by Paul Gilster | Jan 25, 2005 | Outer Solar System
Exactly how big is the Solar System? We used to talk about Pluto as the outermost planet, implying the Solar System ended when you crossed its orbit. Now we talk in terms of the Kuiper Belt, a band of debris and planetesimals far beyond Pluto’s orbit; beyond the Kuiper Belt looms the vast Oort Cloud, a spherical halo of comets that may extend a light year from our Sun. And if one thing is clear from current research, it’s that our old notions of boundaries have to be readjusted.
Take recent work at the Southwest Research Institute, which shows that the process of planetary formation once extended far beyond the orbit of Pluto. As reported in the January 2005 issue of The Astronomical Journal, SwRI’s Alan Stern used planetary formation software to explore how objects like Sedna, a huge planetoid fully 2/3 the diameter of Pluto, could have formed at distances from 75 AU to 500 AU. The two distances represent Sedna’s closest approach and farthest distance from the Sun.
“The model calculations found that objects as large, or even larger, than Sedna could easily form in circular orbits at distances of 75 to 500 AU,” says Stern, “and that their formation time could have been fairly short — just a few percent the age of the solar system. If Sedna did form this far out, it is likely to be accompanied by a cohort of other large planetoids in this very distant region of the solar system. One telltale sign that these objects were formed where they are, rather than in another location, would be if a good fraction of them are on near circular orbits.”
Image: An artist’s conception of Sedna. Credit: NASA/JPL-Caltech.
Note the word ‘circular’ in the above quote. Most astronomers agree that Sedna could not have formed in its present highly elliptical orbit because it would have experienced the kind of violent collisions that would prevent the growth of small objects. What Stern has done is to show that Sedna, however it achieved its later orbital eccentricity, could have formed by natural processes within our Solar System, rather than being captured from a passing star or being ejected from an orbit much closer to the Sun. Another implication is that planet formation operated across a much wider area than previously thought. The Solar System’s boundaries may have been extended again.
Source: S. Alan Stern, “Regarding the Accretion of 2003 VB12 (Sedna) and Like Bodies in Distant Heliocentric Orbits,” Astronomical Journal Vol. 129 No. 1, January 2005.
by Paul Gilster | Jan 24, 2005 | Outer Solar System
The European Space Agency’s Paris conference on the 21st gave us a further look at Titan’s exotic weather systems. In particular, the Gas Chromatograph Mass Spectrometer carried by Huygens produced data showing the malleable nature of methane on the surface of the frigid world. According to John Zarnecki, principal investigator for the Huygens Surface Science Package:
“The Gas Chromatograph Mass Spectrometer has detected a ‘whiff’ of methane evaporating off the surface and the SSP data has also shown indications of gas flowing into its sensing area. These gaseous outbursts were released as heat generated by Huygens warmed the soil beneath the probe. This is a tantalising glimpse of the processes at work on Titan and shows how the weather systems operate with methane forming clouds and raining down on to the surface – producing the drainage channels, river beds and other features that we see in the images.”
And back to that ‘creme brulee’ comparison — Huygens’ penetrometer evidently punched through the thin crust to a depth of between 10 and 15 cm. The material underneath, although similar in consistency to sand or clay, proves to be made up of water ice grains as opposed to rock grains, as would be found on Earth. Expect much more from Huygens, since Zarnecki says “We have only looked at a fraction of the data received…”
Next up for Cassini is another Titan flyby, now due in 21 days. Some nice photos of some of the Huygens team can be found at the Open University Surface Science Package Web site.
And good news for University of Idaho professor David Atkinson, whose Doppler Wind Experiment seemed to have failed when its data were not received aboard Cassini. Atkinson spent 18 years on the experiment. But all is not lost, for it turns out that critical data were recovered by radio telescopes on Earth, as described in this AP story.
It will take considerable work to untangle the information, says Atkinson, but it should be doable. “This sounds simple enough, but to actually change all of our experiment software, calculations, and methods to account for it is going to take some work. There are other issues too. The geometry, the distance, etc. No show stoppers, just lots of issues and considerations we’re not prepared for.”
by Paul Gilster | Jan 23, 2005 | Culture and Society
“Sooner or later for good or ill, a united mankind, equipped with science and power, will probably turn its attention to the other planets, not only for economic exploitation, but also as possible homes for man… The goal for the solar system would seem to be that it should become an interplanetary community of very diverse worlds … each contributing to the common experience its characteristic view of the universe. Through the pooling of this wealth of experience, through this “commonwealth of worlds,” new levels of mental and spiritual development should become possible, levels at present quite inconceivable to man.”
— Olaf Stapledon, in a 1948 address to the British Interplanetary Society.
