Mercury (planet)

Mercury
Mercury in true color (by MESSENGER in 2008)
Designations
Pronunciation/ˈmɜːrkjʊri/ ⓘ
AdjectivesMercurian /mərˈkjʊəriən/,[1]
Mercurial /mərˈkjʊəriəl/[2]
Symbol
Orbital characteristics[3]
Epoch J2000
Aphelion0.466697 AU (69.82 million km)
Perihelion0.307499 AU (46.00 million km)
0.387098 AU (57.91 million km)
Eccentricity0.205630[4]
  • 87.9691 d
  • 0.240846 yr
  • 0.5 Mercury synodic days
115.88 d[4]
Average orbital speed
47.36 km/s[4]
174.796°
Inclination
48.331°
Argument of perihelion
29.124°
SatellitesNone
Physical characteristics
Mean radius
  • 2,439.7±1.0 km[6][7]
  • 0.3829 Earths
Flattening0.0009[4]
  • 7.48×107 km2[6]
  • 0.147 Earths
Volume
  • 6.083×1010 km3[6]
  • 0.056 Earths
Mass
  • 3.3011×1023 kg[8]
  • 0.055 Earths
Mean density
5.427 g/cm3[6]
Surface gravity
3.7 m/s2 (0.38 g0)[6]
Moment of inertia factor
0.346±0.014[9]
4.25 km/s[6]
Synodic rotation period
176 d[10]
Sidereal rotation period
  • 58.646 d
  • 1407.5 h[6]
Equatorial rotation velocity
3.026 m/s
2.04′ ± 0.08′ (to orbit)[9]
(0.034°)[4]
North pole right ascension
North pole declination
61.41° [11]
Albedo
Temperature437 K (164 °C) (blackbody temperature)[14]
Surface temp. min mean max
0°N, 0°W [15] −173 °C 67 °C 427 °C
85°N, 0°W[15] −193 °C −73 °C 106.85 °C
−2.48 to +7.25[16]
−0.4[17]
Angular diameter
4.5–13″[4]
Atmosphere[4][18][19]
Surface pressure
trace (≲ 0.5 nPa)
Composition by volume

Mercury is the first planet from the Sun and the smallest in the Solar System. It is a rocky planet with a trace atmosphere and a surface gravity slightly higher than that of Mars. The surface of Mercury is similar to Earth's Moon, being heavily cratered, with an expansive rupes system generated from thrust faults, and bright ray systems, formed by ejecta. Its largest crater, Caloris Planitia, has a diameter of 1,550 km (960 mi), which is about one-third the diameter of the planet (4,880 km or 3,030 mi). Being the most inferior orbiting planet, it always appears close to the sun in Earth's sky, either as a "morning star" or an "evening star.” It is also the planet with the highest delta-v needed to travel to and from all other planets of the Solar System.

Mercury's sidereal year (88.0 Earth days) and sidereal day (58.65 Earth days) are in a 3:2 ratio, in a spin–orbit resonance. Consequently, one solar day (sunrise to sunrise) on Mercury lasts for around 176 Earth days: twice the planet's sidereal year. This means that one side of Mercury will remain in sunlight for one Mercurian year of 88 Earth days; while during the next orbit, that side will be in darkness all the time until the next sunrise after another 88 Earth days. Above the planet's surface is an extremely tenuous exosphere and a faint magnetic field that is strong enough to deflect solar winds. Combined with its high orbital eccentricity, the planet's surface has widely varying sunlight intensity and temperature, with the equatorial regions ranging from −170 °C (−270 °F) at night to 420 °C (790 °F) during sunlight. Due to its very small axial tilt, the planet's poles are permanently shadowed. This strongly suggests that water ice could be present in the craters.

Like the other planets in the Solar System, Mercury formed approximately 4.5 billion years ago. There are many competing hypotheses about Mercury's origins and development, some of which incorporate collision with planetesimals and rock vaporization; as of the early 2020s, many broad details of Mercury's geological history are still under investigation or pending data from space probes. Its mantle is highly homogeneous, which suggests that Mercury had a magma ocean early in its history, like the Moon. According to current models, Mercury may have a solid silicate crust and mantle overlaying a solid outer core, a deeper liquid core layer, and a solid inner core. Mercury is expected to be destroyed, along with Venus, and possibly the Earth and the Moon, when the Sun becomes a Red Giant in approximately seven or eight billion years[20].

