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By Daniel Fischer Every page present in Europe & the U.S.!
| Ahead | Awards 
The latest issue!
| A German companion - only available here! Current mission news: MGS (latest pictures!) + Cassini + Stardust |
Spanish investigators are continuing their search for meteorite fragments following spectacular sightings of fireballs: BBC (earlier), Guardian, RP, NZ. Quadrantids source found? NSU. Another Martian meteorite? AFP. Venus "spokes": Tor. Star. Again, no leap second: Ast. SOHO in another 'keyhole': ESA Science News. Preview 2004: S&T. Old star gazers: Guard.
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Spirit has stood up, should roll off the platform on Jan. 14NASA's Mars Exploration Rover Spirit has successfully completed its stand-up activities by extending the rear wheels. Mission managers have decided that changing the tilt of the lander platform will not be necessary before the rover drives off, possibly allowing drive-off to occur late on Jan. 13 or early on Jan. 14, Pacific Standard Time. Under best-case conditions, severing the final cable connection is planned for the night of Jan. 11, followed by clockwise turns totaling 120 degrees in the night Jan. 12/13 (to avoid having to run over the airbag that could not be retracted fully), then drive-off toward the northwest on the following martian day. |
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More PanCam images have been received in recent days, and they confirm some predictions about the Gusev
site: Rocks cover less of the ground than at the three previous Mars landing sites - about three percent
of ground area around Spirit compared with about 20 percent of the ground around each of Mars Pathfinder,
Viking 1 and Viking 2. It is without question the smoothest, flattest place NASA s/c have ever landed on
Mars, with the possible exception of Viking 2. Meanwhile traces of carbonate minerals have shown up in the
rover's first survey of the site with its infrared sensing instrument Mini-TES. Carbonates form in the
presence of water, but it's too early to tell whether the amounts detected come from interaction with water
vapor in Mars' atmosphere or are evidence of a watery local environment in the past. The PanCam images also show that the atmosphere at Spirit's site is dustier than at previous landing sites, except during dust storms observed by the Viking landers. The dust colors the sky and affects the appearance of objects on the ground. Higher above the ground, atmospheric densities predicted for Spirit's descent closely matched the true conditions measured from the spacecraft's deceleration: That is a good sign for Opportunity's descent two weeks from now, though risks remain high for any landing on Mars. As a case in point, several more attempts to reach Beagle 2 have failed since the initial Mars Express overflight on Jan. 7 - and questions start being asked whether this cheap lander was such a good idea after all. Meanwhile Mars Express should start delivering science test data from orbit these days, e.g. from the hi-res camera!
Meanwhile on January 6 at 17:05 UTC the first sample of what will be a 360° high-resolution color panorama of Spirit's landing site was first revealed to an eager world (the day before several - German - TV stations had already mistaken anagylph stereo views from the NavCam for »the first color pictures« :-): the mosaic consisted of 12 of what will be 75 frames, each of them 16° x 16° and one megapixel large. The jump in clarity over the NavCam views celebrated the two previous days is immense, and since the new pictures were still quite compressed, there will be another improvement in resolution eventually. Still, NASA had to use HDTV projection for the first time to present the 12 megapixels in full glory. The rocks embedded in the dusty plain are now revealing details: They are mainly very smooth, as if sandblasted - and that could well be what has happened: Gusev crater is a pretty windy place, as the lander had experienced during descent and as Spirit is feeling (through thermal effects) even on the ground. The region is also known - from orbital imaging - for an abundance of dust devils which seem to have removed much dust from the rocks themselves. Which is good for Spirit's rock chemistry instruments, of course. The most intriguing feature seen so far in the 45° PanCam sample is »artificial«, however: when the airbags were retracted, the soil was scratched - and looks like wet mud! Which it can't be, that close to the equator: the effect is simply »bizarre« to several of Spirit's scientists. There is still no decision where the rover will head first when it egresses from the landing platform in mid-January: the planners are just watching »in awe« as the hi-res panorama comes down. Spirit will probably just drive forward, but one of the deflated airbags is partly in the way - it was to be retracted again, to clear the way for Spirit (which will delay the egress for a few days). There are a few technical anomalies under review - such as greater heating than expected, esp. from the UHF transmitter, and some resistance during the first movements of the high gain antenna (which seems to have been resolved already) - but none are deemed serious. Thus Spirit should be able to rise to its wheeled feet as early as January 7.
»Spirit's« success exceeds all expectations - first pictures received within three hours of touchdown!It felt like the 1997 Pathfinder all over again, and then some: When NASA's first Mars Exploration Rover came down in Gusev crater in the night of January 3/4, everything worked at least as well as even the greatest optimists had thought. The project had begun(!) just 3½ years ago (see Update # 198), in the wake of the double loss of the 1999 Mars missions, building on the Pathfinder success but increasing the complexity enormously. Such rushed, difficult projects tend to fail, but with enough enthusiasm, rigor and money NASA has beaten all the odds. The rover Spirit is still on the landing platform and won't roll off until about Mars day (sol) 9, but as of now no showstoppers for a full mission are in sight. Here's then a (partial) list of all that went right:
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The biggest and brightest star?The record for the biggest and intrinsically brightest star may have been broken, though it is not absolutely certain yet that the distant object LBV 1806-20 is not a very tight cluster of a few less massive stars. But even it that would be the case, one of those stars would be the source of most of the light and certainly an extraordinary body. But don't expect to find the star - which is at least 5 million times brighter than the sun - in the night sky: Dust particles between Earth and the star block out all of its visible light. Whereas the sun is located only 8.3 light minutes from Earth, the bright star is 45,000 light years away, on the other side of the galaxy. It is detectable only with instruments that measure infrared light, which has longer wavelengths that can better penetrate the dust.The star is at least as bright as the Pistol Star, the current record holder (so named for the pistol-shaped nebula surrounding it): Whereas the Pistol Star is between 5 million and 6 million times as bright as the Sun, the new contender could be as much as 40 million times the Sun's absolute brightness. High-resolution data prove that the object is not simply a cluster of lower mass stars, although it is possible that it is a collection of a few stars in a tight orbit around each other. Astronomers have known about LBV 1806-20 since the 1990s. At that time, it was identified as a "luminous blue variable star" - a relatively rare, massive and short-lived star. Such stars get their names from their propensity to display light and color variability in the infrared spectrum.
