Changes

| color=Marble white with reddish-brown streaks

| color=Marble white with reddish-brown streaks

| albedo=0.64<ref name=gal1/><ref name=solarviews/>

| albedo=0.64<ref name=gal1/><ref name=solarviews/>

| mfd=0.0024 G<ref name=Kivelson> M. G. Kivelson, K. K. Khurana, S. Joy, C. T. Russell, D. J. Southwood, R. J. Walker, C. Polanskey. "[http://www.sciencemag.org/cgi/content/abstract/276/5316/1239 Europa's Magnetic Signature: Report from Galileo's Pass on 19 December 1996]." ''Science'' 276(5316):1239-1241, May 23, 1997. {{doi|10.1126/science.276.5316.1239}} Accessed May 12, 2008.</ref>

| mfd=0.0024 G<ref name=Kivelson>M. G. Kivelson, K. K. Khurana, S. Joy, C. T. Russell, D. J. Southwood, R. J. Walker, C. Polanskey. "[http://www.sciencemag.org/cgi/content/abstract/276/5316/1239 Europa's Magnetic Signature: Report from Galileo's Pass on 19 December 1996]." ''Science'' 276(5316):1239-1241, May 23, 1997. {{doi|10.1126/science.276.5316.1239}} Accessed May 12, 2008.</ref>

| pmdm=9.13 * 10¹⁸ N-m/T<ref name=calc/>

| pmdm=9.13 * 10¹⁸ N-m/T<ref name=calc/>

| cmdmmt=1.13 * 10²² N-m/T<calc/>

| cmdmmt=1.13 * 10²² N-m/T<calc/>

== Orbital and rotational characteristics ==

== Orbital and rotational characteristics ==

[[Image:Galilean moon Laplace resonance animation.gif|thumb|150 px|left|Orbital resonance of Io, Europa, and Ganymede]]Europa is sixth in order of all of Jupiter's moons, and orbits Jupiter at a semi-major axis of 671,100 km. Its orbit is more eccentric than that of volcanic [[Io]] and is slightly inclined to Jupiter's equator. Europa is in [[tidal lock]] (thus keeping the same face toward Jupiter as it revolves).

[[Image:Galilean moon Laplace resonance animation.gif|thumb|150 px|left|Orbital resonance of Io, Europa, and Ganymede]]Europa is sixth in order of all of Jupiter's moons, and orbits Jupiter at a semi-major axis of 671,100&nbsp;km. Its orbit is more eccentric than that of volcanic [[Io]] and is slightly inclined to Jupiter's equator. Europa is in [[tidal lock]] (thus keeping the same face toward Jupiter as it revolves).

Europa maintains a three-part [[orbital resonance]] or Laplace resonance with Io and Ganymede. These three satellites complete their orbits around Jupiter in the ratio 1:2:4. They also conjoin with one another at their apsides, in a mutually self-correcting manner that allows the resonance to persist. (Most such resonances are unstable and end with one or all bodies changing their orbits.)

Europa maintains a three-part [[orbital resonance]] or Laplace resonance with Io and Ganymede. These three satellites complete their orbits around Jupiter in the ratio 1:2:4. They also conjoin with one another at their apsides, in a mutually self-correcting manner that allows the resonance to persist. (Most such resonances are unstable and end with one or all bodies changing their orbits.)

== Physical characteristics ==

== Physical characteristics ==

[[Image:Europa interior.jpg|thumb|150px|left|Europa cutaway]]At 1,560.8 km in radius, Europa is the fifteenth largest body in the [[solar system]].<ref name=planetsoc/> It is very lightly cratered and thus "geologically young" by [[uniformitarianism|uniformitarian]] standards;<ref name=Arnett/> some authorities suggest an apparent age of 30 million Julian years.<ref name=planetsoc/> Indeed only three craters larger than 5 km in diameter are known to exist on Europa's surface.<ref name=solarviews/><ref name=Arnett/>

[[Image:Europa interior.jpg|thumb|150px|left|Europa cutaway]]At 1,560.8&nbsp;km in radius, Europa is the fifteenth largest body in the [[solar system]].<ref name=planetsoc/> It is very lightly cratered and thus "geologically young" by [[uniformitarianism|uniformitarian]] standards;<ref name=Arnett/> some authorities suggest an apparent age of 30 million Julian years.<ref name=planetsoc/> Indeed only three craters larger than 5&nbsp;km in diameter are known to exist on Europa's surface.<ref name=Arnett/><ref name=solarviews/>

