by Paul Gilster | Jan 20, 2005 | Outer Solar System
Huygens mission scientists will gather tomorrow in Paris to discuss the results of the experiments aboard the probe. Huygens delivered plenty of data: the probe transmitted for several hours from the surface of Titan, even after the Cassini orbiter moved below the horizon. Cassini received one hour and twelve minutes worth of solid information; all told, we have some 474 megabits that include 350 pictures of the descent and landing area.
Early results show that the upper atmosphere is what the European Space Agency calls ‘a uniform mix of methane with nitrogen in the stratosphere.’ As the probe descended, the concentration of methane increased. One unexpected issue was the haze, which the Huygens team assumed the probe would clear at between 75 and 50 kilometers. In fact, Huygens only emerged from the haze at 30 kilometers above the surface. Methane or ethane fog was detected near the ground.
On the table tomorrow in Paris will be data about the texture of Titan’s surface (the famous ‘creme brulee’ comment still stands — we’re dealing with something the consistency of wet sand or clay with a thin crust, though it’s mostly made up of water and hydrocarbon ice). The press conference takes place at 1100 CET (0500 EST) and will be re-broadcast to other ESA sites. A list of conference participants is here, and an animation of the Huygens descent through the clouds can be found on this ESA page.
by Paul Gilster | Jan 19, 2005 | Deep Sky Astronomy & Telescopes
In Blazing Speed: The Fastest Stuff in the Universe, Robert Roy Britt looks at recent studies of a form of matter that moves remarkably close to the speed of light. The material comes in the form of huge jets of hot gas that are ejected from a kind of galaxy called a blazar. Some of these jets attain speeds of 99.9 percent of the speed of light, according to a study presented at the recent AAS meeting by Glenn Piner of Whittier College in Whittier, California. Britt’s article gives an overview of Piner’s work, but dig deeper at Piner’s Web site Quasar Research at Whittier College, where he explains the study’s methodology, which used Very Long Baseline Interferometry. The technique combines data from widely separated telescopes to achieve the same angular resolution as a single telescope with a size equal to the maximum separation between the individual dishes.
From a news release from Whittier:
Blazars are active galactic nuclei — energetic regions surrounding massive black holes at the centers of galaxies. Material being drawn into the black hole forms a spinning disk called an accretion disk. Powerful jets of charged particles are ejected at high speeds along the poles of accretion disks. When these jets happen to be aimed nearly toward the Earth, the objects are called blazars.
This is tricky stuff, because when material from a blazar is moving directly toward the observer, the measurements of its speed are thrown off considerably, resulting in what seem to be speeds far greater than that of light. The phenomenon is called ‘superluminal motion,’ and it is, according to the news release, “…not real, but rather is an illusion caused by the fact that the material in the jet is moving at nearly the speed of light almost directly toward the observer. Because the jet features are moving toward Earth at almost the same speed as the radio waves they emit, they can appear to move across the sky at faster-than-light speeds. Scientists can correct for this geometrical effect to calculate a lower limit to the true speed of the features.”
Image: A sequence of radio observations shows a plasma blob moving away from a blazar’s core (right) over about 8.4 months. CREDIT: Piner et al., NRAO/AUI/NSF
The true speed thus deduced comes to 99.9 percent of light speed. Piner has been working with two facilities, the first being the National Science Foundation’s Very Long Baseline Array (VLBA), which consists of ten radio telescopes in locations ranging from Mauna Kea in Hawaii to St. Croix in the US Virgin Islands. The 5,000 mile baseline thus provided offers sharper vision than any telescope yet built. The VLBI Space Observatory Programme uses a Japanese satellite in conjunction with ground telescopes to make its measurements. USA Today covered Piner’s work in a January 18 story called Fastest Stuff in the Universe Approaches Light Speed.
by Paul Gilster | Jan 18, 2005 | Exoplanetary Science
M-class red dwarf stars are unusually interesting. For one thing, they make up 70 percent of all stars in our galaxy, meaning the great bulk of stars are much less massive than our Sun and far less bright, not to mention being considerably longer-lived. For another thing, the closest known star, Proxima Centauri, is a red dwarf, so anything we could learn about planetary formation there or around other nearby red dwarfs would be all to the good.
But that’s just it — we know very little about what’s happening around red dwarfs. Attempts to find planets around Proxima Centauri have thus far come up short. Best known is a 1994 study that was suggestive (but not conclusive), of a near Jupiter-sized planet orbiting closer than the distance of Mercury to our Sun. Later Hubble data was also no more than suggestive, while observations at the European Southern Observatory found no evidence for planets as large as Jupiter, though remaining moot on the question of smaller worlds.
Image: Illustration of a debris disk surrounding a young red dwarf star. The stellar wind from the red dwarf star removes the dust in the debris disk by causing the dust to slowly spiral into the star. Credit: UCLA.
