Data from a ESA/NASA spacecraft has provided new information that may explain why the Sun's upper atmosphere is heated to temperatures of million degrees, far warmer than its lower layers.
     Solar astronomers using data from the Solar and Heliospheric Observatory (SOHO) believe that the Sun's powerful magnetic fields may be heating the gas in the solar corona, explaining why its temperature is in the millions of degrees while the visible surface of the Sun is only 6,000 degrees Celsius (11,000 degrees Fahrenheit).
     "We now have direct evidence for the upward transfer of magnetic energy from the Sun's surface toward the corona above," said Dr. Alan Title of the Stanford-Lockheed Institute for Space Research in Palo Alto, California. "There is more than enough energy coming up from the loops of the 'magnetic carpet' to heat the corona to its known temperature."
     SOHO observed variations in the visible surface, or photosphere, of the Sun caused by variations in the magnetic field at the surface, something Title termed the "Sun's Magnetic Carpet". The magnetic field observations showed tens of thousands of small concentrations, each with a north and south magnetic pole.
     The concentrations featured magnetic field lines than looped high into the corona while going between the north and south magnetic poles of each concentration. The strong electric currents flowing through these magnetic loops are believed to be the heating source for the corona. Each loop contains as much energy as a hydroelectric power dam, like Hoover Dam, generates in one million years.
     Title noted that the individual concentrations often appear and disappear in as little as 40 hours. "It's very hard to understand how such a short-lived effect could be driven by the magnetic dynamo layer that is over 100,000 miles beneath the surface of the Sun," he said. "This may be evidence that unknown processes are at work in or near the solar surface that continuously form these loops all over the Sun."
     The corona, as bright as the full Moon but only visible to the naked eye only during a total solar eclipse, had puzzled astronomers since its temperature was first measured 55 years ago. The high temperature appeared to violate thermal laws that prevent thermal energy from traveling from cooler to warmer areas.

A fresh volcanic deposit, the size of Arizona, has been discovered on Io by the Galileo spacecraft, evidence for the continuing volcanic activity on the innermost of Jupiter's four Galilean satellites.
     Images of a region of Io taken in September show a large, dark deposit, likely the deposit of a volcanic eruption, that did not appear in images of the same region taken in April. The region, named Pillan Patera after a South American god of thunder, shows up in the September images as a dark circular region about 415 km (250 mi.) in diameter.
     In addition, an active plume over Pillan Patera was observed by Galileo and the Hubble Space Telescope in June, and infrared astronomers reported an intense hot spot in the same area.
     "This is the largest surface change on Io observed by Galileo during its entire two-year tour of the Jovian system," said Dr. Alfred McEwen of the University of Arizona. McEwen is a member of the Galileo imaging team.
     Noting the dark color of the new deposit, McEwen said, "most of the volcanic plume deposits on Io show up as white, yellow or red due to sulfur compounds. However, this new deposit is gray, which tells us it has a different composition, possibly richer in silicates than the other regions."
     "Io is probably primarily composed of silicates, which is the type of volcanic rock found on Earth, " McEwen added, "but the extreme volcanism of Io may have led to the creation of silicate compositions that are unusual on Earth."
     Galileo, which took the Io images while making close flybys of other moons, will enter a new phase of its mission next month. The two-year regular mission comes to an end December 7. At that time an extended mission, dubbed the Galileo Europa Mission (GEM), will run for the next two years.
     The GEM features eight flybys of Europa, four of Callisto, extended studies of Jupiter's atmosphere, and, near the end of the two-year mission, two close flybys of Io, the first since Galileo arrived in 1995. Io has been avoided to date because the powerful radiation environment in its vicinity could damage the spacecraft.
     Galileo performed a flyby of Europa, the last of its regular mission, November 6. A glitch in the Deep Space Network radio antenna in Madrid, Spain, communicating with Galileo six minutes before closest approach meant that some radio science data was lost during the flyby, although other data was stored on the spacecraft's tape recorders. Future Europa flybys should recover the lost data.

One group of astrophysicists has discovered a halo of gamma rays surrounding the galaxy which may be evidence of missing, "dark" matter there, while another group's observations of a black hole have provided another confirmation for Einstein's theory of general relativity.
     A group led by Dave Dixon of the University of California Riverside used data from the Compton Gamma Ray Observatory to detect emissions of gamma rays in a halo around the Milky Way galaxy. The gamma rays, according to Dixon, are not coming from a compact source but appear to be well-distributed throughout the halo.
     "The reason this is interesting is that there isn't any obvious source for these gamma-rays, based on astronomical observations in other wavelengths of light," Dixon said. "That is, as far as we can tell using other telescopes, the space around our galaxy is rather empty of the kinds of things which we would expect to generate gamma rays in the observed brightness distribution."
     Dixon, working with Dieter Hartmann of Clemson University and Eric Kolaczyk of the University of Chicago, said there are three major possible causes for these gamma rays. The gamma rays may be the result of the collision of cosmic rays with lower-energy photons, a number of rapidly-spinning neutron stars, or emission by dark matter.
     The dark matter hypothesis garnered the most attention. "If you look at the wide distribution of where the gamma-rays are coming from, it is very suggestive of a dark matter distribution," Dixon said.
     He cautioned, though, that the cause is still a "wide-open question" with no solution in the foreseeable future. "The only way to nail this thing down is to get better data with a more advanced gamma-ray telescope such as GLAST [Gamma-ray Large Area Space Telescope, a proposed future mission], or to find some smoking gun which can be observed in another wavelength of light."
     Another group, led by MIT astrophysicist Wei Cui, used the Rossi X-Ray Timing Explorer (RXTE) to study the X-ray emissions by matter orbiting around a suspected black hole. They discovered a regular variation in the X-ray pattern, caused by a perturbation in the orbit of the X-ray emitting matter.
     The perturbation, or precession, occurs when orbit shifts around a black hole, which is in turn caused by the movement of the matter itself, shifting space-time as it orbits, a process known as "frame dragging". The observation's by Cui's team was the first evidence of frame dragging seen around a black hole and the first confirmation in general of this phenomenon, predicted by Einstein's theory of General Relativity.
     "If our interpretation is correct, it could demonstrate the presence of frame dragging near spinning black holes," said Cui. "This observation is unique because Einstein's theory has never been tested in this way before."
     A team of Italian astronomers, also using data from the RXTE, also found evidence of frame dragging around a neutron star. their results were reported at the same Colorado conference where Cui announced his findings.