October 21, 2007, 10:15 PM CT

Boosting the accuracy of Rosetta's Earth approach

CEST, the thrusters of ESA's comet chaser, Rosetta, were fired in a planned, 42-second trajectory correction manoeuvre designed to 'fine tune' the spacecraft's approach to Earth. Rosetta is now approaching Earth for its second planetary swing-by of 2007.

After passing Mars in April 2007, Rosetta is now approaching Earth for the second time - the third of four planetary swing-bys that provide fuel-saving gravitational assists enabling the spacecraft to ultimately reach and cross the orbit of comet 64P/Churyumov-Gerasimenko in 2014.

Rosetta's closest approach is predicted for 21:57 CET at a height of 5301 km over the Pacific Ocean and a speed of 45 000 km/h relative to the Earth. The third and last Earth swing-by will take place in November 2009.



Rosetta lines up

"We have a target trajectory for Earth swing-by and regular orbit determinations allow us to decide when to do a correction manoeuvre. Brief burns now allow us to optimise the orbit and make the swing-by more accurate, saving us a lot of precious fuel later on," said Andrea Accommazzo, Rosetta Spacecraft Operations Manager at ESOC. He confirmed that yesterday's manoeuvre results were as expected.

A second trajectory correction slot, on 1 November, may also be used depending on results of an orbit determination scheduled for 30 October......... Posted by: Sean      Read more         Source

October 21, 2007, 10:12 PM CT

Earth from Space: Birth of an iceberg

This animation, comprised of images acquired by Envisat's Advanced Synthetic Aperture Radar (ASAR) instrument, shows the breaking away of a giant iceberg from the Pine Island Glacier in West Antarctica. Spanning 34 km in length by 20 km in width, the new iceberg covers an area nearly half the size of Greater London.

The animation highlights the movement in the area between September 2006 and October 2007. The Pine Island Glacier is visible stretching from the right of the image to the centre. The tongue of Pine Island is shown moving inland between September 2006 and March 2007. Between April and May 2007, the detached iceberg in front of Pine Island moves significantly. Also in May 2007, a crack in Pine Island becomes visible. By October, the new iceberg has completely broken away.

Several different processes can cause an iceberg to form, or 'calve', such as action from winds and waves, the ice shelf grows too large to support part of itself or a collision with an older iceberg. Since Pine Island Glacier was already floating before it calved, it will not cause any rise in the world sea level.

Iceberg calving like this occurs in Antarctica each year and is part of the natural lifecycle of the ice sheet. A 34-year long study of the glacier has shown that a large iceberg breaks off roughly every 5-10 years. The last event was in 2001......... Posted by: Sean      Read more         Source

October 17, 2007, 8:17 PM CT

Heaviest Stellar Black Hole Discovered

Astronomers have located an exceptionally massive black hole in orbit around a huge companion star. This result has intriguing implications for the evolution and ultimate fate of massive stars.

The black hole is part of a binary system in M33, a nearby galaxy about 3 million light years from Earth. By combining data from NASA's Chandra X-ray Observatory and the Gemini telescope on Mauna Kea, Hawaii, the mass of the black hole, known as M33 X-7, was determined to be 15.7 times that of the Sun. This makes M33 X-7 the most massive stellar black hole known. A stellar black hole is formed from the collapse of the core of a massive star at the end of its life.

"This discovery raises all sorts of questions about how such a big black hole could have been formed," said Jerome Orosz of San Diego State University, lead author of the paper appearing in the October 18th issue of the journal Nature.

M33 X-7 orbits a companion star that eclipses the black hole every three and a half days. The companion star also has an uncommonly large mass, 70 times that of the Sun. This makes it the most massive companion star in a binary system containing a black hole.

"This is a huge star that is partnered with a huge black hole," said coauthor Jeffrey McClintock of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "Eventually, the companion will also go supernova and then we'll have a pair of black holes"......... Posted by: Sean      Read more         Source

October 12, 2007, 5:04 AM CT

Cassini on the trail of a runaway mystery

Researchers are on the trail of Iapetus' mysterious dark side, which seems to be home to a bizarre 'runaway' process that is transporting vaporised water ice from the dark areas to the white areas of the Saturnian moon.

This 'thermal segregation' model may explain a number of details of the moon's strange and dramatically two-toned appearance, which have been revealed in exquisite detail in images collected during Cassini's recent close fly-by of Iapetus.

