Antenna III — Neptune & Solar System Reconnaissance Terminal

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📡 Antenna III — Neptune & Solar System Reconnaissance Terminal [Sector Sol-VIII] Antenna III — Sol-VIII

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PLANETARY_TELEMETRY.EXE ▼ ✕

Primary body: Neptune (Sol-VIII)

Equatorial radius24,764 km

Polar radius24,341 km

Flattening0.0171 (b/a 0.9829)

Obliquity28.32°

System III rotation16h 06m 36s

Solar irradiance1.53 W/m²

Transit and link budget

Launch15 Oct 2001

Neptune arrival07 Jan 2025

Cruise duration8,485 days

Heliocentric range29.88 AU

Range to Earth28.89 AU

Spacecraft event time--:--:--

Earth received time--:--:--

One-way light time04h 08m

Selected target

ObjectNEPTUNE

DesignationSol-VIII

ClassificationIce giant primary

Dimensions24,764 km equatorial

Semi-major axisprimary

Sidereal period164.79 years

Eccentricity0.0086

Inclination1.77° to ecliptic

Spin state16.11 h prograde

Geometric albedo0.442

Surface rastersynthesised

Naiad – Thalassa 73:69 resonance

Resonant argument73λₜ − 69λₙ − 4Ωₙ

φ libration180.0°

Naiad node height+0 km

Separation now0 km

At last conjunction—

Published, Brozović 2020~3,540 km

Conjunction pattern· · · ·

FLIGHT_NAVIGATION_DISPATCH ▼ ✕

Target selector, 16 satellites

Resonance display

Simulation dynamics

Ring system

Galle (N42)41,900 km

Le Verrier (N53)53,200 km

Lassell sheet53,200–57,200 km

Arago (N57)57,200 km

Galatea ring61,953 km

Adams, five arcs62,932 km

Telemetry stream connected, Antenna III to Deep Space Network

Kepler solver: Newton, 5 iterations

Target: NEPTUNE

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About Antenna III

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Antenna III
Version 5.0.2026 (Windows XP edition)
Created by Dr Mehzeb Chowdhury

Launched 15 October 2001 under the UKSO mission archive, Antenna III crossed roughly 30 astronomical units and reached Sector Sol-VIII on 7 January 2025, an 8,485 day cruise. It has been on station ever since, returning continuous telemetry on Neptune, the ring system, all sixteen confirmed satellites, and the 73:69 resonance between Naiad and Thalassa.

The clocks are live. Ranges and light time are computed for the moment you open this page, not for the arrival epoch, using Keplerian elements for Earth and Neptune. Neptune sits 29.88 AU from the Sun and drifts inward until its 2042 perihelion. The range to Earth swings between about 28.9 and 30.9 AU over a synodic year of 367 days, so one-way light time runs from roughly 4h 00m at opposition to 4h 17m at conjunction. Spacecraft event time is the clock aboard; Earth received time is when the same packet reaches the ground.

Where the numbers come from. Inner moon elements follow Brozović et al. (2020), Icarus 338, referred to Neptune's equator. Irregular moons use proper (long term averaged) elements referred to the ecliptic, which is why their orbit planes are attached to the ecliptic frame rather than the equatorial one. Triton's 156.885° is its inclination to Neptune's equator, not to the ecliptic.

What is modelled. Positions come from a Kepler solver: mean anomaly advances uniformly, Newton iteration gives the eccentric anomaly, and radius and true anomaly follow. Nereid at e = 0.751 therefore whips through periapsis rather than crawling round at constant rate. Tidally locked moons keep their long axis pointing at Neptune. Nereid spins freely at 11.594 h, because it is not locked.

The 73:69 path. The resonant argument is φ = 73λₜ − 69λₙ − 4Ωₙ. Eliminating Ωₙ gives λₙ − Ωₙ = 73ψ/4 + φ/4, where ψ is Naiad's longitude relative to Thalassa, so in Thalassa's rotating frame Naiad carries 73/4 = 18.25 vertical swings per lap it gains, and the track only closes after four laps. The 4 is the order of the resonance, not a lobe count. Each successive conjunction therefore advances the phase by exactly a quarter cycle, which is where the up, up, down, down sequence comes from, and why the moons pass about 3,540 km apart instead of the 1,851 km their orbits are separated by. φ librates about 180° with an amplitude of roughly 66° over about 1.9 years, following the values measured by Brozović et al. (2020), which is why the separation at conjunction is not the same every time.

