Complex subsurface of Mars imaged by Chinese rover Zhurong

Date:
February 14, 2023
Source:
Geological Society of America
Summary:
Ground-penetrating radar from China's Martian rover Zhurong reveals
shallow impact craters and other geologic structures in the top
five meters of the red planet's surface.


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FULL STORY ========================================================================== Ground-penetrating radar from China's Martian rover Zhurong reveals
shallow impact craters and other geologic structures in the top five
meters of the red planet's surface. The images of the Martian subsurface
are presented in a paper published in Geology Thursday.


==========================================================================
The Zhurong rover was sent to Mars as part of China's Tianwen-1 mission.

Launched in July 2020, the rover landed on the surface on 15 May 2021. The rover was sent to a large plain in the northern hemisphere of Mars named
Utopia Planitia, near the boundary between the lowlands where it landed
and highlands to the south. The region was chosen because it's near
suspected ancient shorelines and other interesting surface features,
where the rover could look for evidence of water or ice. A large body
of underground ice was identified in a nearby part of Utopia Planitia
in 2016 by radar from NASA's Mars Reconnaissance Orbiter. After landing,
the Zhurong rover traveled about 1.9 km south, taking pictures of rocks,
sand dunes, and impact craters, and collecting ground-penetrating radar
data along the way.

Ground-penetrating radar detects features underground by sending electromagnetic pulses into the ground that are reflected back by any subsurface structures it passes over. The Zhurong rover uses two radar frequencies -- a lower frequency that reaches deeper (~80 meters) with
less detail, and a higher frequency used for the latest study, which shows
more detailed features but only reaches ~4.5 meters down. Researchers
hope that imaging the subsurface of Mars will help to shed light on the planet's geologic history, previous climate conditions, and any water
or ice the planet may host now or in the past.

The researchers saw several curving and dipping underground structures in
the Martian soil that they identify as buried impact craters, as well as
other sloping features with less certain origins. They did not see any
evidence of water or ice in the top five meters of soil. Radar images
of the deeper structures revealed layers of sediment left by episodes
of flooding and deposition in the past, but also found no evidence of
water in the present day.

This does not rule out the possibility of water deeper than the eighty
meters imaged with the radar.

In the new paper, the researchers contrast the data from Mars with ground- penetrating radar previously collected from the moon, which shows a
much different shallow subsurface structure. Where the shallow Martian
surface contains several distinct features that show up in the radar,
the top 10 meters of the moon has fine layers but no evidence of other structures like impact crater walls, despite also being subjected to
meteorite bombardment. The walls of impact craters are, however, observed
at greater depths on the moon, buried beneath the 10-meter-thick layer
of fine debris.

The difference may be in the atmosphere -- while Mars' atmosphere
is a meager 1% of the volume of Earth's, the moon has virtually no
atmosphere. With essentially no atmospheric protection, the moon's surface
is bombarded by more of the smallest micrometeorites that rework the
surface, eroding smaller-scale features and leaving behind fine layers
of ejecta. By contrast, the surface of Mars is not being subjected to
as many micrometeorite impacts because these smaller objects burn up in
the atmosphere. In the regions imaged by Zhurong, burial by wind-blown
sediment may have also protected the impact craters from erosion. One
of the craters imaged had its rim exposed at the surface, but the other
crater was buried.

Yi Xu, the lead author on the study, explains, "We found a lot of dunes
on the surface at the landing site, so maybe this crater was quickly
buried by the sand and then this cover reduced space weathering, so we
can see the full shape of these craters walls."
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========================================================================== Story Source: Materials provided by Geological_Society_of_America. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* Images_of_the_Martian_subsurface ========================================================================== Journal Reference:
1. Ruonan Chen, Ling Zhang, Yi Xu, Renrui Liu, Roberto Bugiolacchi,
Xiaoping
Zhang, Lu Chen, Zhaofa Zeng, Cai Liu. Martian soil as revealed by
ground- penetrating radar at the Tianwen-1 landing site. Geology,
2023; DOI: 10.1130/G50632.1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/02/230214153858.htm

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