Mars: Impact Craters In Tyrrhena Terra Clearly Imaged , Water Ice In Crater At Martian North Pole

Daily Science Journal (Aug. 2, 2007) — The High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express obtained images of the Tyrrhena Terra region on Mars.

Tyrrhena Terra, perspective view. (Credit: ESA/DLR/FU Berlin (G. Neukum))

On 10 May 2007, the pictures of the region located at 18° South and 99° East were taken during orbit number 4294 with a ground resolution of approximately 15 metres per pixel.

Tyrrhena Terra is part of the ancient, heavily cratered southern Martian highlands. The region is located north of Hellas Planitia, the largest impact basin on Mars. The image scene exhibits three impact craters, located at the eastern border of Tyrrhena Terra with Hesperia Planum.

The western part of the scene is dominated by a 35 kilometre-wide and approximately 1000 metre-deep impact crater with an extremely steep rim. The rim rises up to 400 metres above the surrounding plains.

The crater is surrounded by multiple layers of material ejected during the impact. These so called ‘ejecta blankets’ spread up to a distance of 50 kilometres around the crater.

Their round, lobate appearance hints at possible ice- and water-rich subsurface material.

The raised feature in the centre of the crater most likely originated from the elastic rebound of compressed subsurface material after the impact. This feature is called 'central peak' or 'central uplift'. This is comparable to what happens when a drop of water hits a puddle.

Another, 18 kilometre-long and approximately 750 metre-deep impact crater, in all likelihood a ‘double impact crater’, is located south of the large crater.

These ‘double impact craters’ develop when two objects, possibly part of the same fragmented object, hit the surface almost simultaneously.

The impact that formed the larger northern crater, which displays an intact crater wall, occurred after the double-impact crater was formed. The ejecta from this later impact has reshaped the double-impact crater.

The northern part has been filled by ejecta and the material is present even at the bottom of the crater, in the direction of the point of impact (towards the larger, neighbouring crater).

The colour scenes have been derived from the three HRSC colour channels and the nadir channel. The perspective views have been calculated from the Digital Terrain Model derived from the HRSC stereo channels. The anaglyph images were calculated by putting together data from the nadir channel and one stereo channel. The black and white high-resolution images were derived from the nadir channel which provides the highest level of detail.

Adapted from materials provided by European Space Agency.

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Water Ice In Crater At Martian North Pole

New images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, show a patch of water ice sitting on the floor of an unnamed crater near the Martian north pole.

Perspective view of crater with water ice - looking east. (Credits: ESA/DLR/FU Berlin (G. Neukum))

The HRSC obtained these images during orbit 1343 with a ground resolution of approximately 15 metres per pixel. The unnamed impact crater is located on Vastitas Borealis, a broad plain that covers much of Mars's far northern latitudes, at approximately 70.5° North and 103° East.

The crater is 35 kilometres wide and has a maximum depth of approximately 2 kilometres beneath the crater rim. The circular patch of bright material located at the centre of the crater is residual water ice.

This white patch is present all year round, as the temperature and pressure are not high enough to allow sublimation of water ice.

It cannot be frozen carbon dioxide since carbon dioxide ice had already disappeared from the north polar cap at the time the image was taken (late summer in the Martian northern hemisphere).

There is a height difference of 200 metres between the crater floor and the surface of this bright material, which cannot be attributed solely to water ice.

It is probably mostly due to a large dune field lying beneath this ice layer. Indeed, some of these dunes are exposed at the easternmost edge of the ice.

Faint traces of water ice are also visible along the rim of the crater and on the crater walls. The absence of ice along the north-west rim and walls may occur because this area receives more sunlight due to the Sun’s orientation, as highlighted in the perspective view.

The colour images were processed using the HRSC nadir (vertical view) and three colour channels. The perspective views were calculated from the digital terrain model derived from the stereo channels.

The 3D anaglyph images were created from the nadir channel and one of the stereo channels. Stereoscopic glasses are needed to view the 3D images Image resolution has been decreased for use on the internet.

Adapted from materials provided by European Space Agency.

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Scientists Gear Up For Mercury Mission Flyby Of Venus

Daily Science Journal (Jun. 5, 2007) — University of Colorado at Boulder researchers will scan Venus during a spacecraft flyby this week using an $8.7 million instrument they designed and built for NASA's MESSENGER Mission, launched in 2004 and speeding toward Mercury.

