. Thus graduate student Jason Cook (Arizona State), who led the team surveying Charon’s surface:
“Charon’s surface is almost entirely water ice. So it must have a vast amount of water under the surface, and much of that should be frozen as well. Only deep inside Charon could water be a liquid. Yet, there is fresh ice on the surface, meaning that some liquid water must somehow reach the surface. The ammonia sitting on the surface provides the clue. It’s the ammonia that helps keep some material liquid. It makes it all feasible. Without ammonia the water could not get out there.”
Start adding up the other places in the Solar System where cryovolcanism is a factor and the list quickly grows. The Uranian moon Ariel, based on Voyager 2 imagery, may well be undergoing the process, and we’ve already seen evidence of water ice reaching out from beneath the surface of Enceladus. Europa, too, shows evidence of water upwelling from within. But unlike these examples, Kuiper Belt Objects like Charon, Quaoar and others are not tidally squeezed (Charon is tidally locked to Pluto). Thus the presence of cryovolcanism has implications for what New Horizons may find elsewhere in the Kuiper Belt.
Image: An artist’s conception of Charon with Pluto in the background. The plumes and brighter spots depicted at left on Charon are thought to be created as water (with some ammonia hydrate mixed in) “erupts” from deep beneath the surface. The material sprays out through cracks in the icy crust, immediately freezes and snows crystalline ice down onto the surface, creating a water-ammonia hydrate ice field. Credit: This composite image includes Pluto and Charon models (enhanced), courtesy of Software Bisque. www.seeker3d.com, with plumes and ice fields added by Mark C. Petersen, Loch Ness Productions. Star field from DigitalSky 2, courtesy Sky-Skan, Inc.
Quaoar, in fact, is possibly laden with ammonia hydrate, a form of ammonia suspected on other KBOs including Charon. Its presence is helpful in this frigid scenario, because ammonia hydrates keep liquid water from freezing solid, making its escape from an inner reservoir to the surface that much easier. Evidence for ammonia hydrates on Charon builds the case for their proliferation in the Kuiper Belt. Says Steven Desch, Cook’s thesis advisor at Arizona State:
“It had been tentatively identified on Charon before by other groups, but the lack of spectral resolution hindered its identification. This clinches it. These spectra are also better than those of other KBOs. I’ve talked to seasoned observers who are convinced for the first time that ammonia hydrates exist on KBOs.”
The possibilities are refreshingly open. From what we know so far, Charon seems rather typical of Kuiper Belt objects. The Gemini observations open the door for reservoirs of water deep beneath the surface of many such objects. Cook believes that if Charon holds an ocean, then all Kuiper Belt objects greater than 500 kilometers across may well have them. There could, in short, be more liquid water — perhaps a lot more — in the Kuiper Belt than on Earth.
The paper is Cook et al., “Near-infrared Spectroscopy of Charon: Possible Evidence for Cryovolcanism on Kuiper Belt Objects,” Astrophysical Journal, Volume 663 (July 10, 2007), pp. 1406-1419 (abstract available).
by Paul Gilster | Jul 19, 2007 | Exoplanetary Science |
Astronomers have found a highly elliptical debris disk around the star HD 15115, one that seen virtually edge-on from Earth gives the appearance of a needle running straight through its star. The disk was first imaged by the Hubble Space Telescope in 2006, its unusual shape causing astronomers to request near-infrared imaging by the W.M. Keck Observatory in Hawaii. Keck’s images, in conjunction with the Hubble data, revealed the disk’s uncommon blue color.
So what’s going on around this F-class star? First of all, let’s distinguish between protoplanetary disks, which give birth to planets, and debris disks like this one, which resemble our own Kuiper Belt. The latter are made up of the remnants of planetary formation. This debris disk seems to extend some ten times further from its star than the Kuiper Belt, according to a Keck news release, though our limited knowledge of the Kuiper Belt makes me a bit wary of the statement, as the latter’s dimensions are still under active investigation.
Image: Dust orbits in a needle-shaped ring around the star HD 15115 in this Hubble Space Telescope image. An occulting mask was used to block out bright starlight. The masks can be seen in the image as the dark circle in the center and the dark bar on the left. Credit: NASA\ESA\UC Berkeley.
But a debris disk in a highly elliptical orbit is an oddity no matter what its extent. One intriguing possibility is the influence of the star HIP 12545, some ten light years away from HD 15115. A close pass at some point in the past? Perhaps, because both stars seem to be part of the Beta Pictoris Moving Group, an expanded cluster of stars thought to have a common birthplace and age that are moving together through space.
