Lubricants are vitally important for the safety and effectiveness of spacecraft during their work, Liu said. Solid lubricants are widely used in spacecraft to reduce friction because they can withstand high temperatures.

By comparing the lubricant samples to those exposed to a simulated space environment in the laboratory, Chinese scientists hope to improve their stability and durability.

"We need to know how the lubricants react to being in a vacuum, atomic oxygen and low temperatures in outer space," Liu said. If scientists find differences between the two exposed lubricants, Liu said, they might be able to predict how other materials will change in outer space.

The solid lubricant samples aboard Shenzhou 7 weighed about 2.2 kg and were exposed to outer space for 44 hours before Zhai retrieved them during the spacewalk.

Several rare herbal plants that were also aboard the spacecraft have been sent to another lab for study.

The plants, including rauwolfia and salvia miltiorrhiza (also known as red sage), were used to produce nanomedicines to treat cancerous tumors, Professor Zhang Yangde, who works at the Central South University's Laboratory of Nanobiotechnology, told Changsha Daily.

Other samples aboard Shenzhou 7 during the mission included the seeds of 25 endangered plants and live aquatic animals and plants.

The Shenzhou 7 spaceship landed safely by parachute on September 28 in China's northern grassland after a 68-hour flight.