Changes

|albedo=0.51<ref name=ssdhoriz/>

|albedo=0.51<ref name=ssdhoriz/>

|mfd=0.228 G (2.28 * 10^-5 T)<ref name=uranusfact/>

|mfd=0.228 G (2.28 * 10^-5 T)<ref name=uranusfact/>

|pmdm=3 * 10²⁴ N-m/T<ref name=Humphreys2>Humphreys, D. R. "[http://www.icr.org/index.php?module=articles&action=view&page=329 Beyond Neptune: Voyager II Supports Creation]." [[Institute for Creation Research]]. Accessed April 30, 2008</ref>

|pmdm=3 * 10²⁴ N-m/T<ref name=Humphreys2>Humphreys, D. R. "[https://www.icr.org/index.php?module=articles&action=view&page=329 Beyond Neptune: Voyager II Supports Creation]." [[Institute for Creation Research]]. Accessed April 30, 2008</ref>

|cmdm=2.05 * 10²⁵ N-m/T<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>

|cmdm=2.05 * 10²⁵ N-m/T<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>

|mdt=3195 a<ref name=calc>Calculated from observed present magnetic dipole moment and expected magnetic dipole moment at creation.</ref>

|mdt=3195 a<ref name=calc>Calculated from observed present magnetic dipole moment and expected magnetic dipole moment at creation.</ref>

|mhl=2215 a<ref name=calc/>

|mhl=2215 a<ref name=calc/>

}}

}}

'''Uranus''' is the seventh [[planet]] from the [[sun]], and the third largest. To superficial appearances, it is featureless and dull. Yet the circumstances of its formation, and the characteristics of the system of moons and rings that encircle it, make it one of the most remarkable planets in all the [[solar system]].

'''Uranus''' is the seventh [[planet]] from the [[Sun]], and the third largest. To superficial appearances, it is featureless and dull. Yet, the circumstances of its formation and the characteristics of the system of moons and rings that encircle it make it one of the most remarkable planets in all the [[Solar System]].

== Discovery ==

== Discovery ==

== Orbital characteristics ==

== Orbital characteristics ==

Uranus's average distance from the sun (semi-major axis) is 19.1 AU, which is close to the 19.6 AU predicted by the [[Titius-Bode law]]. Its sidereal year is 84.02 [[Earth]] years. The orbital excentricity is 0.046, which is nearly circular (though the orbit of Earth is more circular still). Uranus's orbit is very slightly inclined to the plane of the ecliptic; in fact its orbital inclination with respect to the ecliptic is the least of those of all the planets.

Uranus's average distance from the Sun (semi-major axis) is 19.1 AU, which is close to the 19.6 AU predicted by the [[Titius-Bode law]]. Its sidereal year is 84.02 [[Earth]] years. Its orbital eccentricity is 0.046, which means that its orbit is nearly circular (though the orbit of Earth is more circular still). Uranus's orbit is very slightly inclined to the plane of the ecliptic; in fact its orbital inclination with respect to the ecliptic is the least of those of all the planets.

== Rotational characteristics ==

== Rotational characteristics ==

Uranus's sidereal day is 17.24 Earth hours. Uranus's rotation is ''retrograde'' with respect to its orbit around the Sun and the orbits of most of the other planets. Moreover its axis is tilted 97.86° with respect to its orbital plane, so that in a sense the planet is rolling on its side.

Uranus's sidereal day is 17.24 Earth hours. Uranus's rotation is ''retrograde'' with respect to its orbit around the Sun and the orbits of most of the other planets. Moreover, its axis is tilted 97.86° with respect to its orbital plane, so that in a sense the planet is rolling on its side.

 

The planet has a magnetic field, whose axis is oriented 60° away from its rotational axis and, furthermore, does not intercept the planet's center.

