The spacecraft will use reflective materials for thermal control, such as multi-layer insulation (MLI), in which aluminum-plated polymer films such as polyimide look as shiny as gold foil and aluminum foil. Teflon impregnated with fiber cloth is also white and bright.
The structure of the spacecraft itself is mostly aluminum alloy plus titanium alloy and composite materials, and the reflectivity of the first two is also high. Some antenna reflectors on satellites are also very smooth and highly reflective. These have made many spacecraft react strongly.
In addition, some spacecraft will continue to emit light by themselves, mainly all-electric satellites in recent years. Electric thrusters, such as Hall thrusters, replace chemical rockets for orbital climbing. When these propellers work, they emit luminous ion beams and electron beams (for charge neutralization). But these rays are too weak to compare with the reflected sunlight.
A satellite is a celestial body that periodically orbits the planet in a closed orbit. But if two celestial bodies are of equal mass, the system they form is generally called a two-planet system, not a planet and a natural satellite.
Usually, the center of mass of two celestial bodies is within the planet. Therefore, some astronomers believe that Pluto and Pluto should be classified as twin planets, but the discovery of two new Pluto satellites in 2005 made the problem more complicated.