by Paul Gilster | Feb 12, 2006 | Exoplanetary Science |
A fascinating post by Anthony Kendall cites the reasons why Terrestrial Planet Finder is such an important mission and goes on to call for NASA’s being broken into separate entities, to make missions like this more likely to launch. From the Anthonares weblog:
Gradually, constructing, launching, and operating missions in Earth orbits or in Lagrange points should be taken over by consortia similar to those that operate ground-based facilities today. As commercial satellite companies have demonstrated, they are more than capable of managing their own facilities. NASA’s deep space expertise will necessitate the existence of an unmanned space probe agency for several decades at least, and perhaps indefinitely as we look to explore the stars. The TPF missions could be the first in step in this process. If the scientific community wants them badly enough, they have the lobbying ability (as demonstrated with Hubble and New Horizons) to get Congress to fund them. Since private consortia will not have billions extra to absorb cost overruns, TPF will be constructed and launched quickly and more efficiently than within the stifling NASA bureaucracy.
The title says it all: “Terrestrial Planet Finder: The Most Important Mission NASA Should Not Fund.” It’s an interesting take on one way to get around the bureaucratic and political squeeze that has produced a budget with 17 more Shuttle flights while cutting significant science programs like TPF and the Space Interferometry Mission. Be sure to read this, and ponder, too, whether some ideas now emerging from our universities — I am thinking in particular of Webster Cash’s New Worlds Imager — might not offer substantial benefits over the existing design projections at the Jet Propulsion Laboratory TPF site.
by Paul Gilster | Feb 12, 2006 | Administrative
Nothing major, but I do have to do some necessary software upgrading, and beyond that, Centauri Dreams will probably switch to a new theme (which will affect its appearance) some time down the road. The new theme is needed to upgrade the search function, which works much better with the K2 theme than the older Kubrick theme that has run here since September. Expect no major changes, but as I do the first of several upgrades, be prepared for some quirks that I’ll hope to iron out quickly.
by Paul Gilster | Feb 11, 2006 | Deep Sky Astronomy & Telescopes |
The first data from the Radial Velocity Experiment (RAVE) have just been released, marking the first of what promise to be numerous contributions from this extraordinary project. The study of dark matter in particular will be immeasurably enhanced by this spectroscopic survey that measures the radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) of up to one million stars near the Sun.
The new data cover the first year of RAVE’s operations at the Anglo-Australian Observatory (New South Wales). Using the ‘six degree field’ multi-object spectrograph on the 1.2-m UK Schmidt telescope there, the team can get spectroscopic data on 150 stars at a time. Thanks to RAVE, we now have data on line-of-sight motions of 25,000 stars, along with a rich lode of information on their brightness and color.
And here’s an interesting note: one of the astronomers working on RAVE is George Michael Seabroke, whose great-great-grandfather, George Mitchell Seabroke, was a pioneer in measuring stellar velocities. Working at Temple Observatory (Rugby School, Warwickshire) in the 1880s, the elder Seabroke could study the spectrum of only a single star at a time. RAVE’s equipment looks at an area more than 100 times greater than the full Moon, with 100 optical fibres that each act like an eyepiece. What Seabroke senior would have made of RAVE can only be imagined.
Image: George Mitchell Seabroke (1848-1918), a pioneer in stellar velocity measurements. Credit: British Astronomical Association.
The multi-national RAVE has several years to run, and in its progress should tell us much about the evolution of our galaxy. Moreover, the accurate study of stellar motions will help to determine how much dark matter is holding the galaxy together. The fact that dark matter remains an enigma testifies to how much we still have to learn before we can speak with any confidence about the structure of our own stellar neighborhood.
Further news on dark matter comes in a BBC story discussing ongoing work at the Institute of Astronomy at Cambridge. By studying twelve dwarf galaxies near the Milky Way, the Cambridge team has made detailed, three-dimensional maps of the movement of their stars to extrapolate the effects of dark matter. 7000 separate measurements have shown that the galaxies contain 400 times more dark matter than normal (baryonic) matter. “The distribution of dark matter,” says professor Gerry Gilmore, “bears no relationship to anything you will have read in the literature up to now.”
Be sure to read the entire article, which discusses the most unusual of these observations: dark matter particles seem to be far warmer than would have been predicted, moving at about nine kilometers per second. An additional offshoot of these investigations is that the Milky Way is more massive than once thought, larger than Andromeda. How little we know: fully 25 percent of matter in the universe is now thought to be dark, with the stuff you and I and the stars are made of accounting for a mere 5 percent. And of the 70 percent of everything that seems to be ‘dark energy’ we know even less, a reminder of how many surprises the universe has in store.
by Paul Gilster | Feb 10, 2006 | Outer Solar System |
Centauri Dreams is following the Pioneer 10 story with great interest, and not just in terms of the anomalous effects that continue to keep this mission in the news. Ponder that Pioneer 10 was launched in 1972 and consider that even with the technologies of its day, the probe may still be able to communicate with Earth. We have learned so much in the interim about hardened electronics and autonomous self-repair that there is reason to believe probes to even remoter locations in the Kuiper Belt and beyond are feasible providing we can solve the propulsion conundrum.
