Io (moon)

Io
The dark spot just left of the center is the erupting volcano Prometheus. The whitish plains on either side of it are coated with volcanically deposited sulfur dioxide frost, whereas the yellower regions contain a higher proportion of sulfur.
Enhanced color image of Io from the Galileo spacecraft, taken in 1999.
Discovery
Discovered byGalileo Galilei
Discovery date8 January 1610[1]
Designations
Pronunciation/ˈ./[2] or as Greco-Latin Īō (approximated as /ˈ./)[citation needed]
Named after
Ἰώ Īō
Jupiter I
AdjectivesIonian /ˈniən/[3][4]
Orbital characteristics
Periapsis420000 km (0.002808 AU)
Apoapsis423400 km (0.002830 AU)
Mean orbit radius
421700 km (0.002819 AU)
Eccentricity0.0040313019
1.769137786 d (152853.5047 s, 42.45930686 h)
17.334 km/s
Inclination0.05° (to Jupiter's equator)
2.213° (to the ecliptic)
Satellite ofJupiter
GroupGalilean moon
Physical characteristics
Dimensions3,660.0 × 3,637.4 × 3,630.6 km[5]
Mean radius
1821.6±0.5 km (0.28592 Earths)[6]
41698064.7357 km2 (0.082 Earths)
Volume2.5319064907×1010 km3 (0.023 Earths)
Mass(8.931938±0.000018)×1022 kg (0.015 Earths)[6]
Mean density
3.528±0.006 g/cm3 (0.639 Earths)[6]
1.796502844 m/s2 (0.1831923077 g)
0.37824±0.00022[7]
2,558.3174910781 m/s
synchronous
Equatorial rotation velocity
271 km/h
Albedo0.63±0.02[6]
Surface temp. min mean max
Surface 90 K 110 K 130 K[8]
5.02 (opposition)[9]
1.2 arcseconds[10]
Atmosphere
Surface pressure
0.5 to 4 mPa (4.93×10−9 to 3.95×10−8 atm)
Composition by volume90% sulfur dioxide

Io (/ˈ./), or Jupiter I, is the innermost and second-smallest of the four Galilean moons of the planet Jupiter. Slightly larger than Earth's moon, Io is the fourth-largest moon in the Solar System, has the highest density of any moon, the strongest surface gravity of any moon, and the lowest amount of water by atomic ratio of any known astronomical object in the Solar System. It was discovered in 1610 by Galileo Galilei and was named after the mythological character Io, a priestess of Hera who became one of Zeus's lovers.

With over 400 active volcanoes, Io is the most geologically active object in the Solar System.[11][12][13] This extreme geologic activity is the result of tidal heating from friction generated within Io's interior as it is pulled between Jupiter and the other Galilean moons—Europa, Ganymede and Callisto. Several volcanoes produce plumes of sulfur and sulfur dioxide that climb as high as 500 km (300 mi) above the surface. Io's surface is also dotted with more than 100 mountains that have been uplifted by extensive compression at the base of Io's silicate crust. Some of these peaks are taller than Mount Everest, the highest point on Earth's surface.[14] Unlike most moons in the outer Solar System, which are mostly composed of water ice, Io is primarily composed of silicate rock surrounding a molten iron or iron sulfide core. Most of Io's surface is composed of extensive plains with a frosty coating of sulfur and sulfur dioxide.

Io's volcanism is responsible for many of its unique features. Its volcanic plumes and lava flows produce large surface changes and paint the surface in various subtle shades of yellow, red, white, black, and green, largely due to allotropes and compounds of sulfur. Numerous extensive lava flows, several more than 500 km (300 mi) in length, also mark the surface. The materials produced by this volcanism make up Io's thin, patchy atmosphere, and they also greatly affect the nature and radiation levels of Jupiter's extensive magnetosphere. Io's volcanic ejecta also produce a large plasma torus around Jupiter.