Centauri Dreams note: Both C. S. Lewis and Arthur C. Clarke have acknowledged their debt to Stapledon, the British philosopher and science fiction writer whose Last and First Men (1930) and Starmaker (1937) project the human story forward into the remotest of futures. For myth-making, philosophical reflection, theological insight and speculative science on the grand scale, Stapledon should not be missed.
by Paul Gilster | Jan 22, 2005 | Exoplanetary Science
New photos from the Very Large Telescope at Paranal in the Chilean Andes have made it possible to measure the mass of a young object orbiting the star AB Doradus A. The low-mass companion to the star has been under study since the early 1990s, when the characteristic wobble of the parent star suggested a faint companion, either a planet or a brown dwarf. Using a high-contrast camera equipped with adaptive optics, the University of Arizona’s Laird Close has now brought home photographs and measurements of the companion known as AB Dor C (click on the image to enlarge).
Image: ESO PR Photo 03/05 is an enhanced, false-colour near-infrared image of AB Dor A and C. The faint companion “AB Dor C” – seen as the pink dot at 8 o’clock – is 120 times fainter than its primary star. The tiny separation between A and C, only 0.156 arcsec, is smaller than a one Euro coin seen at 20 km distance. Nevertheless, the new NACO SDI camera was able to distinguish it as a “redder” dot surrounded by the “bluer” light from AB Dor A. The orbit of AB Dor C around AB Dor A is shown as a yellow ellipse. It takes 11.75 years for the 93 Jupiter-mass companion to complete this orbit.
AD Doradus A is 48 light years away, its nearness to Earth an advantage in trying to detect faint, young objects. And this object is faint indeed, 120 times fainter than its parent (Hubble tried to detect it but failed). Its current position is approximately 2.3 AU from AB Doradus A, and it completes an orbit every 11.75 years. By relating the object’s location to the star’s known wobble, Close’s team could calculate its mass, which turns out to be roughly one-tenth the mass of the host star, or 93 times more massive than Jupiter. That puts AB Dor C just above brown dwarf territory. A brown dwarf is considered a failed star, too small for normal stellar fusion.
What’s intriguing about these findings — and this is the first time anyone has been able to measure the mass of a young, low-mass object this close to a star — is that AB Dor C’s mass challenges our views of brown dwarfs. As Close puts it: “We were surprised to find that the companion was 400 degrees (Celsius) cooler and 2.5 times fainter than the most recent models predict for an object of this mass. Theory predicts that this low-mass, cool object would be about 50 Jupiter masses. But theory is incorrect: this object is indeed between 88 to 98 Jupiter masses.”
If objects previously identified as brown dwarfs are in fact more massive than previously believed, then they must be low-mass stars rather than brown dwarfs. Also put into question are extrasolar planets not associated with any star, which may turn out to be not ‘free-floating planets’ but small brown dwarfs. Refining the mass model thus changes our view of both the stellar and planetary population.
Source: Close, Lenzen et.al. “A dynamical calibration of the mass-luminosity relation at very low stellar masses and young ages,” Nature 433, 286-289 (20 Jan 2005). An abstract is available here. For more on the adaptive optics camera used in this work, check here.
by Paul Gilster | Jan 21, 2005 | Outer Solar System
ESA’s Paris press conference produced new images and an analysis of data from the six instruments that Huygens took to the surface of Titan. “We now have the key to understanding what shapes Titan’s landscape,” said Dr Martin Tomasko, Principal Investigator for the Descent Imager-Spectral Radiometer (DISR), adding: “Geological evidence for precipitation, erosion, mechanical abrasion and other fluvial activity says that the physical processes shaping Titan are much the same as those shaping Earth.”
That statement appears in this ESA news release, which goes on to discuss the remarkable surface features Titan has yielded up to scrutiny. And while calling Titan an ‘extraordinarily Earth-like world,’ as ESA does here, seems to be stretching the point (especially at surface temperatures cold enough to produce liquid methane), the new images,like the one below, do show a complex meteorology.
Available in both a gaseous and liquid state, methane forms clouds and precipitates onto the surface. From an article by David Noever in Astrobiology Magazine: “Instead of a base chemistry defined by hydrogen and oxygen like Earth’s, Titan offers a eroded landscape shaped by the chemistry of hydrogen and carbon. This new hydrocarbon world is frozen, choking and wind-blown.”
We’re looking at drainage channels merging into rivers and lakebeds; Huygens even spotted what appear to be off-shore islands, as can be seen in other new images at the ESA site. The rivers and lakes seem to be dry, but there is evidence rain may have fallen recently. And in what may rank as the biggest surprise of the mission, Huygens picked up atmospheric argon, evidence of volcanic activity involving water ice and ammonia.
From the news release:
Thus, while many of Earth’s familiar geophysical processes occur on Titan, the chemistry involved is quite different. Instead of liquid water, Titan has liquid methane. Instead of silicate rocks, Titan has frozen water ice. Instead of dirt, Titan has hydrocarbon particles settling out of the atmosphere, and instead of lava, Titanian volcanoes spew very cold ice.
