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"Inferior planet" refers to Mercury and Venus, which are closer to the Sun than Earth is. "Superior planet" refers to Mars, Jupiter, Saturn, Uranus, and Neptune (the latter two added later), which are further from the Sun than Earth is. The terms are sometimes used more generally; for example, Earth is an inferior planet relative to Mars.
[4] [5] Mercury's surface shows intercrater plains, basins, smooth plains, craters, and tectonic features. Mercury's oldest surface is its intercrater plains, [4] [6] which are present (but much less extensive) on the Moon. The intercrater plains are level to gently rolling terrain that occur between and around large craters.
Mercury is the first planet from the Sun and the smallest in the Solar System. In English, it is named after the ancient Roman god Mercurius , god of commerce and communication, and the messenger of the gods. Mercury is classified as a terrestrial planet, with roughly the same surface gravity as Mars.
Before 2006, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto were considered as planets. Below is a partial list of these mnemonics: "Men Very Easily Make Jugs Serve Useful Needs, Perhaps" – The structure of this sentence, which is current in the 1950s, suggests that it may have originated before Pluto's discovery.
The current Venusian atmosphere has only ~200 mg/kg H 2 O(g) in its atmosphere and the pressure and temperature regime makes water unstable on its surface. Nevertheless, assuming that early Venus's H 2 O had a ratio between deuterium (heavy hydrogen, 2H) and hydrogen (1H) similar to Earth's Vienna Standard Mean Ocean Water of 1.6×10 −4, [7] the current D/H ratio in the Venusian atmosphere ...
Mars is the fourth planet from the Sun.The surface of Mars is orange-red because it is covered in iron(III) oxide dust, giving it the nickname "the Red Planet". [22] [23] Mars is among the brightest objects in Earth's sky, and its high-contrast albedo features have made it a common subject for telescope viewing.
For instance, for a large portion of names ending in -s, the oblique stem and therefore the English adjective changes the -s to a -d, -t, or -r, as in Mars–Martian, Pallas–Palladian and Ceres–Cererian; [note 1] occasionally an -n has been lost historically from the nominative form, and reappears in the oblique and therefore in the English ...
The entire orbits of the Moon, [53] Mars, [54] and numerous asteroids also lie within various estimates of the habitable zone. Only at Mars' lowest elevations (less than 30% of the planet's surface) is atmospheric pressure and temperature sufficient for water to, if present, exist in liquid form for short periods. [55]