mission control Heart beats from the dark side The Particle Explorer (DAMPE) is currently in measuring cosmic rays to research their origin and propagation and also to fnd possible hidden signatures of dark matter, emphasizes Principal Investigator Jin Chang.

aryonic matter (including the , the Moon, the Earth, part of our Milky Way Band so on) accounts for only ~5% of the energy density of the current Universe, while dark matter accounts for more than five times more. But dark matter is so difficult to detect that, until now, there is only macroscopic astronomical evidence indicative of its existence. In fact, we have yet to detect a single dark matter particle despite using equipment of the highest sensitivity currently available. There are several options for detecting dark matter particles. One technique, called the indirect method, tries to find hints of dark matter particles by detecting high-energy cosmic rays in space with a large particle spectrometer. The mystery of dark matter could be unravelled using information from these high-energy Fig. 1 | An artist’s impression of DAMPE in Earth orbit. Credit: Hu Yiming, Purple Mountain Observatory cosmic rays, such as the excess of the fraction, which was observed by the PAMELA detector and confirmed the mechanisms of particle acceleration of hadrons and ions are interacting with the by the Alpha Magnetic Spectrometer - 02 operating in astrophysical sources, and the calorimeter by hadron showers). DAMPE’s (AMS-02). But such an excess could be due propagation of cosmic rays in the Milky instruments can observe protons, helium and to nearby pulsars and not dark matter. Way; (2) probing the nature of dark matter; heavier ions from 10 GeV to 100 TeV. DAMPE, nicknamed Wukong after the (3) studying the -ray emission from Their energy spectra could enhance our Monkey King in Chinese mythology, is a Galactic and extragalactic sources. understanding of the origin of cosmic rays. space-based telescope in a Sun-synchronous, DAMPE has proven to be effective at The designed lifetime of DAMPE is at 500 km orbit (Fig. 1). It was launched on measuring and identifying the rare TeV- least three years. The primary observing 17 December 2015. This observatory energy e± signals (Ambrosi, G. et al. (DAMPE mode is a sky survey in Sun-synchronous indirectly detects dark matter particles by Collaboration) Nature https://doi.org/10.1038/ orbit. If needed, it could also turn to target- directly measuring high-energy cosmic rays nature24475; 2017). During the past 23 observing mode. The satellite control system in space. There have been several space- months more than 700 electron and positron of the National Space Science Center expects based projects before DAMPE, such as Fermi events above 1 TeV were successfully detected it will operate five to eight years based on (a gamma ray telescope) and AMS-02 (a high- and reconstructed. This was the first direct the excellent status information in orbit precision magnetic spectrometer). DAMPE detection of the behaviour of the cosmic-ray collected so far. has four sub-detectors: the PSD (plastic electrons and at these energies. DAMPE is under the leadership of the scintillator detector) to measure charge; the DAMPE also aims at detecting high- Purple Mountain Observatory, funded by STK (silicon tracker) to measure particle energy gamma-ray sources by virtue of the strategic priority science and technology trajectories; the BGO (bismuth germinate) the high sensitivity of the calorimeter and projects in space science of the Chinese calorimeter to measure particle energy and the precision of the silicon tracker. The Academy of Sciences. The collaboration has type; and the NUD (neutron detector) again measured and reconstructed gamma-ray over 100 members from nine institutes and to measure particle type. The key feature of signals could help us to understand the universities across three countries. ❐ DAMPE is the BGO calorimeter, which is a puzzling physical processes behind the three-dimensional imaging calorimeter with activities of active galactic nuclei, the Crab Jin Chang1,2 a thickness of about 32 radiation lengths. Nebula flares, and some bright gamma ray 1Key Laboratory of Dark Matter and Space This ensures that DAMPE has very good bursts. Up to now, DAMPE has surveyed Astronomy, Purple Mountain Observatory, Chinese sensitivity (better energy resolution and the full sky four times, producing a Academy of Sciences, Nanjing, China. higher electron/proton separation power) for comprehensive gamma-ray sky map. 2School of Astronomy and Space Science, University high-energy e± and gamma-rays, opening an For heavy ions with energies above 1 TeV of Science and Technology of China, Hefei, China. observing ‘window’ in the TeV energy range per nucleon, DAMPE is expected to have e-mail: [email protected] in space. The BGO is the biggest calorimeter breakthroughs because of the large acceptance in space at present. DAMPE’s main scientific and reasonably long interaction length (~1.6 Published online: 2 January 2018 objectives include: (1) understanding nuclear interaction lengths; this ensures ~80% https://doi.org/10.1038/s41550-017-0357-0

Nature Astronomy | VOL 2 | JANUARY 2018 | 99 | www.nature.com/natureastronomy 99 © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.