Mercury is a classical planet that has been observed and recognized throughout history as a planet (or wandering star). In English, it is named after the ancient Roman god Mercurius (Mercury), god of commerce and communication, and the messenger of the gods. The first successful flyby of Mercury was conducted by Mariner 10 in 1974, and it has since been visited and explored by the MESSENGER and BepiColombo orbiters.

  1. ^ "Mercurian". Lexico UK English Dictionary. Oxford University Press. Archived from the original on March 27, 2020.
  2. ^ "Mercurial". Lexico UK English Dictionary UK English Dictionary. Oxford University Press. Archived from the original on December 22, 2019.
  3. ^ Cite error: The named reference horizons was invoked but never defined (see the help page).
  4. ^ a b c d e f g h Williams, David R. (November 25, 2020). "Mercury Fact Sheet". NASA. Archived from the original on April 3, 2019. Retrieved April 19, 2021.
  5. ^ Cite error: The named reference Souami_Souchay_2012 was invoked but never defined (see the help page).
  6. ^ a b c d e f g Cite error: The named reference nasa was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Seidelmann2007 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Mazarico2014 was invoked but never defined (see the help page).
  9. ^ a b Cite error: The named reference Margot2012 was invoked but never defined (see the help page).
  10. ^ "ESO". ESO. Archived from the original on December 4, 2008. Retrieved June 3, 2021.
  11. ^ a b Archinal, B. A.; Acton, C. H.; A'Hearn, M. F.; Conrad, A.; Consolmagno, G. J.; Duxbury, T.; Hestroffer, D.; Hilton, J. L.; Kirk, R. L.; Klioner, S. A.; McCarthy, D.; Meech, K.; Oberst, J.; Ping, J.; Seidelmann, P. K. (2018). "Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015". Celestial Mechanics and Dynamical Astronomy. 130 (3): 22. Bibcode:2018CeMDA.130...22A. doi:10.1007/s10569-017-9805-5. ISSN 0923-2958.
  12. ^ Cite error: The named reference Mallama was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference MallamaMercury was invoked but never defined (see the help page).
  14. ^ "Atmospheres and Planetary Temperatures". American Chemical Society. July 18, 2013. Archived from the original on January 27, 2023. Retrieved January 3, 2023.
  15. ^ a b Vasavada, Ashwin R.; Paige, David A.; Wood, Stephen E. (February 19, 1999). "Near-Surface Temperatures on Mercury and the Moon and the Stability of Polar Ice Deposits" (PDF). Icarus. 141 (2): 179–193. Bibcode:1999Icar..141..179V. doi:10.1006/icar.1999.6175. ISSN 0019-1035. Figure 3 with the "TWO model"; Figure 5 for pole. Archived (PDF) from the original on November 13, 2012. Retrieved February 18, 2012.
  16. ^ Cite error: The named reference Mallama_and_Hilton was invoked but never defined (see the help page).
  17. ^ "Encyclopedia - the brightest bodies". IMCCE. Archived from the original on July 24, 2023. Retrieved May 29, 2023.
  18. ^ Milillo, A.; Wurz, P.; Orsini, S.; Delcourt, D.; Kallio, E.; Killen, R. M.; Lammer, H.; Massetti, S.; Mura, A.; Barabash, S.; Cremonese, G.; Daglis, I. A.; Angelis, E.; Lellis, A. M.; Livi, S.; Mangano, V.; Torkar, K. (April 2005). "Surface-Exosphere-Magnetosphere System Of Mercury". Space Science Reviews. 117 (3–4): 397–443. Bibcode:2005SSRv..117..397M. doi:10.1007/s11214-005-3593-z. S2CID 122285073.
  19. ^ Berezhnoy, Alexey A. (January 2018). "Chemistry of impact events on Mercury". Icarus. 300: 210–222. Bibcode:2018Icar..300..210B. doi:10.1016/j.icarus.2017.08.034.
  20. ^ "Chapter 6: Aging Into Gianthood - NASA Science". December 11, 2018.
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