== Physical characteristics ==

== Physical characteristics ==

Uranus is a [[gas giant]] having a radius of 25,559 km (15,882 miles). Uranus’s atmosphere is about 83 % [[hydrogen]], 15% [[helium]], and 2% [[methane]]. The methane, more than any other constituent, gives Uranus its color.<ref name=rst/>

Uranus is a [[gas giant]] having a radius of 25,559&nbsp;km (15,882 miles). Uranus's atmosphere is about 83% [[hydrogen]], 15% [[helium]], and 2% [[methane]]. The methane, more than any other constituent, gives Uranus its color.<ref name=rst/>

=== Atmosphere ===

=== Atmosphere ===

=== Magnetosphere ===

=== Magnetosphere ===

Uranus has a magnetic field, whose axis is oriented 60° away from its rotational axis and, furthermore, is displaced from the center of mass by as much as one-third the planet's radius. Comparison of Uranus' present magnetic dipole moment with the expected magnetic dipole moment at creation<ref name=Humphreys/> suggests a magnetic-field half-life of 2215 Julian years, slightly more than 1.5 times the half-life of the magnetic field of [[earth]].

Uranus has a magnetic field whose axis is oriented 60° away from its rotational axis and, furthermore, is displaced from the center of mass by as much as one-third the planet's radius. Comparison of Uranus' present magnetic dipole moment with the expected magnetic dipole moment at creation<ref name=Humphreys/> suggests a magnetic-field half-life of 2215 Julian years, slightly more than 1.5 times the half-life of the magnetic field of [[earth]].

== Ring system ==

== Ring system ==

The [[nebular hypothesis]] would not even have allowed Uranus and its twin, [[Neptune]], to form at its tremendous distance from the [[Sun]] in the time generally allotted. As the journal ''Astronomy'' stated the problem:{{cquote|Pssst … astronomers who model the formation of the solar system have kept a dirty little secret: Uranus and Neptune don’t exist. Or at least computer simulations have never explained how planets as big as the two gas giants could form so far from the sun. Bodies orbited so slowly in the outer parts of the sun’s protoplanetary disk that the slow process of gravitational accretion would need more time than the age of the solar system to form bodies with 14.5 and 17.1 times the mass of Earth.}} <ref>R.N., Birth of Uranus and Neptune, ''Astronomy'' '28'(4):30, 2000</ref>

The [[nebular hypothesis]] would not even have allowed Uranus and its twin, [[Neptune]], to form at its tremendous distance from the [[Sun]] in the time generally allotted. As the journal ''Astronomy'' stated the problem:{{cquote|Pssst … astronomers who model the formation of the solar system have kept a dirty little secret: Uranus and Neptune don’t exist. Or at least computer simulations have never explained how planets as big as the two gas giants could form so far from the sun. Bodies orbited so slowly in the outer parts of the sun’s protoplanetary disk that the slow process of gravitational accretion would need more time than the age of the solar system to form bodies with 14.5 and 17.1 times the mass of Earth.}} <ref>R.N., Birth of Uranus and Neptune, ''Astronomy'' '28'(4):30, 2000</ref>

Of course, the time allotted for the formation of the [[solar system]] is generally taken to be the alloted age of the [[Earth]]. THe problem is that Uranus and Neptune would require more than twice the supposed age of the earth to accrete their present masses. In theory, the solar system could be older than the earth itself, but not much older. The solar system has other bodies in it that are much "younger." Nor does the above account for the body of evidence that the solar system is in fact quite young.

Of course, the time allotted for the formation of the [[Solar System]] is generally taken to be the alloted age of the [[Earth]]. The problem is that Uranus and Neptune would require more than twice the supposed age of the earth to accrete their present masses. In theory, the Solar System could be older than the Earth itself, but not much older. The Solar System has other bodies in it that are much "younger." Nor does the above account for the body of evidence that the solar system is in fact quite young.

Desch<ref name=Desch>Desch, S. J. "[http://eagle.la.asu.edu/desch/papers/2007/Desch2007.pdf Mass Distribution and Planet Formation in the Solar Nebula]." Arizona State University, September 21, 2007. Accessed April 29, 2008.</ref> recognizes the problem, and supports a radical alteration of the nebula hypothesis that calls for a ''decretion'' disk, not an accretion disk. But even his model requires that Uranus and Neptune ''exchange places'' early in the process, primarily because Neptune, though about 10 AU further out from the Sun than is Uranus, is yet more massive.

