US spacecraft lands safely at Mars north pole

10:29 AEST Mon May 26 2008
59 minutes ago
Reuters

A small science probe blazed through the salmon-colored skies of Mars today, touching down on a frozen desert at the planet's north pole to search for water and assess conditions for sustaining life, NASA officials said.

The spacecraft, known as Phoenix, landed at 9.53 (AEST) after a do-or-die plunge through the planet's thin atmosphere. It marked the first time that a spacecraft had successfully landed at one of the planet's polar regions.

Pulled by Mars' gravity, Phoenix was tearing along at 20,400km/h before it entered the atmosphere, which slowed the craft so it could pop out a parachute and fire thruster rockets to gently float to the ground.

"It's down, baby, it's down!," yelled a NASA flight controller, looking at signals from Mars showing that Phoenix had landed.

Scientists found in 2002 that Mars' polar regions have vast reservoirs of water frozen beneath a shallow layer of soil. Phoenix was launched Aug. 4, 2007, to sample the water and determine if the right ingredients for life are present.

NASA attempted a landing on Mars' south pole in 1999, but a problem during the final minutes of descent ended the mission.

The U.S. space agency canceled its next Mars lander but successfully dispatched two rovers, Spirit and Opportunity, to the planet's equatorial region to search for signs of past surface water.

Phoenix was created out of spare parts from the failed Polar Lander mission and the mothballed probe. Unlike the rovers, Phoenix will not be bouncing to the planet's surface in airbags, which are not suitable for larger spacecraft.

Instead, like the 1970s-era Viking probes and the failed Polar Lander mission, it uses a jet pack to lower itself to the ground and fold-out legs to land on.

"We haven't landed successfully on legs and propulsive rockets in 32 years," said NASA's space sciences chief Ed Weiler.

"When we send humans there, women and men, they're going to be landing on rockets and legs, so it's important to show that we still know how to do this."

Read more at NASA news site
http://www.nasa.gov/news/index.html

Nasa's Phoenix lander has unearthed compelling evidence of ice on Mars, mission scientists believe.

Chunks of a bright material found in a trench dug by the craft have disappeared over four Martian days, suggesting they have vapourised.

While digging in another trench, the lander's arm connected with a hard surface at the same depth.

The finds lend weight to suggestions water is locked up in a permafrost layer close to the planet's surface.

Missing matter

"It must be ice," said Dr Peter Smith, Phoenix's principal investigator, who is based at the University of Arizona, Tucson.

"These little clumps completely disappearing over the course of a few days, that is perfect evidence that it's ice," he said.

"There had been some question whether the bright material was salt," he added.

"Salt can't do that." "


M. Sufilight

http://news.bbc.co.uk/1/shared/spl/hi/pop_ups/08/sci_nat_enl_1214080241/html/1.stm

"Scientists have figured out the mysterious white substance unearthed by NASA's Phoenix lander on Mars. It's frozen water.

The breakthrough came last week when Phoenix's stereo camera caught the substance in the act of disappearing. Bathed in martian sunlight for four days, the white substance sublimated — i.e., it transformed from solid to gas without passing through the liquid state.

This is how water behaves on Mars.... Some readers have asked, how do we know the white substance is not frozen CO2 (dry ice) instead of frozen water? Answer: Phoenix's landing site is too warm for dry ice. The average daily temperature is about -70 F while dry ice requires temperatures lower than about -109 F."

Phoenix team prepares for in-depth soil studies
23:33 20 June 2008
NewScientist.com news service
Maggie McKee

Bolstered by images showing water ice in the Martian soil, Phoenix team members are cracking on with plans to analyse the soil in-depth. The composition of the first soil sample delivered to an onboard oven may be known within days, and the lander is already attempting to collect a second sample.

On Thursday, images received from Phoenix showed that several clumps of soil that had appeared in an earlier image of a trench called Dodo-Goldilocks had apparently vaporised over the course of four days.

"Something on the order of eight things [are] missing," team member Mark Lemmon said at a press briefing on Friday. "We believe these things are water ice and in the process of sitting out in the cold but very dry atmosphere, they sublimated."

