Mercury has a rocky surface, but inside is a very large metallic core, part of which is molten (liquid).
Crust: Mercury has a thick crust that is composed mostly of silicate rocks. Mercury may have small ice caps at its north and south poles; this ice stays frozen inside deep craters that are shaded from sunlight.
Mantle: Beneath the crust it is a mantle (also made of silicate rocks) that is hundreds of kilometers thick.
Core: At the center of Mercury is a partly-molten iron core about 2,300 miles (7,500 km) in diameter (almost half of the diameter of Mercury). This core accounts for about 80% of Mercury’s mass. This core generates a magnetic field (which is how we know that Mercury has an iron core).
Density: Mercury has a density of 5,430 kg/m3, slightly less than that of Earth. Mercury is the second-densest planet in the solar system (after Earth) because of its large iron core.
People have been observing Mercury for a very long time, but nobody knows who discovered it. Sometimes it can be seen from Earth around sunset and sunrise. Sunrise and sunset on Mercury are spectacles to behold. Two and one half times larger in the sky than seen on Earth, the sun appears to rise and set twice during a Mercurian day. It rises, then arcs across the sky, stops, moves back toward the rising horizon, stops again, and finally restarts its journey toward the setting horizon. These aerial maneuvers occur because Mercury rotates three times for every two orbits around the sun and because Mercury’s orbit is very elliptical.
Visible at night: Mercury is not the only planet that can be seen with the naked eye. Mercury can generally be observed with a naked eye as it has the sun as a bright backdrop. Mercury is best observed with the naked eye during times right before and after the sun has set, which gives enough light pollution to contrast the shadow of Mercury. A general time to try and view Mercury with your naked eye is 90 minutes before sunrise or after sunset.
Picture Credit : Google