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EI2GYB > ASTRO 18.10.25 10:03l 121 Lines 7248 Bytes #23 (0) @ WW
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Subj: New Research Says the "Dark Side" of the Moon is Also the C
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New Research Says the "Dark Side" of the Moon is Also the Cold Side
When the Apollo astronauts returned from the Moon, they brought with them
samples of lunar soil (regolith) and rock. The analysis of these samples
forever changed our perceptions of how the Earth-Moon system formed and
evolved. Similarly, the samples returned by China's Chang'e program are also
leading to breakthroughs in our understanding of Earth's only satellite,
especially its so-called "dark side." As a tidally-locked body, the Moon's near
side is constantly facing towards Earth while its far (or "dark") side faces
outward to space.
According to new findings by a team of Chinese researchers, the far side of the
Moon is also its colder side. Their conclusions are based on the samples
returned by the Chang'e-6 mission in 2024, which were collected from the Apollo
Crater located in the Moon's South Pole-Aitken Basin. After analyzing the
samples to determine their chemical composition, the team estimated that they
formed from lava deep within the Moon's mantle at a temperature of about 1,100
øC (2,012 øF) - roughly 100 øC (212 øF) cooler than samples obtained from the
near side.
The team consisted of researchers from the Beijing Research Institute of
Uranium Geology (BRUIG) - part of the China National Nuclear Corporation - the
School of Earth and Space Sciences at Peking University, University College
London (UCL), and the School of Space Science and Technology at Shandong
University. Their results were reported in a paper published in Nature
Geoscience. Based on decades of robotic exploration, it is known that the far
side of the Moon is more mountainous and cratered than the near side and
experienced less volcanism, leading to fewer dark patches of basalt rock.
In their study, the researchers suggest that the mantle on the far side of the
Moon is cooler because it contains fewer elements, such as uranium, thorium,
and potassium, which release heat during their radioactive decay process. On
the Moon, these elements tend to occur together alongside rare earth elements
and phosphorus, forming material that scientists refer to as KREEP-rich (K
denoting the chemical symbol for potassium, REE for rare earth elements, and P
for phosphorus). Previous research has suggested that this uneven distribution
may have resulted from a massive impact on the far side, which pushed these
denser materials to the other side.
Another theory suggests that the Moon has experienced two impacts in the past
from moonlets with varying compositions, with one containing more radioactive
elements than the other. Yet another theory is that the Earth's gravitational
pull led to increased heating in the near side's mantle. As co-author Yang Li,
a Professor with UCL's Department of Earth and Space Sciences at Peking
University, explained in a UCL News release:
For their study, the team examined the 300 grams (~10.5 oz) of lunar soil
(mainly basalt rock) that was allotted to the Beijing Research Institute of
Uranium Geology. In total, 1,935.3 grams (~4.6 lbs) of lunar soil and rock were
obtained by the Chang'e-6 mission, which were the first samples ever returned
from the far side of the Moon. They then mapped selected parts of the sample
with an electron probe to determine their chemical composition. These probes
fire concentrated beams of electrons at a sample, causing the sample to emit
X-rays that are examined to identify the chemical elements that make it up.
They then targeted lead isotopes in the samples, which are produced by the
natural decay of uranium, using a Secondary Ion Mass Spectrometer (SIMS). This
allowed them to detect tiny variations in the lead content of the samples, from
which they obtained an age estimate of 2.8 billion years. Finally, the team
estimated the temperature at which the samples formed in the mantle during
different stages in the Moon's evolution. The first step was to compare the
results of their mineral analysis to computer simulations that estimated the
temperature at which the minerals crystallized.
The second was to infer the temperature of the rock, which melted into magma
and re-solidified to form the basalt rock from which the samples were obtained.
Both of these results were compared to near-side samples collected by the
Apollo missions, both revealing a temperature difference of 100 øC (212 øF).
They also collaborated with a team from Shandong University to estimate parent
rock temperatures using satellite data of the Chang'e-6 landing site. They
compared this to satellite data from the near side, which also indicated a
temperature difference, but of 70 øC (158 øF) this time.
"These findings take us a step closer to understanding the two faces of the
Moon," said co-author Mr Xuelin Zhu, a PhD student at Peking University. "They
show us that the differences between the near and far side are not only at the
surface but go deep into the interior." The most widely held theory about the
Moon's formation is that a Mars-sized body (Theia) collided with a primordial
Earth about 4.5 billion years ago, causing material from both bodies to become
liquid into hot magma (the Giant Impact Hypothesis). This magma coalesced as it
cooled and solidified, ultimately forming the Earth-Moon system we see today.
However, the KREEP materials were incompatible with the solidifying material
and remained in the magma for longer periods. Rather than being evenly
distributed across the Moon, these materials appeared to have collected on the
near side, possibly explaining the heightened volcanic activity there. These
questions will need to be addressed by future studies, possibly by astronauts
and taikonauts conducting direct studies on the lunar surface.
More info at:
https://www.universetoday.com/articles/new-research-says-the-dark-side-of-the-mn
oo-is-also-the-cold-side
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