by Paul Gilster | Dec 13, 2005 | Outer Solar System
Finding new objects in the Kuiper Belt is getting to be almost routine. But what makes the latest find intriguing is the shape of its orbit. Designated 2004 XR 190 by the International Astronomical Union and nicknamed ‘Buffy,’ the new object is currently 58 AU from the Sun, about twice the distance to Neptune. But an analysis of its orbit shows that it does not approach closer than 50 AU, complicating theories on how Kuiper Belt objects wind up in the positions they occupy.
Here’s the problem: the few objects discovered beyond 50 AU (where the main Kuiper Belt seems to end), have all been in extremely eccentric, or non-circular orbits. Bear in mind that these high eccentricity orbits have been assumed to be the result of gravitational interactions with Neptune or some other outer Solar System body. The encounter was assumed to have acted as a gravitational slingshot to fling the KBO objects into the deep.
But Buffy confounds these theories by coming nowhere near Neptune; another issue is that its orbit is tilted 47 degrees compared to the rest of the Solar System. And in a final gesture of irreverence toward our theories, its orbit is remarkably circular, although it will take several years of observation to measure the orbital parameters precisely. A circular orbit makes the ‘slingshot’ hypothesis far-fetched even if we could figure out around what object Buffy had been slung.
The enigmatic Buffy was discovered during routine operation of the Canada-France Ecliptic Plane Survey. From a news release from the Canada-France-Hawaii Telescope (CFHT):
Astronomer Lynne Allen of the University of British Columbia was the first to lay eyes on the new object, as she completed the initial identification in the course of processing CFEPS data from December 2004. “It was quite bright compared to the usual Kuiper belt objects we find”, said Dr. Allen, “but what was more interesting was how far away it was.”
Brightness is useful in allowing some inferences as to the object’s size; this one is thought to be between 500 and 1000 kilometers in diameter (300 to 600 miles). A useful comparison is Sedna, the only other detected object that stays further than 50 AU out throughout its entire orbit. In sharp contrast to Buffy, Sedna’s orbit is quite elliptical, moving between 76 AU and a whopping 900 AU from the Sun. Buffy’s range of 52 to 62 AU is a puzzle.
Centauri Dreams‘ take: Nothing should surprise us about the Kuiper Belt these days. Each new discovery seems to bring its own share of uncertainties, and what it will take to resolve them is a systematic exploration of the Kuiper Belt that will amass sufficient data to fit objects like Buffy into our current theories of Solar System formation. We know precious little about the so-called ‘Extended Scattered Disk,’ made up of those objects — like Sedna — whose orbits seem to have been perturbed by an object other than Neptune. What that object was — a passing star? — is only one subject for future work.
A more extended discussion of Buffy can be found here.
by Paul Gilster | Dec 12, 2005 | Deep Sky Astronomy & Telescopes
Gravitational lensing is tricky enough to measure, but how can we use it to track down the elusive ‘dark matter’ that constitutes the great bulk of the matter in the universe? Remarkably, researchers at Johns Hopkins, working with the Space Telescope Science Institute, think they have found a way. Using the Hubble telescope, they’ve measured how gravity from unseen dark matter creates small distortions in the shapes of galaxies as seen from Earth. Their work has focused on two galactic clusters in the southern sky roughly 7 billion light years away; each contains more than 400 galaxies.
That dark matter is a mystery needs no elaboration here, as it’s always been a reminder that our knowledge of the universe is limited to a small subset of the things we can see and understand. Indeed, dark matter is only part of the story. Some 70 percent of the entire universe is now thought to be ‘dark energy,’ an even more mysterious ingredient that plays a role in the expansion of the cosmos. With another 25 percent of all things being tied up in dark matter, that leaves the normal, visible matter we take for granted in things like water, trees, stars and galaxies as merely five percent of everything that is out there.
Dark matter is thus a confounding challenge to our everyday perceptions, but one slowly yielding to analysis. The current dark matter work proceeds on a key assumption: that visible matter and dark matter should coalesce at the same places because gravity pulls them together. In other words, concentrated dark matter should attract visible matter, and thus have a role in the formation of stars and galaxies themselves. The team’s work has resulted in computer-simulated images showing the location of dark matter in relation to the galactic clusters under study.