Patches of hard white material also faded over the four-day period. That suggests the white material is also water ice – and not salt or other materials, the team says.

Salt would not make such a disappearing act, and it is currently too warm on the northern plains of Mars for carbon dioxide ice to exist for any length of time. "It would be the equivalent of having water ice on a 140° day on Earth," Lemmon said. "It's not going to be there very long – not long enough to take its picture."

The team had expected water ice to exist about 5 centimeters below the surface, where it was found, since NASA's Mars Odyssey orbiter had previously found evidence of widespread subsurface ice around the poles.

Habitable environment

Also, when Phoenix peeked below its body shortly after landing, it saw a bright, hard surface – thought to be ice that had been exposed by its landing thrusters.

Discovering that similar patches of material are water ice is a great relief for the team. "One of our great fears was that we'd see ice – for example, under the lander – and the arm wouldn't be able to reach it," said principal investigator Peter Smith of the University of Arizona in Tucson, US.

What's next for the lander? "Finding out what is mixed in with the ice and to what extent it's a habitable environment," Lemmon said.

That means trying to find clues that liquid water occasionally exists at the site – possibly as a result of periodic changes in the planet's tilt that warm up the poles. Salts might provide such clues, since they might be left behind by the evaporation of liquid water, even in small amounts.

Extreme heat

Clues about whether the environment was ever habitable would come from organic materials – molecules containing carbon. These molecules would provide food for any life in the region, and would "have to be there if you're going to have a habitable zone on Mars".

The team plans to look for such signs in soil samples taken from a variety of depths – beginning around the surface, then from lower down, around the boundary between soil and ice.

Soil collected from the surface at one trench is already being studied in one of eight ovens on an instrument called TEGA (Thermal Evolved Gas Analyzer). The soil fell into oven number 4 more than a week ago, but some software problems – now in the process of being fixed – caused delays in the experiment. As early as today, mission members may receive the results from that sample, though it is likely to take several more days to analyse them.

TEGA heats samples to 1000 °C to study their composition. It takes advantage of the fact that hydrated minerals – which have been altered by water in the past – thermally decompose, or change into another form, when heated to a given temperature.

Second sample

This decomposition either gives off or takes in heat – changes that TEGA can study to decode the soil's minerals, says team member Ray Arvidson of Washington University in St Louis, Missouri, US.

TEGA can also study the composition of any volatiles, such as ice, in the sample, which will vaporise when heated. The resulting gases can be separated according to their mass inside TEGA.

The soil in oven 4 is not expected to contain ice, however, since it sat on top of the oven for several days before falling in, allowing any ice it contained to sublimate away. But in the future, mission planners are hoping to deliver icy soil samples to TEGA ovens in less than 30 minutes, which should be fast enough to prevent the ice from vaporising.

Today, the lander is also trying to dig up soil to put into a second TEGA oven, called oven number 5. It is collecting the soil sample, dubbed "Rosy Red," from the surface of a polygonal section of soil dubbed "Cheshire Cat".

Hard ice

It began collecting the soil after digging a nearby trench called "Snow White 2". About 5 cm below the surface of Snow White 2, the lander had to stop digging because it reached something too hard to dig through.

That hard material "looks like an ice layer and feels like an ice layer", Arvidson said. Curiously, it is more bluish than the white ice layer seen in the Dodo-Goldilocks trench. "We've got hard layers that are different – we hope to learn a lot from those differences," said Lemmon.

At some point, the team hopes to return to Snow White 2 to try dig into the ice a bit with various instruments on its robotic arm, including a scraper and a motorised grinder called a rasp. But the team does not expect to dig very far into the ice. "Ice at -80 or -90 °C is as hard as a table top," Smith said.

The team is also preparing the first of four wet chemistry cells in MECA (Microscopy, Electrochemistry, and Conductivity Analyzer) to receive a soil sample. MECA will dissolve small amounts of soil in water to determines the pH, mineral abundance and conductivity of the soil.