The paper on this work cites evidence for the stellar flyby idea, from which this excerpt:
This geometry is consistent with the dynamical simulation of a disk disrupted by a stellar ?yby… [T]he long end of a highly perturbed disk is located in the direction of periastron. The perturber follows a parabolic trajectory such that in a later epoch it is located in the direction opposite of periastron, or in the direction of the truncated side of the disk. Periastron in these models is ?700 AU, with an initial disk radius of ?500 AU. Overall, the ensemble of evidence favors further consideration of HD 15115 and HIP 12545 as a possible wide-separation multiple system with a highly eccentric orbit (e > 0.95).
It is also notable that the debris disk around HD 15115 shows significantly less dust than disks observed around three other stars in this group. Paul Kalas (UC-Berkeley), lead author of the paper, thinks the missing matter is connected to the disk’s elliptical shape, saying “The missing mass is quite interesting. Perhaps the mechanism which perturbed the disk into its current asymmetric morphology also shaved away a significant fraction of the mass.” Kalas plans further work on both stars this fall, using Keck’s adaptive optics. It will be interesting to see whether HIP 12545, a M-class red dwarf, has a disk of its own.
A second hypothesis to account for the disk’s odd shape is closer to home: Disturbances caused by planets near the star. Here the obvious analogue is not only Neptune’s influence on Kuiper Belt objects but the theory that Neptune may originally have formed inside the orbit of Saturn and Uranus, only to be pushed to its present position by gravitational disturbances as the orbits of Jupiter and Saturn stabilized. Whether true of Neptune or not, profound planetary upheaval of this magnitude could also explain the disk asymmetry around HD 15115.
The paper is Kalas et al., “Discovery of extreme asymmetry in the debris disk surrounding HD 15115,” accepted by Astrophysical Journal Letters and available as a preprint. The team plan to present a more detailed analysis of dust scattering and thermal emission around this star in a future paper.
Addendum: Curious about the stellar flyby scenario and the stability of the debris disk around HD 15115, I wrote Dr. Kalas. Here is part of his response:
The stellar flyby hypothesis that we invoked as one possible explanation is extremely rare and the effects are short-lived (<1 Myr). Since 1 km/s = 1 pc / Myr, and the present separation is ~3 pc between HD 15115 and the suspected perturber, the perturber must have passed by HD 15115 by at least 3 km/s, which is not implausible, and which can be tested by future observations.
Dr. Kalas also provided this link to his earlier work on the stellar flyby model and asymmetric disk environments.
by Paul Gilster | Jul 18, 2007 | Culture and Society |
I’m not very good at playing odds, though I do seem to pick up money routinely from a friend who is a Chicago Cubs fan (this year may be different — we’ll see). But bringing odds into the discussion of the Fermi Paradox can be an interesting exercise, and Princeton astrophysicist Richard Gott has already given the matter some thought. Let’s assume, for example, that you and I are not particularly special. We’re simply representative of the living beings who populate the universe.
If that’s the case, the odds say we’re probably living in one of the older civilizations, and one of the larger ones. That’s because more people would have lived in these cultures than in short-lived, smaller civilizations. It’s the Copernican principle at work, the notion that there is nothing special about the particular moment at which we’re observing what’s around us. Gott would say this has implications for other worlds.
“The sobering facts,” Dr. Gott says, “are that in a 13.7 billion-year-old universe, we’ve only been around 200,000 years, and we’re only on one tiny planet. The Copernican answer to Enrico Fermi’s famous question — Where are the extraterrestrials? — is that a significant fraction must be sitting on their home planets.”
Must be sitting there, that is, because that is precisely what we find ourselves doing. As to the argument that scientific progress is unstoppable, Dr. Gott notes in this New York Times article (from which the above quote is drawn) that civilizations like China’s abandoned exploration after making major inroads in world discovery. Just how representative was the Chinese experience? Indeed, the possibility exists that the window for a civilization to get into space and stay there is vanishingly small. We may not be at the beginning of the space program but near the middle of it. The odds on that are 50 percent.
We’re now entering a philosophical debate that is rather robust, and needless to say, Dr. Gott has his critics as well as his supporters. Here’s a link to an article by Bradley Monton and Brian Kierland that appeared in the Philosophical Quarterly (PDF warning). And have a look at John Tierney’s follow-up to his Times article. Here he quotes Monton (University of Kentucky) on Gott’s ideas on space colonization:
…I think Gott is right — it should be a major priority that we work on establishing self-sufficient colonies on other planets. Technology hasn’t been around very long, and in the absence of evidence this should lead us to think that it’s likely that it won’t be around very long in the future. But we shouldn’t be fatalistic about Copernican Principle predictions — there are things we can do to make it more likely that technology-adept intelligent life will continue to be around in the future. Besides the obvious things we can do (e.g. controlling loose nukes, preventing pandemics), establishing self-sufficient colonies will clearly make a difference.
