Triton (moon)

William Lassell, the discoverer of Triton
The orbit of Triton (red) is opposite in direction and tilted −23° compared to a typical moon's orbit (green) in the plane of Neptune's equator.
Animation of Triton
The Kuiper belt (green), in the Solar System's outskirts, is where Triton is thought to have originated.
Artist's impression of Triton, showing its tenuous atmosphere just over the limb.
Clouds observed above Triton's limb by Voyager 2.
Interpretative geomorphological map of Triton
Triton's bright south polar cap above a region of cantaloupe terrain
Cantaloupe terrain viewed from 130,000 km by Voyager 2, with crosscutting Europa-like double ridges. Slidr Sulci (vertical) and Tano Sulci form the prominent "X".
Tuonela Planitia (left) and Ruach Planitia (center) are two of Triton's cryovolcanic "walled plains". The paucity of craters is evidence of extensive, relatively recent, geologic activity.
NASA illustration detailing the studies of the proposed Trident mission
Neptune (top) and Triton (bottom) three days after flyby of Voyager 2
thumb|Close up of the volcanic province of Leviathan Patera, the caldera in the center of the image. Several pit chains extend radially from the caldera to the right of the image, while the smaller of the two cryolava lakes is seen to the upper left. Just off-screen to the lower left is a fault zone aligned radially with the caldera, indicating a close connection between the tectonics and volcanology of this geologic unit.
thumb|Dark streaks across Triton's south polar cap surface, thought to be dust deposits left by eruptions of nitrogen geysers
thumb|Two large cryolava lakes on Triton, seen west of Leviathan Patera. Combined, they are nearly the size of Kraken Mare on Titan. These features are unusually crater free, indicating they are young and were recently molten.

Largest natural satellite of the planet Neptune, and was the first Neptunian moon to be discovered, on October 10, 1846, by English astronomer William Lassell.

- Triton (moon)

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Photograph taken by NASA's Voyager 2 in 1989

Neptune

Eighth and farthest-known Solar planet from the Sun.

Eighth and farthest-known Solar planet from the Sun.

Photograph taken by NASA's Voyager 2 in 1989
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Galileo Galilei
Urbain Le Verrier
A size comparison of Neptune and Earth
Combined colour and near-infrared image of Neptune, showing bands of methane in its atmosphere, and four of its moons, Proteus, Larissa, Galatea, and Despina
Bands of high-altitude clouds cast shadows on Neptune's lower cloud deck.
The Great Dark Spot (top), Scooter (middle white cloud), and the Small Dark Spot (bottom), with contrast exaggerated.
Four images taken a few hours apart with the NASA/ESA Hubble Space Telescope Wide Field Camera 3
Neptune (red arc) completes one orbit around the Sun (centre) for every 164.79 orbits of Earth. The light blue object represents Uranus.
A diagram showing the major orbital resonances in the Kuiper belt caused by Neptune: the highlighted regions are the 2:3 resonance (plutinos), the nonresonant "classical belt" (cubewanos), and the 1:2 resonance (twotinos).
A simulation showing the outer planets and Kuiper belt: a) before Jupiter and Saturn reached a 2:1 resonance; b) after inward scattering of Kuiper belt objects following the orbital shift of Neptune; c) after ejection of scattered Kuiper belt bodies by Jupiter
Natural-colour view of Neptune with Proteus (top), Larissa (lower right), and Despina (left), from the Hubble Space Telescope
Neptune's moon Proteus
A composite Hubble image showing Hippocamp with other previously discovered inner moons in Neptune's ring system
Neptune's rings
In 2018, the European Southern Observatory developed unique laser-based methods to get clear and high-resolution images of Neptune from the surface of Earth.
A Voyager 2 mosaic of Triton
The appearance of a Northern Great Dark Spot in 2018 is evidence of a huge storm brewing.<ref>{{cite web |title=A storm is coming |url=https://www.spacetelescope.org/images/potw1907a/ |website=spacetelescope.org |access-date=19 February 2019 |language=en |archive-url=https://web.archive.org/web/20190220062857/https://www.spacetelescope.org/images/potw1907a/ |archive-date=20 February 2019 |url-status=live }}</ref>
The Northern Great Dark Spot and a smaller companion storm imaged by Hubble in 2020<ref>{{cite web|url=https://hubblesite.org/contents/news-releases/2020/news-2020-59.html|title=Dark Storm on Neptune Reverses Direction, Possibly Shedding Fragment|author1=Michael H. Wong|author2=Amy Simon|publisher=Hubblesite|date=15 December 2020|access-date=25 December 2020|archive-date=25 December 2020|archive-url=https://web.archive.org/web/20201225153808/https://hubblesite.org/contents/news-releases/2020/news-2020-59.html|url-status=live}}</ref>
The Great Dark Spot, as imaged by Voyager 2
Neptune's shrinking vortex<ref>{{cite web|title=Neptune's shrinking vortex|url=http://www.spacetelescope.org/images/potw1808a/|website=spacetelescope.org|access-date=19 February 2018|archive-url=https://web.archive.org/web/20180219125043/http://www.spacetelescope.org/images/potw1808a/|archive-date=19 February 2018|url-status=live}}</ref>

