Autor Subiect: Norii de pe Saturn  (Citit de 17890 ori)

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Offline pri3st3ss

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Raspuns: Norii de pe Saturn
« Răspuns #30 : 22 Martie 2008, 20:45:14 »
Titan, luna planetei Saturn, ar putea adãposti viaþã


Imaginile radar din timpul misiunii Cassini-Huygens întãresc predicþiile cã sub crusta groasã de gheaþã de pe Titan, satelitul planetei Saturn, ar exista rezerve de apã lichidã.
Dacã acest lucru este confirmat, atunci Titan deþine sursa vieþii - apa ºi moleculele organice.
Anul 2004 a reprezentat începutul misiunii Cassini, când la o primã observaþie s-a crezut cã suprafaþa era acoperitã în totalitate de un strat gros de hidrocarburi. În momentul în care naveta a schimbat poziþia radarului cãtre lunã, în 2004, ºi când sonda Huygens a fost lansatã un an mai târziu, a fost descoperitã o nouã imagine. S-a constatat cã suprafaþa era tare, cu forme geologice sub formã de dune, canale ºi cratere traversate de "râuri" vaste.
Ultimele cercetãri pe Titan aruncã o nouã privire asupra acestor elemente, iar spre surprinderea cercetãtorilor de la NASA, formele geologice nu se mai aflã unde ar fi trebuit.
Datele sugereazã cã modificãrile sezonale ale rotirii satelitului nu pot exista decât dacã sub crusta solidã ar exista un ocean lichid.
Cercetãtorii, conduºi de Dr. Ralph Lorenz de la Johns Hopkins University Applied Physics Laboratory, SUA, spun cã aceste predicþii pot fi verificate în misiuni ulterioare pe Titan.
"Nu ar fi imposibil de crezut cã pe Titan ar putea exista surse de energie, poate energie geotermalã, cum avem pe Pãmânt la fundul oceanelor", a declarat John Zarnecki, profesor de ªtiinþa Spaþiului, la Open University, din Marea Britanie.
Titan este a doua lunã ca mãrime din Sistemul Solar, dupã satelitul lui Jupiter, Ganymede.
Observaþiile din trecut subliniau cã Titan se aseamãnã Pãmântului, în perioada sa de la început, mai ales în ceea ce priveºte componenþa atmosferei. Singura diferenþã este reprezentatã de temperaturile extrem de scãzute de lângã Saturn.

Sursa: bbc.co.uk

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Raspuns: Norii de pe Saturn
« Răspuns #31 : 27 Martie 2008, 20:38:52 »
Ocean may exist beneath Titan's crust


Cassini has discovered evidence that points to the existence of an underground ocean of water and ammonia on Saturn's moon Titan. The findings were made using radar measurements of Titan's rotation.
"With its organic dunes, lakes, channels and mountains, Titan has one of the most varied, active and Earth-like surfaces in the solar system," said Ralph Lorenz, lead author of the paper and Cassini radar scientist at the Johns Hopkins Applied Physics Laboratory in Maryland, USA. "Now we see changes in the way Titan rotates, giving us a window into Titan's interior beneath the surface."
Members of the mission's science team used Cassini's Synthetic Aperture Radar to collect imaging data during 19 separate passes over Titan between October 2005 and May 2007. The radar can see through Titan's dense, methane-rich atmospheric haze, detailing never-before-seen surface features and establishing their locations on the moon's surface.
Using data from the radar's early observations, the scientists and radar engineers established the locations of 50 unique landmarks on Titan's surface. They then searched for these same lakes, canyons and mountains in the reams of data returned by Cassini in its later flybys of Titan.
They found that prominent surface features had shifted from their expected positions by up to 30 km. A systematic displacement of surface features would be difficult to explain unless the moon's icy crust was decoupled from its core by an internal ocean, making it easier for the crust to move. 
 
 
 Possible liquid ocean beneath Titan's surface
"We believe that about 100 km beneath the ice and organic-rich surface is an internal ocean of liquid water mixed with ammonia," said Bryan Stiles of NASA's Jet Propulsion Laboratory, California, USA. Stiles is a contributing author to the paper reporting the findings.
The study of Titan is a major goal of the Cassini-Huygens mission because it may preserve, in deep-freeze, many of the chemical compounds that preceded life on Earth. Titan is the only moon in the solar system that possesses a dense atmosphere. The moon's atmosphere is 1.5 times denser than Earth's. It is also the largest of Saturn's moons, bigger than the planet Mercury.
"The combination of an organic-rich environment and liquid water is very appealing to astrobiologists," Lorenz said. "Further study of Titan's rotation will let us understand the watery interior better, and because the spin of the crust and the winds in the atmosphere are linked, we might see seasonal variation in the spin in the next few years."
Cassini scientists will not have long to wait before another go at Titan. On March 25, just prior to its closest approach at an altitude of 1000 km, Cassini will employ its Ion and Neutral Mass Spectrometer to examine Titan's upper atmosphere. Immediately after closest approach, the spacecraft's Visual and Infrared Mapping Spectrometer will capture high-resolution images of Titan's southeast quadrant
 