One finding is that dark matter clumps around the cluster galaxies, which implies that dark matter particles do not collide and scatter, but actually pass through each other. From a Johns Hopkins news release, quoting Myungkook James Jee, an assistant research scientist at Hopkins’ Krieger School of Arts and Sciences:
“Collision-less particles do not bombard one another, the way two hydrogen atoms do. If dark matter particles were collisional, we would observe a much smoother distribution of dark matter, without any small-scale clumpy structures,” Jee said.
Jee goes on to say “The images we took show clearly that the cluster galaxies are located at the densest regions of the dark matter haloes, which are rendered in purple in our images,” an observation that supports the association of dark and visible matter. In such ways do we learn how to study a form of matter that emits no light, and whose composition and effects may have much to say about how the visible universe around us formed.
The team’s findings appear as Jee, White, Ford et al., “Hubble Space Telescope Advanced Camera for Surveys Weak-Lensing and Chandra X-Ray Studies of the High-Redshift Cluster MS 1054-0321,” Astrophysical Journal 634 (December 1, 2005). An abstract is available here. 12/14 update: Cosmic Variance has been carrying on an interesting discussion on these findings.
by Paul Gilster | Dec 10, 2005 | Exoplanetary Science
Proxima Centauri is not exactly an imposing star. In fact, this tiny M-class red dwarf would not be noticeable even in the skies near Centauri A and B except for its huge parallax, an indication to local sky-watchers that it was in the vicinity and moving fast. Some astronomers have suggested that Alpha Centauri may, in fact, not be a triple-star system after all, that Proxima is simply an independent star passing through the neighborhood. But the jury is still out on that one.
Image credit & copyright: David Malin, UK Schmidt Telescope, DSS, AAO.
Nonetheless, the interest Proxima exerts is almost hypnotic, because at 4.22 light years, it is the closest of all known stars (Centauri Dreams leaves open the possible, and in my view likely, discovery of a red or brown dwarf even closer). The image above (click for a closeup) was selected by the good people at Goddard Space Flight Center as Astronomy Picture of the Day last week, and it’s the best image I’ve ever seen of the tiny star. You’ll find it in the dead center of the picture, a red flare star that invites curiosity and, we may hope, a future probe.
If the question of Proxima’s real position in the Alpha Centauri system intrigues you, the paper to consult is Robert Matthews and Gerard Gilmore, “Is Proxima Really in Orbit About Alpha CEN A/B?” Royal Astronomical Society Monthly Notices 261, no. 2 (1993), pages L5-L7.
by Paul Gilster | Dec 9, 2005 | Antimatter, Breakthrough Propulsion, Sail Concepts |
In an article on interstellar propulsion options at Physorg.com, writer Chuck Rahls focuses on three technologies that have been proposed to make a trip to Alpha Centauri possible. Of the three, laser-pushed lightsails are indeed in the running, and have been since Robert Forward realized the implication of the laser while working at Hughes Aircraft. Also employed by Hughes in the company’s research laboratories was Theodore Maiman, who had shown how to make a functional laser in 1960. Forward wrote the concept up as an internal memo at Hughes in 1961, and later went public in the journal Missiles and Rockets. In the same year (1962), he described the idea in an article in Galaxy Science Fiction.
Rahls writes about a laser-driven craft weighing 16 grams making it to the Centauri stars in ten years. It’s a grand concept — Forward came up with it, too, and gave it the wonderful name Starwisp, though he used not lasers but microwaves to drive it — but Geoffrey Landis has convincingly shown that Starwisp could never fly, the intensity of the microwaves needed to accelerate it being sufficient to vaporize the entire spacecraft. Forward knew this and was working on other solutions at his death.
Centauri Dreams also has serious reservations about the second concept addressed here, the Bussard ramscoop. One problem is that enormous speeds are needed just to ‘light’ the ramscoop’s engine. But a more profound issue is that physicists have shown the ramscoop idea to be unworkable because of drag. In fact, Dana Andrews and Robert Zubrin demonstrated in the late 1980s that a spacecraft of Bussard’s design would experience more drag from its enormous electromagnetic ‘scoop’ than thrust. The real beauty of the ramscoop concept is that it generated an equally interesting — and workable — notion: use an electromagnetic sail tens of kilometers in diameter that could be pushed by particle beam, or used in the destination solar system for braking upon arrival.
