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]
115.88 d[4]
47.36 km/s[4]
174.796°
Inclination
48.331°
29.124°
SatellitesNone
Physical characteristics
  • 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]
3.7 m/s2 (0.38 g0)[6]
0.346±0.014[9]
4.25 km/s[6]
176 d[10]
  • 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]
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. In English, it is named after the ancient Roman god Mercurius (Mercury), god of commerce and communication, and the messenger of the gods. Mercury is classified as a terrestrial planet, with roughly the same surface gravity as Mars. The surface of Mercury is heavily cratered, as a result of countless impact events that have accumulated over billions of years. 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). Similarly to the Earth's Moon, Mercury's surface displays an expansive rupes system generated from thrust faults and bright ray systems formed by impact event remnants.

Mercury's sidereal year (88.0 Earth days) and sidereal day (58.65 Earth days) are in a 3:2 ratio. This relationship is called spin–orbit resonance, and sidereal here means "relative to the stars". 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.

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 the very small axial tilt, the planet's poles are permanently shadowed. This strongly suggests that water ice could be present in the craters. Above the planet's surface is an extremely tenuous exosphere and a faint magnetic field that is strong enough to deflect solar winds. Mercury has no natural satellite.

As of the early 2020s, many broad details of Mercury's geological history are still under investigation or pending data from space probes. Like other planets in the Solar System, Mercury was formed approximately 4.5 billion years ago. 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 overlying a solid outer core, a deeper liquid core layer, and a solid inner core. There are many competing hypotheses about Mercury's origins and development, some of which incorporate collision with planetesimals and rock vaporization.

  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). 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.