Notes for editors:
 
These findings appear in ‘Titan's Rotation Reveals an Internal Ocean and Changing Zonal Winds’ by R. Lorenz et al. in the March 21 issue of the journal Science.
The Cassini-Huygens mission is a cooperative project of NASA, the ESA and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, USA, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington.
The Cassini orbiter was designed, developed and assembled at JPL. ESA developed the Huygens lander, while ASI managed the development of the high-gain antenna and other instruments of its participation. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.



Cassini 'tastes' organic brew at Saturn’s geyser moon

 The Cassini spacecraft tasted and sampled a surprising organic brew erupting in geyser-like fashion from Saturn's moon Enceladus during a close flyby on 12 March. Scientists are amazed that this tiny moon is so active, ‘hot’ and brimming with water vapour and organic chemicals.
New heat maps of the surface show higher temperatures than previously known in the south polar region, with hot tracks running the length of giant fissures. Additionally, scientists say the organics ‘taste and smell’ like some of those found in a comet. The jets themselves harmlessly peppered Cassini, exerting measurable torque on the spacecraft, and providing an indirect measure of the plume density.
 
 Gas and dust jets match up
"A completely unexpected surprise is that the chemistry of Enceladus, what's coming out from inside, resembles that of a comet," said Hunter Waite, principal investigator for the Cassini Ion and Neutral Mass Spectrometer at the Southwest Research Institute in San Antonio. "To have primordial material coming out from inside a Saturn moon raises many questions on the formation of the Saturn system."
"Enceladus is by no means a comet. Comets have tails and orbit the sun, and Enceladus's activity is powered by internal heat while comet activity is powered by sunlight. Enceladus's brew is like carbonated water with an essence of natural gas," said Waite.
The Ion and Neutral Mass Spectrometer saw a much higher density of volatile gases, water vapour, carbon dioxide and carbon monoxide, as well as organic materials, some 20 times denser than expected. This dramatic increase in density was evident as the spacecraft flew over the area of the plumes.
New high-resolution heat maps of the south pole by Cassini's Composite Infrared Spectrometer show that the so-called tiger stripes, giant fissures that are the source of the geysers, are warm along almost their entire lengths, and reveal other warm fissures nearby. These more precise new measurements reveal temperatures of at least minus 93º Celsius. That is 17º warmer than previously seen and 93º Celsius warmer than other regions of the moon. The warmest regions along the tiger stripes correspond to two of the jet locations seen in Cassini images.
 
"These spectacular new data will really help us understand what powers the geysers. The surprisingly high temperatures make it more likely that there's liquid water not far below the surface," said John Spencer, Cassini scientist on the Composite Infrared Spectrometer team at the Southwest Research Institute in Colorado, USA.
Previous ultraviolet observations showed four jet sources, matching the locations of the plumes seen in previous images. This indicates that gas in the plume blasts off the surface into space, blending to form the larger plume.
Images from previous observations show individual jets and mark places from which they emanate. New images show how hot spot fractures are related to other surface features. In future imaging observations, scientists hope to see individual plume sources and investigate differences among fractures.
"Enceladus has got warmth, water and organic chemicals, some of the essential building blocks needed for life," said Dennis Matson, Cassini project scientist at NASA's Jet Propulsion Laboratory in California, USA. "We have quite a recipe for life on our hands, but we have yet to find the final ingredient, liquid water, but Enceladus is only whetting our appetites for more."
At closest approach, Cassini was only about 48 km from Enceladus. When it flew through the plumes it was about 193 km from the moon's surface. Cassini's next flyby of Enceladus is in August.
Notes for editors:
 
The Cassini-Huygens mission is a cooperative project of NASA, the ESA and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, USA, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington.
The Cassini orbiter was designed, developed and assembled at JPL. ESA developed the Huygens lander, while ASI managed the development of the high-gain antenna and other instruments of its participation. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.
 
