Article written by: Apostolos Christou
The rapidly-approaching 2019 will let us mark a half-century since human beings took the first steps on a body other than the Earth, namely our own Moon. But, come the New Year, lunar exploration is likely to make the headlines for one other reason: a number of robotic spacecraft built by three different nations will attempt to repeat the feat accomplished by the Apollo programme and land on the Moon’s surface.
First off will be China’s Chang’e 4 spacecraft, expected to be launched at 18:15-18:34 GMT on Friday 7th December at the time of this writing. As the name suggests, it is the fourth in a series of probes China has sent to the moon over the last 10 years. The previous one, Chang’e 3, landed near a region called Sinus Iridum in 2013, the first lunar soft landing by a human artefact since 1976 [Remarkably, the Chang’e 3 lander is still sending back data after 5 years on the Moon].
Chang’e 4 will attempt another first: landing on the far side of the moon, in other words the part that is constantly out of view of observers on the Earth. For an observer on the far side, the sun comes and goes just as it does on the near side, but the Earth is always below the local horizon. The challenge of such a mission – probably the reason it wasn’t attempted before — is that the lander has no direct communications link with ground control on Earth, as the bulk of the Moon is in the way.
Chinese engineers and scientists have got around that problem by launching a separate satellite to sit high above the lunar far side and relay data from the lander to Earth. This satellite, now named Queqiao or “Magpie Bridge” in Chinese, is already on-station and ready to act as the relay for the Chang’e lander. The intended landing site for the spacecraft is a 180-km wide crater called Von Carman at 45 deg south, roughly the latitude of New Zealand on Earth. Landing would probably take place on or around January 3, 2019. Like its predecessor, Chang’e 4 also carries a small rover that is intended to roam about the lunar landscape and study the surface far from the lander’s immediate vicinity.
The objectives of the mission are two-fold: First, the Moon itself. Von Carman crater forms part of an even larger depression thousands of km across, called the South-Pole Aitken basin or SPA for short. SPA is thought to be the largest and oldest crater on the Moon, formed when an asteroid or comet 100km or so across slammed on the then-newly-formed Moon 4.2 billion years ago, digging up material from deep within. By landing on SPA and sampling the soil, scientists hope to find out what the deep interior of the Moon is made of, test current models of how it formed and check that SPA is as old as they think it is.
The other scientific aim of the mission concerns the unique environment of the lunar far side.
Just as sunlight scattered by the Earth’s atmosphere prevents one from doing optical astronomy during the daytime, electronic devices on Earth – anything from microwave ovens to mobile phone networks – generate radio waves that prevent a really sensitive exploration of natural radio sources in the universe from the Earth’ surface and, in fact, anywhere in the solar system. But with the bulk of the moon effectively blocking all Earth-based transmissions, the lunar far side should be a much better place for astronomical radio observations. If Chang’e 4 confirms this, the day will not be far away where space-faring nations establish radio observatories on the lunar surface to explore the cosmos with unprededented sensitivity.
[Update on 08 Dec]: Chang’e 4 was successfully launched at 18:23:34 GMT yesterday upon a Long March 3B rocket from the Xichang Satellite Launch Centre in China and is now on its way to the Moon!
[Update on 12 Dec]: According to Chinese media, Chang’e 4 is now in orbit around the Moon. It will probably wait until the first few days of 2019 to make its landing attempt on the far side. The following excellent article by Emily Lakdawalla of The Planetary Society explains why.
[Update on 30 Dec]: According to the Xinhua news agency, the spacecraft has trimmed its orbit around the Moon in preparation for the landing, which is likely to take place sometime in the next 4-5 days.
[Update on 3 Jan]: Chinese, international and UK news media report that Chang’e 4 has successfully landed within Von Karman crater on the far side of the Moon. The landing time is reported to be 02:26 GMT on 3 January 2019. This article on the BBC website includes a picture taken by Chang’e 4 from the surface.
Detailed information on the mission, including a number of videos, may be found here:
Article on China’s near-term lunar exploration plans, incl Chang’e 4: http://www.planetary.org/explore/the-planetary-report/china-new-lunar-missions.html