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Possible salty ocean hidden in depths of Saturn moon

...NASA's Cassini spacecraft has provided strong evidence that Saturn's moon Enceladus harbours a salty ocean below its icy shell, a discovery that offers exciting possibilities in the search for extraterrestrial life...

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Galaxies come of age in cosmic blobs

...Growing supermassive black holes and bursts of star formation have been discovered in cosmic blobs - immense reservoirs of hydrogen gas located in the early Universe - representing the coming of age of galaxies...

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Cosmic rays efficiently accelerated by exploded stars

...astronomers have shown that cosmic rays from the Milky Way are very efficiently accelerated in the remnants of exploded stars...

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Video archive

STS-120 day 2 highlights

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


STS-120 day 1 highlights

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


STS-118: Highlights

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

 Full presentation
 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.


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.

 Full coverage

Dawn: Launch preview

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

 Launch | Science

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Stuck rover exposes fresh clues on Martian environment



Posted: 26 June, 2009

NASA’s plucky Mars Exploration Rover Spirit, which is still stuck in a patch of soil, has been taking advantage of the situation to learn more about the planet’s environmental history.

The sand trap, dubbed Troy, has been holding the rover hostage since April, with Spirit’s rotating wheels digging more than hub deep into the sand. Engineers have prepared test escape maneuvers at NASA’s Jet Propulsion Laboratory in order to help free the stranded rover. Not to be beaten by the situation, Spirit is studying the composition of the soil while it waits further instruction on how to leave the sandpit.

The situation underneath the rover's belly, as photographed by Spirit. Image: NASA/ JPL/USGS.

“By serendipity, Troy is one of the most interesting places Spirit has been,” says Ray Arvidson of Washington University and deputy principal investigator for the science payloads on Spirit and its twin rover, Opportunity. “We are able here to study each layer, each different colour of the interesting soils exposed by the wheels.”

As Spirit’s wheels churned the soil, it exposed coloured sandy materials and a miniature cliff of cemented sands in tan, yellow, white and red. Scientists analysing the data suggest that differences in colours may come from differences in the hydration states of iron sulfates.

“The layers have basaltic sand, sulfate-rich sand and areas with the addition of silica-rich materials, possibly sorted by wind and cemented by the action of thin films of water,” says Arvidson. “We’re still at a stage of multiple working hypotheses. This may be evidence of much more recent processes than the formation of Home Plate. Or is Home Plate being slowly stripped back by wind, and we happened to stir up a deposit from billions of years ago before the wind got to it?”

The soft soil exposed when Spirit's wheels dug into a patch of ground dubbed "Troy" exhibit variations in hue visible in this image, in which the colours have been stretched to emphasize the differences. The two rocks near the upper right corner of this view are each about 10 centimetres long and 2 to 3 centimetres wide. Image: NASA/JPL-Caltech/Cornell University.

The analysis was further enhanced by the fact a dust storm recently gave Spirit’s solar panels a spring clean. “The exceptional amount of power available from cleaning of Spirit’s solar arrays by the wind enables full use of all of the rover’s science instruments,” says Richard Moddis of the Johnson team. “If your rover is going to get bogged down, it’s nice to have it be at a location so scientifically interesting.”

The mock-up Martian soil combines diatomaceous earth, powdered clay and play sand. Engineers are preparing several tons of the mixture into contours to match Troy. A test rover will be put through its paces to find the safest way to proceed on Mars, a problem magnified by Spirit’s lame right-front wheel.

“With the improved power situation, we have the time to explore all the possibilities to get Spirit out,” says JPL’s John Callas, project manager for Spirit and Opportunity. “We are optimistic. The last time Spirit spun its wheels, it was still making progress. The ground testing will help us avoid doing things that could make Spirit’s situation worse.”