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| Risultati della ricerca nelle immagini - "Flagstaff" |
ARP 295.jpgARP 295: a pair of galaxies with connecting "bridge"86 visite"...Naturam fraenare potes, sed vincere numquam..."
(Properzio)
"...Puoi frenare la (tua) Natura, ma (non potrai) mai vincerla..."
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HR8799b.jpgExoplanet HR8799b55 visiteA powerful, newly refined image-processing technique may allow astronomers to discover extrasolar planets that are possibly lurking in over a decade's worth of Hubble Space Telescope archival data.
David Lafreniere of the University of Toronto, Ontario, Canada, has successfully demonstrated this new strategy for planet hunting by identifying an exoplanet that went undetected in Hubble images taken in 1998 with its Near Infrared Camera and Multi-Object Spectrometer (NICMOS). In addition to illustrating the power of new data-processing techniques, this finding underscores the value of the Hubble data archive, on which those new techniques can be used.
The planet, estimated to be at least seven times Jupiter's mass, was originally discovered in images taken with the Keck and Gemini North telescopes in 2007 and 2008. It is the outermost of three massive planets known to orbit the dusty young star HR 8799, which is 130 light-years away. NICMOS could not see the other two planets because its coronagraphic spot a device which blots out the glare of the star also interferes with observing the two inner planets.
"We've shown that NICMOS is more powerful than previously thought for imaging planets," says Lafreniere. "Our new image-processing technique efficiently subtracts the glare from a star that spills over the coronagraph's edge, allowing us to see planets that are one-tenth the brightness of what could be detected before with Hubble." Lafreniere adapted an image reconstruction technique that was first developed for ground-based observatories.
Using the new technique, he recovered the planet in NICMOS observations taken 10 years before the Keck/Gemini discovery. The Hubble picture not only provides important confirmation of the planet's existence, it provides a longer baseline for demonstrating that the object is in an orbit about the star. "To get a good determination of the orbit we have to wait a very long time because the planet is moving so slowly (it has a 400-year period)," says Lafreniere. "The 10-year-old Hubble data take us that much closer to having a precise measure of the orbit."
NICMOS's view provided new insights into the physical characteristics of the planet, too. This was possible because NICMOS works at near-infrared wavelengths that are severely blocked by Earth's atmosphere due to absorption by water vapor.
"The planet seems to be only partially cloud covered and we could be detecting the absorption of water vapor in the atmosphere," says Travis Barman of Lowell Observatory, Flagstaff, Ariz. "The infrared light measured from the Hubble data is consistent with a spectrum showing a broad water absorption feature (at 1.4-1.49 microns), but the level of absorption seen is lower than it would be if the photosphere were completely devoid of dust. Dust clouds can smooth out many of the spectral features that would otherwise be thereincluding water absorption bands," Barman says. "Measuring the water absorption properties will tell us a great deal about the temperatures and pressures in the atmospheres, in addition to the cloud coverage. If we can accurately measure the water absorption features for the outermost planet around HR 8799, we will learn a great deal about their atmospheric properties. Hubble, situated well above the Earth's atmosphere, is excellently located for such a study."
"During the past 10 years Hubble has been used to look at over 200 stars with coronagraphy, looking for planets and disks. We plan to go back and look at all of those archived images and see if anything can be detected that has gone undetected until now," says Christian Marois of the Herzberg Institute of Astrophysics, Victoria, Canada. "We'll need a baseline of a few years for most objects to detect Keplerian motion and hence confirm their status as planets. The hardest part is to find them in the first place."
If his team sees a companion object to a star in more than one NICMOS picture, and it appears to have moved along an orbit, follow-up observations will be made with ground-based telescopes. If they see something once but its brightness and separation from the star would be reasonable for a planet, they will also do follow-up observations with ground-based telescopes.
Taking the image of an exoplanet is not an easy task. Planets can be billions of times fainter than the star around which they orbit and are typically located at separations smaller than 1/2000th the angular size of the full moon from their star. The planet recovered in the NICMOS data is about 100,000 times fainter than the star when viewed in the near-infrared.
"Even when using the best telescopes available, with the best resolution, the light from the bright star spills out in the area where the much fainter planets are located, making them impossible to see. It is essential to subtract out this bright glare of stellar light from the image to see faint dots, i.e., planets, that could be hidden underneath," says Rene Doyon of the University of Montreal.