Io played a significant role in the development of astronomy in the 17th and 18th centuries; discovered in January 1610 by Galileo Galilei, along with the other Galilean satellites, this discovery furthered the adoption of the Copernican model of the Solar System, the development of Kepler's laws of motion, and the first measurement of the speed of light. Viewed from Earth, Io remained just a point of light until the late 19th and early 20th centuries, when it became possible to resolve its large-scale surface features, such as the dark-red polar and bright equatorial regions. In 1979, the two Voyager spacecraft revealed Io to be a geologically active world, with numerous volcanic features, large mountains, and a young surface with no obvious impact craters. The Galileo spacecraft performed several close flybys in the 1990s and early 2000s, obtaining data about Io's interior structure and surface composition. These spacecraft also revealed the relationship between Io and Jupiter's magnetosphere and the existence of a belt of high-energy radiation centered on Io's orbit. Io receives about 3,600 rem (36 Sv) of ionizing radiation per day.[15]

Further observations have been made by Cassini–Huygens in 2000, New Horizons in 2007, and Juno since 2017, as well as from Earth-based telescopes and the Hubble Space Telescope.

  1. ^ Cite error: The named reference IAUMoonDiscoveries was invoked but never defined (see the help page).
  2. ^ "Io". Lexico UK English Dictionary. Oxford University Press. Archived from the original on 29 February 2020.
    "Io". Merriam-Webster.com Dictionary.
  3. ^ S. W. Kieffer (1982) "Ionian Volcanism", in David Morrison, ed., Satellites of Jupiter, vol. 3, International Astronomical Union
  4. ^ "Electron Beams and Ion Composition Measured at Io and in Its Torus", Science, 1996 October 18
  5. ^ Thomas, P. C.; et al. (1998). "The Shape of Io from Galileo Limb Measurements". Icarus. 135 (1): 175–180. Bibcode:1998Icar..135..175T. doi:10.1006/icar.1998.5987.
  6. ^ a b c d Yeomans, Donald K. (13 July 2006). "Planetary Satellite Physical Parameters". JPL Solar System Dynamics.
  7. ^ Schubert, G.; Anderson, J. D.; Spohn, T.; McKinnon, W. B. (2004). "Interior composition, structure and dynamics of the Galilean satellites". In Bagenal, F.; Dowling, T. E.; McKinnon, W. B. (eds.). Jupiter : the planet, satellites, and magnetosphere. New York: Cambridge University Press. pp. 281–306. ISBN 978-0521035453. OCLC 54081598.
  8. ^ Rathbun, J. A.; Spencer, J.R.; Tamppari, L.K.; Martin, T.Z.; Barnard, L.; Travis, L.D. (2004). "Mapping of Io's thermal radiation by the Galileo photopolarimeter-radiometer (PPR) instrument". Icarus. 169 (1): 127–139. Bibcode:2004Icar..169..127R. doi:10.1016/j.icarus.2003.12.021.
  9. ^ "Classic Satellites of the Solar System". Observatorio ARVAL. Archived from the original on 9 July 2011. Retrieved 28 September 2007.
  10. ^ "Io". www.eso.org. 5 December 2001. Retrieved 21 May 2022.
  11. ^ Rosaly MC Lopes (2006). "Io: The Volcanic Moon". In Lucy-Ann McFadden; Paul R. Weissman; Torrence V. Johnson (eds.). Encyclopedia of the Solar System. Academic Press. pp. 419–431. ISBN 978-0-12-088589-3.
  12. ^ Lopes, R. M. C.; et al. (2004). "Lava lakes on Io: Observations of Io's volcanic activity from Galileo NIMS during the 2001 fly-bys". Icarus. 169 (1): 140–174. Bibcode:2004Icar..169..140L. doi:10.1016/j.icarus.2003.11.013.
  13. ^ Cite error: The named reference NYT-20190626 was invoked but never defined (see the help page).
  14. ^ Schenk, P.; et al. (2001). "The Mountains of Io: Global and Geological Perspectives from Voyager and Galileo". Journal of Geophysical Research. 106 (E12): 33201–33222. Bibcode:2001JGR...10633201S. doi:10.1029/2000JE001408.
  15. ^ "2000 February 29, SPS 1020 (Introduction to Space Sciences)". CSUFresno.edu. 29 February 2000. Archived from the original on 25 July 2008.