The probe, renamed "Wukong" - or Monkey King -  shortly before launch, blasted off on a Long March 2D rocket from the  Jiuquan Satellite Launch Centre in the Gobi Desert, Inner Mongolia at  00:12 UTC on Thursday, December 17(08:12 Beijing time).

The 1,900 kg satellite was inserted into a  sun-synchronous orbit, where it is expected to function for 3 years at  an altitude of 500 km.

It will carry out both indirect detection of dark matter and studies into high energy cosmic rays.

The probe, originally known as DAMPE (DArk Matter  Particle Explorer), was built in collaboration with the University of  Geneva and Italian universities in Bari, Lecce and Perugia. It was then  tested at CERN in Switzerland.

Professor Fan Yizhong, a member of the mission team  at the Purple Mountain Observatory of the Chinese Academy of Sciences in  Nanjing, explained the thinking behind the mission.

“The nature of dark matter is one of the most  fundamental questions for the physicists and astrophysicists. It is  known that the total mass of the dark matter particles is about five  times that of “normal” matter, but no-one really knows what the dark  matter particles are.”

“Dark matter particles may annihilate or decay and  then produce high energy gamma-rays or cosmic rays - in particular  electron/positron pairs.

“DAMPE will measure the spectra of gamma-rays and  cosmic rays with very high energy resolution and then look for possible  signal of dark matter annihilation or decay.”

Helpfully, DAMPE has the widest observation spectrum and highest energy resolution of any dark matter probe in the world.

Fan says says that as a high energy gamma-ray and  cosmic ray detector, Wukong can measure cosmic ray electrons in the  energy range of 10 GeV-10 TeV (1GeV=1 billion electron volts; 1 TeV=1000  billion electron volts) and cosmic ray protons and nuclei in the energy  range of 100 GeV-a few 100 TeV.

There are four payloads: a plastic scintillator detector, a silicon-Tungsten Tracker, a BGO calorimeter and a neutron detector.

These instruments will variously measure the energy,  charge of cosmic rays, converting gamma-rays into electron/positron  pairs and then measuring, and distinguishing between electrons and  protons or other heavier particles.

The probe will also seek to address the  ‘electron/positron anomaly’ found by the collaborative PAMELA and  FERMI-LAT satellites and other experiments, in which more positrons –  the antimatter version of electrons – have been detected than expected.

With its ability to look for higher energy electrons  and positrons, New Scientist writes that DAMPE may be able to determine  which of two suspects - dark matter annihilations or pulsars – is  responsible for the anomaly.

The probe was renamed via a public competition, with  the winning name taken from the famous protagonist in the Chinese story  Journey to the West.

Dark matter?

Chris Impey, distinguished professor of astronomy at  the University of Arizona, explains that while scientists don't know  what dark matter is, they know it is there, and discovering its nature  is a question of fundamental importance.

"Evidence started accumulating in the 1970's, when  radio and optical data showed that spiral galaxies rotated too rapidly  in their outer regions for it to be explained by gravity from the  visible stars in the galaxy," Impey says.

"The discrepancy was large, a factor of 5-8. And for  a while people doubted the data, but by the late 1980's the evidence  had become compelling that some invisible form of matter formed most of  the mass of every galaxy astronomers analysed.

"The alternative to dark matter's existence is to  say that Newton's law of gravity is wrong and there is no evidence for  that on large scales and for weak gravity."

Impey states that, by a process of elimination, dark  matter must be a new form of fundamental subatomic particle, with  substantial mass and weak or absent interactions with radiation - hence  dark.

Dark matter accounts for about a quarter of the  universe, Impey notes, with dark energy totalling two-thirds, and normal  matter the rest. Dark matter holds galaxies together and dominated the  expansion of the universe for most of its early history.

"The dark matter particle is an extension to the  otherwise very successful standard model of particle physics, most  probably the lightest stable particle in models of supersymmetry.

"But awkwardly for this expectation, the LHC [Large  Hadron Collider at CERN] has not affirmed the most likely supersymmetry  models, so the battleground has shifted to a set of underground physics  detectors trying identify the particle by its occasional and weak  interactions with normal matter.

"Hence the intense interest in astronomy missions  like DAMPE that have a chance of pinning down dark matter or giving us a  clue to its nature. The stakes are very high and it's is one of the  biggest unanswered questions in both physics and astronomy."

Fan hopes the mission will provide clues to the  nature of dark matter and also help scientists working on cosmic ray  physics. To this he adds that some gamma-ray data are expected to be  made publicly available a few years after the launch.

For more information about this study，visit the story at 

http://gbtimes.com/china/china-launches-worlds-most-sensitive-dark-matter-hunting-probe