 

Planet in Progress? Evidence Of A Huge Planet Forming In Star System

Astrophysicists have a new window into the formation of planets. Ben R. Oppenheimer, Assistant Curator in the Department of Astrophysics at the American Museum of Natural History, and colleagues have imaged a structure within the disk of material coalescing from the gas and dust cloud surrounding a well-studied star, AB Aurigae. Within that structure, it appears that an object is forming, either a small body currently accreting dust or a brown dwarf (a body intermediate between stars and planets) between 5 and 37 times the mass of Jupiter. The observations, accepted for publication in the Astrophysical Journal, represent a significant step toward direct imaging and study of exoplanets (planets orbiting stars other than the Sun), and may bear on theories of planet and brown dwarf formation.
Young stars generally have material widely spread around them that organizes itself into a disk over time. Astronomers believe that this is where planets form. The new image, which is sensitive to the dust around the star but not starlight, shows a horseshoe-shaped structure orbiting AB Aurigae with two denser, brighter clumps of material in a ring around the star next to a darker area. This darker area, a structure relatively depleted of widespread material previously predicted in models of planet formation but never seen before, is thought to be the point at which material is coalescing into a planet or brown dwarf.
Further imaging of this area shows a barely visible spot dead center, a spot too bright to be light reflected off a formed planet but consistent with an object in the process of development that is accreting new material. The two brighter clumps, equidistant from the hole and presumably trailing and leading it in its orbit around the star, seem similar to the Trojan objects that orbit the Sun along with Jupiter. Such a structure has been predicted to form in disks where a planet is present, because of the gravitational interaction between the planet and the star it orbits.
“The deficit of material could be due to a planet forming and sucking material onto it, coalescing into a small point in the image and clearing material in the immediate surroundings. This would look like a hole in the disk,” says Oppenheimer. “We are seeing something happening in the disk that seems to be indicative of the formation of a small body, either a planet or a brown dwarf.”
Finding planets outside of our solar system is a new phenomenon. It is only in the last 15 years that nearly 300 extrasolar planets have been identified around distant stars. Most of these objects are more massive than Jupiter, orbit very close to their stars, and are identified by indirect methods such as the wobble created by the gravitational pull. None of the known exoplanets have yet been imaged or seen directly, because the light of a star overwhelms the faint glow of a nearby planet.
Oppenheimer and his colleagues circumvented this glare by attaching a coronagraph to a unique U.S. Air Force telescope on Maui, Hawaii. The telescope compensates for turbulence in the Earth’s atmosphere, permitting extremely high image quality from the ground. The Lyot Project coronagraph, built on a floating table in a clean-room optics lab at the Rose Center for Earth and Space at the Museum and named for the French astronomer who invented solar coronagraphy, blocks light from the center of the image of a nearby star to reveal faint objects around it. Stellar coronagraphs have been routinely used for several decades, but the Lyot Project’s is more precise and exceeds the resolution of the Hubble Space Telescope.
Oppenheimer’s team used additional polarization filters to detect even fainter objects much closer to the star than previously possible. Polarization selects light scattered off the disk, distinguishing it from the light of the star, which is not generally polarized. The technology enabled the team to see the disk of material around AB Aurigae with unprecedented sensitivity. Objects up to 100,000 times fainter than and just half an arcsecond from the star (an angle about 100 times finer than the human eye can discern) could be imaged. This is thousands of times better than other instruments.
AB Aurigae is well-studied because it is young, between one and three million years old, and can therefore provide information on how stars and objects that orbit them form. One unresolved question about planet formation is how the initial thick, gas-rich debris disk evolves into a thin, dusty region with planets. The observation of stars slightly older than AB Aurigae shows that at some point the gas is removed, but no one knows how this happens. AB Aurigae could be in an intermediate stage, where the gas is being cleared out from the center, leaving mainly dust behind.

“More detailed observations of this star can help solve questions about how some planets form, and can possibly test competing theories,” says Oppenheimer. “And if this object is a brown dwarf, our understanding of them must be revamped.”  Brown dwarfs have been found orbiting stars since a team (which included Oppenheimer) first discovered one in 1995, but they are not believed to form in circumstellar material.
The team contributing to this research included Douglas Brenner, Anand Sivaramakrishnan, and Remi Soummer of the Department of Astrophysics, AMNH; Sasha Hinkley and Neil Zimmerman of the Department of Astronomy, Columbia University; Jeffrey Kuhn and David Harrington of the Institute for Astronomy, University of Hawaii; James Graham and Marshall Perrin of the Department of Astronomy, University of California at Berkeley; James Lloyd of the Department of Astronomy, Cornell University; and Lewis Roberts of the Boeing Company, now at NASA’s Jet Propulsion Laboratory.
The research was funded in part by the National Science Foundation, NASA’s Terrestrial Planet Finder Program, and individual donors. The U.S. Air Force provided access to the AEOS telescope and significant financial support for the project.
This depleted region and the denser clumps near the ends of the white guide lines seem to indicate the formation of a small body within the depleted region. The scale of the image is indicated by the arrow, which corresponds to about 300 times the distance between the Earth and Sun. The orbit of a planet like Neptune, if it were orbiting this star, would be at the edge of the black circle on this scale.



