by Paul Gilster | Nov 17, 2006 | Asteroid and Comet Deflection, Missions, Research Tools |
The recent National Science Foundation report recommending scaling back support for the Arecibo radio telescope raises eyebrows here. Arecibo has just been instrumental in identifying the near-Earth asteroid 1999 KW4 as a binary, one that provides useful information about the mass, shape and density of its components and hence about near-Earth asteroids in general. That’s the kind of knowledge we need as we ponder how to analyze Earth-crossing objects to prevent future planetary disasters.
But while focusing on ongoing radio astronomy work, the report gives short shrift to Arecibo’s radar capabilities, which make this kind of investigation possible. In a letter to the NSF’s Division of Astronomical Sciences, Guy Consolmagno SJ, who is head of the Department for Planetary Sciences of the American Astronomical Society, had this to say:
There is in fact only one reference to radar in the entire 78 page document, and no mention at all of asteroids. But the Arecibo radar results are key to understanding near earth object sizes, shapes, and dynamics. Besides having a central scientific importance, both of themselves and as samples derived from the main asteroid belt, near earth asteroids may represent a significant hazard to Earth and also a potential source of future resources. To decommission one of our primary tools for studying them would deal a serious blow to both our science and our safety.
That’s troublesome news, though an article by Larry Klaes in the Ithaca Times provides a needed perspective. Cornell University has managed Arecibo since 1963, so it’s useful to know that Cornell astronomers remain optimistic about its survival. Klaes quotes astronomy professor Jim Cordes on the issue:
“Cornell has no plans to close Arecibo,” said Cordes. “In fact, the NSF has provided funds to maintain the facility in the form of $5 million to conduct a high-tech paint job on the telescope. This should go far in keeping the observatory operating for another 20 years.”
Let’s hope that optimism is well founded, as it seems to be. Arecibo’s powerful radar is vital for continuing studies of near-Earth asteroids, a point driven home by NASA’s interest in a possible manned mission to such an object. An asteroid mission would obviously provide a valuable read on these survivors from the early Solar System, while also offering a useful shakedown in a near-Earth environment for new space technologies. It’s a win/win proposition, and one that builds our database as we ponder possible strategies for avoiding catastrophic impacts.
by Paul Gilster | Oct 11, 2006 | Exoplanetary Science, Research Tools |
Just how representative are the 200+ planets we have now found around other stars? Consider that the most frequently used detection method involves radial velocity searches, looking for the tiny wobbles in a star’s motion that provide clues to the gravitational presence of a planet. It’s a solid technique that has found numerous ‘hot Jupiters,’ but the method introduces a bias for the kind of massive planets close to their star that create effects most visible from Earth.
And consider other factors: telescope time is sharply limited, and so are the swatches of sky most likely to be observed based on where the best telescopes are housed. We get more data on some exoplanetary systems, much less on others, and our view of what may be representative needs serious work.
Which is why the Systemic project was created, and why it is clearly gaining momentum. Regular Centauri Dreams readers know that Systemic is a simulation based on a dataset of 100,000 stars, one that can be accessed at the project’s Web site. What’s fascinating here is that whether you’re an astronomer or just an interested layman with a PC, you can play around with exoplanet properties like mass and vary the orbital parameters of hypothetical worlds to find a workable fit.
Make no mistake, these are simulated planet searches, but they perform a valuable function. Taking observational biases based on our methods into consideration, Systemic can get a better idea of how accurate our current search process is. “How good are we at detecting strange systems? Stars with three planets instead of two? Two instead of one? There are a lot of questions like this that can be addressed with a large-scale simulation,” said Greg Laughlin, who founded the project with a team of collaborators.
Consider this a renewed call for volunteers. You don’t need an expensive telescope to get involved, just an Internet connection and a desire to participate in a hunt that to my mind is one of the most exciting things going. Like SETI@home, which also uses the distributed power of legions of small computers around the world, Systemic relies on wide-scale involvement. The introductory phase it’s now in is a good time to learn to use the powerful software tools it offers.
by Paul Gilster | Aug 15, 2006 | Deep Sky Astronomy & Telescopes, Research Tools |
When is a galactic grouping ‘compact’? Take a look at the four closely grouped galaxies in the image below; they’re most of the galaxies in Stephan’s Quintet (the fifth is off-image to the lower right). Redshift measurements indicate that the top three of these are at the same distance from us, about 300 million light years away in Pegasus. A group is considered compact when it shares the same gas reservoir, or so I learned while reading about a presentation on the subject made by C. Mendes de Olivera at the ongoing IAU meeting in Prague.
