Team of international scientists shares analysis of first fresh samples from the moon in more than 40 years
From:
Washington University in Saint Louis
October 7, 2021 -- A lunar probe
launched by the Chinese space agency recently brought back the first fresh
samples of rock and debris from the moon in more than 40 years. Now an
international team of scientists -- including an expert from Washington
University in St. Louis -- has determined the age of these moon rocks at close
to 1.97 billion years old.
"It is the perfect sample to close
a 2-billion-year gap," said Brad Jolliff, the Scott Rudolph Professor of
Earth and Planetary Sciences in Arts & Sciences and director of the
university's McDonnell Center for the Space Sciences. Jolliff is a U.S.-based
co-author of an analysis of the new moon rocks led by the Chinese Academy of
Geological Sciences, published Oct. 7 in the journal Science.
The age determination is among the first
scientific results reported from the successful Chang'e-5 mission, which was
designed to collect and return to Earth rocks from some of the youngest
volcanic surfaces on the moon.
"Of course, 'young' is
relative," Jolliff said. "All of the volcanic rocks collected by
Apollo were older than 3 billion years. And all of the young impact craters
whose ages have been determined from the analysis of samples are younger than 1
billion years. So the Chang'e-5 samples fill a critical gap."
The gap that Jolliff references is
important not only for studying the moon, but also for studying other rocky
planets in the solar system.
As a planetary body, the moon itself is
about 4.5 billion years old, almost as old as the Earth. But unlike the Earth,
the moon doesn't have the erosive or mountain-building processes that tend to
erase craters over the years. Scientists have taken advantage of the moon's
enduring craters to develop methods of estimating the ages of different regions
on its surface, based in part on how pocked by craters the area appears to be.
This study shows that the moon rocks
returned by Chang'e-5 are only about 2 billion years old. Knowing the age of
these rocks with certainty, scientists are now able to more accurately
calibrate their important chronology tools, Jolliff said.
"Planetary scientists know that the
more craters on a surface, the older it is; the fewer craters, the younger the
surface. That's a nice relative determination," Jolliff said. "But to
put absolute age dates on that, one has to have samples from those
surfaces."
"The Apollo samples gave us a
number of surfaces that we were able to date and correlate with crater
densities," Jolliff explained. "This cratering chronology has been
extended to other planets -- for example, for Mercury and Mars -- to say that
surfaces with a certain density of craters have a certain age."
"In this study, we got a very
precise age right around 2 billion years, plus or minus 50 million years,"
Jolliff said. "It's a phenomenal result. In terms of planetary time,
that's a very precise determination. And that's good enough to distinguish
between the different formulations of the chronology."
Other interesting findings from the
study relate to the composition of basalts in the returned samples and what
that means for the moon's volcanic history, Jolliff noted.
The results presented in the Science
paper are just the tip of the iceberg, so to speak. Jolliff and colleagues are
now sifting through the regolith samples for keys to other significant lunar
science issues, such as finding bits and pieces tossed into the Chang'e 5
collection site from distant, young impact craters such as Aristarchus, to
possibly determining the ages of these small rocks and the nature of the
materials at those other impact sites.
Jolliff has worked with the scientists
at the Sensitive High Resolution Ion MicroProbe (SHRIMP) Center in Beijing that
led this study, including study co-author Dunyi Liu, for over 15 years. This
long-term relationship is possible through a special collaboration agreement
that includes Washington University and its Department of Earth and Planetary
Sciences, and Shandong University in Weihai, China, with support from
Washington University's McDonnell Center for the Space Sciences.
"The lab in Beijing where the new
analyses were done is among the best in the world, and they did a phenomenal
job in characterizing and analyzing the volcanic rock samples," Jolliff
said.
"The consortium includes members
from China, Australia, the U.S., the U.K. and Sweden," Jolliff continued.
"This is science done in the ideal way: an international collaboration,
with free sharing of data and knowledge -- and all done in the most collegial
way possible. This is diplomacy by science."
Jolliff is a specialist in mineralogy
and provided his expertise for this study of the Chang'e-5 samples. His
personal research background is focused on the moon and Mars, the materials
that make up their surfaces and what they tell about the planets' history.
As a member of the Lunar Reconnaissance
Orbiter Camera science team and leader of the Washington University team in
support of NASA's Apollo Next Generation Sample Analysis (ANGSA) program,
Jolliff investigates the surface of the moon, relating what can be seen from
orbit to what is known about the moon through the study of lunar meteorites and
Apollo samples -- and now, from Chang'e-5 samples.
https://www.sciencedaily.com/releases/2021/10/211007145754.htm
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