The stability of how light is scattered in the NICMOS camera, called the point spread function (PSF), is key for using Hubble images to recover planets. This technique works by taking images of different stars and combining them to create a PSF of a star that closely resembles the star that is being studied for planets. This requires a reasonably steady PSF because images of different stars are taken on different days. Atmospheric conditions would vary from day-to-day for ground-based telescopes, but not for a space telescope that enjoys unprecedented image stability over repeated visits to a target.
MareKromium
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Pluto-421596main_s1006ay-2.jpgSurface Color-Variations on Pluto53 visiteNASA today released the most detailed set of images ever taken of the distant dwarf planet Pluto. The images taken by NASA's Hubble Space Telescope show an icy and dark molasses-colored, mottled world that is undergoing seasonal changes in its surface color and brightness. Pluto has become significantly redder, while its illuminated Northern Hemisphere is getting brighter. These changes are most likely consequences of surface ices sublimating on the sunlit Pole and then refreezing on the other Pole as the dwarf planet heads into the next phase of its 248-year-long seasonal cycle. The dramatic change in color apparently took place in a two-year period, from 2000 to 2002.
The Hubble images will remain our sharpest view of Pluto until NASA's New Horizons probe is within 6 months of its Pluto flyby. The Hubble pictures are proving invaluable for picking out the planet's most interesting-looking hemisphere for the New Horizons spacecraft to swoop over when it flies by Pluto in 2015.
Though Pluto is arguably one of the public's favorite planetary objects, it is also the hardest of which to get a detailed portrait because the world is small and very far away. Hubble resolves surface variations a few hundred miles across, which are too coarse for understanding Surface Geology. But in terms of surface color and brightness Hubble reveals a complex-looking and variegated world with white, dark-orange, and charcoal-black terrain. The overall color is believed to be a result of UltraViolet radiation from the distant Sun breaking up Methane that is present on Pluto's Surface, leaving behind a dark and red carbon-rich residue.
When Hubble pictures taken in 1994 are compared with a new set of images taken in 2002 to 2003, astronomers see evidence that the northern polar region has gotten brighter, while the southern hemisphere has gotten darker. These changes hint at very complex processes affecting the visible surface, and the new data will be used in continued research.
The images are allowing planetary astronomers to better interpret more than three decades of Pluto observations from other telescopes, says principal investigator Marc Buie of the Southwest Research Institute in Boulder, Colo. "The Hubble observations are the key to tying together these other diverse constraints on Pluto and showing how it all makes sense by providing a context based on weather and seasonal changes, which opens other new lines of investigation."
The Hubble pictures underscore that Pluto is not simply a ball of ice and rock but a dynamic world that undergoes dramatic atmospheric changes. These are driven by seasonal changes that are as much propelled by the Planet's 248-year elliptical orbit as its axial tilt, unlike Earth where the tilt alone drives seasons. The seasons are very asymmetric because of Pluto's elliptical orbit. Spring transitions to Polar Summer quickly in the Northern Hemisphere because Pluto is moving faster along its orbit when it is closer to the Sun.
Ground-based observations, taken in 1988 and 2002, show that the mass of the atmosphere doubled over that time. This may be due to warming and sublimating Nitrogen ice. The new Hubble images from 2002 to 2003 are giving astronomers essential clues about how the seasons on Pluto work and about the fate of its atmosphere.
The images, taken by the Advanced Camera for Surveys, are invaluable to planning the details of the New Horizons flyby in 2015. New Horizons will pass by Pluto so quickly that only one hemisphere will be photographed in the highest possible detail. Particularly noticeable in the Hubble image is a bright spot that has been independently noted to be unusually rich in carbon monoxide frost. It is a prime target for New Horizons. "Everybody is puzzled by this feature," says Buie. New Horizons will get an excellent look at the boundary between this bright feature and a nearby region covered in pitch-black surface material.
"The Hubble images will also help New Horizons scientists better calculate the exposure time for each Pluto snapshot, which is important for taking the most detailed pictures possible," says Buie. With no chance for re-exposures, accurate models for the surface of Pluto are essential in preventing pictures that are either under- or overexposed.
The Hubble images are a few pixels wide. But through a technique called dithering, multiple, slightly offset pictures can be combined through computer-image processing to synthesize a higher-resolution view than could be seen in a single exposure. "This has taken four years and 20 computers operating continuously and simultaneously to accomplish," says Buie, who developed special algorithms to sharpen the Hubble data.
The Hubble research results appear in the March 2010 issue of the Astronomical Journal. Buie's science team members are William Grundy of Lowell Observatory in Flagstaff, Ariz., and Eliot Young, Leslie Young, and Alan Stern of Southwest Research Institute in Boulder, Colo.
