INSUBCONTINENT EXCLUSIVE:
Image copyrightGetty ImagesImage caption
An employee inspects a 1:8 scale model of the Chang'e-4 lunar probe
China is preparing to make the first attempt at landing robotic spacecraft on the Moon's far side.A static lander and rover are expected
to be deployed to the surface in the next day, state media reports.The vehicles are carrying a suite of instruments designed to characterise
the region's geology, as well as a biological experiment.In recent days, the Chang'e-4 spacecraft had lowered its orbit in preparation for
landing.At the weekend, Chinese state media said the probe had entered an elliptical path around the Moon, bringing the vehicles to within
15km (9 miles) of the lunar surface at its closest point.Authorities have not specified the exact time of the attempt to touch down in the
But a report in the state-run China Daily newspaper suggests Chang'e-4 could begin descending on its thrusters sometime from 2-3
January.Targeting the far side turns this mission into a riskier and more complex venture than its predecessor, Chang'e-3 - which touched
down in the Moon's Mare Imbrium region in 2013
But China's latest moon shot will pave the way for the country to deliver samples of lunar rock and dust to Earth
Andrew Coates, professor of physics at UCL's Mullard Space Science Laboratory in Surrey, told TheIndianSubcontinent News: "This daring
mission will land nearly 50 years on from the historic Apollo landings and will be followed in late 2019 by a Chinese sample return
mission."Image copyrightNASAImage caption
The near side (L) and far side (R) of the Moon have some key differences
Because of a phenomenon called "tidal locking", we see only one "face" of the Moon from Earth
This is because the Moon takes just as long to rotate on its own axis as it takes to complete one orbit of Earth.The lunar far side is often
referred to as the "dark side", though "dark" in this case means "unseen" rather than "lacking light"
In fact, both the near and far sides of the Moon experience daytime and night-time.But the far side has a thicker, older crust that is
is located within a much larger feature - the South Pole-Aitken (SPA) Basin - thought to have been formed by a giant impact early in the
Moon's history."This huge structure is over 2,500km in diameter and 13km deep, one of the largest impact craters in the Solar System and the
largest, deepest and oldest basin on the Moon," Prof Coates told me.And therein lies the scientific interest
The event responsible for carving out the SPA basin is thought to have been so powerful, it punched through the outer layer of the Moon,
known as the crust, and down into the zone called the mantle
Researchers will want to train the instruments on any mantle rocks exposed by the calamity
Image copyrightCNSAImage caption
Artwork: The Chang'e-4 rover will explore a huge impact basin on the far side
Image copyrightCNSAImage caption
Artwork: The lander and the rover were originally built as back-ups for a
previous Moon mission
The science team also hopes to study parts of the sheet of melted rock that would have filled the
newly formed South Pole-Aitken Basin, allowing them to identify variations in its composition.A third objective is to study the far side
regolith, the broken up rocks and dust that make up the surface."The in-situ composition information in particular will be hugely valuable
in understanding the formation of the Moon," Andrew Coates commented.Landing challengeUp until now, China has followed in the footsteps of
US and Soviet missions, carefully building up its capabilities
But this mission marks a first for any space agency.The rugged character of the far side, with its undulating topography, poses particular
challenges for landing the vehicles safely
Touching down on a jagged outcrop would spell instant mission failure - and be a significant setback for the Chinese exploration
programme.Image copyrightGetty ImagesImage caption
A mock-up of the Chang'e-4 lander and rover, on display in Dongguan,
the South Pole-Aitken basin, according to Chinese scientists.The descent to the lunar surface is split into six phases
The first three - initial deceleration, quick attitude and reorientation adjustment, and approach - will be controlled from Earth
For the final three - hovering, hazard avoidance, and slow descent - the lander will take over, assuming autonomous control.Seeds and
eggsThe lander and rover were originally built as back-ups for 2013's Chang'e-3 mission
However, they have received important modifications for the ambitious touchdown on the far side.Chang'e-4's static lander is carrying two
cameras; a German-built radiation experiment called LND; and a spectrometer that will perform low-frequency radio astronomy
observations.Scientists believe the far side could be an excellent place to perform radio astronomy, because it is shielded from the radio
The spectrometer work will aim to test this idea.The lander will also carry a 3kg (6.6lb) container with potato and arabidopsis plant seeds
- as well as silkworm eggs - to perform biological studies
The "lunar mini biosphere" experiment was designed by 28 Chinese universities.The rover will carry a panoramic camera; a radar to probe
beneath the lunar surface; an imaging spectrometer to identify minerals; and an experiment to examine the interaction of the solar wind (a
stream of energised particles from the Sun) with the lunar surface.In an article for the US-based Planetary Society in September, Dr Long
Xiao from the China University of Geosciences (Wuhan), said: "Chang'e-4 will be humanity's first landed exploration of the lunar far side
The challenge faced by a far side mission is communications
With no view of Earth, there is no way to establish a direct radio link."Thus, the landers must communicate with Earth using a relay
satellite named Queqiao, launched by China in May this year.Queqiao orbits 65,000km (40,000mi) beyond the Moon, around a Lagrange point - a
kind of gravitational parking spot in space where it will remain visible to ground stations in China and other countries such as
Argentina.The lander and rover was launched from Xichang Satellite Launch Center in China on 7 December; the vehicles arrived in lunar orbit
on 12 December.The mission is part of a larger Chinese programme of lunar exploration
The first and second Chang'e missions were designed to gather data from orbit, while the third and fourth were built for surface operations
Chang'e-5 and 6 are sample return missions, delivering lunar rock and soil to laboratories on Earth.Follow Paul on Twitter.
