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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 15 May 2013 12:16:49 -0700 (PDT)
Message-ID: <201305151916.r4FJGn9a004888_at_zagami.jpl.nasa.gov>

May 15, 2013

Dwayne Brown
Headquarters, Washington
dwayne.c.brown at nasa.gov

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov

Daniel Stolte
University of Arizona, Tucson
stolte at email.arizona.edu

RELEASE: 13-142


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

"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

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:


For more information about HiRISE, visit:


For more about MRO, visit:

Received on Wed 15 May 2013 03:16:49 PM PDT

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