Oamenii de ºtiinþã au descoperit cel mai mare meteorit care a lovit Marea Britanie

S-a izbit de pãmânt cu o vitezã de 61142 km/h ºi a explodat la impact cu forþa a 1000 de bombe nucleare.
Meteoritul a cãzut în nord-vestul Scoþiei în urmã cu 1,2 miliarde de ani. Totuºi, abia de curând, oamenii de ºtiinþã au descoperit punctul de impact, care mãsura aproape un kilometru în diametru ºi unde s-a format un crater de peste 12 kilometri lãrgime.
Ken Amor, de la Departamentul de Studii ale Pãmântului al Universitãþii Oxford, a declarat: "Este cea mai spectaculoasã dovadã a impactului unui meteorit în Insulele Britanice".


Un meteorit cãzut în Peru dã peste cap teoriile cercetãtorilor
Cercetãtorii au anunþat cã un meteorit care a cãzut în luna septembrie în Peru se deplasa mai repede ºi a lovit pamântul mai puternic decât se aºteptau.
Meteoritul, care a fãcut un crater de 15 metri, avea o structurã din rocã ºi ar fi trebuit sã se dezintegreze cu mult înainte de a atinge Pamântul, a declarat Peter Schultz, profesor la Universitatea Brown din Rhode Island.
În general, doar meteoriþii din metal ating suprafaþa Pamântului intacþi, sãpând un crater. Cei din rocã intrã în atmosferã, încetinesc ºi explodeazã, ceea ce poate forma o gaurã în sol, ca un puþ, dar nu un crater.
Acest meteorit s-a deplasat cu o vitezã de 40-50 de ori mai mare faþã de cea normalã ºi a aterizat pe terenul unui râu secat, gaura formatã umplându-se de apã subteranã.
Dupã Schultz, în urma cercetãrilor fãcute de echipa sa, ar trebui rediscutatã teoria lovirii planetelor de cãtre obiecte strãine.


În Spania au fost descoperite fosile umane vechi de 1,2 milioane de ani

Omul a apãrut pe continentul european cu mult mai mult timp înainte decât se credea pânã acum. Dovada în acest sens au adus-o paleoantropologii spanioli, care au publicat date privind descoperirea unor fosile umane vechi de aproximativ 1,2 milioane de ani.
Savanþii au descoperit într-o peºterã situatã în apropiere de oraºul Burgos, din nordul Spaniei, o mandibulã, câþiva dinþi ºi câteva unelte rudimentare din cremene. Aceste fosile au fost datate ca fiind mai vechi cu 400.000 de ani decât cele descoperite în apropiere cu 14 ani în urmã.
Ele sunt similare celor descoperite la Atapuerca în 1994 ºi aduc noi argumente în sprijinul ipotezei potrivit cãreia fiinþele umane apãrute în Africa au venit în Europa nu prin strâmtoarea Gibraltar, ci prin Orientul Mijlociu.
Mandibula descoperitã lângã Burgos seamãnã cu un fragment fosil similar din Georgia, datat cu circa 1,7 milioane de ani în urmã. Mai mult, ele duc la o nouã teorie: cãlãtoria strãmoºilor omului dinspre continentul negru spre celelalte regiuni ale lumii a început cu aproape douã milioane de ani în urmã, ºi nu cu doar 50.000, cum se credea.




Un craniu gãsit în România ar putea schimba teoriile despre omul de Neanderthal

Un craniu cu o vechime de 40.000 de ani, gãsit în Peºtera cu Oase din sud-vestul României, are atât trãsãturile omului modern, cât ºi pe cele ale unui om de Neanderthal. Craniul ar putea demonstra cã aceºtia ar fi putut interacþiona, înainte ca ultimul sã disparã, potrivit Reuters.
Dacã descoperirile vor fi confirmate, craniul va reprezenta cea mai veche descoperire a rãmãºiþelor unui om modern, în Europa.
Craniul are multe din trãsãturile unui om modern, dar este ºi un pic mai îndesat decât cei mai mulþi dintre aceºtia ºi are molarii superiori foarte mari, trãsãturã specificã mai ales celor de Neanderthal.
Studiul despre descoperire, publicat de revista "Proceedings of the National Academy of Sciences" (PNAS), vine în contextul unei dezbateri legate de douã ipoteze: Homo sapiens, omul modern, ºi-a omorât pur ºi simplu "verii" de Neanderthal sau Ei au interacþionat mai întâi.
Mulþi cercetãtori cred cã neanderthalienii au dispãrut din cauza schimbãrilor climatice sau din cauza competiþiei cu humanoizii moderni. Dar alþii considerã cã aceºtia s-au încruciºat cu nou-veniþii ºi au contribuit la tezaurul genetic al omului modern.


Sursa: NewsIn
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