Look! Tianwen-1 posted a message on WeChat Moments! It's a "big potato"!

Two years after the launch of Tianwen-1, high-definition images of Phobos were transmitted back.

Today marks the second anniversary of the launch of the Tianwen-1 mission, and the orbiter has sent back images of Phobos.

Recently, the Tianwen-1 operation team seized the opportunity when the orbiter was close to Phobos and used a high-resolution camera to image Phobos, obtaining a clear image of the "full moon" state.

Phobos is one of the two natural satellites of Mars, with a size of about 27 km × 22 km × 18 km. It operates in a near-circular orbit at an altitude of about 6,000 km from the surface of Mars, orbiting Mars about three times a day. The orbiter operates in a polar elliptical orbit with a perigee altitude of about 220 km, an apogee altitude of about 10,800 km, and a period of about 7 hours. Due to the orbital relationship between Phobos and the orbiter, as well as the lighting requirements during imaging, the operation team made precise calculations and precise control, and obtained clear images with a resolution of about 50 meters when the two were about 5,100 kilometers apart.

The image shows that Phobos is an irregularly shaped small celestial body, shaped like a potato. Stripes can be seen on the surface in the upper left part of the image, which may have been formed by the impact process. There is an obvious impact crater in the upper right part of the image, with a diameter of about 2 kilometers, named Öpik crater (Öpik is an Estonian astronomer famous for his research on asteroids and meteorites).

Another satellite of Mars is Deimos, with an average radius of only about 6.2 kilometers. The two satellites are named after the two sons of Ares, the god of war in ancient Greek mythology. The ancient Greeks once called Mars Ares. Both satellites are irregular small celestial bodies. Many scientists believe that they were captured by the gravity of Mars and entered the orbit of Mars, but their origins are still controversial.

Source: China Lunar Exploration Project

Image source: National Astronomical Observatory

Author: Geng Yan, Chen Gang