SOLAR SYSTEM

Detailed explanation-1: -Mercury is the smallest planet in our solar system.

Detailed explanation-2: -All of the planets in our solar system, and some of its smaller bodies too, have an outer layer of gas we call the atmosphere. The atmosphere usually sits atop a denser, rocky crust or planetary core.

Detailed explanation-3: -Mercury lacks an atmosphere to speak of. Even though most of its surface is very hot, there is strong evidence that water ice exists in locations near its north and south poles which are kept permanently shaded by crater walls. This evidence comes from Earth-based radar observations of the innermost planet.

Detailed explanation-4: -Small planets and moons have insufficient gravity to hold an atmosphere. The gas molecules escape to space, leaving the planet or moon without an insulating blanket or a protective shield. Earth & Venus are the right size to hold a sufficient-sized atmosphere.