Chinese research vessel Kexue, or Science, sits at a dock after completing its month-long research voyage and returned to Xiamen, East China's Fujian province on June 22, 2019. [Photo provided to chinadaily.com.cn]

Chinese research vessel Kexue, or Science, completed its month-long expedition to the western Pacific Ocean and returned to Xiamen, East China's Fujian province, on June 22.

It was the vessel's fifth investigation of sea mounts and scientists aboard explored a series of the underwater mountains in the southern part of the Mariana Trench, the deepest place on earth, according to the Institute of Oceanology of Chinese Academy of Sciences.

They collected a host of biological and geological samples, acquired data and took several videos, according to the institute, which is based in Qingdao, East China's Shandong province.

"During the expedition, Discovery, a remote operated vehicle aboard Kexue, made 19 dives and collected 255 species in the collections, accounting for the total species we have collected in two expeditions in the past few years," said Xu Kuidong, chief scientist aboard and a researcher at the academy.

The vessel started its research voyage on May 18 in Qingdao, with 80 researchers aboard. They are from research institutions and universities, such as the academy's Institute of Oceanology, Shandong University and its Qingdao Institute of Bioenergy and Bioprocess Technology.