Mercury is the smallest planet in the solar system, only slightly larger than the moon.It is the nearest to the sun. It has no atmosphere. The temperature difference between day and night is huge. It takes 88 Earth days to circle the sun.Because the temperature is too high and too close to the sun, it is difficult for scientists to study it.The discovery of Mariner 10 and other missions highlights the unusual features of Mercury: Venus, Earth, Mars and other rocky planets all have thick mantle and crust, but Mercury's mantle and crust are unexpectedly thin relative to the core.Mercury has an unusual proportion of chemical substances on its surface. Its thorium concentration is close to that of Mars, and thorium will be evaporated under the extreme high temperature of the sun.Scientists put forward a hypothesis about these unusual phenomena: Mercury was originally formed at a place far away from the sun, close to Mars, and its initial mass was equivalent to that of the Earth. However, at some point in its evolution, Mercury collided with an object the size of another planet, causing it to spin and fly to the sun.Such collisions may scrape away the crust and most of the mantle, but leave behind huge liquid cores. https://www.bbc.com/future/article/20240410-mercury-the-solar-systems-smallest-planet-may-once-have-been-as-large-as-earth