An artists rendition of NASA's MESSENGER spacecraft, which will make its first flyby of Mercury in 2008. (Credit: Image courtesy of University of Colorado at Boulder)

Built by CU-Boulder's Laboratory for Atmospheric and Space Physics, the instrument will make measurements of the thick clouds and shrouded surface of Venus during the June 5th flyby, said LASP Senior Research Associate William McClintock, a mission co-investigator who led the CU-Boulder instrument development team. Known as the Mercury Atmospheric and Surface Composition Spectrometer, or MASCS, the instrument will compare the atmosphere of Venus with data from other spacecraft that have visited the planet in the past four decades.

"This is our first opportunity for a close flyby of a solar system object with MESSENGER, and we should be able to tell if the atmosphere of Venus has been changing in recent years, " said McClintock. "As importantly, we are using Venus as a test case to learn more about our instrument performance in preparation for the spacecraft's ultimate destination of Mercury."

Carrying seven instruments, MESSENGER will be the first spacecraft ever to orbit Mercury and the first to return data from the hot, rocky planet in more than 30 years. The circuitous, 4.9 billion mile journey to Mercury, which requires more than seven years and 13 loops around the sun, is using the gravity of Venus during its flyby this week to guide it closer to Mercury's orbit.

MESSENGER will make its first flyby of Mercury in January 2008, zipping by it again at a top speed of 141,000 miles per hour in October 2008 before flying by a third time in September 2009 and finally settling into orbit in March 2011. "This is a mission that requires some patience," said Mark Lankton, LASP's program manager for the MASCS instrument. "We are anticipating a brief symphony of action at Venus, and we have a lot of data to take in a hurry."

Dozens of CU-Boulder undergraduate and graduate students will be involved in data analysis from MESSENGER in the coming years, said Lankton.

MASCS's ultraviolet and visible spectrometer will be looking at the cloud composition of Venus. While the surface of Venus is hot enough to melt lead and its atmosphere is filled with noxious carbon dioxide gases and acid rain, Earth and Venus were virtual twins at birth, scientists believe.

The miniaturized MASCS instrument, which took more than three years to develop, weighs less than seven pounds and was built to last, said McClintock. "Many space instruments have a lifetime of only three to four years," he said. "But we knew we had to make this one robust enough to work for more than a decade under harsh conditions."

The MESSENGER spacecraft is about the size of a small economy car and is equipped with a semi-cylindrical thermal shade to protect it from the sun. More than half of the weight of the 1.2-ton spacecraft consists of propellant and helium. "We like to call it the little spacecraft that could," said McClintock.

"This event at Venus will be a very good tune-up for our first flyby of Mercury next January," said LASP Director Daniel Baker, also a co-investigator on the MESSENGER team. "The first encounter with Mercury will be extremely valuable, as it will essentially double the amount of information we now have about the planet."

A space physicist, Baker is interested in the magnetic field of Mercury and its interaction with the solar wind, including "substorms" associated with Mercury's magnetic field that occur in the planet's vicinity. Understanding Mercury's surface, tenuous atmosphere and magnetic field are the keys to understanding the evolution of the inner solar system, he said.

Mercury was visited only once before by a spacecraft, in 1974 and 1975, when NASA's Mariner 10 spacecraft made three flybys and mapped roughly 45 percent of the planet's rocky surface at the time.

MASCS will probe the mineral composition of Mercury's surface, the distribution of gases in its tenuous atmosphere and the workings of a giant, comet-like sodium gas cloud enveloping the planet, said McClintock. The researchers also hope to determine if Mercury ever had volcanoes on its surface and if the permanently shadowed craters at Mercury's poles contain water-ice.

MESSENGER is equipped with a large sunshield and heat-resistant ceramic fabric because Mercury is about two-thirds of the way nearer to the sun than Earth and is bombarded with 10 times the solar radiation. Sandwiched by the sun and Mercury -- which has daytime temperatures of about 800 degrees Fahrenheit -- the spacecraft will "essentially be on a huge rotisserie," said Baker.

Adapted from materials provided by University of Colorado at Boulder.

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