Based on nuclear test data and volcano research
information, a Northern Arizona University astronomer has described a
new category of impact crater – dubbed Low-Aspect-Ratio Layered Ejecta
(LARLE) craters.
According a presentation by Nadine Barlow
this week at the American Astronomical Society Division for Planetary
Sciences in Denver, the LARLE craters feature a thin-layered outer
residue that reaches beyond the typical range of material thrown up by
an impact, known as ejecta.
Barlow said she noticed the LARLE craters while examining
high-resolution images of the surface of Mars during an effort to update
her popular catalog of Martian craters.
“I had to ask, ‘What is going on here?’” Barlow said.
After researching “explosion literature,” Barlow said she
and her collaborators theorized that a phenomenon known as ‘base surge’
may have something do to with the look of these novel impact craters.
Base surge occurs after a large explosion and is marked by a cloud of
fine material that forms and pushes out along the impact or eruption
surface. The rolling cloud erodes the surface and picks up material in
the process, eventually resulting in a widespread outer deposit.
After adjusting their equations from volcano research for
Martian conditions, the researchers said they could precisely explain
the “thin, sinuous, almost flame-like deposits.”
“So we think we’re on to something,” Barlow said.
These impact craters are primarily seen at higher
latitudes, essentially locations with thick, fine-grained sedimentary
deposits and subsurface ice.
“The combination helps vaporize the materials and create a
base flow surge,” Barlow said. The low aspect ratio refers to how thin
the deposits are relative to the area they cover.
According to the team, their work was dependent on the
stream of data currently flowing from the surveillance of Mars. While
data from the older Mars Odyssey Orbiter was used for a global survey, the team used high-resolution images from the Mars Reconnaissance Orbiter for more detailed examinations of the Martian surface.
“We’re looking in more detail at these deposits to find out
what their characteristics are,” Barlow said. “We can see dune-like
structures and the hollows that occur in the outer deposit.”
Barlow said she plans to complete the revision of her
catalog within a year, and hopes to find additional surprises, like the
LARLE craters, along the way.
“That’s part of the fun of science, to see something and
say, ‘Whoa, what’s that?’” she said. “Projects like this end up leading
to proposals.”
The Mars Odyssey orbiter was launched in April 2001 and
became the longest serving Mars-based craft in 2010, a title that was
previously held by the Mars Global Surveyor. The Odyssey has served as
NASA’s primary communications conduit for its ground-based assets and
continues to do so for the Curiosity rover.
Launched in August 2005, the Mars Reconnaissance Orbiter
(MRO) was charged with the task of creating a high resolution map of the
Martian surfaces, with a particular emphasis on finding potential
landing sites. The MRO has also used its on-board instruments to gather
information on Mars’ weather, atmosphere, and geology.
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