The third, and perhaps most exciting in today’s terms of Rahls’ technologies is antimatter. Here the options are proliferating, and because we know how to harvest only the minutest quantities of the stuff, we’re finding ways to make fast propulsion systems that use antimatter only as a catalyst, igniting fusion, perhaps, or using it to interact with an uranium-coated sail. The latter concept is Steve Howe’s (I referred to it in these pages just the other day), a proposal so ingenious that any star-minded reader should make haste to the NASA Institute for Advanced Concepts site to download Howe’s “Antimatter Driven Sail for Deep Space Missions.”
NASA’s John Cole told me at Marshall Space Flight Center back in 2003 that the power released by Howe’s design is on the order of 2000 kilowatts per kilogram. “It’s just an enormous figure,” Cole said. So even if Howe’s figures are an order of magnitude off, even two orders of magnitude off, a factor of 100, he is still in realm of where we can have human exploration of the outer planets.”
The Andrews/Zubrin article mentioned above, by the way, is a key work in the development of interstellar concepts. It’s titled “Magnetic Sails and Interstellar Travel,” found as International Astronautical Federation Paper IAF-88-5533 (Bangalore, India, October 1988). If I had to put money on the proposition, I’d bet a particle-driven magnetic sail will be our first true star mission, a robotic probe launched around 2100. But that’s the last bet you’ll get out of me.
by Paul Gilster | Dec 8, 2005 | Outer Solar System |
With the launch of the New Horizons mission to Pluto, Charon and beyond a scant month away, it’s fitting to acknowledge the 100th birthday of Gerard P. Kuiper, who predicted the existence of the band of debris and minor planets we now call the Kuiper Belt in 1950. It would take forty years for confirmation of the prediction, but the study of objects large and small beyond the orbit of Neptune now has high visibility, and is one of the reasons for the New Horizons mission.
Kuiper’s work was hardly limited to the now famous belt. He was also a pioneer in the study of Cepheid variables, those highly useful ‘standard candles’ that allow us to assess stellar distances (the period of a Cepheid variable being related to its intrinsic luminosity). Other objects of Kuiper’s interest included eclipsing binaries, and he played a key role in early work on Titan’s atmosphere. Add to this that his students included the likes of William Hartmann, Carl Sagan, and New Horizons Science Team Co-Investigator Dale Cruikshank (NASA Ames).
From a news release from Southwest Research Institute (San Antonio) about the man sometimes called ‘the father of planetary science”:
“Kuiper studied the planets at a time, 50 years ago, when they were scarcely of interest to other astronomers,” says Dr. Bill McKinnon, New Horizons co-investigator and professor of Planetary Sciences at Washington University in St. Louis, Mo. “But with new telescopes and instrumentation, he showed that there were great things to discover, which is as true today as then — witness the recent discovery of two new moons of Pluto. His planetary expertise later proved invaluable to NASA as well, especially during the early days of the race to our moon.”
Centauri Dreams‘ take: Kuiper’s birthday is justly celebrated, as is his career, but students of the Kuiper Belt also know that the first detailed discussion of a debris ring beyond Neptune was advanced by Kenneth Edgeworth in 1943, some years before Kuiper. Edgeworth made his case for an outer debris belt a second time in 1949, this time in a paper written for the Monthly Notices of the Royal Astronomical Society. John Davies tells the tale of this eccentric British soldier, engineer and amateur astronomer in his fine book Beyond Pluto (Cambridge University Press, 2001), and speculates on the reasons why Kuiper, who surely knew of Edgeworth’s prior work, chose to ignore him (the options are several, none of them surprising to anyone who has worked in academics).
As for New Horizons, launch is scheduled during the 35-day window that opens on January 11, with Pluto encounter in 2015. Although five striking workers from the International Association of Machinists and Aerospace Workers were involved in the final assembly of the vehicle’s third-stage, Boeing was able to replace the strikers with non-striking workers, each of whom has a minimum of eight years of experience with Boeing upper stage engines like this mission’s STAR 48 solid-propellant kick motor. The New Horizons team seems confident, but to these eyes the early November strike has injected an unwelcome dose of drama into the launch.
