* Astronomy

Spirit Discovers New Class of Igneous Rocks
During the past two-and-a-half years of traversing the central part of Gusev Crater, NASA's Mars Exploration Rover Spirit has analysed the brushed and ground-into surfaces of multiple rocks using the alpha particle X-ray spectrometer, which measures the abundance of major chemical elements. In the process, Spirit has documented the first example of a particular kind of volcanic region on Mars known as an alkaline igneous province. The word alkaline refers to the abundance of sodium and potassium, two major rock-forming elements from the alkali metals on the left-hand side of the periodic table.


Credit: NASA/JPL-Caltech/University of Tennessee

All of the relatively unaltered rocks -- those least changed by wind, water, freezing, or other weathering agents -- examined by Spirit have been igneous, meaning that they crystallised from molten magmas. One way geologists classify igneous rocks is by looking at the amount of potassium and sodium relative to the amount of silica, the most abundant rock-forming mineral on Earth. In the case of volcanic rocks, the amount of silica present gives scientists clues to the kind of volcanism that occurred, while the amounts of potassium and sodium provide clues about the history of the rock. Rocks with more silica tend to erupt explosively. Higher contents of potassium and sodium, as seen in alkaline rocks like those at Gusev, may indicate partial melting of magma at higher pressure, that is, deeper in the Martian mantle. The abundance of potassium and sodium determines the kinds of minerals that make up igneous rocks. If igneous rocks have enough silica, potassium and sodium always bond with the silica to form certain minerals.

The Gusev rocks define a new chemical category not previously seen on Mars, as shown in this diagram plotting alkalis versus silica, compiled by University of Tennessee geologist Harry McSween. The abbreviations "Na2O" and "K2O" refer to oxides of sodium and potassium. The abbreviation "SiO2" refers to silica. The abbreviation "wt. %" indicates that the numbers tell what percentage of the total weight of each rock is silica (on the horizontal scale) and what percentage is oxides of sodium and potassium (on the vertical scale). The thin lines separate volcanic rock types identified on Earth by different scientific names such as foidite and picrobasalt. Various classes of Gusev rocks (see box in upper right) all plot either on or to the left of the green lines, which define "alkaline" and "subalkaline" categories (subalkaline rocks have more silica than alkaline rocks).

Members of the rover team have named different classes of rocks after specimens examined by Spirit that represent their overall character. During the rover's travels, Spirit discovered that Adirondack-class rocks littered the Gusev plains; that Backstay, Irvine, and Wishstone-class rocks occurred as loose blocks on the northwest slope of "Husband Hill"; and that outcrops of Algonquin-class rocks protruded in several places on the southeast face.
These rocks have less silica than all previously analysed Mars samples, which are subalkaline. The previously analysed Mars samples include Martian meteorites found on Earth and rocks analysed by the Mars Pathfinder rover in 1997. Gusev is the first documented example of an alkaline igneous province on Mars.

SPIRIT UPDATE: Spirit Checking 'Korolev' - sol 929-932, August 18, 2006:

Spirit is healthy and continues to make progress on its winter science campaign.
Spirit is finishing the "McMurdo mega-panorama" by acquiring touch-up images (dubbed "grout" by engineers). Spirit is nearly complete with the coverage of the ground around the rover.
Spirit continues making a series of atmospheric observations at the same time each day.
Spirit is collecting about 280 watt-hours of electrical power each sol from the rover's solar array.

Sol-by-sol summaries:

Sol 929 (Aug. 14, 2006): Spirit studied a target called "Halley Brunt" with the panoramic camera and microscopic imager.

Sol 930: Spirit took a tau measurement, an observation during which the rover evaluates atmospheric opacity to estimate dust height.

Sol 931: Spirit took pictures with the panoramic camera of targets named "Korolev" and "McMurdo grout 10." Spirit also used the panoramic camera to take a tau measurement.

Sol 932 (Aug. 17, 2006): Spirit took a tau measurement with the panoramic camera, surveyed the sky and ground with the miniature thermal emission spectrometer, and took measurements of a target named "Vernadsky" along with a background stare with the miniature thermal emission spectrometer.

Odometry:
As of sol 932 (Aug. 17, 2006), Spirit's total odometry remained at 6,876.18 metres.

Spirit Sol 929


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SPIRIT UPDATE: Spirit Survives Second Winter Solstice on Mars - sol 922-928, August 11, 2006:

Spirit has now survived the rover's second Martian winter solstice -- the shortest day of the year with the least amount of sunlight and solar energy. The solstice arrived on the rover's 923rd Martian day, or sol (Aug. 8, 2006). Spirit is healthy and continues to make progress on its winter science campaign.
Having completed the "McMurdo mega-panorama," Spirit is currently filling cracks between frames by acquiring touch-up images (dubbed "grout" by engineers). The rover is also spending this week and next making a series of atmospheric observations at the same time each day.
Spirit continues to collect about 280 watt-hours of electrical power each sol from the rover's solar array (a hundred watt-hours is the amount of electricity needed to light one 100-watt bulb for one hour).

Sol-by-sol summaries:

Sol 922 (Aug. 7, 2006): Spirit measured atmospheric dust opacity (known as a tau measurement) with the panoramic camera, surveyed the sky and ground with the miniature thermal emission spectrometer, and acquired fill-in images with the panoramic camera for column 24A (a single frame) of the McMurdo pan.

Sol 923: Spirit took a tau measurement with the panoramic camera, surveyed the sky and ground with the miniature thermal emission spectrometer, and acquired morning fill-in images for the McMurdo pan with the panoramic camera.

Sol 924: Spirit took a tau measurement with the panoramic camera, surveyed the sky and ground with the miniature thermal emission spectrometer, and acquired panoramic camera images of the "El Dorado" dune field (a two-by-one mosaic). The rover acquired images of fine ripples with the hazard avoidance cameras and a rearward-looking view with the left eye of the right rear hazard avoidance camera. Spirit also acquired morning fill-in images for the McMurdo pan.

Sol 925: Spirit took a tau measurement with the panoramic camera, surveyed the sky and ground with the miniature thermal emission spectrometer, and acquired morning fill-in images for the McMurdo pan with the panoramic camera. Spirit also took a sunset tau measurement, an observation during which the rover evaluates atmospheric opacity at sunset to estimate dust height.

Sol 926: Plans called for Spirit to take a tau measurement with the panoramic camera, survey the sky and ground with the miniature thermal emission spectrometer, and acquire morning fill-in images for the McMurdo pan.

Sol 927: Plans called for Spirit to take a tau measurement with the panoramic camera, survey the sky and ground with the miniature thermal emission spectrometer, and acquire compositional data on a rock-and-soil target known as "Halley Brunt Offset 2" using the alpha particle X-ray spectrometer. Plans also called for Spirit to complete a morning sky survey using the panoramic camera.

Sol 928 (Aug. 13, 2006): Plans called for Spirit to take a tau measurement with the panoramic camera, survey the sky and ground with the miniature thermal emission spectrometer, and acquire morning fill-in images for the McMurdo pan.

Odometry:
As of sol 924 (Aug. 9, 2006), Spirit's total odometry remained at 6,876.18 metres.