Mercury

The smallest planet in the Solar System, and the closest planet to the Sun. Explore the planet of Mercury here!

Formation

After the Sun ignited hydrogen and began to supply energy to the Solar System, space around the Sun was immediately showered by a pressure wave of radiation, pushing the lighter gas and dust far out into the Solar System. Heavier rocky material was not affected, and over time collided to form larger planetesimals. These planetesimals fuel the planets’ formation as they fall under the gravitational pull of the increasing planetary mass, eventually forming Mercury.

Composition

Like the other terrestrial planets, Mercury has a silicate crust and a molten iron core. Mercury is the second densest planet in the Solar System, with only Earth being denser. If the effects of gravity were factored out, Mercury is easily the densest planet in the Solar System thanks to the heavy rocky material that survived the Sun’s initial radiation blast!

Surface

The surface of Mercury is riddled with craters, evidence left behind of a time where comets and asteroids collided with Mercury in the young Solar System. Mercury experienced geological activity, evidenced by the various smooth plains between crater impacts, but has been inactive for billions of years. Mercury experiences the most drastic temperature differences in the Solar System. At the equator during a Mercury Day, the temperature reaches 800 degrees Fahrenheit, while during the night, the temperature is a frigid -280 degrees Fahrenheit! Mercury has a very thin atmosphere. In fact, it’s so diffuse that it regularly loses and replenishes the gas molecules that make up the atmosphere, giving the atmosphere a designation as an exosphere.

Magnetic Field

Mercury has a magnetic field that is only one hundredth that of Earth’s magnetic field. Due to Mercury’s close proximity to the Sun, some of the particles in the Solar winds will travel down the magnetic field of Mercury in a tornado like fashion, striking the poles of Mercury and causing Solar weathering. The majority of the particles are deflected. The magnetic field of Mercury is also found to be breaking and reforming thanks to the strength of the Sun’s magnetic field and the close proximity of Mercury to the Sun.

Satellites

There have been only two satellites to visit Mercury, with a third on its way. Mariner 10 was the first satellite to visit multiple planets, visiting Venus to correct its speed enough to allow close encounters with Mercury. Mariner 10 made three flybys of Mercury, detecting a magnetic field in its first encounter, imaging half the planet on the second, and taking more detailed magnetic field measurements on the satellite’s last encounter.

The second satellite to visit Mercury was MESSENGER. Designed to answer questions about the high density of Mercury, the structure of the magnetic field, determining if Mercury has an atmosphere, and even if there is water ice at the poles. MESSENGER accomplished many of these tasks over the satellites two year program, taking detailed pictures of the planet’s surface and measurements of the magnetic field. MESSENGER informed us of water ice at the poles of Mercury, and organic compounds on the surface. After two years of orbiting Mercury, MESSENGER was crashed into the surface concluding the mission.

Currently the satellite BepiColombo is in transit to orbit Mercury, passing by the planet in a close encounter in 2021. BepiColombo will have two separate missions, with one probe designed to image the surface of Mercury in even better detail than MESSENGER, while the other will study the planets magnetic field. The satellite will not be in orbit around Mercury until 2025, at which point the two missions will begin in earnest.