The astrophysicist Steven J. Desch<ref name=Desch>Desch, S. J. "[http://eagle.la.asu.edu/desch/papers/2007/Desch2007.pdf Mass Distribution and Planet Formation in the Solar Nebula]." Arizona State University, September 21, 2007. Accessed April 29, 2008.</ref> recognizes the problem, and supports a radical alteration of the nebula hypothesis that calls for a ''decretion'' disk, not an [[Accretion Disk|accretion disk]]. But even his model requires that Uranus and Neptune ''exchange places'' early in the process, primarily because Neptune, though about 10 AU further out from the Sun than is Uranus, is yet more massive.

=== Orientation of the Uranian system ===

=== Orientation of the Uranian system ===

According to evolutionary theories of how the solar system formed (i.e., the [[nebular hypothesis]]), Uranus's axis should not be tilted 98 degrees with respect to its orbit. Moreover its moons orbit Uranus around its equator, like the hands of a clock around a clock face. Uranus' thirteen rings also are around its equator, so they look vertical. The nebular hypothesis predicts none of these observations.

According to evolutionary theories of how the solar system formed (i.e., the [[nebular hypothesis]]), Uranus's axis should not be tilted 98 degrees with respect to its orbit. Moreover, its moons orbit Uranus around its equator, like the hands of a clock around a clock face. Uranus' thirteen rings also are around its equator, so they look vertical. The nebular hypothesis predicts none of these observations.

Naturalistic [[Astronomy|astronomers]] theorize that Uranus originally formed upright, but suffered a collision with another object, producing its severe tilt. This, however, raises more questions:

Naturalistic [[Astronomy|astronomers]] theorize that Uranus originally formed upright, but suffered a collision with another object, producing its severe tilt. This, however, raises more questions:

# Why is its orbit less eccentric than those of all the other planets except only those of [[Venus]], [[Neptune]], and [[Earth]]?

# Why is its orbit less eccentric than those of all the other planets except only those of [[Venus]], [[Neptune]], and Earth?

# Why is Uranus's orbit less inclined to the ecliptic than is that of any planet except Earth?

# Why is Uranus's orbit less inclined to the ecliptic than is that of any planet except Earth?

# Why are the orbits of Uranus's moons so slightly inclined with respect to Uranus's present equator?<ref name=AiG>Psarris, Spike. "[http://www.answersingenesis.org/creation/v24/i3/uranus.asp Entry for Uranus]." ''Creation'', 24(3):38-40, June 2002. Now hosted by [[Answers in Genesis]]. Accessed April 25, 2008.</ref> Indeed, the vertical orientation of Uranus's moons and of some of its rings was already well-known to astronomers before the Voyager 2 flyby. If the moons formed before the collision, then another series of precisely timed collisions would have been required to change the azimuths of all the orbits, ''and'' the rings&mdash;an absurd violation of [[Occam's razor]]. And if they formed after the collision, then in the absence of any condensing gas cloud, they ought to be inclined at random.

# Why are the orbits of Uranus's moons so slightly inclined with respect to Uranus's present equator?<ref name=AiG>Psarris, Spike. "[http://www.answersingenesis.org/creation/v24/i3/uranus.asp Entry for Uranus]." ''Creation'', 24(3):38-40, June 2002. Now hosted by [[Answers in Genesis]]. Accessed April 25, 2008.</ref> Indeed, the vertical orientation of Uranus's moons and of some of its rings was already well known to astronomers before the Voyager 2 flyby. If the moons formed before the collision, then another series of precisely timed collisions would have been required to change the azimuths of all the orbits, ''and'' the rings&mdash;an absurd violation of [[Occam's razor]]. And if they formed after the collision, then in the absence of any condensing gas cloud, they ought to be inclined at random.

Naturalists try to explain that last by suggesting that Uranus's moons are leftover debris from the collision that tilted its axis. However, Uranus's moons make up only one hundredth of one percent of the mass of the planet, and an impact violent enough to knock the giant over would have produced far more debris than that. (Earth's [[Moon]], also supposed to be the result of a giant collision involving its primary, has a mass of 1.23% that of earth.)<ref name=AiG/><ref name=Psarris>Psarris, Spike. ''Our Created Solar System'' Seattle Creation Conference, 2006.</ref> Moreover, not only are the moons of Uranus oriented well to Uranus's equator, but many of them orbit retrograde to Uranus's own rotation.

