Mercury (planet)

Mercuryplanet MercuryMercurioDe GraftMercurianMercury’splanet(Mercury)3:2 spin–orbit resonancea planet
Mercury is the smallest and innermost planet in the Solar System.wikipedia
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Solar System

outer Solar Systeminner Solar SystemSol system
Mercury is the smallest and innermost planet in the Solar System. Mercury is one of four terrestrial planets in the Solar System, and is a rocky body like Earth.
Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.

List of Solar System objects by size

largestequatorial radiusfifteenth-largest object
It is the smallest planet in the Solar System, with an equatorial radius of 2439.7 km. Mercury is also smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan.
For instance, Uranus is larger than Neptune but less massive, and although Ganymede and Titan are larger than Mercury, they have less than half Mercury's mass. This means some objects in the lower tables, despite their smaller radii, may be more massive than objects in the upper tables because they have a higher density.

Ganymede (moon)

GanymedeAtmosphere of GanymedeGanymedans
It is the smallest planet in the Solar System, with an equatorial radius of 2439.7 km. Mercury is also smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan.
It has a diameter of 5,268 km and is 8% larger than the planet Mercury, although only 45% as massive.

BepiColombo

MioStrofio
The BepiColombo spacecraft is planned to arrive at Mercury in 2025.
BepiColombo is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) to the planet Mercury.

Venus

Morning Starevening starCytherocentric
Like Venus, Mercury orbits the Sun within Earth's orbit as an inferior planet, and never exceeds 28° away from the Sun when viewed from Earth.
Venus is by far the hottest planet in the Solar System, with a mean surface temperature of 735 K, even though Mercury is closer to the Sun.

MESSENGER

MErcury Surface, Space ENvironment, GEochemistry and RangingMESSENGER Mercury probeMLA
Two spacecraft have visited Mercury: Mariner 10 flew by in 1974 and 1975; and MESSENGER, launched in 2004, orbited Mercury over 4,000 times in four years before exhausting its fuel and crashing into the planet's surface on April 30, 2015.
Messenger (stylized as MESSENGER, a backronym for "MErcury Surface, Space ENvironment, GEochemistry, and Ranging"; the name is a reference to the messenger deity of the same name from Roman mythology) was a NASA robotic spacecraft that orbited the planet Mercury between 2011 and 2015.

Titan (moon)

TitanSaturn's moon Titanatmosphere
It is the smallest planet in the Solar System, with an equatorial radius of 2439.7 km. Mercury is also smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan.
It is the second-largest moon in the Solar System after Jupiter's moon Ganymede, and is larger than the smallest planet, Mercury, but only 40% as massive.

Planet

planetsFormer classification of planetsplanetary-mass object
Mercury is the smallest and innermost planet in the Solar System.
In order of increasing distance from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four giant planets, Jupiter, Saturn, Uranus, and Neptune.

Terrestrial planet

terrestrial planetsrockyrocky planet
Mercury is one of four terrestrial planets in the Solar System, and is a rocky body like Earth.
Within the Solar System, the terrestrial planets are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth, and Mars.

Planetary core

corecoresmetallic core
Although Earth's high density results appreciably from gravitational compression, particularly at the core, Mercury is much smaller and its inner regions are not as compressed.
In the Solar System, core size can range from about 20% (Moon) to 85% of a planet's radius (Mercury).

Geology of Mercury

geologycrustal modificationgeologic map
Because knowledge of Mercury's geology had been based only on the 1975 Mariner 10 flyby and terrestrial observations, it is the least understood of the terrestrial planets.
This stems largely from Mercury's proximity to the Sun which makes reaching it with spacecraft technically challenging and Earth-based observations difficult.

List of craters on Mercury

crater on MercuryCraters on Mercurycrater in Mercury
Craters on Mercury range in diameter from small bowl-shaped cavities to multi-ringed impact basins hundreds of kilometers across.
This is a list of named craters on Mercury, the innermost planet of the Solar System (for other features, see list of geological features on Mercury).

Mars

Martianplanet MarsRed Planet
Mercury's surface is more heterogeneous than either Mars's or the Moon's, both of which contain significant stretches of similar geology, such as maria and plateaus.
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury.

