麻豆传媒

Observers seem to have had little or no warning that China鈥檚 Chang鈥檈 1 lunar orbiter was going to crash into the Moon on Sunday, meaning little scientific data was likely gleaned from the impact. The lack of information has been a hallmark of the mission, which launched in October 2007.

Chang鈥檈 1 crashed into the Moon on Sunday in a planned decommissioning, according to the state news agency .

In doing so, Chang鈥檈 1 joined the ranks of the European Space Agency鈥檚 SMART-1, which was sent crashing into the Moon in 2006 after the craft began running low on fuel. The crash was an opportunity to study the physics of lunar impacts, a rare occasion when something of known mass and velocity ploughed into the lunar surface.

SMART-1鈥檚 demise was well documented. Plans were broadcast in advance, and ground telescopes were able to catch the flash of its impact and monitor the spread of debris.

But Chang鈥檈 was probably not so well observed. Unlike SMART-1, which crashed in nighttime conditions so the glare of light from the Moon鈥檚 sunlit side would not overwhelm observations, Chang鈥檈 seems to have crashed on the day side, Sky & Telescope鈥檚 Kelly Beatty .

That may be in part because it鈥檚 hard to orchestrate a crash so that it occurs where it can be observed, says SMART-1鈥檚 project scientist Bernard Foing. 鈥淚t is indeed very difficult to ensure an accurate time and place for a crash,鈥� he told 麻豆传媒. 鈥淚t took operations engineers very delicate manoeuvres to ensure it.鈥�

Impact site

Engineering challenges aside, the international community seems to have had little or no warning of the impending smash.

鈥淚 do not know of any plans that were prepared to observe the plume when Chang鈥檈 impacted,鈥� says Carle Pieters of Brown University, a member of both Japan鈥檚 and India鈥檚 missions, which are now orbiting the Moon.

Those orbiters will undoubtedly observe the impact site when viewing conditions are favourable, she says, adding: 鈥淪ince all spacecraft currently orbiting the Moon will eventually crash into the surface, I hope the next several [impact] events will be planned to allow a broad range of observers.鈥�

Without observations of the crash itself, lunar researchers will have to settle for results from Chang鈥檈鈥檚 16-month mission itself, although it is unclear what will emerge.

First image

The last big news from the mission came in November 2007, when researchers released the probe鈥檚 first image.

Initial reports suggested Chang鈥檈 had found a new crater not seen in images taken in 1994 by the US orbiter . But later analysis showed the crater was actually an artifact of the way Chang鈥檈鈥檚 lunar mosaic was assembled.

Since then, little has been heard from the mission. 鈥淎fter that was resolved, it was sort of like they picked up their ball and went home,鈥� says Paul Spudis, a planetary geologist with the Lunar and Planetary Institute in Houston, Texas. Spudis has worked on instruments for both Chandrayaan-1 and NASA鈥檚 Lunar Reconnaissance Orbiter, which is set to launch in May 2009.

鈥楩airly guarded鈥�

鈥淭hey鈥檝e been fairly guarded in the release of information,鈥� agrees planetary scientist of Washington University in St Louis.

But Jolliff, who is working on setting up a computing centre with China鈥檚 Shandong University that might eventually be used to share planetary data internationally, says that may change.

鈥淲e鈥檙e really hoping, as the Chinese become comfortable with their own capabilities and with the open-access data sharing that has been established by many other countries, that they鈥檒l be moving down that pathway, and I鈥檓 sure they will,鈥� Jolliff says.

Global image

Those first steps might not be so far off. A small contingent of Chang鈥檈 1 researchers from the Chinese Academy of Sciences seems to be on track for presenting at the (LPSC) in Texas later this month.

One team plans to present a new global image of the Moon, first by China鈥檚 space agency in November 2008. According to the LPSC abstracts, the probe鈥檚 stereo camera, one of the orbiter鈥檚 鈥渕ost important payloads鈥�, seems to be capable of taking images of the Moon with 120-metre resolution.

For comparison, NASA has used the Goldstone radar dish in California to create images of the Moon鈥檚 south pole with 20-metre accuracy. Kaguya鈥檚 Terrain Camera has a spatial resolution of just 10 metres.

Soil depth

Chang鈥檈鈥檚 relatively low-resolution images are not likely to yield new results. But the orbiter also carries a radiometer that operates at microwave frequencies. Although it鈥檚 not yet clear whether the instrument worked or exactly what its capabilities were, it might produce a global map of the depth of the lunar regolith, the soil-like layer of the Moon鈥檚 surface, which was created by countless impacts, Jolliff says.

Many estimates of regolith depth are made on a local basis only, by examining ejected material surrounding impact craters, says Jolliff.

And if the news reports are right, Chang鈥檈 1 is just a fledgling step in a larger robotic exploration mission. According to Xinhua, China plans to send more probes to the Moon, including a 2017 rover that will return samples of the Moon to Earth.