Its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining 13 known moons were located telescopically until the 20th century.

Europa's trailing hemisphere in approximate natural colour. 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.

Europa (moon)

Smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 80 known moons of Jupiter.

Smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 80 known moons of Jupiter.

Europa's trailing hemisphere in approximate natural colour. 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.
Animation of the Laplace resonance of Io, Europa and Ganymede (conjunctions are highlighted by color changes)
Size comparison of Europa (lower left) with the Moon (top left) and Earth (right)
Approximate natural color (left) and enhanced color (right) Galileo view of leading hemisphere
Realistic-color Galileo mosaic of Europa's anti-Jovian hemisphere showing numerous lineae
Enhanced-color view showing the intricate pattern of linear fractures on Europa's surface
Two possible models of Europa
Europa - internal structure
(artwork; 25 May 2021)
Closeup views of Europa obtained on 26 September 1998; images clockwise from upper left show locations from north to south as indicated at lower left.
Water plumes on Europa detected by the Galileo space probe
Photo composite of suspected water plumes on Europa
Magnetic field around Europa. The red line shows a trajectory of the Galileo spacecraft during a typical flyby (E4 or E14).
A black smoker in the Atlantic Ocean. Driven by geothermal energy, this and other types of hydrothermal vents create chemical disequilibria that can provide energy sources for life.
Europa – possible effect of radiation on biosignature chemicals

Europa is one of the only moons in our solar system with a quantifiable atmosphere, next to Titan, Io, and Triton.

Pictured in 2012 in natural color. The thick atmosphere is orange due to a dense haze.

Titan (moon)

Largest moon of Saturn and the second-largest natural satellite in the Solar System.

Largest moon of Saturn and the second-largest natural satellite in the Solar System.

Pictured in 2012 in natural color. The thick atmosphere is orange due to a dense haze.
Christiaan Huygens discovered Titan in 1655.
Titan's orbit (highlighted in red) among the other large inner moons of Saturn. The moons outside its orbit are (from the outside to the inside) Iapetus and Hyperion; those inside are Rhea, Dione, Tethys, Enceladus, and Mimas.
True-color image of layers of haze in Titan's atmosphere
Trace organic gases in Titan's atmosphere—HNC (left) and HC3N (right).
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Methane clouds (animated; July 2014).
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False-color Cassini radar mosaic of Titan's north polar region. Blue coloring indicates low radar reflectivity, caused by hydrocarbon seas, lakes and tributary networks filled with liquid ethane, methane and dissolved . About half of the large body at lower left, Kraken Mare, is shown. Ligeia Mare is at lower right.
Mosaic of three Huygens images of channel system on Titan
Rimmed lakes of Titan (artist concept)
Near-infrared radiation from the Sun reflecting off Titan's hydrocarbon seas
Radar image of a 139 km-diameter impact crater on Titan's surface, showing a smooth floor, rugged rim, and possibly a central peak.
Ligeia Mare – SAR and clearer despeckled views.
Near-infrared image of Tortola Facula, thought to be a possible cryovolcano
False-color VIMS image of the possible cryovolcano Sotra Patera, combined with a 3D map based on radar data, showing 1000-meter-high peaks and a 1500-meter-deep crater.
Sand dunes in the Namib Desert on Earth (top), compared with dunes in Belet on Titan
Titan - three dust storms detected in 2009–2010.
Voyager 1 view of haze on Titan's limb (1980)
Cassini's Titan flyby radio signal studies (artist's concept)
The balloon proposed for the Titan Saturn System Mission (artistic rendition)
Global map of Titan – with IAU labels (August 2016).
Titan – infrared views (2004–2017)
Titan's North Pole (2014)
Titan's South Pole (2014)

