[meteorite-list] Meteorite Found On Mars Yields Clues About Planet's Past

Ron Baalke baalke at zagami.jpl.nasa.gov
Mon Aug 10 20:04:43 EDT 2009



August 10, 2009

Dwayne Brown 
Headquarters, Washington 
202-358-1726 
dwayne.c.brown at nasa.gov 

Guy Webster 
Jet Propulsion Laboratory, Pasadena, Calif. 
818-354-6278 
gay.y.hill at jpl.nasa.gov   

RELEASE: 09-186

METEORITE FOUND ON MARS YIELDS CLUES ABOUT PLANET'S PAST

PASADENA, Calif. -- NASA's Mars Rover Opportunity is investigating a 
metallic meteorite the size of a large watermelon that is providing 
researchers more details about the Red Planet's environmental 
history. 

The rock, dubbed "Block Island," is larger than any other known 
meteorite on Mars. Scientists calculate it is too massive to have hit 
the ground without disintegrating unless Mars had a much thicker 
atmosphere than it has now when the rock fell. Atmosphere slows the 
descent of meteorites. Additional studies also may provide clues 
about how weathering has affected the rock since it fell. 

Two weeks ago, Opportunity had driven approximately 600 feet past the 
rock in a Mars region called Meridiani Planum. An image the rover had 
taken a few days earlier and stored was then transmitted back to 
Earth. The image showed the rock is approximately 2 feet in length, 
half that in height, and has a bluish tint that distinguishes it from 
other rocks in the area. The rover team decided to have Opportunity 
backtrack for a closer look, eventually touching Block Island with 
its robotic arm. 

"There's no question that it is an iron-nickel meteorite," said Ralf 
Gellert of the University of Guelph in Ontario, Canada. Gellert is 
the lead scientist for the rover's alpha particle X-ray spectrometer, 
an instrument on the arm used for identifying key elements in an 
object. "We already investigated several spots that showed elemental 
variations on the surface. This might tell us if and how the metal 
was altered since it landed on Mars." 

The microscopic imager on the arm revealed a distinctive triangular 
pattern in Block Island's surface texture, matching a pattern common 
in iron-nickel meteorites found on Earth. 

"Normally this pattern is exposed when the meteorite is cut, polished 
and etched with acid," said Tim McCoy, a rover team member from the 
Smithsonian Institution in Washington. "Sometimes it shows up on the 
surface of meteorites that have been eroded by windblown sand in 
deserts, and that appears to be what we see with Block Island." 

Opportunity found a smaller iron-nickel meteorite, called "Heat Shield 
Rock," in late 2004. At about a half ton or more, Block Island is 
roughly 10 times as massive as Heat Shield Rock and several times too 
big to have landed intact without more braking than today's Martian 
atmosphere could provide. 

"Consideration of existing model results indicates a meteorite this 
size requires a thicker atmosphere," said rover team member Matt 
Golombek of NASA's Jet Propulsion Laboratory in Pasadena, Calif. 
"Either Mars has hidden reserves of carbon-dioxide ice that can 
supply large amounts of carbon-dioxide gas into the atmosphere during 
warm periods of more recent climate cycles, or Block Island fell 
billions of years ago." 

Spectrometer observations have already identified variations in the 
composition of Block Island at different points on the rock's 
surface. The differences could result from interaction of the rock 
with the Martian environment, where the metal becomes more rusted 
from weathering with longer exposures to water vapor or liquid. 

"We have lots of iron-nickel meteorites on Earth. We're using this 
meteorite as a way to study Mars," said Albert Yen, a rover team 
member at JPL. "Before we drive away from Block Island, we intend to 
examine more targets on this rock where the images show variations in 
color and texture. We're looking to see how extensively the rock 
surface has been altered, which helps us understand the history of 
the Martian climate since it fell." 

When the investigation of Block Island concludes, the team plans to 
resume driving Opportunity on a route from Victoria Crater, which the 
rover explored for two years, toward the much larger Endeavour 
Crater. Opportunity has covered about one-fifth of the 12-mile route 
plotted for safe travel to Endeavour since the rover left Victoria 
nearly a year ago. 

Opportunity and its twin rover, Spirit, landed on Mars in January 2004 
for missions originally planned to last for three months. Both rovers 
show signs of aging but are still very able to continue to explore 
and study Mars. 

NASA'S JPL manages the Mars Exploration Rovers Opportunity and Spirit 
for NASA's Science Mission Directorate in Washington. To see the 
image and obtain more information about the rovers, visit: 

http://www.nasa.gov/rovers   
	
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