Changes

|sidereal=2.520379 da<ref name=uranussatfact/>

|sidereal=2.520379 da<ref name=uranussatfact/>

|orbitspeed=5.52 km/s<ref name=Hamilton/>

|orbitspeed=5.52 km/s<ref name=Hamilton/>

|inclination=0.31°<ref name=uranussatfact/><ref name=Hamilton/>

|inclination=0.31°<ref name=Hamilton/><ref name=uranussatfact/>

|siderealday=2.520379 da<ref name=uranussatfact/><ref name=Hamilton/>

|siderealday=2.520379 da<ref name=Hamilton/><ref name=uranussatfact/>

|rotatespeed=16.7 m/s<ref name=calc/>

|rotatespeed=16.7 m/s<ref name=calc/>

|axialtilt=0°<ref name=uranussatfact/>

|axialtilt=0°<ref name=uranussatfact/>

== Orbital characteristics ==

== Orbital characteristics ==

Ariel is in a slightly eccentric orbit around Uranus at an average distance of 191,020 km. Its sidereal month is about 2.52 Earth days. The orbit of Ariel is only slightly inclined from the equator of Uranus but is severely inclined to the ecliptic.

Ariel is in a slightly eccentric orbit around Uranus at an average distance of 191,020&nbsp;km. Its sidereal month is about 2.52 Earth days. The orbit of Ariel is only slightly inclined from the equator of Uranus but is severely inclined to the ecliptic.

Tittemore<ref name=Tittemore/> suggests that Ariel was once in a 4:1 orbital resonance with [[Titania]]. If it was, it is no longer in such a resonance. For this reason, some astronomers suggest that Ariel was much hotter in the past than it is today.<ref name=Arnett/>

Tittemore<ref name=Tittemore/> suggests that Ariel was once in a 4:1 orbital resonance with [[Titania]]. If it was, it is no longer in such a resonance. For this reason, some astronomers suggest that Ariel was much hotter in the past than it is today.<ref name=Arnett/>

=== Surface ===

=== Surface ===

The surface of Ariel has relatively few impact craters, and also a system of interconnecting valleys and rifts.<ref name=Arnett/><ref name=Hamilton/> Some of these valleys bear signs of smoothing by a fluid. Liquid water would not smooth the valley floors in this fashion, and for this reason astronomers suspect that the fluid might have been liquid ammonia or methane. Other valleys and canyons appear to have formed by faulting.

The surface of Ariel has relatively few impact craters, and also a system of interconnecting valleys and rifts.<ref name=Hamilton/><ref name=Arnett/> Some of these valleys bear signs of smoothing by a fluid. Liquid water would not smooth the valley floors in this fashion, and for this reason astronomers suspect that the fluid might have been liquid ammonia or methane. Other valleys and canyons appear to have formed by faulting.

Most of the surface of Ariel appears relatively "young" by [[uniformitarianism|uniformitarian]] standards. In fact, some authorities say that Ariel's surface is the youngest such surface among the major moons of Uranus.<ref name=Britannica/>

Most of the surface of Ariel appears relatively "young" by [[uniformitarianism|uniformitarian]] standards. In fact, some authorities say that Ariel's surface is the youngest such surface among the major moons of Uranus.<ref name=Britannica/>

== Observation and Exploration ==

== Observation and Exploration ==

Ariel is visible from Earth with any telescope having an aperture of 30 cm or more.

Ariel is visible from Earth with any telescope having an aperture of 30&nbsp;cm or more.

The one spacecraft to visit Ariel was [[Voyager 2]]. Voyager approached to within 127,000 km of Ariel on January 24, 1986, and took several images.<ref name=Voyager1>"[http://pds-rings.seti.org/voyager/mission/#v2uenc Voyager Mission Description: Voyager 2 Uranus Encounter]." February 19, 1997. Accessed June 13, 2008.</ref><ref name=Smith>Smith, B.A., Soderblom, L.A., Beebe, R., ''et al.'' "[http://adsabs.harvard.edu/abs/1986Sci...233...43S Voyager 2 in the Uranian system - Imaging science results]." ''Science'' 233:43-64, July 4, 1986. Accessed June 13, 2008.</ref>

The one spacecraft to visit Ariel was [[Voyager 2]]. Voyager approached to within 127,000&nbsp;km of Ariel on January 24, 1986, and took several images.<ref name=Voyager1>"[http://pds-rings.seti.org/voyager/mission/#v2uenc Voyager Mission Description: Voyager 2 Uranus Encounter]." February 19, 1997. Accessed June 13, 2008.</ref><ref name=Smith>Smith, B.A., Soderblom, L.A., Beebe, R., ''et al.'' "[http://adsabs.harvard.edu/abs/1986Sci...233...43S Voyager 2 in the Uranian system - Imaging science results]." ''Science'' 233:43-64, July 4, 1986. Accessed June 13, 2008.</ref>

Today the [[Hubble Space Telescope]] is the most powerful telescope to take images of Ariel.

Today the [[Hubble Space Telescope]] is the most powerful telescope to take images of Ariel.