Luminous blue variable stars are extremely large, with LBV 1806-20 probably at least 150
times larger than the Sun. The stars are also extremely young by stellar time: LBV 1806-20
is estimated at less than 2 million years old. One of the mysteries about the star is how
it got so big. Current theories of star formation suggest they should be limited to about
120 solar masses because the heat and pressure from such big stars' cores force matter away
from their surfaces. One possibility is that the big star was formed in a process called
shock-induced star formation, which occurs when a supernova blows up and slams the gaseous
material in a molecular cloud together into a massive star. The star's size is not its only
distinguishing characteristic: It is located in a small cluster of highly unusual or extremely rare
stars, including a soft gamma ray repeater and an extremely young infant star.
Ten years after this cataclysmic event, a European/University of Hawaii team of astronomers has
now peered deep into the glowing remnants of SN 1993J using the Hubble Space Telescope's Advanced
Camera for Surveys (ACS) and the giant Keck telescope on Mauna Kea in Hawaii. They have discovered
a massive star exactly at the position of the supernova that is the long sought companion to the
supernova progenitor. This is the first supernova companion star ever to be detected and it
represents a triumph for the theoretical models. It is now clear that during the last 250 years
before the explosion 10 solar masses of gas were torn violently from the red supergiant by its
partner. By observing the companion closely in the coming years it may even be possible to detect a
neutron star or black hole emerge from the remnants of the explosion 'in real time'.
Already, four different effects beyond those explained with simple Newtonian gravity have been measured and are completely consistent with Albert Einstein's theory. Future observations of the two stars will measure their slow spiral in towards each other as they radiate gravitational radiation - a dance of death leading to their ultimate fusion into what may become a black hole. General relativity predicts that the two stars will slowly wobble like spinning tops allowing new tests of the theory. Another unique aspect of the new system is the strong interaction between radiation from the two stars. By chance, the orbit is seen nearly edge on to us, and the signal from one pulsar is eclipsed by the other. |
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Galaxy's fatal plunge into cluster detailedTrailing 200,000-light-year-long streamers of seething gas, the galaxy C153 that was once like our Milky Way is being shredded as it plunges at 4.5 million miles per hour through the heart of a distant cluster of galaxies, Abell 2125. In this unusually violent collision with ambient cluster gas, the galaxy is stripped down to its skeletal spiral arms as it is eviscerated of fresh hydrogen for making new stars. The galaxy's untimely demise is offering new clues to solving the mystery of what happens to spiral galaxies in a violent universe. Astronomers are using a wide range of telescopes and analysis techniques to conduct a through look at what is happening to this galaxy inside its cluster's rough neighborhood. Though such "distressed" galaxies have been seen before, this one's demise is unusually swift and violent.The galaxy belongs to a cluster of galaxies that slammed into another cluster about 100 million years ago. This galaxy took the brunt of the beating as it fell along a trajectory straight through the dense core of the colliding cluster. The first suggestion of galactic mayhem in this cluster came in 1994 when the Very Large Array detected an unusual number of radio galaxies in Abell 2125. The radio observations also showed that C153 stood out from the other galaxies as an exceptionally powerful radio source. X-ray observations from the ROSAT satellite demonstrated that the cluster contains vast amounts of 20 million Kelvin gas that envelops the galaxies. The gas is concentrated into two main lumps rather than smoothly distributed across the cluster, as is more commonly the case. This bolstered the suspicion that two galaxy clusters are actually colliding. Spectroscopy then identified many star-forming systems and even active galactic black holes fueled by the collision. And the Hubble Space Telescope resolved a bizarre shape of C153: it looks unusually clumpy with many young star clusters and chaotic dust features. Besides the disrupted features in the galaxy's disk, HST also showed that the light in the tail is mostly attributed to recent star formation, providing a direct link to the stripping of the galaxy as it passed through the cluster core. Gas compressed along the galaxy's leading edge, like snow before a plow, ignited a firestorm of new star birth. Evidence of recent star formation also comes from the optical spectrum, while optical images show a very long tail of extended gas coming off the galaxy. This tail was apparently generated in part by a hurricane of stellar winds boiling off the new star-birth regions and being blown backwards as the galaxy streaks through the surrounding hot gas of the cluster. Spectroscopic observations allowed astronomers to age-date the starburst. They find that 90 percent of C153's blue light is from a population of stars that are 100 million years old. This age corresponds to the time the galaxy should have gone careening through the densest gas in the cluster core. According to the spectra the stars are in a regular pattern of orbital motion around the center, as usual for disk galaxies. However, there are multiple widespread clouds of gas moving independently of the stars. The galaxy C153 is destined to lose the last vestiges of its spiral arms and become a bland S0-type galaxy having a central bulge and disk, but no spiral-arm structure: These types of galaxies are common in the dense galaxy clusters seen today. |
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All other historical issues can be found in the Archive.
The U.S. site of this Cosmic Mirror has been visited
since it was issued (the German site has no counter).
Compiled and written by Daniel Fischer