It is second in terms of relative diameter of moons to a gas giant; Titan being 1/22.609 of Saturn's diameter, Triton is larger in diameter relative to Neptune at 1/18.092.

Daniel Rutherford, discoverer of nitrogen

Nitrogen

Chemical element with the symbol N and atomic number 7.

Chemical element with the symbol N and atomic number 7.

Daniel Rutherford, discoverer of nitrogen
The shapes of the five orbitals occupied in nitrogen. The two colours show the phase or sign of the wave function in each region. From left to right: 1s, 2s (cutaway to show internal structure), 2px, 2py, 2pz.
Table of nuclides (Segrè chart) from carbon to fluorine (including nitrogen). Orange indicates proton emission (nuclides outside the proton drip line); pink for positron emission (inverse beta decay); black for stable nuclides; blue for electron emission (beta decay); and violet for neutron emission (nuclides outside the neutron drip line). Proton number increases going up the vertical axis and neutron number going to the right on the horizontal axis.
Molecular orbital diagram of dinitrogen molecule, N2. There are five bonding orbitals and two antibonding orbitals (marked with an asterisk; orbitals involving the inner 1s electrons not shown), giving a total bond order of three.
Solid nitrogen on the plains of Sputnik Planitia on Pluto next to water ice mountains
Structure of [Ru(NH3)5(N2)]2+ (pentaamine(dinitrogen)ruthenium(II)), the first dinitrogen complex to be discovered
Mesomeric structures of borazine, (–BH–NH–)3
Standard reduction potentials for nitrogen-containing species. Top diagram shows potentials at pH 0; bottom diagram shows potentials at pH 14.
Nitrogen trichloride
Nitrogen dioxide at −196 °C, 0 °C, 23 °C, 35 °C, and 50 °C. converts to colourless dinitrogen tetroxide at low temperatures, and reverts to  at higher temperatures.
Fuming nitric acid contaminated with yellow nitrogen dioxide
Schematic representation of the flow of nitrogen compounds through a land environment
A container vehicle carrying liquid nitrogen.

It forms a significant dynamic surface coverage on Pluto and outer moons of the Solar System such as Triton.

Nereid imaged by Voyager 2 in 1989

Nereid (moon)

Third-largest moon of Neptune.

Third-largest moon of Neptune.

Nereid imaged by Voyager 2 in 1989
Nereid's highly eccentric orbit around Neptune.

The unusual orbit suggests that it may be either a captured asteroid or Kuiper belt object, or that it was an inner moon in the past and was perturbed during the capture of Neptune's largest moon Triton.

Photograph of Uranus in true colour (by Voyager 2 in 1986)

Uranus

Seventh planet from the Sun.

Seventh planet from the Sun.

