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The adjectival forms of the names of astronomical bodies are not always easily predictable. Attested adjectival forms of the larger bodies are listed below, along with the two small Martian moons; in some cases they are accompanied by their demonymic equivalents, which denote hypothetical inhabitants of these bodies.
Exceptions to this rule are valleys and craters on Mars and Venus; naming conventions for these features differ according to size. One feature classification, regio, was originally used on early maps of the Moon and Mercury (drawn from telescopic observations) to describe vague albedo features. It is now used to delineate a broad geographic region.
According to the IAU's explicit count, there are eight planets in the Solar System; four terrestrial planets (Mercury, Venus, Earth, and Mars) and four giant planets, which can be divided further into two gas giants (Jupiter and Saturn) and two ice giants (Uranus and Neptune). When excluding the Sun, the four giant planets account for more than ...
The density at the surface is 65 kg/m 3 (4.1 lb/cu ft), 6.5% that of water [88] or 50 times as dense as Earth's atmosphere at 293 K (20 °C; 68 °F) at sea level. The CO 2 -rich atmosphere generates the strongest greenhouse effect in the Solar System, creating surface temperatures of at least 735 K (462 °C; 864 °F).
In the astronomical literature it was simply referred to as "the satellite of Neptune". Later, the second known moon, Nereid, was named by its discoverer in 1949, Gerard P. Kuiper, soon after its discovery. Current IAU practice for newly discovered Neptunian moons is to accord with these first two choices by naming them after Greek sea deities.
Over the following three centuries, only a few more moons were discovered. Missions to other planets in the 1970s, most notably the Voyager 1 and 2 missions, saw a surge in the number of moons detected, and observations since the year 2000, using mostly large, ground-based optical telescopes, have discovered many more, all of which are irregular.
The Moon's atmosphere is extremely thin, consisting of a partial vacuum with particle densities of under 10 7 per cm −3. [115] Mars (1.38–1.67 AU) [D 6] has a radius about half of that of Earth. [116] Most of the planet is red due to iron oxide in Martian soil, [117] and the polar regions are covered in white ice caps made of water and ...
Many TNOs are often just assumed to have Pluto's density of 2.0 g/cm 3, but it is just as likely that they have a comet-like density of only 0.5 g/cm 3. [ 4 ] For example, if a TNO is incorrectly assumed to have a mass of 3.59 × 10 20 kg based on a radius of 350 km with a density of 2 g/cm 3 but is later discovered to have a radius of only 175 ...