NASA Probe Counts Space Rock Impacts On Mars

                 NASA Probe Counts Space Rock Impacts On Mars

PR Newswire

WASHINGTON, May 15, 2013

WASHINGTON, May 15, 2013 /PRNewswire-USNewswire/ -- 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. It 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

To see images of the craters, visit:

For more information about HiRISE, visit:

For more about MRO, visit:


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