What is not real. Surfaces are procedural: there is no imagery of any inner Neptunian moon at better than a few kilometres per pixel, and none at all for the irregulars. Neptune's enhanced colour view reproduces the familiar Voyager 2 look, which Irwin et al. (2024) showed is a contrast stretch; the true colour view is the paler greenish blue. Bodies are enlarged and outer orbits are compressed by default, with both factors reported in the panels and both switchable to 1:1.

Surface source. If a Neptune raster is supplied at NEPTUNE_TEXTURE_URL near the top of the engine script, it is fetched once at boot and used for the planet. The synthesised cloud deck is only a fallback for when that file is missing or blocked, and the Surface raster row in the telemetry panel always states which of the two you are looking at. Satellite and ring surfaces are synthesised regardless.

Render engine: WebGL, seeded procedural cartography.

Sources and bibliography

None of this would exist without the work listed below, twenty-seven centuries of it, from the poets whose sea nymphs lend these moons their names to the engineers who flew a camera past them in 1989. With thanks to everyone who made Neptune real for the rest of us, and to whoever goes back.

Brozović, M., Showalter, M. R., Jacobson, R. A., French, R. S., Lissauer, J. J., & de Pater, I. (2020). Orbits and resonances of the regular moons of Neptune. Icarus, 338, Article 113462. https://doi.org/10.1016/j.icarus.2019.113462

Mean orbital elements for all seven inner regular moons, and the resonant argument φ = 73λₜ − 69λₙ − 4Ωₙ together with its measured libration of about 66° over roughly 1.9 years, which the panel reproduces.

Cabello, R., & three.js contributors. (2021). three.js (Revision 128) [Computer software]. https://threejs.org

The WebGL renderer. Nothing else is loaded at run time except, optionally, the Neptune raster.

de Pater, I., Gibbard, S. G., Chiang, E., Hammel, H. B., Macintosh, B., Marchis, F., Martin, S. C., Roe, H. G., & Showalter, M. (2005). The dynamic neptunian ring arcs: Evidence for a gradual disappearance of Liberté and resonant jump of Courage. Icarus, 174(1), 263–272. https://doi.org/10.1016/j.icarus.2004.10.020

Basis for the caution that the five Adams arcs are drawn in their 1989 configuration and that Liberté and Courage have since changed.

Galle, J. G. (1846). Account of the discovery of Le Verrier’s planet Neptune, at Berlin, Sept. 23, 1846. Monthly Notices of the Royal Astronomical Society, 7(9), 153. https://doi.org/10.1093/mnras/7.9.153

Discovery of the primary body.

Hesiod. (2006). Theogony; Works and days; Testimonia (G. W. Most, Ed. & Trans.; Loeb Classical Library No. 57). Harvard University Press. (Original work composed ca. 700 BCE)

Theogony 240–264, the catalogue of the Nereids, names Sao, Galatea, Halimede, Laomedea, Psamathe and Neso. Theogony 930–933 gives Triton as the son of Poseidon and Amphitrite. Six of the sixteen satellite names come from this one passage.

Holman, M. J., Kavelaars, J. J., Grav, T., Gladman, B. J., Fraser, W. C., Milisavljevic, D., Nicholson, P. D., Burns, J. A., Carruba, V., Petit, J.-M., Rousselot, P., Mousis, O., Marsden, B. G., & Jacobson, R. A. (2004). Discovery of five irregular moons of Neptune. Nature, 430(7002), 865–867. https://doi.org/10.1038/nature02832

Discovery of Halimede, Sao, Laomedeia, Psamathe and Neso, and the division of the outer satellites into prograde and retrograde families.

Homer. (1995). Odyssey: Books 1–12 (A. T. Murray, Trans.; G. E. Dimock, Rev.; Loeb Classical Library No. 104). Harvard University Press. (Original work composed ca. 8th century BCE)

Odyssey 4.349–570, Menelaus and Proteus, the shape-changing old man of the sea, after whom the largest inner moon is named.

