Dust Devils, Ancient Habitable Environments & More
NASA's Opportunity Mars rover has now been exploring the Red Planet for a decade. The golf-cart-size robot landed on the night of Jan. 24, 2004, three weeks after its twin, Spirit. <br><br>
<a href="http://www.space.com/18766-spirit-rover.html">Spirit</a> and <a href="http://www.space.com/18289-opportunity-rover.html">Opportunity</a> were originally tasked with 90-day missions that called for them to search for signs of past water activity on the Red Planet. Both rovers far outlasted their warranties; Spirit was declared dead in 2011, and Opportunity continues roving to this day. And they both made big discoveries that have fundamentally reshaped scientists' understanding of Mars and its environmental history. <br><br>
Rover deputy principal investigator Ray Arvidson, of Washington University in St. Louis, submitted a Spirit and Opportunity Top 10 list to SPACE.com to mark the mission's 10 years of Mars exploration. To be clear, these are Arvidson's personal opinions, not a consensus of the mission team.
<br><br>FIRST STOP: Mars Atmosphere Dynamics
<a href="http://www.space.com/9726-rover-tracks.html">Spirit and Opportunity</a>: Using argon as a tracer of atmospheric dynamics. Both rovers employed their APXS instrument to measure the <a bref="http://www.space.com/16903-mars-atmosphere-climate-weather.html">atmosphere of Mars</a> and detect argon.
<p>NEXT: Martian Dust Devils
Martian Dust Devils
Spirit and Opportunity: <a href="http://www.space.com/8847-mars-rover-opportunity-finally-sees-martian-dust-devil.html">Dust devil</a> frequency and dynamics, showing how dust and sand are moved by wind in Mars' very thin atmosphere. [<a href="http://www.space.com/14980-twister-mars-orbiter-captures-dust-devil-reaching-atmosphere-video.html">VIDEO: See a Mars Dust Devil from Space</a>]
<p>NEXT: Modern Water or Frost
Modern Water or Frost
Spirit: Complex coatings on olivine basalts; Gusev Crater plains showing modern <a href="http://www.space.com/17048-water-on-mars.html">water on Mars</a>, or possibly frost, has altered rock surfaces. [<a href="http://www.space.com/12542-mars-water-photos-red-planet-images.html">Photos: The Search for Water on Mars</a>]
<p>NEXT: Modern Waters, Part 2
Modern Waters, Part 2
Spirit: Ferric sulfates were moved down the soil column by <a href="http://www.space.com/7692-mars-rover-discovery-spinning-wheels.html">modern waters at Troy</a>, Husband Hill, Gusev Crater. [<a href="http://www.space.com/9417-trapped-mars-rover-finds-signs-buried-martian-water.html">Related: Trapped Mars Rover Finds Signs of Buried Martian Water in Recent Past</a>]
<p>NEXT: Water Meets Hot Rocks
Water Interacting with Hot Rock
Spirit: Iron-magnesium carbonates at the Comanche outcrop, <a href="http://www.space.com/1384-spirited-assault-mars-rover-nears-summit-husband-hill.html">Husband Hill</a>, Gusev Crater, showing that water interacted with magma.
<p>NEXT: Ancient Hydrothermal System
An Ancient Hydrothermal System
Spirit: Opaline silica at Home Plate, Gusev Crater, formed in volcanic fumeroles and/or hydrothermal vents. Again, showing that water was interacting with magma. [<a href="http://www.space.com/9433-habitable-hotspots-mars-volcano-vents-signs.html">Related: Habitable Hotspots on Mars? Volcano Vents May Be Signs</a>]
<p>NEXT: Wind-Blown Ripples
Opportunity: <a href="http://www.space.com/21865-mars-rover-opportunity-10th-birthday.html">Wind-blown ripples</a> on the Meridiani plains are relict from previous wind regime, probably when Mars' spin axis tilt was different than today’s value.
Opportunity: The rover has found several <a href="http://www.space.com/9209-opportunity-rover-finds-6th-mars-meteorite.html">meteorites on Mars</a> dispersed across Meridiani plains. [<a href="http://www.space.com/19097-mars-meteorites-photos.html">Photos: Meteorites from Mars</a>]
<p>NEXT: Habitable Environment Long Ago
A Habitable Environment Long Ago
Opportunity: The rover has found evidence that <a href="http://www.space.com/24386-mars-could-support-life-opportunity-rover.html">ancient Mars may have been habitable for millions of years</a>. At the rim of Endeavour Crater, Cape York; the rover discovered ferric and aluminous smectite clays in finely layered Matijevic formation rocks that pre-exist the Endeavour impact event. Alteration in moderately acidic and reducing waters, perhaps mildly oxidizing for ferric smectites. These are the oldest rocks examined by Opportunity (roughly 4 billion years old), and they were exposed to waters much more habitable than the waters that led to the Burns formation. [<a href="http://www.space.com/20193-mars-could-have-supported-life-nasa-finds-video.html">Video: Mars Could Have Supported Life, NASA Finds</a>]
<p>NEXT: Ancient Acidic Lakes
Ancient Acidic Lakes
Opportunity: The Meridiani plains' Burns formation as sulfate-rich sandstones with hematitic concretions formed in ancient acidic and oxidizing shallow lakes and reworked into sand dunes and cemented by rising groundwaters.
<p>More Mars Rover Reading:
<li><a href="http://www.space.com/topics/mars-rover-opportunity-spirit-news/">Latest News About Mars Rovers Opportunity and Spirit
</a></li><li><a href="http://www.space.com/27-latest-mars-shots-spirit-opportunity.html">Latest Mars Rover Photos from Spirit and Opportunity</a></li>
<li><a href="http://www.space.com/24394-mars-rovers-spirit-opportunity-explained-infographic.html">How NASA's Mars Rovers Spirit and Opportunity Work (Infographic)</a></li>
<li><a href="http://www.space.com/9726-rover-tracks.html">Rover Tracks on Mars | SPACE.com Video Show</a></li>
<li><a href="http://www.space.com/19409-mars-discoveries-spirit-opportunity-rovers.html">10 Amazing Mars Discoveries by Spirit & Opportunity</a></li>
<li><a hreef="http://www.space.com/24194-mars-rover-s-90-day-mission-now-in-10th-year-vide.html">Mars Rover's '90 Day Mission' Now In 10th Year | Video</a></li>
<li><a href="http://www.space.com/16575-mars-exploration-robot-red-planet-missions-infographic.html">Occupy Mars: History of Robotic Red Planet Missions (Infographic)</a></li>
<li><a href="http://www.space.com/12404-mars-explored-landers-rovers-1971.html">Mars Explored: Landers and Rovers Since 1971 (Infographic)</a></li></ul>