Changes

|inclination=1.769°<ref name=neptunefact/>

|inclination=1.769°<ref name=neptunefact/>

|reference=the ecliptic

|reference=the ecliptic

|siderealday=16.11 h<ref name=neptunefact/><ref name=Britannica> "[http://www.britannica.com/eb/article-9110153 Neptune]." ''Encyclopædia Britannica''. 2008. Encyclopædia Britannica Online. Accessed May 6, 2008.</ref>

|siderealday=16.11 h<ref name=neptunefact/><ref name=Britannica>"[http://www.britannica.com/eb/article-9110153 Neptune]." ''Encyclopædia Britannica''. 2008. Encyclopædia Britannica Online. Accessed May 6, 2008.</ref>

|axialtilt=28.32°<ref name=neptunefact/>

|axialtilt=28.32°<ref name=neptunefact/>

|mass=1.0243 * 10²⁶ kg<ref name=neptunefact/>

|mass=1.0243 * 10²⁶ kg<ref name=neptunefact/>

== Physical characteristics ==

== Physical characteristics ==

Neptune is 24,764 km (15,388 miles) in radius. It’s atmosphere is about 80% [[hydrogen]], 19% [[helium]], and 1.5% [[methane]]. Despite being the farthest planet from the sun, Neptune radiates more than twice as much heat as it receives from the Sun. The winds of Neptune are the strongest in the [[solar system]], at 2000 km/hr.<ref name=Arnett/><ref name=Hamilton>Hamilton, Calvin J. "[http://www.solarviews.com/eng/neptune.htm Entry for Neptune]." ''Views of the Solar System'', 2001. Accessed May 7, 2008.</ref> The source of the energy that fuels these winds remains unsettled.<ref name=Arnett/>

Neptune is 24,764&nbsp;km (15,388 miles) in radius. It’s atmosphere is about 80% [[hydrogen]], 19% [[helium]], and 1.5% [[methane]]. Despite being the farthest planet from the sun, Neptune radiates more than twice as much heat as it receives from the Sun. The winds of Neptune are the strongest in the [[solar system]], at 2000&nbsp;km/hr.<ref name=Arnett/><ref name=Hamilton>Hamilton, Calvin J. "[http://www.solarviews.com/eng/neptune.htm Entry for Neptune]." ''Views of the Solar System'', 2001. Accessed May 7, 2008.</ref> The source of the energy that fuels these winds remains unsettled.<ref name=Arnett/>

The planet’s most prominent feature was its Great Dark Spot, a storm similar to [[Jupiter| Jupiter’s]] Great Red Spot. In 1989, when Voyager 2 revealed it, it moved westward at 300 km/s.<ref name=Arnett/><ref name=Smith/> Voyager 2 also revealed an irregular, eastward-moving cloud, called the "scooter," evidently moving with the planet's rotation. Most astronomers believe that this is a plume rising from a deeper deck of clouds.<ref name=Arnett/><ref name=Hamilton/>

The planet’s most prominent feature was its Great Dark Spot, a storm similar to [[Jupiter| Jupiter’s]] Great Red Spot. In 1989, when Voyager 2 revealed it, it moved westward at 300&nbsp;km/s.<ref name=Arnett/><ref name=Smith/> Voyager 2 also revealed an irregular, eastward-moving cloud, called the "scooter," evidently moving with the planet's rotation. Most astronomers believe that this is a plume rising from a deeper deck of clouds.<ref name=Arnett/><ref name=Hamilton/>

When the [[Hubble Space Telescope]] photographed Neptune in 1994, the Great Dark Spot had disappeared. Another great storm of comparable size formed a few months later.<ref name=Arnett/>

When the [[Hubble Space Telescope]] photographed Neptune in 1994, the Great Dark Spot had disappeared. Another great storm of comparable size formed a few months later.<ref name=Arnett/>

=== Magnetosphere ===

=== Magnetosphere ===

Neptune's magnetic field has a magnetic dipole moment variously estimated as 1.5 * 10²⁴ or 2.1 * 10²⁴ N-m/T. The axis of the dipole is also inclined about 47 degrees from the axis of rotation, and displaced from the center by about 13,500 km.<ref name=Hamilton/>

Neptune's magnetic field has a magnetic dipole moment variously estimated as 1.5 * 10²⁴ or 2.1 * 10²⁴ N-m/T. The axis of the dipole is also inclined about 47 degrees from the axis of rotation, and displaced from the center by about 13,500&nbsp;km.<ref name=Hamilton/>

== Ring system ==

== Ring system ==

Boss, in 2002, suggested reviving the old disk-instability hypothesis of planet formation, in which Uranus and Neptune formed through gravitational instability in a gaseous protoplanetary disk, after which a passing star blasted away much of the gaseous envelopes of the two worlds, leaving them much as they are today.<ref name=Boss>Boss, Alan P. "[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-46SVX4B-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=8356c9b57117437b185f44aca5ae71d0 Formation of gas and ice-giant planets]." ''Earth and Planetary Science Letters'' 202(3-4):513-523, September 30, 2002. {{doi|10.1016/S0012-821X(02)00808-7}} Accessed May 7, 2008.</ref> Thommes ''et al.'' suggested another theory: that Uranus and Neptune formed at the same general distance from the Sun as [[Jupiter]] and [[Saturn]] and then ''migrated'' to their present orbits.<ref name=Thommes>Thommes, Edward W., Duncan, Martin J., and Levison, Harold F. "[http://arxiv.org/abs/astro-ph/0111290 The formation of Uranus and Neptune among Jupiter and Saturn]." ''Astron. J.'' 123:2862, 2002. {{arXiv|astro-ph/0111290v1|pdf}} Accessed May 7, 2008.</ref>

Boss, in 2002, suggested reviving the old disk-instability hypothesis of planet formation, in which Uranus and Neptune formed through gravitational instability in a gaseous protoplanetary disk, after which a passing star blasted away much of the gaseous envelopes of the two worlds, leaving them much as they are today.<ref name=Boss>Boss, Alan P. "[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-46SVX4B-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=8356c9b57117437b185f44aca5ae71d0 Formation of gas and ice-giant planets]." ''Earth and Planetary Science Letters'' 202(3-4):513-523, September 30, 2002. {{doi|10.1016/S0012-821X(02)00808-7}} Accessed May 7, 2008.</ref> Thommes ''et al.'' suggested another theory: that Uranus and Neptune formed at the same general distance from the Sun as [[Jupiter]] and [[Saturn]] and then ''migrated'' to their present orbits.<ref name=Thommes>Thommes, Edward W., Duncan, Martin J., and Levison, Harold F. "[http://arxiv.org/abs/astro-ph/0111290 The formation of Uranus and Neptune among Jupiter and Saturn]." ''Astron. J.'' 123:2862, 2002. {{arXiv|astro-ph/0111290v1|pdf}} Accessed May 7, 2008.</ref>

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>, on the other hand, 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.

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> on the other hand, 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.

=== Weather ===

=== Weather ===