Homer. (1999). Iliad: Books 13–24 (A. T. Murray, Trans.; W. F. Wyatt, Rev.; Loeb Classical Library No. 171). Harvard University Press. (Original work composed ca. 8th century BCE)

Iliad 18.37–49, the gathering of the Nereids, the second ancient catalogue behind the naming convention for this system.

Irwin, P. G. J., Dobinson, J., James, A., Teanby, N. A., Simon, A. A., Fletcher, L. N., Roman, M. T., Orton, G. S., Wong, M. H., Toledo, D., Pérez-Hoyos, S., & Beck, J. (2024). Modelling the seasonal cycle of Uranus’s colour and magnitude, and comparison with Neptune. Monthly Notices of the Royal Astronomical Society, 527(4), 11521–11538. https://doi.org/10.1093/mnras/stad3761

Reprocessing of the Voyager 2 filter images showing that the familiar deep azure is a contrast stretch. Source of the true colour and enhanced colour distinction in the Analysis menu.

Jacobson, R. A. (2009). The orbits of the Neptunian satellites and the orientation of the pole of Neptune. The Astronomical Journal, 137(5), 4322–4329. https://doi.org/10.1088/0004-6256/137/5/4322

Pole orientation, and therefore the 28.32° obliquity that defines the equatorial frame the inner moons and rings are attached to.

Jacobson, R. A., Brozović, M., Gladman, B., Alexandersen, M., Nicholson, P. D., & Veillet, C. (2012). Irregular satellites of the outer planets: Orbital uncertainties and astrometric recoveries in 2009–2011. The Astronomical Journal, 144, Article 132. https://doi.org/10.1088/0004-6256/144/5/132

Orbits of the irregular satellites, which is why their inclinations are referred to the ecliptic in this model rather than to Neptune’s equator.

Jacobson, R. A., & Owen, W. M., Jr. (2004). The orbits of the inner Neptunian satellites from Voyager, Earth-based, and Hubble Space Telescope observations. The Astronomical Journal, 128(3), 1412–1417. https://doi.org/10.1086/423037

Laplace plane precession rates for the inner system, superseded for elements by Brozović et al. (2020) but still the reference for the frame.

Jet Propulsion Laboratory. (2019). NASA finds Neptune moons locked in ‘dance of avoidance’. NASA. https://www.jpl.nasa.gov/news/nasa-finds-neptune-moons-locked-in-dance-of-avoidance/

Plain-language account of the Naiad–Thalassa geometry and the source of the widely quoted separation of about 3,540 km at conjunction.

Jet Propulsion Laboratory Solar System Dynamics Group. (n.d.). Approximate positions of the planets: Keplerian elements and rates, 1800–2050 [Data set]. NASA. Retrieved 14 September 2026, from https://ssd.jpl.nasa.gov/planets/approx_pos.html

The element table driving the live ephemeris. Checked against JPL DE430 for the 26 September 2026 opposition: published 28.88 AU, this model 28.87 AU.

Jet Propulsion Laboratory Solar System Dynamics Group. (n.d.). Planetary satellite mean orbital parameters [Data set]. NASA. Retrieved 14 September 2026, from https://ssd.jpl.nasa.gov/sats/elem/

Cross-check on every semi-major axis, period, eccentricity and inclination in the satellite table, and the only source used for S/2021 N 1.

Karkoschka, E. (2003). Sizes, shapes, and albedos of the inner satellites of Neptune. Icarus, 162(2), 400–407. https://doi.org/10.1016/S0019-1035(03)00002-2

Triaxial semi-axes from 87 resolved Voyager images: 48 × 30 × 26 km for Naiad, 54 × 50 × 26 km for Thalassa, 90 × 74 × 64 km for Despina, 102 × 92 × 72 km for Galatea, 108 × 102 × 84 km for Larissa. Also the geometric albedos, 0.07 at Naiad to 0.10 at Proteus, which set how dark the inner moons are rendered.

Kopp, G., & Lean, J. L. (2011). A new, lower value of total solar irradiance: Evidence and climate significance. Geophysical Research Letters, 38(1), Article L01706. https://doi.org/10.1029/2010GL045777

The 1361 W/m² solar constant used to compute irradiance at Neptune’s live heliocentric distance.

Kuiper, G. P. (1949). The second satellite of Neptune. Publications of the Astronomical Society of the Pacific, 61(361), 175–176. https://doi.org/10.1086/126166

Discovery of Nereid.

