Funding for this research was provided by:
Chinese Academy of Science Space Science Pilot Project (XDA15000000)
Natural Science Foundation of China Astronomical Joint Project (U1631117)
Article History
Received: 24 April 2019
Accepted: 8 January 2020
First Online: 21 January 2020
Disclosure of Potential Conflicts of Interest
: The authors declare that there are no conflicts of interest.