The next attempt to contact the venerable spacecraft would occur in March, if it occurs at all, and you can hear more about it in an interview conducted by Planetary Radio. The guest is JPL senior research scientist John Anderson, who discusses the mission, its current communications challenges, and the possible reasons for what appears to be its deceleration as it moves away from the Sun.
Or is the effect really a deceleration? A new paper called “Pioneer Anomaly: What Can We Learn from LISA?” has just appeared on the arXiv site, making the case that there is a second explanation: an anomalous blueshift of the radio signal. Authors Denis Defrère (University of Liege) and Andreas Rathke (Institute for Theoretical Physics, University of Cologne) examine the effects such a blueshift might have on the upcoming Laser Interferometer Space Antenna (LISA) mission to detect gravitational waves.
It would be useful if LISA could be used to verify the Pioneer data; it appears to be the earliest spacecraft that could make such an attempt. But the authors’ conclusion is discouraging: the anomalous blueshift is always overwhelmed by one or another noise source in the LISA interferometer.
And if LISA cannot test the Pioneer Anomaly, what can? From the paper:
More promising – and probably mandatory if the Pioneer anomaly represents a force and not a blueshift – would be a test in the outer Solar system by radio-tracking of a deep space vehicle with very well known onboard systematics. Preferably this would be a dedicated mission to explore the anomaly although a planetary exploration spacecraft which has been designed with the secondary goal to test the Pioneer anomaly could already gain considerable insights. The analysis of the full archive of Pioneer 10 and 11 Doppler data, that is currently being initiated, might further help to identify mission scenarios that are especially suited for a test of the anomaly.
It’s too late for New Horizons, of course, but any followup Pluto/Kuiper Belt mission would have such an opportunity. On that score, see T. Bondo, R. Walker, A. Rathke et al., “Preliminary Design of an Advanced Mission to Pluto,” scheduled to appear in the proceedings of the 24th International Symposium on Space Technology and Science, Miyazaki, Japan, June 2004, and already available online (PDF warning).
by Paul Gilster | Feb 9, 2006 | Exoplanetary Science |
The key lesson of exoplanetary science is surely humility. Over and over again, starting with the discovery of the first ‘hot Jupiters,’ we’ve been brought face to face with the fact that assumptions long enshrined in our thinking have to be reevaluated. Thus it’s no surprise to learn of a new study identifying what appear to be enormous debris disks around two giant stars. In the past, stars of their size were considered unlikely candidates for planetary systems.
The stars are R 66 and R 126, both located in the Large Magellanic Cloud; the former is 30 times more massive than our Sun, the latter 70 times. Both are thought to be descendants of the massive objects called type O stars, large enough that, if they were located in our own Solar System, they would swallow all the inner planets including Earth.
Image: This illustration compares the size of a gargantuan star and its surrounding dusty disk (top) to that of our solar system. Monstrous disks like this one were discovered around two “hypergiant” stars by NASA’s Spitzer Space Telescope. Astronomers believe these disks might contain the early “seeds” of planets or, possibly, leftover debris from planets that already formed. Credit: NASA/JPL-Caltech/R. Hurt.
NOTE: The orbital distances in this picture are plotted on a logarithmic scale. This means that a given distance shown here represents proportionally smaller actual distances as you move to the right. The sun and planets in our solar system have been scaled up in size for better viewing.
Studied with the Spitzer Space Telescope, the two stars show dust disks that spread 60 times as far as Pluto’s orbit around the Sun, and seem to contain ten times the mass currently estimated to be in the Kuiper Belt. Are we looking at planetary formation? Joel Kastner of the Rochester Institute of Technology in New York, first author of a paper on this work that is about to appear in the Astrophysical Journal Letters, thinks the answer may well be yes. “These disks may be well-populated with comets and other larger bodies called planetesimals,” said Kastner. “They might be thought of as Kuiper Belts on steroids.”
Further evidence: the dust seems to show the presence of silicates, and the disk around R66 showed signs of dust clumping in the form of silicate crystals and larger dust grains. These are the processes astronomers believe lead to planets, but whatever worlds might form will likely have a short life. Massive stars like these burn out quickly and become supernovae, leaving little time for life to evolve. Ahead for the team is the study of new Spitzer spectra of other hypergiant stars to see how many more are circled by disks of dust.