Photograph of Uranus in true colour (by Voyager 2 in 1986)
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Simulated Earth view of Uranus from 1986 to 2030, from southern summer solstice in 1986 to equinox in 2007 and northern summer solstice in 2028.
Size comparison of Earth and Uranus
Diagram of the interior of Uranus
Uranus's atmosphere taken during the Outer Planet Atmosphere Legacy (OPAL) program.
Aurorae on Uranus taken by the Space Telescope Imaging Spectrograph (STIS) installed on Hubble.
The magnetic field of Uranus
(animated; 25 March 2020)
The first dark spot observed on Uranus. Image obtained by the HST ACS in 2006.
Uranus in 2005. Rings, southern collar and a bright cloud in the northern hemisphere are visible (HST ACS image).
Major moons of Uranus in order of increasing distance (left to right), at their proper relative sizes and albedos (collage of Voyager 2 photographs)
Uranus's aurorae against its equatorial rings, imaged by the Hubble telescope. Unlike the aurorae of Earth and Jupiter, those of Uranus are not in line with its poles, due to its lopsided magnetic field.
Crescent Uranus as imaged by Voyager 2 while en route to Neptune

The Uranian satellite system is the least massive among those of the giant planets; the combined mass of the five major satellites would be less than half that of Triton (largest moon of Neptune) alone.

Header of the Discovery Program website (January 2016)

Discovery Program

Series of Solar System exploration missions funded by the US National Aeronautics and Space Administration through its Planetary Missions Program Office.

Series of Solar System exploration missions funded by the US National Aeronautics and Space Administration through its Planetary Missions Program Office.

Header of the Discovery Program website (January 2016)
Depictions of the Lucy and Psyche missions
Asteroid Eros regolith, as viewed by Discovery's NEAR Shoemaker mission
Possible configuration of a lunar sample return spacecraft
Mercury by Discovery's MESSENGER
Mars Geyser Hopper would investigate 'spider' features on Mars, as imaged by an orbiter. Image size: 1 km across.
The Venus Multiprobe Mission involved sending 16 atmospheric probes into Venus in 1999.
Mars Pathfinder's Sojourner rover taking its Alpha Particle X-ray Spectrometer measurement of the Yogi Rock (1997)
Thorium concentrations on the Moon, as mapped by Lunar Prospector
Deep Impact impacted a comet nucleus
Scale comparison of Vesta, Ceres, and the Moon
Kepler spacecraft artist's impression
Artist's impression of proposed TiME lake lander for Saturn's moon Titan
NASA made ion thruster technology available for proposals for the thirteenth Discovery Program mission.
alt=An image of a rocky asteroid|Asteroid 253 Mathilde
alt=A view of the rocky Martian surface|Mars Pathfinder{{'}}s view of Ares Vallis
alt=An animation of the rotation of an asteroid|Animation of the rotation of 433 Eros.
alt=The surface of Mercury|MESSENGER imaging Mercury's surface hollows at Sholem Aleichem.<ref>{{cite web|url=http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=1349 |title=High-resolution Hollows |work=MESSENGER Featured Images |date=March 12, 2014 |publisher=JHU – APL |archive-url=https://web.archive.org/web/20140314010953/http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=1349 |archive-date=March 14, 2014 |url-status=dead }}</ref>
alt=InSight being built|InSight lander in assembly (April 2015, NASA)

Trident, a probe that would conduct a flyby of Neptune and its moon Triton.

Irregular satellites of Jupiter (red), Saturn (yellow), Uranus (green) and Neptune (blue) (excluding Triton). The horizontal axis shows their distance from the planet (semi-major axis) expressed as a fraction of the planet's Hill sphere's radius. The vertical axis shows their orbital inclination. Points or circles represent their relative sizes. Data as of August 2006.

Irregular moon

Irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit.

Irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit.