Image: Four of the galaxies of Stephan’s Quintet. The galaxy at bottom left is a foreground object, but the other three are at the same distance from us and engaged in spectacular gravitational interactions. Credit: Jane C. Charlton (Penn State) et al., HST, ESA, NASA.
I owe the opportunity to learn about these matters to Ph.D student Thomas Marquart, who is working in the Galaxy Group at Uppsala Astronomical Observatory in Sweden. Marquart is posting regular entries on the IAU’s General Assembly on a weblog and is inviting (though with little result so far) other participants in the meeting to post their own thoughts as the sessions continue. In any case, his own observations, largely focusing on galactic evolution, make for lively reading and offer a sense of participation in a major scientific event.
One that, it must be said, has more to do than focus on the status of Pluto, despite newspaper stories implying that the subject has conference goers on the edge of their seats. Better by far to read about the IAU’s work at a site like this, and let’s hope that weblogs, which are easy to set up, become a regular part of such scientific gatherings. Sure, they’re unofficial, and that’s their interest. They give you inside thoughts rather than press releases, with comments on the hot issues and insights into the personalities involved.
And yes, as to Pluto, my thinking remains the same. Whatever the IAU decides is fine by me, though if it were my decision, I would leave Pluto with a planetary designation and simply declare its size the lower limit for planets. There are good reasons for acknowledging its properties as a Kuiper Belt object, but it’s also true that we have much to learn about the Kuiper Belt and what it contains. The safer course, keeping us from changing our nomenclature every few decades, would be to defer any change of planetary status until we’ve had a closer look at Pluto and other Kuiper Belt objects, starting with New Horizons in 2015. More on this tomorrow and then on to more pressing things.
by Paul Gilster | Aug 14, 2006 | Research Tools, Tau Zero Foundation |
The annual New Trends in Astrodynamics and Applications conference meets for the third time this week in Princeton, with Ed Belbruno calling the house to order on Wednesday. From an interstellar perspective, this year’s conference is packed — last year we had but three interstellar papers, whereas the 2006 meeting will feature two complete sessions and no fewer than nine papers on topics ranging from collecting antimatter from natural sources in the Solar System (James Bickford) to spacecraft miniaturization (Mason Peck) and antimatter/nuclear hybrids (Gerald Jackson). You can find the list of speakers and their topics at the program site.
This year the focus on near-term precursor concepts is robust. Greg Matloff will report on interim missions as a way to ‘prep for Centaurus,’ while Les Johnson and Sandy Montgomery (NASA MSFC) will present the latest solar sail developments, and Claudio Maccone will examine the FOCAL mission to the Sun’s gravity lens. I had been looking forward to renewing conversations with both Matloff and Maccone and haven’t seen Johnson or Montgomery since researching my book in 2003, but unexpected developments scuttled my travel plans.
Nonetheless, Centauri Dreams should be able to report on many of these papers after the fact, and from what I’ve seen already, they should make for fascinating reading. Marc Millis’ presentation on the “Incessant Obsolescence Postulate and Practical Interstellar Flight” makes shrewd points about mission times and targets that will provide fodder for lengthy discussion, and Jordin Kare will be on hand to talk about his ‘Sailbeam’ concept for probes moving at a tenth of lightspeed.
All this good material reminds me that two years have gone by since I first talked about making the re-creation of a yearly interstellar bibliography a prime goal of the Tau Zero Foundation (which in those days was being developed under a different name). I say ‘re-creating’ because the first interstellar bibliography was produced by Robert Forward and Eugene Mallove over a quarter of a century ago. Its last appearance was in the Journal of the British Interplanetary Society in 1980, with 2700 items in 70 subject categories. That a working bibliography is a basic tool for research in these disciplines is obvious, and my hope is to begin work on the new one before year’s end.
by Paul Gilster | Aug 1, 2006 | Deep Sky Astronomy & Telescopes, Research Tools |
What could galaxies along the line of sight between Earth and distant objects like quasars have anything to do with those objects themselves? Yet in a remarkable finding, the sightlines to quasars seem to be four times less likely to be populated with galaxies than the sightlines to gamma-ray bursts. Odd? Believe it. “The result contradicts our basic concepts of cosmology, and we are struggling to explain it,” said Jason X. Prochaska (UC-Santa Cruz).
