- Galaxy Cluster Smiles at You
- Opportunity Rover Nearing Marathon Achievement
- Comet 67P/Churyumov-Gerasimenko 'Shedding Its Skin' in the Heat of the South
- Cassini Spacecraft Unveils the Chemical Model of Enceladus' Ocean
|
Posted: 10 Feb 2015 02:55 PM PST
In the center of this image, taken with the NASA/ESA Hubble Space Telescope, is the galaxy cluster SDSS J1038+4849 — and it seems to be smiling. You can make out its two orange eyes and white button nose. In the case of this “happy face”, the two eyes are very bright galaxies and the misleading smile lines are actually arcs caused by an effect known as strong gravitational lensing. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.
Galaxy clusters are the most massive structures in the Universe and exert such a powerful gravitational pull that they warp the spacetime around them and act as cosmic lenses which can magnify, distort and bend the light behind them. This phenomenon, crucial to many of Hubble’s discoveries, can be explained by Einstein’s theory of general relativity.
In this special case of gravitational lensing, a ring — known as an Einstein Ring — is produced from this bending of light, a consequence of the exact and symmetrical alignment of the source, lens and observer and resulting in the ring-like structure we see here.
Hubble has provided astronomers with the tools to probe these massive galaxies and model their lensing effects, allowing us to peer further into the early Universe than ever before. This object was studied by Hubble’s Wide Field and Planetary Camera 2 (WFPC2) and Wide Field Camera 3 (WFC3) as part of a survey of strong lenses.
Credit: spacetelescope.org
 | ||
|
Posted: 10 Feb 2015 01:59 PM PST
.jpg "In February 2015, NASA's Mars Exploration Rover Opportunity is approaching a cumulative driving distance on Mars equal to the length of a marathon race. This map shows the rover's position relative to where it could surpass that distance. Image Credit: NASA/JPL-Caltech/Univ. of Arizona")
NASA's Mars Exploration Rover Opportunity is nearing a location on Mars at which its driving distance will surpass the length of a marathon race. A drive on Feb. 8, 2015, put the rover within 220 yards (200 meters) of this marathon accomplishment. An Olympic marathon is 26.219 miles (42.195 kilometers). Opportunity is headed for a portion of the western rim of Endeavour Crater where observations by NASA's Mars Reconnaissance Orbiter have detected multiple types of clay minerals. These minerals are indicative of an ancient wet environment where water was more neutral rather than harshly acidic. More than six months ago, the rover team informally named that destination "Marathon Valley," having estimated what the odometry would total by the time Opportunity gets there.
"When Opportunity was in its prime mission 11 years ago, no one imagined this vehicle surviving a Martian winter, let alone completing a marathon on Mars," said Mars Exploration Rover Project Manager John Callas of NASA's Jet Propulsion Laboratory, Pasadena, California. "Now, that achievement is within reach as Opportunity approaches a strategic science destination. What's most important about the longevity and driving distance the mission keeps extending are not numerical thresholds, but the wealth of scientific information returned about Mars, made possible by these feats."
Before driving Opportunity into Marathon Valley, the team plans to use the rover for observations of an impact crater called "Spirit of Saint Louis Crater," at the entrance to the valley.
The team is operating Opportunity in a mode that avoids use of the rover's flash memory. In this mode, data gathered during each Martian day are stored in volatile memory and transmitted to an orbiter before the rover's overnight, energy-conserving "sleep." NASA orbiters Mars Odyssey and Mars Reconnaissance Orbiter relay the rover data to Earth.
Opportunity engineers plan in coming weeks to upload a software revision they have developed to enable resuming use of non-volatile flash memory. It is designed to restore Opportunity's capability to store data overnight or longer, for transmitting later.
During its original three-month prime mission, beginning after landing on Jan. 25, 2004, UST (Jan. 24, 2004, PST) Opportunity drove 0.48 mile (771.5 meters). Its twin, NASA's Mars Exploration Rover Spirit, landed three weeks earlier and covered 0.39 mile (635 meters) in its three-month prime mission. Both Spirit and Opportunity have returned compelling evidence about wet environments on ancient Mars. Spirit's mission ended in 2010. Since 2011, Opportunity has been investigating the western rim of Endeavour, a crater that is 14 miles (22 kilometers) in diameter.
The rover climbed to its highest elevation on the Endeavour rim on Jan. 6, 2015, reaching a point about 440 feet (135 meters) above the local plains. It has driven about 440 yards (400 meters) since then, mainly southward toward the entrance to Marathon Valley.
JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for NASA's Science Mission Directorate in Washington.
