There about eight planets inside the solar system, as the different planets and stars hold greater significance inside the system when it comes to there position inside the solar system. While, the distances of the planets from the Sun inside the solar system also plays a great value and holds different properties with respect to each other.
Mercury is considered as the planet which is the most closest of all the planets to the sun inside the solar system. As it gains more amount of energy, resulting from a higher level of exposure to the Sun's ultraviolet rays. Now, the temperature,T of the planet is far much higher then any other planet inside the solar system, just because its surface receives the much high level of UV lights from the red giant.Mars is far hot for any living life to spend on it, as the planet lacks any back up for the objects to shield itself from any foreign entities or any amount of energy.
While, the Earth is far away from the Sun to receive the optimum level of heat from the Star inside the solar system. As earth has much distance to cover for the sunlight to reach it. Along, with which the Earth has a set of layers to shield itself from any Ultra violet rays coming from the star in the middle of the solar system. The temperatures,T value of the Earth is far less and is able to sustain life on the planet. And that is also due to the balance formed of energy,E levels in the layers of the planet.
The difference would be that Mercury has a denser, warmer atmosphere and Earth has a not that dense and gassy atmosphere. The Earth's atmosphere also has a lot of layers while Mercury's doesn't. Those would be the reasons for them both being different. Hope this helped!