Europa is likely surfaced with [[water]] ice and rock, with a 50-km-deep subterranean ocean deep to this, resting on a silicate floor that surrounds a metallic core. The surface has multiple dark streaks, some measuring 20 km broad. Their origin is uncertain but suspected to be volcanic or geothermal.<ref name=Arnett/>

Europa is likely surfaced with [[water]] ice and rock, with a 50-km-deep subterranean ocean deep to this, resting on a silicate floor that surrounds a metallic core. The surface has multiple dark streaks, some measuring 20&nbsp;km broad. Their origin is uncertain but suspected to be volcanic or geothermal.<ref name=Arnett/>

Detailed measurements by the spacecraft Galileo (December 19, 1996<ref name=Kivelson/>) revealed that Europa does have its own magnetic field, though it is very weak&mdash;only 2.4 milligauss at its equator. This corresponds to a magnetic dipole moment of 9.13 * 10¹⁸ N-m/T. (The dipole is oblique to the currents of the magnetic field of Jupiter, and thus it is more likely internal than external.<ref name=Kivelson/>) Europa's mass suggests a magnetic dipole moment at creation of 1.13 * 10²² N-m/T, according to the [[Russell Humphreys]] magnetic-field model.<ref name=Humphreys>Humphreys, D. R. "[http://www.creationresearch.org/crsq/articles/21/21_3/21_3.html The Creation of Planetary Magnetic Fields]." ''[[Creation Research Society Quarterly]]'' 21(3), December 1984. Accessed April 29, 2008.</ref> Thus the decay time for this field is 861.93 Julian years, and the half-life is 597.45 Julian years. All of the above are consistent with Europa having a small but significantly conductive core and possibly a liquid ocean holding electrolytes in solution.

Detailed measurements by the spacecraft Galileo (December 19, 1996<ref name=Kivelson/>) revealed that Europa does have its own magnetic field, though it is very weak&mdash;only 2.4 milligauss at its equator. This corresponds to a magnetic dipole moment of 9.13 * 10¹⁸ N-m/T. (The dipole is oblique to the currents of the magnetic field of Jupiter, and thus it is more likely internal than external.<ref name=Kivelson/>) Europa's mass suggests a magnetic dipole moment at creation of 1.13 * 10²² N-m/T, according to the [[Russell Humphreys]] magnetic-field model.<ref name=Humphreys>Humphreys, D. R. "[http://www.creationresearch.org/crsq/articles/21/21_3/21_3.html The Creation of Planetary Magnetic Fields]." ''[[Creation Research Society Quarterly]]'' 21(3), December 1984. Accessed April 29, 2008.</ref> Thus the decay time for this field is 861.93 Julian years, and the half-life is 597.45 Julian years. All of the above are consistent with Europa having a small but significantly conductive core and possibly a liquid ocean holding electrolytes in solution.

The [[Hubble Space Telescope]] has detected evidence of an "atmosphere" at pressure 10^-11 bar, containing [[oxygen]].<ref name=Arnett/><ref name=planetsoc/> Most authorities ''do not'' suggest that this oxygen is biotic. Rather, they suggest that sunlight and the charged particles of Jupiter's radiation belt cause the water ice on Europa to vaporize and then to split into [[hydrogen]] and oxygen--and the hydrogen, being much lighter, tends to escape Europa's light gravity (0.135 ''g'') and leave the oxygen.<ref name=Arnett/><ref name=planetsoc/>

The [[Hubble Space Telescope]] has detected evidence of an "atmosphere" at pressure 10⁻¹¹ bar, containing [[oxygen]].<ref name=Arnett/><ref name=planetsoc/> Most authorities ''do not'' suggest that this oxygen is biotic. Rather, they suggest that sunlight and the charged particles of Jupiter's radiation belt cause the water ice on Europa to vaporize and then to split into [[hydrogen]] and oxygen—and the hydrogen, being much lighter, tends to escape Europa's light gravity (0.135 ''g'') and leave the oxygen.<ref name=Arnett/><ref name=planetsoc/>

[[Image:Europa sulfuric.jpg|150 px|right]]More recently, [[sulfuric acid]] has been found on Europa.<ref name=acid>"[http://science.nasa.gov/newhome/headlines/ast30sep99_1.htm Sulfuric Acid Found on Europa]." ''Science@NASA'', September 30, 1999. Accessed February 29, 2008.</ref> This might explain the red striations; they might be composed largely of elemental sulfur.