Now ponder Gott’s analysis against the familiar science fiction idea that we are a young civilization moving into a galaxy filled with far advanced races. As Tierney notes, pick any American at random and you’ve probably picked one from a town that’s larger than median size, because that’s where the population is. Similarly, we’re probably in a relatively representative civilization right now. I like Tierney’s finish:
In fact, we could assume that the typical civilization reaches our stage of development, applies the Copernican principle, realizes that it’s 95-percent certain to go extinct unless it takes an extraordinary step like colonizing other planets — and then goes extinct even though it’s aware of its eventual doom.
Is that going to happen to us, too? What can we do to beat those odds?
Beating the odds is something we seem suited to doing. But it requires resolve and a commitment to living for more than the present. The stakes are huge, for if we cluster all our resources on a single world, we run the risk of losing everything. “Sooner or later something will get us if we stay on one planet,” says Gott. “By the time we’re in trouble and wish we had that colony on Mars, it may be too late.” That means we’d better get to Mars sooner rather than later before the window closes.
The Monton and Kierland article is “How to Predict Future Duration from Present Age,” The Philosophical Quarterly Volume 56, Number 222 (January 2006), pp. 16-38. Those familiar with Richard Gott (and I count myself a great admirer), will know about his Time Travel in Einstein’s Universe: The Physical Possibilities of Travel Through Time (New York: Houghton Mifflin, 2001), a book I can’t recommend too highly. A quote apropos to our work here: “…one of the things we should understand about time is that we have just a little.” Using it wisely should be our greatest concern.
by Paul Gilster | Jul 17, 2007 | Deep Sky Astronomy & Telescopes |
We’re so used to thinking of our Sun as a solitary object that having two Suns in the sky inspires the imagination of artist and writer alike. But what about whole clusters of stars? Evidence is mounting that the Sun was actually born in such a cluster. That’s quite a jump from the era, not so long ago, when astronomers assumed stars like ours formed without companions, but cosmochemists like the wonderfully named Martin Bizzarro (University of Copenhagen) think they have the data to prove it.
So here’s the new notion: Most single stars like the Sun evolve in multiple systems, clusters of stars that also contain massive stars that burn their hydrogen and explode while the cluster is still producing young stars. If this is the case, then we should expect the early history of the surviving younger stars to be affected by the nearby fireworks. Bizzarro’s team studied short-lived isotopes like aluminum-26 (26Al) and iron-60 (60Fe) as found in meteorites to see whether stellar debris from such explosions left its mark.
The trick, as discussed in a fine summary by G. Jeffrey Taylor in Planetary Science Research Discoveries, is that these short-lived isotopes no longer exist in most meteorites, their half lives ranging from 0.1 to 100 million years. But they have left decay products including 60Ni (from the decay of 60Fe and 26Mg (from the decay of 26Al). Taylor’s article goes through the process of isotope measurement to determine the ratio of decay products to common isotopes.
This, in fact, is where Bizzarro’s work will receive the most scrutiny, since not all such studies agree. But working with terrestrial samples, Martian meteorites, chondritic meteorites and differentiated meteorites — from asteroids that melted at an early stage of protoplanetary development — the team comes up with its result. One thing stands out: The lack of 60Fe in the differentiated meteorites, which represent the oldest planetesimals to form in the Solar System. Let Taylor summarize:
Formation of the Sun might have involved the formation and rapid life span (only 4 million years) of a massive star, 30 times more massive than the Sun. Astronomical observations indicate that such stars pass through a stage in which they lose mass–up to an Earth mass per day!– rapidly by blowing it into space at a couple of thousand kilometers per hour. These stellar winds contain 26Al, but 60Fe is still ensconced in the interior. At some point the star blows up, sending the products of nuclear fusion into interstellar space, including 60Fe. Note the sequence here: 26Al leaves with the strong stellar winds, which possibly triggered the collapse of a cloud of gas and dust to form a new star, our Sun. There is good evidence that 26Al was uniformly distributed throughout the Solar System… The 60Fe comes about a million years later when the star explodes, but also after many planetesimals differentiated. They did not contain any 60Fe, but had their full complement of 26Al. In fact, they had enough 26Al to heat up internally and melt.
Was the exploding star that left its mark on these meteorites a Wolf-Rayet star? Such stars blow off heavier elements on their way to eventual supernova explosion. It’s an interesting hypothesis that it was just such a star that helped give birth to our Sun and its accompanying system. What should emerge next is a series of further analyses of such meteorites to pin down the data on 60Fe deficiency. These investigations are nowhere near conclusion, but we are at least developing a working theory on stellar formation that may depict our Sun’s earliest era.
The paper is Bizzarro et al., “Evidence for a later supernova injection of 60Fe into the protoplanetary disk,” Science, Vol. 316 (2007), pp. 1178-1181 (abstract). The Taylor article, called “The Sun’s Crowded Delivery Room,” is from the July 6, 2007 issue of Planetary Science Research Discoveries, available online.
