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Powerful nearby supernova caught 10 years later

...astronomers have finally identified one of the nearest supernovae of the last 25 years, over a decade after it exploded...

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Hibernating magnetar springs to life

...a mysterious celestial object that emitted 40 visible light flashes before disappearing again could be a missing link in the family of neutron stars...

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A smart look at the peak of eternal light

...new three-dimensional images taken by SMART-1's AMIE camera show the ‘peak of eternal light’ in new light...

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STS-120 day 2 highlights

Flight Day 2 of Discovery's mission focused on heat shield inspections. This movie shows the day's highlights.

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STS-120 day 1 highlights

The highlights from shuttle Discovery's launch day are packaged into this movie.

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STS-118: Highlights

The STS-118 crew, including Barbara Morgan, narrates its mission highlights film and answers questions in this post-flight presentation.

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 Mission film

STS-120: Rollout to pad

Space shuttle Discovery rolls out of the Vehicle Assembly Building and travels to launch pad 39A for its STS-120 mission.

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Dawn leaves Earth

NASA's Dawn space probe launches aboard a Delta 2-Heavy rocket from Cape Canaveral to explore two worlds in the asteroid belt.

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Dawn: Launch preview

These briefings preview the launch and science objectives of NASA's Dawn asteroid orbiter.

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Mars polar cap mystery solved
BY DR EMILY BALDWIN
ASTRONOMY NOW

Posted: September 30, 2008

The Martian weather system and a giant impact crater could explain why the residual ice cap at the south pole of Mars is offset by several degrees.

Mars has frozen polar caps just like the Earth, but the Martian caps are made of carbon dioxide ice as well as water ice. During the southern hemisphere's summer much of the ice cap sublimates, that is, turns straight from solid ice to gas, leaving behind what is known as the residual polar cap. But until recently, scientists had been baffled as to why this residual cap is offset from the south pole by 3-4 degrees, when the northern cap lies symmetrically across the north pole.

Thanks to ESA's Mars Express, new information is now available to explain things in more detail. The Planetary Fourier Spectrometer (PFS) instrument was used to measure the temperature of the Martian atmosphere from the ground up to an altitude of 50 kilometres in the southern hemisphere for over half a Martian year.

This is a mosaic of images taken by the Mars Express’s Visible and Infrared Mineralogical Mapping Spectrometer, OMEGA. It shows the residual south polar cap at the end of northern winter on the Red Planet. The cap appears clearly asymmetric, its centre being displaced by 3° from the geographic pole. Image: ESA/ Image Courtesy of F. Altieri (IFSI-INAF) and the OMEGA team.

"It is not a straightforward process,” says Marco Giuranna of the Istituto di Fisica dello Spazio Interplanetario CNR (IFSI), Italy. ”We found that two regional weather systems developed from mid-fall through the winter."

These weather systems are derived from strong eastward winds that characterise the Martian atmospheric circulation at mid-latitudes. The winds blow straight into the Hellas Basin, a 2,300 kilometre wide and 7 kilometre deep impact crater, which deflects the winds, rerouting them towards the south pole. Such winds are known as Rossby waves on the Earth, and are essentially large scale meanders in high-altitude winds, such as the jet stream. On Mars, this action creates a strong low-pressure system in the western hemisphere and a high-pressure system in the eastern hemisphere, both near the south pole.

The Mars Express scientists found that the temperature of the low-pressure system permits carbon dioxide gas to condense and fall as snow, which builds up on the ground. In the high-pressure system, the conditions are too warm for snow, so only ground frost forms, resulting in two different mechanisms to build the south polar ice cap. Because the regions with extensive snow cover reflect more light than the larger and rougher frost grains, it is the frosty zones that sublimate more rapidly in the summer months. This gives rise to the eastern area of frost disappearing completely, explaining why the residual cap is not symmetrically placed around the south pole.

"This has been a Martian curiosity for many years," says Giuranna. A curiosity that has, thanks to Mars Express, now been solved.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
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Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
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3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
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