Credit: NASA
 | ||
|
Posted: 10 Feb 2015 12:40 PM PST
Comet 67P/Churyumov-Gerasimenko could lose up to 20 metres of surface material from its previously unilluminated south side when it heats up, starting in May 2015. The increasing heat as the comet approaches the Sun will trigger this 'diet', during which gases and solid materials will be ejected into space. Horst Uwe Keller and Stefano Mottola from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), who have estimated the possible erosion of 67P using data acquired by the Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS), suggest that the northern hemisphere will lose much less mass. Their model reveals that, in its orbit around the Sun, the comet will lose a large part of its surface – particularly on its south side – during a brief but very intense 'summer'. "The comet sheds its surface almost constantly, revealing fresh material on its surface, which has not yet been aged by cosmic radiation," said Ekkehard Kührt, who leads the Rosetta mission science team at DLR.
It takes Comet 67P/Churyumov-Gerasimenko about six Earth years and five months to complete one orbit around the Sun. Its highly elliptical orbit takes it far away from the Sun for long periods of time. the next closest approach to the Sun (perihelion) will occur in August 2015. The inclination of comet's rotational axis – tilted 53 degrees with respect to its orbital plane – compared to just 23 degrees for Earth – means that the seasons in its two hemispheres are dramatically different. The northern hemisphere has a long, yet not particularly intense summer. The southern hemisphere summer will last for 10 months, but as it will occur during perihelion, it will be particularly severe. The Rosetta orbiter and its lander, Philae, will have an excellent view of the comet as it awakens and ejects gases and dust into space.
To estimate the loss of cometary material, the OSIRIS scientists used a surface model of the comet and divided it into 100,000 small triangles. It was necessary to consider the existence of shaded areas, for example in the craters, and that the rugged mountain walls reflect solar radiation onto nearby slopes, reinforcing it. "Our model calculation assumes that the water ice in the active regions is covered by a very porous, thin layer of dust," said Keller. In addition, the researchers assume in their simulation that about four times more dust than ice being ejected into space.
"The result is that the southern side – not currently illuminated by the Sun and still new territory for the scientists – will lose up to 20 metres of its surface during this hot summer," said Mottola. "In the northern hemisphere, the outlook is quite different – only the peaks and cliffs will lose up to 10 metres." The current, particularly, active narrow region between the two comet lobes is calculated to be poorly lit during the overall orbit, and thus only moderately active generally.
The Philae lander will be able to take advantage of the summer; at its location near the equator, it may receive sufficient sunlight to 'wake up' from its current hibernation state. This might occur as early as March, but the probability that the Lander Control Center will resume contact and be able to send commands will be greatest in May.
Credit: DLR
 | ||
|
Posted: 10 Feb 2015 10:50 AM PST
Saturn’s moon Enceladus is one of the most fascinating places in the Solar System, with its huge geysers of water vapor erupting from cracks in the surface at the south pole. The massive plumes are now thought to originate in a subsurface ocean or sea of salty liquid water, similar perhaps to an underground ocean on Jupiter's moon Europa. Now, new analysis is providing a more detailed look at the chemical makeup of this unique alien environment and its potential to support life. Observational data from NASA/ESA Cassini spacecraft were used to obtain a chemical model of ocean water on Enceladus. The model indicates that Enceladus' ocean is a Na-Cl-CO3 solution with an alkaline pH of ~11-12. The dominance of aqueous NaCl is a feature that Enceladus' ocean shares with terrestrial seawater, but the ubiquity of dissolved Na2CO3 suggests that soda lakes are more analogous to the Enceladus ocean.
This may sound like a rather inhospitable environment, but at least on Earth, that is not true. Such high-salinity soda lakes host complex ecosystems with a rich variety of prokaryotes (bacteria and archaeabacteria), eukaryotic algae, protists, and fungi. Brine shrimp and fish have also been found in some of the lesser alkaline soda lakes. Some species, known as alkaliphiles, have adapted specifically to the soda lakes and would be unable to live in a more neutral-pH environment.
The high pH implies that the hydroxide ion should be relatively abundant, while divalent metals should be present at low concentrations owing to buffering by clays and carbonates on the ocean floor. The high pH is interpreted to be a key consequence of serpentinization of chondritic rock, as predicted by prior geochemical reaction path models; although degassing of CO2 from the ocean may also play a role depending on the efficiency of mixing processes in the ocean. Serpentinization leads to the generation of H2, a geochemical fuel that can support both abiotic and biological synthesis of organic molecules such as those that have been detected in Enceladus' plume.
Serpentinization and H2 generation should have occurred on Enceladus, like on the parent bodies of aqueously altered meteorites; but it is unknown whether these critical processes are still taking place, or if Enceladus' rocky core has been completely altered by past hydrothermal activity. The high pH also suggests that the delivery of oxidants from the surface to the ocean has not been significant, and the rocky core did not experience partial melting and igneous differentiation. On the other hand, the pH is compatible with life as we know it; life on Earth may have begun under similar conditions, and serpentinites on Earth support microbial communities that are centered on H2 that is provided by water-rock reactions.
Credit: arxiv.org, americaspac
 |
댓글 없음:
댓글 쓰기