First global map of rockfalls on the Moon

Date:
June 8, 2020
Source:
ETH Zurich
Summary:
A research team counted over 136,000 rockfalls on the moon caused
by asteroid impacts. Even billions of years old landscapes are
still changing.



FULL STORY ==========================================================================
In October 2015, a spectacular rockfall occurred in the Swiss Alps:
in the late morning hours, a large, snow-covered block with a volume of
more than 1500 cubic meters suddenly detached from the summit of Mel de
la Niva. It fell apart on its way downslope, but a number of boulders
continued their journey into the valley. One of the large boulders
came to a halt at the foot of the summit next to a mountain hut, after travelling more than 1.4 kilometers and cutting through woods and meadows.


==========================================================================
On the Moon, time and again boulders and blocks of rock travel downslope, leaving behind impressive tracks, a phenomenon that has been observed
since the first unmanned flights to the Moon in the 1960s. During the
Apollo missions, astronauts examined a few such tracks on site and
returned displaced rock block samples to Earth. However, until a few
years ago, it remained difficult to gain an overview of how widespread
such rock movements are and where exactly they occur.

Researchers at the Max Planck Institute for Solar System Research (MPS)
in Germany and ETH Zurich have analyzed an archive of more than two
million images of the lunar surface and present the first global map of rockfalls on the Moon in today's edition of Nature Communications.

"The vast majority of displaced boulders on the Moon have a diameter of
between seven and ten meters," explains Valentin Bickel of MPS and ETH
Zurich, first author of the new study. "Earlier space probes that have
studied the Moon were unable to detect such small features on a global
scale," he adds. It was not until 2010, with the launch of NASA's Lunar Reconnaissance Orbiter, that imagery of the entire lunar surface, with
the necessary spatial resolution and coverage, has been available.

The result is a map of the lunar surface between 80 degrees northern
and southern latitude that shows 136,610 rockfalls with diameters of
more than two and a half meters. "For the first time, this map enables
us to systematically analyze the occurrence and causes of rockfalls on
another celestial body," says Dr. Urs Mall from MPS.

Previously, scientists had assumed that lunar quakes in particular
were responsible for the displacement of boulders. The new global map
of rockfalls indicates that impacts from asteroids may play a much
more important role. They are apparently -- directly or indirectly -- responsible for more than 80 percent of all observed rockfalls.

"Most of the rockfalls are found near crater walls," says Prof. Dr. Simon
Loew of ETH Zurich. Some of the boulders are displaced soon after the
impact, others much later. The researchers hypothesize that impacts cause
a network of cracks that extend in the underlying bedrock. Parts of the
surface can thus become unstable even after very long periods of time.

Surprisingly, even in the oldest lunar landscapes, which formed up to
4 billion years ago or even earlier, traces of rockfall events can be
found. Since such imprints would typically disappear after a few million
years, these surfaces are apparently still subject to erosion through
rockfall, even billions of years after they were formed.

"Apparently, impacts influence and modify the geology of a region over
very, very long time scales," says Bickel. The results also suggest that
very old surfaces on other airless bodies such as Mercury or the large
asteroid Vesta may still be evolving as well.


========================================================================== Story Source: Materials provided by ETH_Zurich. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Valentin Tertius Bickel, Jordan Aaron, Andrea Manconi, Simon
Loew, Urs
Mall. Impacts drive lunar rockfalls over billions of years. Nature
Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-16653-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200608122339.htm

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