Lassell, W. (1846). Discovery of supposed ring and satellite of Neptune. Monthly Notices of the Royal Astronomical Society, 7(9), 157.

Discovery of Triton, seventeen days after the planet. The supposed ring in the title was an artefact of Lassell’s mirror; the real rings waited for Voyager 2.

Namouni, F., & Porco, C. C. (2002). The confinement of Neptune’s ring arcs by the moon Galatea. Nature, 417(6884), 45–47. https://doi.org/10.1038/417045a

The corotation resonance with Galatea that keeps the Adams arcs from spreading, modelled here as arcs orbiting at the 62,932 km Keplerian rate.

Ovid. (1984). Metamorphoses: Books 9–15 (F. J. Miller, Trans.; G. P. Goold, Rev.; Loeb Classical Library No. 43). Harvard University Press. (Original work published 8 CE)

Metamorphoses 13.738–897, the fullest ancient treatment of Galatea, and the route by which the Nereid names reached Latin and then modern usage.

Pausanias. (1935). Description of Greece: Books 8.22–10 (W. H. S. Jones, Trans.; Loeb Classical Library No. 297). Harvard University Press. (Original work composed ca. 175 CE)

Book 8.37, the cult of Despoina at Lycosura, daughter of Poseidon and Demeter, after whom Despina is named.

Porco, C. C. (1991). An explanation for Neptune’s ring arcs. Science, 253(5023), 995–1001. https://doi.org/10.1126/science.253.5023.995

The original corotation model, and the arc names Fraternité, Égalité, Liberté and Courage used in the ring group.

Reitsema, H. J., Hubbard, W. B., Lebofsky, L. A., & Tholen, D. J. (1982). Occultation by a possible third satellite of Neptune. Science, 215(4530), 289–291. https://doi.org/10.1126/science.215.4530.289

First detection of the body later named Larissa, seven years before Voyager 2 confirmed it.

Showalter, M. R., de Pater, I., Lissauer, J. J., & French, R. S. (2019). The seventh inner moon of Neptune. Nature, 566, 350–353. https://doi.org/10.1038/s41586-019-0909-9

Discovery of Hippocamp, its 17 km mean radius, and the case that it is a fragment of Proteus. Source of the classification shown for both bodies.

Smith, B. A., Soderblom, L. A., Banfield, D., Barnet, C., Basilevsky, A. T., Beebe, R. F., Bollinger, K., Boyce, J. M., Brahic, A., Briggs, G. A., Brown, R. H., Chyba, C., Collins, S. A., Colvin, T., Cook, A. F., II, Crisp, D., Croft, S. K., Cruikshank, D., Cuzzi, J. N., … Veverka, J. (1989). Voyager 2 at Neptune: Imaging science results. Science, 246(4936), 1422–1449. https://doi.org/10.1126/science.246.4936.1422

The flyby itself: discovery of six inner moons, the ring system, the cantaloupe terrain and south polar plumes on Triton, and the Great Dark Spot that had gone by 1994.

Smith, R. S., & Trzaskoma, S. M. (Trans.). (2007). Apollodorus’ Library and Hyginus’ Fabulae: Two handbooks of Greek mythology. Hackett.

Later handbook catalogues of the Nereids, and the genealogy in which Thalassa is the sea personified. Thalassa is not a Nereid and does not appear in Hesiod’s list.

Thomas, P., Veverka, J., & Helfenstein, P. (1991). Voyager observations of Nereid. Journal of Geophysical Research, 96, 19253–19259.

Nereid’s size, its 0.24 geometric albedo and its non-synchronous 11.594 h rotation, the one satellite here that is not tidally locked.

Thomas, P. C. (2000). The shape of Triton from limb profiles. Icarus, 148(2), 587–588. https://doi.org/10.1006/icar.2000.6511

Triton’s 1,353.4 km mean radius and its near-perfect sphericity, which is why Triton is the one moon here rendered with almost no relief.

United States Geological Survey. (n.d.). Gazetteer of planetary nomenclature. International Astronomical Union Working Group for Planetary System Nomenclature. Retrieved 14 September 2026, from https://planetarynames.wr.usgs.gov/

Authority for the satellite names and Roman numerals, and for surface feature names such as Pharos on Proteus and Leviathan Patera on Triton.