Buie plans to use Hubble's new Wide Field Camera 3 to make further Pluto observations prior to the arrival of New Horizons.MareKromium
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The_Earth_from_Clementine-000.jpg400 - The Earth from Clementine190 visiteView of the full Earth taken by Clementine while orbiting the Moon. This image is a mosaic of color, HR frames. Africa is clearly visible on the right and South America is visible on the left. This is a false-color version that makes vegetation appear red".
Image processing by United States Geological Survey (USGS), Flagstaff, Arizona
Nota: la vegetazione, in questo frame ed in accordo a quanto l'USGS stessa dice in chiare lettere, appare rossa (mentre dovrebbe essere di un bel color verde scuro) mentre le sabbie dei deserti - e questo lo diciamo noi - appaiono di color arancio-giallo (e dovrebbero vedersi esattamente come si vedono).
Curiosa questa "alterazione cromatica selettiva" in virt della quale alcuni colori cambiano radicalmente mentre altri restano quello che sono.
Pensate adesso alle fotografie amatoriali di Marte ottenute da Terra ed a quelle "professionali&scientifiche" ottenute dall'HST e dalle Sonde che girano attorno al Pianeta Rosso. Colta la provocazione?!? Fateci sapere...
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Titan-PIA11001.jpgEthane Lake on Titan55 visiteNASA scientists have concluded that at least one of the large lakes observed on Saturn's moon Titan contains liquid hydrocarbons, and have positively identified the presence of ethane. This makes Titan the only body in our solar system beyond Earth known to have liquid on its surface.
Scientists made the discovery using data from an instrument aboard the Cassini spacecraft. The instrument identified chemically different materials based on the way they absorb and reflect infrared light. Before Cassini, scientists thought Titan would have global oceans of methane, ethane and other light hydrocarbons. More than 40 close flybys of Titan by Cassini show no such global oceans exist, but hundreds of dark, lake-like features are present. Until now, it was not known whether these features were liquid or simply dark, solid material.
"This is the first observation that really pins down that Titan has a surface lake filled with liquid," said Bob Brown of the University of Arizona, Tucson. Brown is the team leader of Cassini's visual and mapping instrument. The results will be published in the July 31 issue of the journal Nature.
Ethane and several other simple hydrocarbons have been identified in Titan's atmosphere, which consists of 95 percent nitrogen, with methane making up the other fiver percent. Ethane and other hydrocarbons are products from atmospheric chemistry caused by the breakdown of methane by sunlight.
Some of the hydrocarbons react further and form fine aerosol particles. All of these things in Titan's atmosphere make detecting and identifying materials on the surface difficult, because these particles form a ubiquitous hydrocarbon haze that hinders the view. Liquid ethane was identified using a technique that removed the interference from the atmospheric hydrocarbons.
The visual and mapping instrument observed a lake, Ontario Lacus, in Titan's south polar region during a close Cassini flyby in December 2007. The lake is roughly 20,000 square kilometers (7,800 square miles) in area, slightly larger than North America's Lake Ontario.
"Detection of liquid ethane confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan," said Larry Soderblom, a Cassini interdisciplinary scientist with the U.S. Geological Survey in Flagstaff, Ariz. "The fact we could detect the ethane spectral signatures of the lake even when it was so dimly illuminated, and at a slanted viewing path through Titan's atmosphere, raises expectations for exciting future lake discoveries by our instrument."
The ethane is in a liquid solution with methane, other hydrocarbons and nitrogen. At Titan's surface temperatures, approximately 300 degrees Fahrenheit below zero, these substances can exist as both liquid and gas. Titan shows overwhelming evidence of evaporation, rain, and fluid-carved channels draining into what, in this case, is a liquid hydrocarbon lake.
Earth has a hydrological cycle based on water and Titan has a cycle based on methane. Scientists ruled out the presence of water ice, ammonia, ammonia hydrate and carbon dioxide in Ontario Lacus. The observations also suggest the lake is evaporating. It is ringed by a dark beach, where the black lake merges with the bright shoreline. Cassini also observed a shelf and beach being exposed as the lake evaporates. "During the next few years, the vast array of lakes and seas on Titan's north pole mapped with Cassini's radar instrument will emerge from polar darkness into sunlight, giving the infrared instrument rich opportunities to watch for seasonal changes of Titan's lakes," Soderblom said.
More information is available at: http://www.nasa.gov/cassini, http://saturn.jpl.nasa.gov and http://wwwvims.lpl.arizona.edu .
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