Naturalists try to explain that last by suggesting that Uranus's moons are leftover debris from the collision that tilted its axis. However, Uranus's moons make up only one hundredth of one percent of the mass of the planet, and an impact violent enough to knock the giant over would have produced far more debris than that. (Earth's [[Moon]], also supposed to be the result of a giant collision involving its primary, has a mass of 1.23% that of earth.)<ref name=AiG/><ref name=Psarris>Psarris, Spike. ''Our Created Solar System'' Seattle Creation Conference, 2006.</ref> Moreover, not only are the moons of Uranus oriented well to Uranus's equator, but many of them orbit retrograde to Uranus's own rotation.

=== The magnetic field ===

=== The magnetic field ===

The strength of Uranus' magnetic field presented a problem for the evolutionary model when Voyager 2 flew by the planet in 1986. According to the classic dynamo theory, Uranus should not have an appreciable magnetic dipole moment. That it has, did not surprise creationists, because Dr. Russell Humphreys predicted its strength from his own model of the creation of celestial magnetic fields. Humphreys published his model two years before Voyager reconnoitered Uranus.<ref name=Humphreys/><ref name=Humphreys2/>

The strength of Uranus' magnetic field presented a problem when Voyager 2 flew by the planet in 1986. According to the classic dynamo theory, Uranus should not have an appreciable magnetic dipole moment. That it has, did not surprise creationists, because Dr. Russell Humphreys predicted its strength from his own model of the creation of celestial magnetic fields. Humphreys published his model two years before Voyager reconnoitered Uranus.<ref name=Humphreys2/><ref name=Humphreys/>

As mentioned, Uranus' magnetic axis is 60 degrees displaced from Uranus' axis of rotation. It is also displaced from the planet's center by about one-third of the planet's radius. The dynamo theory cannot account for such vast discrepancies. Humphreys' model says nothing about the alignment of a body's magnetic axis with respect to its rotational axis, so these findings do not compromise this model. Humphreys suggests that the displacement results from the asymmetric accretion of additional matter into Uranus' core after the planet's creation. The dynamo theory would have difficulty with this concept, because a dynamo requires a liquid core.<ref name=Humphreys2/>

As mentioned, Uranus' magnetic axis is 60 degrees displaced from Uranus' axis of rotation. It is also displaced from the planet's center by about one-third of the planet's radius. The dynamo theory cannot account for such vast discrepancies. Humphreys' model says nothing about the alignment of a body's magnetic axis with respect to its rotational axis, so these findings do not compromise this model. Humphreys suggests that the displacement results from the asymmetric accretion of additional matter into Uranus' core after the planet's creation. The dynamo theory would have difficulty with this concept, because a dynamo requires a liquid core.<ref name=Humphreys2/>

== Satellites ==

== Satellites ==

Uranus has twenty-seven named satellites and a number of concentric rings. The orbits of its satellites are slightly inclined to Uranus's own equator. Remarkably, many of the revolutions of Uranus's moons are retrograde. Uranus's satellites include [[Miranda]], easily the most remarkable natural satellite in all the [[solar system]].

Uranus has twenty-seven named satellites and a number of concentric rings. The orbits of its satellites are slightly inclined to Uranus's own equator. Remarkably, many of the revolutions of Uranus's moons are retrograde. Uranus's satellites include [[Miranda]], easily the most remarkable natural satellite in all the [[Solar System]].

== Missions to Uranus ==

== Missions to Uranus ==

The only deep-space probe to visit Uranus thus far has been [[Voyager 2]], which flew by Uranus on January 24, 1986. Voyager 2 discovered ten of Uranus's twenty-seven satellites, and two previously unknown rings. Voyager 2 then continued onward to [[Neptune]] before heading out of the [[solar system]].

The only deep-space probe to visit Uranus thus far has been [[Voyager 2]], which flew by Uranus on January 24, 1986. Voyager 2 discovered ten of Uranus's twenty-seven satellites, and two previously unknown rings. Voyager 2 then continued onward to Neptune before heading out of the Solar System.

== Gallery ==

== Gallery ==