Infrared observations from the fly-by confirm that the dark material is warm enough (approximately -146 degree C or 127 Kelvin) for very slow release of water vapour from water ice, and this process is probably a major factor in determining the distinct brightness boundaries.

"The side of Iapetus that faces forward in its orbit around Saturn is being darkened by some mysterious process," said John Spencer, Cassini scientist with the composite infrared spectrometer team from the Southwest Research Institute, USA.

Using multiple instruments on Cassini, researchers are piecing together a complex story to explain the countenance of Iapetus. But yet to be fully understood is where the black material is coming from. Is it native or from outside the moon? It has long been hypothesised that this material did not originate from within Iapetus but was derived from other moons orbiting at a much greater distance from Saturn in a direction opposite to Iapetus......... Posted by: Sean      Read more         Source

October 11, 2007, 10:59 PM CT

Drizzly mornings on Xanadu

Noted for its bizarre hydrocarbon lakes and frozen methane clouds, Saturn's largest moon, Titan, also appears to have widespread drizzles of methane, as per a team of astronomers at the University of California, Berkeley. New near-infrared images from ESO's Very Large Telescope (VLT) in Chile and the W. M. Keck Observatory in Hawaii show for the first time a nearly global cloud cover at high elevations and, dreary as it may seem, a widespread and persistent morning drizzle of methane over the western foothills of Titan's major continent, Xanadu.

In most of the Keck and VLT images, liquid methane clouds and drizzle appear at the morning edge of Titan, the arc of the moon that has just rotated into the light of the sun.

"Titan's topography could be causing this drizzle," said Imke de Pater, member of the team that made the discovery. "The rain could be caused by processes similar to those on Earth: moisture laden clouds pushed upslope by winds condense to form a coastal rain".

Lead author Mt dmkovics noted that only areas near Xanadu exhibited morning drizzle, and not always in the same spot. Depending on conditions, the drizzle could hit the ground or turn into a ground mist. The drizzle or mist seems to dissipate after local mid-morning, which, because Titan takes 16 Earth days to rotate once, is about three Earth days after sunrise. "Maybe only Xanadu has misty mornings," he said......... Posted by: Sean      Read more         Source

October 10, 2007, 5:56 PM CT

Isotope may add to Venus' greenhouse effect

Planetary researchers on both sides of the Atlantic have tracked down a rare molecule in the atmospheres of both Mars and Venus. The molecule, an exotic form of carbon dioxide, could affect the way the greenhouse mechanism works on Venus.

The discovery is being announced recently at the annual meeting of the American Astronomical Societys Division of Planetary Sciences in Orlando, Florida. Its presence could affect the way the greenhouse mechanism works on Venus.

The mystery began back in April 2006, soon after ESAs Venus Express arrived at the second planet in the Solar System.

A European team including members from France, Belgium and Russia lead by Jean-Loup Bertaux, Service d'Aeronomie du CNRS, France and Ann-Carine Vandaele, Institut d'Aeronomie Spatiale de Belgique, were using their Infrared Atmospheric Spectrometer (SOIR) instrument to measure solar occultations.

To do this, the instrument watches the Sun set behind Venus, allowing the researchers to study the way specific wavelengths of light are absorbed by the planets atmosphere. These wavelengths and the level of absorption then give away the identity and amount of gases in the atmosphere.

The team saw an unidentified signature at 3.3 micrometres in the mid-infrared region of the spectrum. It was conspicuous and systematic, increasing with depth in the atmosphere during the occultation, so we knew it was real, says Bertaux......... Posted by: Sean      Read more         Source

October 10, 2007, 4:41 AM CT

Knowing Origin of Cosmic Rays

Recent observations from NASA and Japanese X-ray observatories have helped clarify one of the long-standing mysteries in astronomy -- the origin of cosmic rays.

Outer space is a vast shooting gallery of cosmic rays. Discovered in 1912, cosmic rays are not actually rays at all; they are subatomic particles and ions (such as protons and electrons) that zip through space in all directions at near-light speed, with energies tens of thousands of times greater than particles produced in Earth's largest particle accelerators. Cosmic rays incessantly bombard Earth, smashing into the atoms and molecules high up in the atmosphere, and producing cascades of secondary particles that reach the surface.

