Editing Mars Pathfinder (section)

===''Sojourner''{{'}}s rock analysis===
[[File:Sojourner and Barnacle Bill.jpg|thumb|''Sojourner'' next to the rock [[Barnacle Bill (Mars)|Barnacle Bill]]]]
The first analysis on a rock started on Sol 3 with Barnacle Bill. The [[APXS|Alpha Particle X-ray Spectrometer]] (APXS) was used to determine its composition, the spectrometer taking ten hours to make a full scan of the sample. It found all the elements except [[hydrogen]], which constitutes just 0.1 percent of the rock's or soil's mass.

The APXS works by irradiating rocks and soil samples with [[alpha particle]]s ([[helium]] [[atomic nucleus|nuclei]], which consist of two [[proton]]s and two [[neutron]]s). The results indicated that "Barnacle Bill" is much like Earth's [[andesite]]s, confirming past [[volcano|volcanic]] activity.  The discovery of andesites shows that some Martian rocks have been remelted and reprocessed.  On Earth, andesite forms when magma sits in pockets of rock while some of the iron and magnesium settle out.  Consequently, the final rock contains less iron and magnesiums and more silica.  Volcanic rocks are usually classified by comparing the relative amount of alkalis (Na<sub>2</sub>O and K<sub>2</sub>O) with the amount of silica (SiO<sub>2</sub>).  Andesite is different from the rocks found in meteorites that have come from Mars.<ref name="Golombek, M 1997"/><ref name="nssdc.gsfc.nasa.gov">{{cite web |url=http://nssdc.gsfc.nasa.gov/planetary/marspath/apxs.html |title=APXS Composition Results |work=NASA |access-date=June 10, 2015 |archive-url=https://web.archive.org/web/20160603120939/http://nssdc.gsfc.nasa.gov/planetary/marspath/apxs.html |archive-date=June 3, 2016 |url-status=live }}</ref><ref name="Bruckner, J. 2001">{{cite journal |last1=Bruckner |first1=J. |first2=G. |last2=Dreibus |first3=R. |last3=Rieder |first4=H. |last4=Wanke |year=2001 |title=Revised Data of the Mars Pathfinder Alpha Proton X-ray spectrometer: Geochemical Behavior of Major and Minor Elements |journal=Lunar and Planetary Science XXXII|page=1293 |bibcode=2001LPI....32.1293B }}</ref>

Analysis of the Yogi rock again using the APXS showed that it was a [[basalt]]ic rock, more primitive than Barnacle Bill. Yogi's shape and texture show that it was probably deposited there by a [[flood]].

Another rock, named Moe, was found to have certain marks on its surface, demonstrating erosion caused by the wind. Most rocks analyzed showed a high content of [[silicon]]. In another region known as Rock Garden, ''Sojourner'' encountered crescent moon-shaped dunes, which are similar to [[dunes|crescentic dunes]] on Earth.

By the time that final results of the mission were described in a series of articles in the journal ''Science'' (December 5, 1997), it was believed that the rock Yogi contained a coating of dust, but was similar to the rock Barnacle Bill.  Calculations suggest that the two rocks contain mostly the minerals orthopyroxene (magnesium-iron silicate), feldspars (aluminum silicates of potassium, sodium, and calcium), and quartz (silicon dioxide), with smaller amounts of magnetite, ilmenite, iron sulfide, and calcium phosphate.<ref name="Golombek, M 1997"/><ref name="nssdc.gsfc.nasa.gov"/><ref name="Bruckner, J. 2001"/>
{{Wide image|PIA01153.jpg|1200px|Annotated panorama of [[Rock (geology)|rocks]] near the [[Sojourner (rover)|''Sojourner'' rover]] (December 5, 1997)}}