Irregular satellites of Jupiter (red), Saturn (yellow), Uranus (green) and Neptune (blue) (excluding Triton). The horizontal axis shows their distance from the planet (semi-major axis) expressed as a fraction of the planet's Hill sphere's radius. The vertical axis shows their orbital inclination. Points or circles represent their relative sizes. Data as of August 2006.
Phoebe, Saturn's largest irregular satellite
The power law for the size distribution of objects in the Kuiper belt, where q ≈ 4 and thus N ~ D−3. That is, for every Kuiper beld object of a particular size, there are approximately 8 times as many objects half that size and a thousands times as many objects one-tenth that size.
This diagram illustrates the differences of colour in the irregular satellites of Jupiter (red labels), Saturn (yellow) and Uranus (green). Only irregulars with known colour indices are shown. For reference, the centaur Pholus and three classical Kuiper belt objects are also plotted (grey labels, size not to scale).
For comparison, see also colours of centaurs and KBOs.
The orbits of Jupiter's irregular satellites, showing how they cluster into groups. Satellites are represented by circles that indicate their relative sizes. An object's position on the horizontal axis shows its distance from Jupiter. Its position on the vertical axis indicates its orbital inclination. The yellow lines indicate its orbital eccentricity (i.e. the extent to which its distance from Jupiter varies during its orbit).
Animation of Himalia's orbit. ··
Irregular satellites of Saturn, showing how they cluster into groups. For explanation, see Jupiter diagram
Irregular satellites of Uranus (green) and Neptune (blue) (excluding Triton). For explanation, see Jupiter diagram
Distant Cassini image of Himalia
Animation of Saturn's Inuit group of satellites {{legend2|RoyalBlue| Kiviuq}}{{·}}{{legend2|Lime| Ijiraq}}{{·}}{{legend2|Gold| Paaliaq}}{{·}}{{legend2|OrangeRed| Siarnaq}}{{·}}{{legend2|Cyan|Tarqeq}}
Animation of Phoebe's orbit. {{legend2|RoyalBlue| Saturn}}{{·}}{{legend2| Magenta | Phoebe}}{{·}}{{legend2|Cyan|Titan}}
71 irregular moons of Jupiter (with Callisto for comparison)
58 irregular moons of Saturn (with Iapetus for comparison)
9 irregular moons of Uranus
6 irregular moons of Neptune (excluding Triton)

The term does not refer to shape as Triton is a round moon, but is considered irregular due to its orbit.

Voyager 2

Space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere.

Space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere.

see diagram
Animation of Voyager 2s trajectory around Jupiter ·····
The trajectory of Voyager 2 through the Jovian system
Voyager 2 left the heliosphere on November 5, 2018.
Voyager 1 and 2 speed and distance from Sun
On Voyager 2, both PWS and PRS have remained active, whereas on Voyager 1 the PRS has been off since 2007
NASA map showing trajectories of the Pioneer 10, Pioneer 11, Voyager 1, and Voyager 2 spacecraft.
The current position of Voyager 2 as of December 2018. Note the vast distances condensed into an exponential scale: Earth is one astronomical unit (AU) from the Sun; Saturn is at 10 AU, and the heliopause is at around 120 AU. Neptune is 30.1 AU from the Sun; thus the edge of interstellar space is around four times as far from the Sun as the last planet.
Voyager Golden Record
RTG inner heat source
RTG assembly
RTG unit
Voyager 2 launch on August 20, 1977, with a Titan IIIE/Centaur.
thumb|Animation of Voyager 2{{'s}} trajectory from August 20, 1977, to December 30, 2000
Trajectory of Voyager 2 primary mission.
Plot of Voyager 2{{'s}} heliocentric velocity against its distance from the Sun, illustrating the use of gravity assists to accelerate the spacecraft by Jupiter, Saturn and Uranus. To observe Triton, Voyager 2 passed over Neptune's north pole, resulting in an acceleration out of the plane of the ecliptic, and, as a result, a reduced velocity relative to the Sun.<ref>{{cite web |url=https://solarsystem.nasa.gov/basics/bsf4-1.php |title=Basics of space flight: Interplanetary Trajectories}}</ref>

Five hours after Voyager 2 made its closest approach to Neptune, it performed a close fly-by of Triton, the larger of Neptune's two originally known moons, passing within about 40000 km.

William Lassell

English merchant and astronomer.

English merchant and astronomer.

In 1846, Lassell discovered Triton, the largest moon of Neptune, just 17 days after the discovery of Neptune itself by German astronomer Johann Gottfried Galle, using his self-built instrument.