-Daniel aka Obsidian
Why
China wants to land a spacecraft on the mysterious far side of the moon
Updated by Joseph
Stromberg on May 27, 2015, 9:40 a.m. ET @josephstromberg
joseph@vox.com
China's
previous lunar rover, Yutu, landed in 2013 and was photographed by the Chang'e
3 lander as it drove away. (Chinese Academy of Sciences)
China appears to be planning a space
mission to a place no nation has ever been — the far side of the moon.
The China National Space
Administration (CNSA) currently plans to launch Chang'e 4, a craft that will
carry the country's second lunar rover, in 2020. According to comments recently
made by Wu Weiren, the Lunar Exploration Program's chief engineer, the rover
will likely touch down on the side of the moon that faces away from Earth.
"We probably will choose a site
on which it is more difficult to land and more technically challenging," Wu recently told the state broadcaster CCTV.
"Other countries have chosen to land on the near side of the moon. Our
next move probably will see some spacecraft land on the far side of the
moon."
Since 2007, China's ambitious lunar
program has already placed two probes in the moon's orbit and one lander on its
surface. Putting a rover on the far side could provide new data on the moon's
geologic history — and demonstrate the CNSA's growing expertise in and
dominance of lunar exploration.
China's
ambitious lunar exploration program
The Chang'e 3 lander, which touched
down on the moon in 2013. (Chinese Academy of Sciences)
Though China began launching satellites
and conducting other activities in space all the way back in the 1970s, the country's space agency has
made its biggest strides since 2000, becoming the third nation to send
astronauts into space in 2003. Since then, the CNSA has focused on a
destination that NASA and other space agencies have mostly overlooked as of
late: the moon.
In 2007, the CNSA sent its first
spacecraft — named Chang'e 1, after the Chinese goddess of the moon — into
lunar orbit. That was followed by the orbiter Chang'e 2 in 2010 and the lander
Chang'e 3 in 2013, the latter of which brought a small rover (called Yutu) to
the moon, and became the first craft to make a soft-landing there since the
1970s.
A close-up of Yutu, the rover
carried to the moon by Chang'e 3 in 2013. (Chinese Academy of Sciences)
The next few missions will go even
further. Chang'e 5, to be launched in 2017, will collect a rock sample and launch it back up to an orbiter, in order to
bring it back to Earth. (Confusingly, Chang'e 5 is launching before Chang'e 4
because the latter was originally built as a backup to Chang'e 3, then sat in
storage for a few years and has since been retrofitted for the new mission.)
Plans call for Chang'e 4 to launch
in 2020. Though Chang'e 3 successfully landed, mechanical problems prevented the rover it
carried from traveling more than 100 meters. If all goes as planned, the new
craft's rover will be able to gather much more data — and perhaps explore the
moon's relatively unknown far side.
The
mysterious far side of the moon
Because the moon rotates at the same
rate it orbits the Earth, it's tidally locked, as shown at left — and the same
side always faces Earth. If it didn't rotate, we'd see both sides equally, as
shown at right. (Stigmatella aurantiaca)
From Earth, we always see one side
of the moon because it's tidally
locked: it rotates at the same speed that it orbits us.
As a result, we know much less about
the far side (calling it the "dark side," while a bit more poetic,
isn't really accurate, because it gets just as much sunlight). And because
there's no direct line of sight from the Earth to the far side, landing a craft
there would require all communications to be routed through an orbiter before
reaching the lander.
But as difficult as it sounds, a
mission to the far side would yield plenty of rewarding data. Though the moon's
entire surface has been extensively photographed by orbiting probes — starting
with the USSR's Luna 3, in 1959, and currently by NASA's Lunar Reconnaissance
Orbiter — no lander or rover has ever documented the far side up close.
The moon's near side (left) has far
more dark basaltic plains than the far side (right). (NASA/GSFC/Arizona State University)
We already know the near side of the
moon is covered in dark spots, which are plains of basalt that
formed after volcanoes erupted billions of years ago and their lava cooled.
The far side is different: it has
few dark spots and lots of craters, though scientists don't fully understand
why. It may be that underneath its surface, there were never as many volcanoes,
but that explanation still isn't fully proven. Chang'e 4 might tell us more, by
collecting data on the rock that covers the far side's surface.
Depending on where the rover is
sent, it could also provide some information on the moon's
interior. The far side features the giant South Pole–Aitken
basin — a huge crater in which the crust might be so thin that mantle rock
peeks through. Data on this rock could help scientists better understand the layers that make up the moon.
Mantle material might be accessible
in the South Pole-Aitken basin, on the southern end of the far side. (JAXA)
Finally, there's some speculation that China might be interested in
visiting the moon's far side and conducting sample-return missions for an
entirely different purpose: harvesting helium-3,
an isotope of helium that could someday be used for both nuclear weapons and
energy production.
The isotope is much more abundant on
the moon than on Earth, where it's extremely rare. And the moon's far side is
believed to have the highest concentrations of it, because it's exposed to much
more solar wind, which deposits helium-3 in the first place.
It's not certain that this is
China's goal. In order to get usable quantities of helium-3, a craft would need
to harvest way more rock than Chang'e 5 will be capable of doing. The CNSA,
meanwhile, has never explicitly said that it's planning on mining helium-3.
Still, Ouyang Ziyuan, chief
scientist of CNSA's Lunar Exploration Program, has previously mentioned helium-3 as a long-term
potential benefit of the Chang'e program. It's conceivable that one reason for
returning lunar samples and exploring the moon's far side is to collect initial
data needed for this sort of ambitious extraction project.
