South Korea set off for the moon on Thursday. But it doesn’t want to stop there.
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“We are also
considering using the moon as an outpost for space exploration,” Kwon
Hyun-joon, director-general of space and nuclear energy at South Korea’s
Ministry of Science, said in a written response to questions. “Although we hope
to explore the moon itself, we also recognize its potential to act as a base
for further deep space exploration such as Mars and beyond.”
South Korea’s
lunar spacecraft, named Danuri, was launched on a
SpaceX Falcon 9 rocket from
Florida, setting out on a roundabout but fuel-efficient path that will have it
arriving at the moon in mid-December. There, it will begin an orbit at an
altitude of 100km above the moon’s surface. The main mission is scheduled to
last for one year.
Originally known
as the Korea Pathfinder Lunar Orbiter, the mission was given the name Danuri
after it became the winning entry in a naming contest. It is a portmanteau of
the Korean words for “moon” and “enjoy.”
Danuri will join
spacecraft from
NASA, India, and China that are currently exploring Earth’s
companion. Much like the UAE, which launched toward Mars on a Japanese rocket
in 2020, South Korea is the latest country with a small but ambitious space
program to set out on a beyond low-Earth orbit. And also like the UAE’s Hope
orbiter, the Danuri mission is intended to make meaningful scientific
contributions to global efforts to explore and understand the solar system.
Kwon said the
main goal of the Danuri mission was to develop basic technologies like the
design of orbital trajectories, deep space navigation, a high-thrust propulsion
system and a 35m antenna to communicate with distant spacecraft.
But the
spacecraft’s scientific payload is sophisticated and will aid scientists in
South Korea and globally in studying the moon’s magnetic field, measuring its
quantities of elements and molecules like uranium, water and helium-3 and
photographing the dark craters at the lunar poles, where the sun never shines.
In addition to providing one of the instruments, called ShadowCam, NASA chose
nine scientists to participate on Danuri.
One of its most
important scientific instruments is a magnetometer. The moon’s interior no
longer generates a magnetic field, but it once did, and that primordial field
is preserved in lava flows that hardened during this era.
“We have two
major scientific objectives,” said Ho Jin, a professor of astronomy and space
science at Kyung Hee University and the principal investigator for the
magnetometer. “One is the space environment of near-moon space and the other is
to understand the early history of lunar evolution.”
Ian
Garrick-Bethell, a professor of planetary science at the University of
California,
Santa Cruz and a participating scientist on the Danuri mission,
said that the early magnetic field appears to have been surprisingly strong —
potentially even as much as double the strength of Earth’s current magnetic
field.
Garrick-Bethell
said it was puzzling that “such a small little iron core could have generated
such a strong magnetic field.”
He is hoping that
after the spacecraft’s primary mission of one year is complete, South Korea
could choose to move Danuri much closer to the moon’s surface, within 20km or less, where the magnetometer could get a
much better look at the magnetized rocks.
“Even a few
passes at those low altitudes could help constrain how strongly magnetized
those rocks are,” he said.
Garrick-Bethell
is also looking to use the magnetometer to study magnetic fields generated
within the moon as it is buffeted by the solar wind, a stream of charged
particles emanating from the sun.
The rise and fall
in the strength of the magnetic field in the solar wind induces electric
currents in the moon, and those electric currents in turn generate magnetic
fields that will be measured by Danuri. The characteristics of the magnetic
field will give hints of the structure and composition of the moon’s interior.
Scientists will
use another of Danuri’s instruments, a gamma-ray spectrometer, to measure
quantities of different elements on the moon’s surface. Danuri’s device can
pick up a wider spectrum of lower energy gamma rays than similar instruments on
earlier lunar missions, “and this range is full of new information to detect
elements on the moon,” said Naoyuki Yamashita, a New Mexico-based scientist who
works for the Planetary Science Institute in Arizona. He is also a
participating scientist on Danuri.
Yamashita is
interested in radon, which forms from the decay of uranium. Because radon is a
gas, it could travel from the moon’s interior to its surface. (This is the same
process that sometimes causes the buildup of radon, which is also radioactive,
in the basements of houses.)
The amounts of
the radioactive elements could provide a history explaining when various parts
of the moon’s surface cooled and hardened, Yamashita said, helping scientists
to work out which of the moon’s lava flows are older or younger.
The Korean
Aerospace Research Institute, South Korea’s equivalent of NASA, will use
Danuri’s high-resolution camera to scout the lunar surface for potential sites
for a robotic lander mission in 2031, Kwon said.
A second camera
will measure polarized sunlight bouncing off the lunar surface, revealing details
about the size of particles that make up the lunar soil. Because constant
bombardment by solar wind, radiation and micrometeorites breaks the soil apart,
the size of grains found in a crater could give an estimate of its age.
(Smaller grains would suggest an older crater.)
The polarized
light data will also be used to map abundances of titanium on the moon, which
could one day be mined for use on Earth.
NASA supplied one
of the cameras, a ShadowCam, which is sensitive enough to pick up the few
photons that bounce off the terrain into the moon’s dark, permanently shadowed
craters.
One of the main
purposes of ShadowCam is to find the ice. But even with Danuri’s sophisticated
instruments, that could be challenging. Shuai Li, a researcher at the University
of Hawaii and a Danuri participating scientist, thinks the concentrations might
be so low that they will not be obviously brighter than areas not containing
ice.
“If you don’t
look at it carefully, you might not be able to see it,” Li said.
Researchers will have to
wait several months for the science to begin. The spacecraft is taking a long,
energy-efficient route to the moon. It first heads toward the sun, then loops
back around to be captured in lunar orbit on December 16. This “ballistic
trajectory” takes longer but does not require a large engine firing to slow the
spacecraft when it gets to the moon.
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