China's Monkey King sharpens eyes to search for dark matter

BEIJING -- Scientists have begun calibrating China's first dark matter probe in order to produce more accurate data, more than a month after the detector started to search for signals of the invisible material.

The Dark Matter Particle Explorer (DAMPE) Satellite, dubbed "Wukong" after the Monkey King character from the Chinese "Journey to the West" legend, was launched on Dec. 17, 2015, on a Long March 2-D rocket from Jiuquan Satellite Launch Center.

Like the Monkey King who can see through objects with his sharp eyes, the satellite has the most sensitive and accurate detectors especially designed for dark matter. These started working a week after the satellite entered a sun-synchronous orbit.

Chang Jin, DAMPE chief scientist and vice director of the Purple Mountain Observatory, said Wukong has already collected more than 100 million high energy particles, including protons, alpha and cosmic-ray particles and nuclides. Scientists will look for high-energy electrons and gamma rays among them, which could be residue of dark matter's annihilation or decay.

"Now the payload looks perfect, but it's not enough. If the calibration goes well, the signs we seek will pop out from the data," said Chang.

The payload has four major parts - a plastic scintillator array detector, a silicon array detector, a BGO calorimeter, and a neutron detector - together comprising about 76,000 minor detectors. DAMPE scientific application chief designer Wu Jian said the payload was designed with very high accuracy, but colliding with cosmic rays will change the detectors' performance, so they need constant calibration.

Wukong is sending back about 20 GB of data a day. DAMPE advanced data process sub-system designer Zang Jingjing said all the data will be analyzed by a special computer equipped with 128 10-cored CPUs.

"After calibration, the detectors will collect more useful data and screen out signal noises. That will save us a lot of time," said Zang.

Dark matter, which does not emit or reflect electromagnetic radiation that can be observed directly, is one of the huge mysteries of modern science. Exploration of dark matter could give scientists a clearer understanding of the past and future of galaxies and the universe, and would revolutionize the fields of physics and space science.

Wukong is designed to undertake a three-year mission, but scientists hope it can last five years. It will scan space nonstop in all directions in the first two years and then focus on areas where dark matter is most likely to be observed. Initial findings will be published as early as the second half of this year.