# Europa (moon)

Europa
Europa's trailing hemisphere in approximate natural color. The prominent crater in the lower right is Pwyll and the darker regions are areas where Europa's primarily water ice surface has a higher mineral content. Imaged on 7 September 1996 by Galileo spacecraft.
Discovery
Discovered byGalileo Galilei
Simon Marius
Discovery date8 January 1610
Designations
Jupiter II
Orbital characteristics[2]
Epoch 8 January 2004
Periapsis664862 km[a]
Apoapsis676938 km[b]
670900 km[1]
Eccentricity0.009[1]
3.551181 d[1]
13.740 km/s[1]
Inclination0.470° (to Jupiter's equator)
1.791° (to the ecliptic)[1]
Satellite ofJupiter
Physical characteristics
1560.8±0.5 km (0.245 Earths)[3]
3.09×107 km2 (0.061 Earths)[c]
Volume1.593×1010 km3 (0.015 Earths)[d]
Mass(4.799844±0.000013)×1022 kg (0.008 Earths)[3]
Mean density
3.013±0.005 g/cm3[3]
1.314 m/s2 (0.134 g)[e]
0.346±0.005[4] (estimate)
2.025 km/s[f]
Synchronous
0.1°[5]
Albedo0.67 ± 0.03[3]
Surface temp. min mean max
Surface ≈ 50 K 102 K (−171.15°C) 125 K
5.29 (opposition)[3]
Atmosphere
Surface pressure
0.1 µPa (10−12 bar)[6]

Europa is a large moon of the planet Jupiter. It is a little smaller than Earth's Moon and it is the sixth largest moon in the solar system.

Europa's diameter is about 3000 kilometers. It probably has an iron core, and an atmosphere that's mostly oxygen. The surface is icy and very smooth. There are not a lot of craters, but there are some cracks and lines. Because the surface is so young and smooth, scientists believe that there is a liquid ocean under the surface, a so-called subsurface (below the surface) ocean, and that it is kept warm by tidal heating.[7] In other words, Jupiter's strong gravitational pull on Europa makes it warm.

The moon Europa was found by Simon Marius in December 1609. Galileo Galilei first saw the moon in January 1610 (he did not know Marius had found it). Simon Marius was the one who had the idea of the name 'Europa'.

The moon Europa is named after a princess from Greek mythology who became the first queen of Crete. However, people usually called Europa 'Jupiter II' until the middle of the 20th century.

## References

1. "Overview of Europa Facts". NASA. Archived from the original on 26 March 2014. Retrieved 27 December 2007.
2. "JPL HORIZONS solar system data and ephemeris computation service". Solar System Dynamics. NASA, Jet Propulsion Laboratory. Retrieved 10 August 2007.
3. Yeomans, Donald K. (13 July 2006). "Planetary Satellite Physical Parameters". JPL Solar System Dynamics. Retrieved 5 November 2007.
4. Showman, A. P.; Malhotra, R. (1 October 1999). "The Galilean Satellites". Science. 286 (5437): 77–84. doi:10.1126/science.286.5437.77. PMID 10506564.
5. Bills, Bruce G. (2005). "Free and forced obliquities of the Galilean satellites of Jupiter". Icarus. 175 (1): 233–247. Bibcode:2005Icar..175..233B. doi:10.1016/j.icarus.2004.10.028.
6. McGrath (2009). "Atmosphere of Europa". In Pappalardo, Robert T.; McKinnon, William B.; Khurana, Krishan K. (eds.). Europa. University of Arizona Press. ISBN 978-0-8165-2844-8.
7. Greenberg, Richard; Europa: The Ocean Moon: Search for an Alien Biosphere, Springer Praxis Books, 2005

Notes

1. Periapsis is derived from the semimajor axis (a) and eccentricity (e): a(1−e).
2. Apoapsis is derived from the semimajor axis (a) and eccentricity (e): a(1+e).
3. Surface area derived from the radius (r): 4πr 2
4. Volume derived from the radius (r): 4/3πr 3
5. Surface gravity derived from the mass (m), the gravitational constant (G) and the radius (r): Gm/r 2
6. Escape velocity derived from the mass (m), the gravitational constant (G) and the radius (r): ${\displaystyle \textstyle {\sqrt {\frac {2Gm}{r}}}}$