[[Image:Europa sulfuric.jpg|150 px|right]]More recently, [[sulfuric acid]] has been found on Europa.<ref name=acid>"[http://science.nasa.gov/newhome/headlines/ast30sep99_1.htm Sulfuric Acid Found on Europa]." ''Science@NASA'', September 30, 1999. Accessed February 29, 2008.</ref> This might explain the red striations; they might be composed largely of elemental sulfur.

More than any other extraterrestrial body (except perhaps for [[Mars]]), Europa has long been the subject of intense speculation as to whether it harbors [[extraterrestrial life]]. The Voyager data fueled this speculation, which began with Richard C. Hoagland's startling proposal that Europa might have a liquid ocean that harbored life.<ref name=hoagland>Hoagland, Richard C. "The Europa Enigma." ''Star and Sky'', January, 1980, pp. 16-31. Reproduced in full at ''[http://www.enterprisemission.com/europa.html The Enterprise Mission]'', 1996. Accessed February 29, 2008.</ref> NASA authorities, except for [[Robert Jastrow]], were unsympathetic and highly skeptical of Hoagland's theories.  [[Arthur C. Clarke]], a prominent [[science fiction]] writer, used the concept of life on Europa as a plot point for his [[novel]]s ''2010: Odyssey II'' (later adapted into the [[motion picture]] ''2010: The Year We Make Contact'') and ''2061: Odyssey III''.<ref name=enterprise>Review and history of the Richard C. Hoagland paper at ''[http://www.enterprisemission.com/europa.html The Enterprise Mission]'', 1996. Accessed February 29, 2008.</ref>

More than any other extraterrestrial body (except perhaps for [[Mars]]), Europa has long been the subject of intense speculation as to whether it harbors [[extraterrestrial life]]. The Voyager data fueled this speculation, which began with Richard C. Hoagland's startling proposal that Europa might have a liquid ocean that harbored life.<ref name=hoagland>Hoagland, Richard C. "The Europa Enigma." ''Star and Sky'', January, 1980, pp. 16-31. Reproduced in full at ''[http://www.enterprisemission.com/europa.html The Enterprise Mission]'', 1996. Accessed February 29, 2008.</ref> NASA authorities, except for [[Robert Jastrow]], were unsympathetic and highly skeptical of Hoagland's theories.  [[Arthur C. Clarke]], a prominent [[science fiction]] writer, used the concept of life on Europa as a plot point for his [[novel]]s ''2010: Odyssey II'' (later adapted into the [[motion picture]] ''2010: The Year We Make Contact'') and ''2061: Odyssey III''.<ref name=enterprise>Review and history of the Richard C. Hoagland paper at ''[http://www.enterprisemission.com/europa.html The Enterprise Mission]'', 1996. Accessed February 29, 2008.</ref>

With the arrival of Galileo and the data from Galileo's early exploration of Europa, the speculation became even more feverish.<ref name=resa>"[http://www.resa.net/nasa/europa_life.htm Life on Europa]." ''[http://www.resa.net/nasa/xlife_intro.htm Life on Other Planets in the Solar System]'', October 22, 1998. Accessed February 29, 2008.</ref><ref name=solarviews/><ref name=Arnett/> Even the finding of sulfuric acid, a harsh chemical, on Europa has not dampened that speculation.<ref name=acid/>

With the arrival of Galileo and the data from Galileo's early exploration of Europa, the speculation became even more feverish.<ref name=Arnett/><ref name=solarviews/><ref name=resa>"[http://www.resa.net/nasa/europa_life.htm Life on Europa]." ''[http://www.resa.net/nasa/xlife_intro.htm Life on Other Planets in the Solar System]'', October 22, 1998. Accessed February 29, 2008.</ref> Even the finding of sulfuric acid, a harsh chemical, on Europa has not dampened that speculation.<ref name=acid/>

== Problems for Uniformitarian Theories ==

== Problems for Uniformitarian Theories ==