The Swift satellite is the vehicle for this work, which used mission data to study the transient yet bright afterglow of long-duration gamma ray bursts (GRBs). Now the paper, by Prochaska and graduate student Gabriel Prochter, is awaiting publication in Astrophysical Journal Letters, but its appearance as a draft on the arXiv site is already spawning new work attempting to answer its questions.
Working with 15 GRBs, the duo found strong absorption signatures indicating the presence of galaxies along 14 of the GRB sightlines. Such signatures occur because some frequencies are absorbed by the gas associated with a galaxy, providing a marker for the galaxy even when there is little visible evidence. But data from the Sloan Digital Sky Survey showing the incidence of galaxies along the sightlines to quasars had the team expecting fewer than four galaxies.
What causes the higher number relating to GRBs? One possibility among three discussed here may be in the way the intervening galaxy acts as a gravitational lens, enhancing the brightness of the background object. If that lensing produces different effects for quasars than GRBs, this could provide an answer, but Prochaska says gravitational lensing experts tell him such a variation is unlikely to hold up, nor do two other explanations involving galactic dust or dust associated with the GRBs themselves. What’s needed to move on to a more convincing explanation is to extend the GRB sample significantly, using data from the extended Swift mission.
Prochaska would like to quadruple the sample size. A good idea indeed, for as the paper notes: “At present, we have not identi?ed a satisfactory single explanation for this phenomenon. Our results suggest that at least one of our fundamental assumptions underpinning extragalactic absorption line research is ?awed.”
Centauri Dreams note: This is another instance of print publication being significantly anticipated by the online preprint process. As scholarly publishing evolves in digital directions, notice how ideas are refined through online venues from e-mail to mailing list, weblog, authorial archive and pre-print server long before they finally see fixed publication in a journal. The added benefit to preprints is, of course, that the audience of judges for submitted papers is enormously extended, and authors can receive input far more quickly than before.
by Paul Gilster | Jul 27, 2006 | Research Tools |
We are entering a great era when it comes to research tools for the study of deep space. But as new technologies create datasets we’re able to distribute globally, we need to consolidate our gains to make them available to broader audiences. That’s why the creation of a Web-based utility called COSMOS SkyWalker is such heartening news. Using it, huge and minutely detailed images from sources like the Hubble Space Telescope’s Advanced Camera for Surveys can be managed for presentations and study over the Internet.
The problem is no small one. Compare the Hubble Ultra Deep Field (UDF), which contains some 10,000 galaxies, to the Cosmological Evolution Survey (COSMOS), housing no less than 2 million. The image areas on these surveys are contiguous and made up of an extraordinary number of data pixels, some 1010 pixels for COSMOS. That kind of scale makes it all but impossible to show both size and detail at the same time. Shipping the complete COSMOS ACS image over the Internet, even in compressed JPEG format, is not feasible, nor are average PCs up to the challenge of displaying such imagery.
SkyWalker can be used to browse large images and view any part of them on the screen. Because it works with HTML and JavaScript only (integrated in Web browsers like Firefox and Internet Explorer), it is usable without specialized software. The key to SkyWalker is that images can be browsed without downloading them in their entirety, allowing the user to pan around in the image, moving a pointer and tapping several zoom levels for study and presentation.
Yes, there are dedicated scientific data viewers, but SkyWalker fills a notable gap, being useful for quick access to ACS imagery and especially handy for those of us who occasionally present live material to non-scientific audiences. The COSMOS ACS mosaic is now available on the SkyWalker site, but other datasets are being added. For background on how the software works, check Jahnke, Sanchez and Koekemoer, “Seeing the Sky Through Hubble’s Eye: The COSMOS SkyWalker,” avalable here.