Crust (geology)

crustEarth's crustcrustal
Based on data from the Mariner 10 mission and Earth-based observation, Mercury's crust is estimated to be 35 km thick.
The crusts of Earth, Moon, Mercury, Venus, Mars, Io, and other planetary bodies formed via igneous processes, and were later modified by erosion, impact cratering, volcanism, and sedimentation.

Escarpment

scarpscarpsescarpments
Escarpments or rupēs are named for ships of scientific expeditions.
On other Solar System bodies such as Mercury, Mars, and the Moon, the Latin term rupes is used for an escarpment.

Impact crater

cratercratersimpact basin
The largest known crater is, with a diameter of 1,550 km. The impact that created the Caloris Basin was so powerful that it caused lava eruptions and left a concentric ring over 2 km tall surrounding the impact crater.
Impact craters are the dominant geographic features on many solid Solar System objects including the Moon, Mercury, Callisto, Ganymede and most small moons and asteroids.

Caloris Planitia

CalorisCaloris impact
During this time Mercury was volcanically active; basins such as the Caloris Basin were filled by magma, producing smooth plains similar to the maria found on the Moon.
Caloris Planitia is a plain within a large impact basin on Mercury, informally named Caloris, about 1,550 km in diameter.

Late Heavy Bombardment

heavy bombardmentintense early bombardmentEarliest evidence for life
Mercury was heavily bombarded by comets and asteroids during and shortly following its formation 4.6 billion years ago, as well as during a possibly separate subsequent episode called the Late Heavy Bombardment that ended 3.8 billion years ago.
During this interval, a disproportionately large number of asteroids are theorized to have collided with the early terrestrial planets in the inner Solar System, including Mercury, Venus, Earth, and Mars.

Space weathering

space-weathereddarkenslighter, disturbed soil
Like the Moon, the surface of Mercury has likely incurred the effects of space weathering processes, including Solar wind and micrometeorite impacts.
Bodies without atmospheres (including the Moon, Mercury, the asteroids, comets, and most of the moons of other planets) take on many weathering processes:

Inferior and superior planets

inferior planetsuperior planetinferior planets
Like Venus, Mercury orbits the Sun within Earth's orbit as an inferior planet, and never exceeds 28° away from the Sun when viewed from Earth.
In the reference frame of the Earth, in which the terms were originally used, the inferior planets are Mercury and Venus, while the superior planets are Mars, Jupiter, Saturn, Uranus and Neptune.

Moon

lunarthe MoonLuna
Mercury's surface is more heterogeneous than either Mars's or the Moon's, both of which contain significant stretches of similar geology, such as maria and plateaus. Like the Moon, the surface of Mercury has likely incurred the effects of space weathering processes, including Solar wind and micrometeorite impacts. Mercury's surface appears heavily cratered and is similar in appearance to the Moon's, indicating that it has been geologically inactive for billions of years.
Similar shrinkage features exist on Mercury.

Ice

water iceicyicing
On November 29, 2012, NASA confirmed that images from MESSENGER had detected that craters at the north pole contained water ice.
In the Solar System, ice is abundant and occurs naturally from as close to the Sun as Mercury to as far away as the Oort cloud objects.

Inter-crater plains on Mercury

Inter-crater plainsintercrater plainsplains in the regions between craters
Gently rolling, hilly plains in the regions between craters are Mercury's oldest visible surfaces, predating the heavily cratered terrain.
Inter-crater plains on Mercury are a land-form consisting of plains between craters on Mercury.

Orbital resonance

1:1 resonanceresonancemean-motion resonance
Mercury is tidally locked with the Sun in a 3:2 spin-orbit resonance, and rotates in a way that is unique in the Solar System.
Numerical simulations have suggested that the eventual formation of a perihelion secular resonance between Mercury and Jupiter (g 1 = g 5 ) has the potential to greatly increase Mercury's eccentricity and possibly destabilize the inner Solar System several billion years from now.

Tolstoj (crater)

TolstojTolstoj crater
A notable basin is the 400 km wide, multi-ring Tolstoj Basin that has an ejecta blanket extending up to 500 km from its rim and a floor that has been filled by smooth plains materials.
Tolstoj is a large, ancient impact crater at latitude −15, longitude 165 on Mercury.