[meteorite-list] MRO Counts Space Rock Impacts on Mars

[Ron Baalke]

May 15, 2013

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

Guy Webster 
Jet Propulsion Laboratory, Pasadena, Calif. 
818-354-6278 
guy.webster at jpl.nasa.gov 

Daniel Stolte 
University of Arizona, Tucson 
520-626-4402 
stolte at email.arizona.edu 


RELEASE: 13-142

NASA PROBE COUNTS SPACE ROCK IMPACTS ON MARS

WASHINGTON -- Scientists using images from NASA's Mars Reconnaissance 
Orbiter (MRO) have estimated that the planet is bombarded by more 
than 200 small asteroids or bits of comets per year forming craters 
at least 12.8 feet (3.9 meters) across. 

Researchers have identified 248 new impact sites on parts of the 
Martian surface in the past decade, using images from the spacecraft 
to determine when the craters appeared. The 200-per-year planetwide 
estimate is a calculation based on the number found in a systematic 
survey of a portion of the planet. 

MRO's High Resolution Imaging Science Experiment (HiRISE) camera took 
pictures of the fresh craters at sites where before-and-after images 
by other cameras bracketed when the impacts occurred. This 
combination provided a new way to make direct measurements of the 
impact rate on Mars. This will lead to better age estimates of recent 
features on Mars, some of which may have been the result of climate 
change. 

"It's exciting to find these new craters right after they form," said 
Ingrid Daubar of the University of Arizona, Tucson, lead author of 
the paper published online this month by the journal Icarus. "It 
reminds you Mars is an active planet, and we can study processes that 
are happening today." 

These asteroids or comet fragments typically are no more than 3 to 6 
feet (1 to 2 meters) in diameter. Space rocks too small to reach the 
ground on Earth cause craters on Mars because the Red Planet has a 
much thinner atmosphere. 

HiRISE targeted places where dark spots had appeared during the time 
between images taken by the spacecraft's Context Camera (CTX) or 
cameras on other orbiters. The new estimate of cratering rate is 
based on a portion of the 248 new craters detected. If comes from a 
systematic check of a dusty fraction of the planet with CTX since 
late 2006. The impacts disturb the dust, creating noticeable blast 
zones. In this part of the research, 44 fresh impact sites were 
identified. 

The meteor over Chelyabinsk, Russia, in February was about 10 times 
bigger than the objects that dug the fresh Martian craters. 

Estimates of the rate at which new craters appear serve as scientists' 
best yardstick for estimating the ages of exposed landscape surfaces 
on Mars and other worlds. 

Daubar and co-authors calculated a rate for how frequently new craters 
at least 12.8 feet (3.9 meters) in diameter are excavated. The rate 
is equivalent to an average of one each year on each area of the 
Martian surface roughly the size of the U.S. state of Texas. Earlier 
estimates pegged the cratering rate at three to 10 times more craters 
per year. They were based on studies of craters on the moon and the 
ages of lunar rocks collected during NASA's Apollo missions in the 
late 1960s and early 1970s. 

"Mars now has the best-known current rate of cratering in the solar 
system," said HiRISE Principal Investigator Alfred McEwen of the 
University of Arizona, a co-author on the paper. 

MRO has been examining Mars with six instruments since 2006. 

"The longevity of this mission is providing wonderful opportunities 
for investigating changes on Mars," said MRO Deputy Project Scientist 
Leslie Tamppari of NASA's Jet Propulsion Laboratory, Pasadena, Calif. 


The University of Arizona Lunar and Planetary Laboratory operates the 
HiRISE camera, which was built by Ball Aerospace & Technologies Corp. 
of Boulder, Colo. Malin Space Science Systems of San Diego built and 
operates the Context Camera. JPL manages the Mars Reconnaissance 
Orbiter for NASA's Science Mission Directorate in Washington. 
Lockheed Martin Space Systems of Denver, built the orbiter. 

To see images of the craters, visit: 

http://uahirise.org/sim 

For more information about HiRISE, visit: 

http://hirise.lpl.arizona.edu 

For more about MRO, visit: 

http://www.nasa.gov/mro 
	
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