Solar System objects

People are always curious about when objects in our solar system were discovered. Records about Mercury and Mars date back to 400 BC. Venus was recorded in 600 BC. Jupiter and Saturn were first observed in 1610, while Uranus was first observed in 1781. Neptune was discovered in 1846 relative to its position to Jupiter, Saturn and Uranus.

The arrangement of solar system objects based on their orbits would have the planets centered on the sun before the view moved on to Mercury. From Mercury, there are a number of crosser asteroids, followed by Venus. There are also crosser asteroids from Venus, as well as quasi-satellite 2002 VE68. After Venus comes Earth. The familiar calm lunar glow heralds the moon. There’s a possible Kordylewski Cloud away from Earth’s orbit and near-Earth asteroids, including 99942 Apophis. The nearest planet to earth is Mars, accompanied by moons Deimos and Phobos. The dwarf planet Ceres is contained within an asteroid belt.

Some of the asteroids in the belt have been named, e.g. Juno, Vesta and Pallas. The next planet is Jupiter, ringed by its own asteroid belt, and orbited by moons. The largest are Io, Ganymede, Europa and Callisto. Saturn and its rings are next, and its moons are Enceladus, Mimas, Tethys, Rhea, Dione, Rings of Rhea, Iapetus, Titan and Hyperion. After Saturn is Uranus. Its moons are Miranda, Titania, Ariel, Umbriel and Oberon. Neptune and its moons Proteus, Nereid and Triton come after that. Objects beyond Neptune’s orbit are called Trans-Neptunian objects and Kuiper Belt objects. Pluto is in this region with the moons Charon, Hydra and Nix. There are also other dwarf planets Haumea (moons: Namaka and Hi’iaka), Makemake and Eris.

The largest objects in our solar system exceed 200km in radius. This includes planets, dwarf planets, satellite moons and asteroids. These are the sun, Saturn, Jupiter, Neptune, Uranus, Mars, Earth, Venus, Titan, Ganymede, Io, Mercury, Pluto, Callisto, Triton, the Moon, Europa, Rhea, Eris, Makemake, Titania, Sedna, Oberon, Dione, Umbriel, Iapetus, Charon, Miranda, Ariel, Haumea, Ceres, Tethys, Mimas, Pallas, Vesta, Proteus and Enceladus.

Objects 100-200km wide are generally planetary moons and asteroids: Nereid, Europa, Hyperion, Davida, Sylvia, Hi’iaka and Phoebe. Objects 50-100km wide are usually asteroids. However, Larissa, Despina and Galatea (Neptune satellites), Janus and Epimetheus (Saturn’s moons), Amalthea and Himalia (Jupiter’s satellites), Namaka (Haumea’s satellite), Portia, Puck and Sycorax (Uranus’ satellites) and Dysnomia (Eris’ moon) are counted among these relatively small objects.

Objects 20-50km wide include Thebe, Pasiphaë and Elara (Jupiter’s satellites), Caliban, Cressida, Desdemona, Rosalind, Juliet and Belinda (Uranus’ satellite), Nix and Hydra (Pluto’s satellite), Pandora and Prometheus (Saturn’s satellite), Thalassa, Neso, Naiad and Halimede (Neptune’s satellite).

Solar system objects have hydrostatic equilibrium when gravity has overcome internal rigidity, thus allowing a planet to take ellipsoid shape. The following star and planets are in hydrostatic equilibrium: the sun, Neptune, Venus, Saturn, Mars, Uranus, Earth, Jupiter and Mercury. Dwarf planets in hydrostatic equilibrium: Makemake, Pluto, Haumea, Ceres and Eris. There are also 19 satellites in hydrostatic equilibrium: Moon, Ganymede, Europa, Mimas, Callisto, Ariel, Enceladus, Io, Rhea, Tethys, Iapetus, Dione, Titan, Triton Miranda, Titania, Umbriel, Oberonand Charon.

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