Mercury is the innermost and smallest planet in the solar system, orbiting the Sun once every 88 days. It can only be seen in morning or evening twilight.

Physically, Mercury is similar in appearance to the Moon as it is heavily cratered. It has no natural satellites and no substantial atmosphere. The planet has a large iron core which generates a magnetic field about 0.1% as strong as that of the Earth.

Mercury is one of the four terrestrial planets, being a rocky body like the Earth. It consists of approximately 70% metallic and 30% silicate material. The density of the planet is the second-highest in the solar system at 5.43 g/cm³, only slightly less than Earth’s density.

Mercury is the innermost and smallest planet in the solar system, orbiting the Sun once every 88 days. It can only be seen in morning or evening twilight.

Physically, Mercury is similar in appearance to the Moon as it is heavily cratered. It has no natural satellites and no substantial atmosphere. The planet has a large iron core which generates a magnetic field about 0.1% as strong as that of the Earth.

Mercury is one of the four terrestrial planets, being a rocky body like the Earth. It consists of approximately 70% metallic and 30% silicate material. The density of the planet is the second-highest in the solar system at 5.43 g/cm³, only slightly less than Earth’s density.

Earth is the third planet from the Sun and the fifth largest. Home to the human species, it is also referred to as "Planet Earth", "Gaia", "Terra", and "the World".

71% of the Earth's surface is covered with water. The Earth is the first planet known to have liquid water on the surface and is the only place in the universe known to harbor life. The heat capacity of the oceans is also very important in keeping the Earth's temperature relatively stable.

The Earth formed around 4.57 billion years ago. At present, the Earth orbits the Sun once for every 366.26 times it rotates about its axis (which is equal to 365.26 solar days). The Earth's axis of rotation is tilted 23.5° (away from the perpendicular to its orbital plane), producing seasonal variations on the planet's surface.

Solarsystem

The Sun is by far the largest object in the solar system. It is the star at the center of the Solar System. The Earth and other matter (including other planets, asteroids, meteoroids, comets and dust) orbit the Sun. Energy from the Sun (sunlight) supports almost all life on Earth via photosynthesis, and drives the Earth's climate and weather.

The Sun contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest). At present, the mass of the Sun is about 70% hydrogen, 28% helium by mass, other metals amount to less than 2%. This changes slowly over time as the Sun converts hydrogen to helium in its core.

The Sun's energy output (
3.86e33 ergs/second or 386 billion billion megawatts) is produced by nuclear fusion reactions. As it travels out toward the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light.