Astronomy Now Home
Home Magazine Resources Store

On Sale Now!

The October 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). Astronomy Now is the only astronomy magazine specially designed to be read on tablets and phones. Download the app from Google Play Store or the Apple App Store.

Top Stories

Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...

Stepping into the
Martian past

Posted: 12 February 2010

Bookmark and Share

Images captured by the Mars Reconnaissance Orbiter (MRO) of 152 kilometre-wide Gale crater provide a detailed window into the past environmental changes on the red planet.

Each layer of rock on any planet records the local conditions at the time the rocks were laid down; the hundreds of exposed layers in Gale crater's four kilometre tall central mound tracks the region's environmental history over billions of years.

This oblique view shows geological layers of rock exposed on a mound inside Gale Crater. This is a lower portion of the mound, with the crater floor at the left (and lowest) edge of the image. Layers near the bottom of the mound contain clay and sulphate minerals that indicate wet conditions. Overlying rock layers contain sulphates with little or no clay, consistent with these layers forming in an environment in which water was evaporating and Mars was drying out. Image: NASA/JPL-Caltech/University of Arizona/USGS.

“Looking at the layers from the bottom to the top, from the oldest to the youngest, you see a sequence of changing rocks that resulted from changes in environmental conditions through time,” explains Ralph Milliken of NASA’s Jet Propulsion Laboratory. “This thick sequence of rocks appears to be showing different steps in the drying-out of Mars.”

Miliken and colleagues report that clay minerals, which form under very wet conditions, are concentrated in layers near the bottom of Gale crater's central stack. Layers above those contain sulphate minerals – which are often deposited when the water in which they are dissolved evaporates – as well as clays. Progressing further up the stack sees the concentration of clays gradually decline, while at the very top a thick formation of regularly spaced layers bears no evidence of any water-related minerals.

Layers of rock in the upper portion of the mound exhibit a regular thickness of several metres, unlike the less regular pattern of layers in the lower formation. Sulphate and clay minerals that have been observed in the lower formation have not been detected in the upper formation, where bedrock may be covered with dust. NASA/JPL-Caltech/University of Arizona.

Rock exposures with compositions matching various individual layers of the Gale stack have been found elsewhere on Mars, but Gale crater is the first location where a single series of layers has been found to contain these clues in a clearly defined sequence from older rocks to younger rocks. The findings suggest that initial clay-producing conditions were followed by sulphate-producing conditions and then dry conditions as Mars 'dried out'.

“If you could stand there, you would see this beautiful formation of Martian sediments laid down in the past, a stratigraphic section that’s more than twice the height of the Grand Canyon, though not as steep,” says Bradley Thomson of the Johns Hopkins University Applied Physics Laboratory.

Layers of rock exposed in the lower portion of the mound exhibit variations in thickness and range between dark and light tones. This view of layering in the mound's lower formation covers an area about 950 metres wide. Observations by the Compact Reconnaissance Imaging Spectrometer for Mars indicate the presence of sulphate salts and clay minerals in these rock layers. Image: NASA/JPL-Caltech/University of Arizona.

The findings were made possible by combing data from three MRO instruments. The High Resolution Imaging Science Experiment camera captured stereo images of the crater, which the US Geological Survey used to create three-dimensional models to discern elevation differences as small as a metre. Observations by the Compact Reconnaissance Imaging Spectrometer for Mars provided information about the chemistry of the minerals within the crater and the Context Camera provided context by seeing how the layers relate to geological features in the surroundings.

“This work demonstrates the synergy of the instruments on the Mars Reconnaissance Orbiter,” adds Thomson. “We wouldn’t have as complete a picture if we were missing any of the components.”

Gale Crater is one of four finalist landing sites for the Mars Science Laboratory rover, Curiosity, which is scheduled to launch in 2011. All locations have evidence for past water activity and the new report clearly demonstrates the importance of evaluating potential landing sites for their scientific merit in great detail prior to the mission.

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.

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.

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!


© 2014 Pole Star Publications Ltd.