Since the 1960s researchers have pointed to supernova remnants -- the tattered, gaseous remains of supernovae -- as the breeding ground of most cosmic rays. These remnants expand into the surrounding interstellar gas, an energetic interaction that produces a shock front containing magnetic fields that can accelerate charged particles to enormous energies, producing cosmic rays.

As per theory, charged subatomic particles bounce like pinballs around the shock front. They pick up speed until they move nearly the speed of light. Last year, observations from NASA's Chandra X-ray Observatory suggested that electrons are being accelerated rapidly (as fast as theory allows) to high energies in the supernova remnant Cassiopeia A......... Posted by: Sean      Read more         Source

October 9, 2007, 9:02 PM CT

Pluto-Bound New Horizons Sees Changes

The voyage of NASA's Pluto-bound New Horizons spacecraft through the Jupiter system earlier this year provided a bird's-eye view of a dynamic planet that has changed since the last close-up looks by NASA spacecraft.

New Horizons passed Jupiter on Feb. 28, riding the planet's gravity to boost its speed and shave three years off its trip to Pluto. It was the eighth spacecraft to visit Jupiter - but a combination of trajectory, timing and technology allowed it to explore details no probe had seen before, such as lightning near the planet's poles, the life cycle of fresh ammonia clouds, boulder-size clumps speeding through the planet's faint rings, the structure inside volcanic eruptions on its moon Io, and the path of charged particles traversing the previously unexplored length of the planet's long magnetic tail.

"The Jupiter encounter was successful beyond our wildest dreams," says New Horizons Principal Investigator Alan Stern, of NASA Headquarters, Washington. "Not only did it prove out our spacecraft and put it on course to reach Pluto in 2015, it was a chance for us to take sophisticated instruments to places in the Jovian system where other spacecraft couldn't go, and to return important data that adds tremendously to our understanding of the solar system's largest planet and its moons, rings and atmosphere"......... Posted by: Sean      Read more         Source

October 4, 2007, 9:52 PM CT

Scientists 'Weigh' Tiny Galaxy Halfway Across Universe

A tiny galaxy, nearly halfway across the universe, the smallest in size and mass known to exist at that distance, has been identified by an international team of researchers led by two from the University of California, Santa Barbara.

The researchers used data collected by NASA's Hubble Space Telescope and the W. M. Keck Observatory in Hawaii. This galaxy is about half the size, and approximately one-tenth the "weight" of the smallest distant galaxies typically observed, and it is 100 times lighter than our own Milky Way.

The findings would be reported in the December 20, 2007 issue of the Astrophysical Journal. The article is now available on-line at http://arxiv.org/abs/0710.0637.

"Even though this galaxy is more than six billion light years away, the reconstructed image is as sharp as the ordinary ground-based images of the nearest structure of galaxies, the Virgo cluster, which is 100 times closer to us," said lead author Phil Marshall, a postdoctoral fellow at UC Santa Barbara.

Second author Tommaso Treu, assistant professor of physics at UCSB, explained that the imaging is made possible by the fact that the newly discovered galaxy is positioned behind a massive galaxy, creating an "Einstein ring." The matter distribution in the foreground bends the light rays in much the same way a magnifying glass does. By focusing the light rays, this gravitational lensing effect increases the apparent brightness and size of the background galaxy by more than a factor of 10......... Posted by: Sean      Read more         Source

October 4, 2007, 5:05 AM CT

Conditions 'Just Right' for Building an Earth

An Earth-like planet is likely forming 424 light-years away in a star system called HD 113766, say astronomers using NASA's Spitzer Space Telescope.

Researchers have discovered a huge belt of warm dust - enough to build a Mars-size planet or larger - swirling around a distant star that is just slightly more massive than our sun. The dust belt, which they suspect is clumping together into planets, is located in the middle of the system's terrestrial habitable zone. This is the region around a star where liquid water could exist on any rocky planets that might form. Earth is located in the middle of our sun's terrestrial habitable zone.

At approximately 10 million years old, the star is also at just the right age for forming rocky planets.

"The timing for this system to be building an Earth is very good," says Dr. Carey Lisse, of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. "If the system was too young, its planet-forming disk would be full of gas, and it would be making gas-giant planets like Jupiter instead. If the system was too old, then dust aggregation or clumping would have already occurred and all the system's rocky planets would have already formed."

As per Lisse, the conditions for forming an Earth-like planet are more than just being in the right place at the right time and around the right star - it's also about the right mix of dusty materials......... Posted by: Sean      Read more         Source