Now a team of UCLA astronomers has approached the red dwarf question from another angle. They began with a curiosity in past observations: almost none of the debris disks we’ve thus far found (and we’ve found many) have circled red dwarfs. Since our models of planetary formation suggest that planets grow out of primordial debris disks around stars, we should expect such disks around red dwarfs. But only AU Microscopium (AU Mic) and GJ 182 fit the bill. All other red dwarfs studied have lacked significant disks.
The UCLA team sampled nearby red dwarfs with the Long Wavelength Spectrometer, an infrared camera at the Keck Observatory on Mauna Kea. None showed any evidence of warm dust. The new theory that grew out of this work: red dwarfs have stronger magnetic fields than other stars, and correspondingly stronger stellar winds (particles pushed from the star by magnetic fields at hundreds of kilometers per second). It is the strong stellar wind that removes all traces of planetary formation around red dwarfs, even though the planets may indeed be there.
The ‘missing disk’ paper was presented at the American Astronomical Society’s recent meeting in San Diego. For more, see this UCLA news release.
On earlier attempts to find planets around Proxima Centauri, see G. F. Benedict et al., “Searching for Planets Near Proxima Centauri: A Status Report.” Bulletin of the American Astronomical Society 26 (1994): 930. The Hubble work is found in A. B. Schultz et al., “A Possible Companion to Proxima Centauri,” Astronomical Journal 115 (1998): 345-50.
by Paul Gilster | Jan 17, 2005 | Exoplanetary Science
The dust disk around the star Beta Pictoris has been under study since 1983, when it was detected in IRAS (Infrared Astronomy Satellite) data. Last October, astronomers in Japan found three rings of planetismals circling the star, with a possible planet at 12 AU. Now the Gemini South 8-meter telescope in Chile has found telling new details in the disk. The upshot: a collision between large planetary bodies may have occurred there within the last few decades.
This is intriguing news for those scientists who believe such collisions are a necessary part of planetary formation. From a Gemini Observatory news release:
“It is as if we were looking back about 5 billion years and watching our own solar system as it was forming into what we see today,” said Dr. Charles Telesco of the University of Florida who led the team. “Our research is a bit like a detective dusting for fingerprints to figure out a crime scene, only in this case we use the dust as a tracer to show what has happened within the cloud. The properties of the dust show not only that this was a huge collision, but that it probably happened recently in both astronomical and even human timescales.”
The clue to the recent collision is the lopsided nature of the debris disk, and the presence of fine dust grains in one part of it. Such tiny particles should have been pushed away by the parent star long ago. Says team member Dr. Scott Fisher, “The fact that we still see them in our observations means that the collision probably happened in the past 100 years or so. Almost assuredly my grandparents were alive when this collision occurred.”
Image: Gemini mid-infrared images of Beta Pictoris as obtained with T-ReCS on Gemini South. Differences in the shape and strength of dust emissions within the disk can be seen as the observed wavelength changes. Note:The clump where the suspected collision occurred is to the right of the central white core at a distance of 52 Astronomical Units (AU). Credit: Gemini Observatory.
More on the new Beta Pictoris findings, which were presented at the recent American Astronomical Society meeting, can be found in the January 13 issue of Nature.
by Paul Gilster | Jan 15, 2005 | Outer Solar System
Of all the Titan images released so far, this one may be the most provocative. Surely these are drainage channels, and is it possible we’re looking at a coastline in the lower part of the picture? Is there still liquid out there? If so, it’s not water but liquid methane or ethane, and it may have drained long ago into the surface. Months of analysis will be needed before we start getting answers to such questions. The image was taken at approximately 8 kilometers altitude. Note what may be fog near the ‘shoreline.’
Image: A boundary between high, lighter-coloured terrain and and darker lowland area on Titan. Credit: European Space Agency.
More images from ESA are here.
The Huygens Atmospheric Structure Instrument (HASI) recorded the sounds of Huygens’ descent, now available online. A member of the HASI science team describes the descent audio as including a ‘lot of acoustic noise,’ which I assume refers to the sound you would have heard within the probe during the descent; the audio is incomplete, but the probe seems to be swinging back and forth in a strong wind.
And the only bad news, which may be remediable (via Emily Lakdawalla in Darmstadt):
There was some glitch somewhere–some mistake made, into which there will be a formal ESA inquiry–that resulted in the complete loss of one of two “channels” on which Huygens was sending data to Cassini. These were supposed to be two fully redundant systems, but a couple of the experiments depended on both channels working, in particular the Doppler Wind Experiment. This experiment relied on the Doppler shift of the carrier signal being transmitted from Huygens to Cassini and also to the Earth to reconstruct a vertical wind profile of Titan’s thick atmosphere. The Cassini component of this experiment was lost because, apparently, Cassini just wasn’t listening.
Fortunately for the Doppler Wind Experiment, though, radio telescopes all over Earth were listening, and even more fortunately, they were able to hear Huygens’ signal loud and clear. So although they lost the data set they wanted, they will be able to recover their investigation’s goals by using the radio telescope data. It will take “an enormous amount of work,” ESA Science Director David Southwood told us, but “scientists love work. That’s what they live for.” (I’m sure that the DWE team would say, though, that they could have done with a little less work, thank you.)
