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Neptune vs. Mercury - Comparison of sizes
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Neptune vs Mercury - Comparison

Neptune
Mercury
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Neptune

Neptune

Diameter (km)49.528
Distance to sun (km)4501000000
Equator (km)155600
Temperature-201

<p>Neptune is the eighth and farthest known planet from the Sun in the Solar System. </p>In the Solar System, it is the fourth-largest planet by the third-most-massive planet diameter, and the densest giant planet. Neptune is 17 times the mass of Earth, slightly more massive than its near-twin Uranus. Neptune is physically smaller than Uranus and thicker because its mass causes gravitational compression of its atmosphere. Neptune orbits the Sun once every 164.8 years at a mean distance of 30.1 AU (4.5 billion km; 2.8 billion mi). It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the god Neptune's trident. Neptune is not visible to the unaided eye and is the only planet in the Solar System found by forecast as opposed to by empirical observation. Changes in the orbit of Uranus directed Alexis Bouvard to deduce that its orbit was subject to gravitational perturbation. The position of Neptune was calculated from Bouvard's observations by John Couch Adams and Urbain Le Verrier following his death. Neptune was observed with a telescope on 23 by Johann Galle within a degree of the position predicted by Le Verrier. Though none of the remaining 13 known moons of the planet were located before the 20th century its largest moon, Triton, was discovered soon thereafter. The distance from Earth of the planet gives it a very small apparent size, which makes it challenging to research with Earth-based telescopes. Voyager 2 visited neptune, when it flew by the planet on 25 August 1989; Voyager 2 remains the only spacecraft to visit Neptune.



The advent of the Hubble Space Telescope and large ground-based telescopes with adaptive optics has allowed for further observations from afar. Like Jupiter and Saturn, Neptune's atmosphere is composed primarily of hydrogen and helium, together with traces of hydrocarbons and possibly nitrogen, even though it includes a higher proportion of"ices" such as water, ammonia and methane. However, similar to Uranus, its interior is primarily composed of ices and rock; Uranus and Neptune are normally considered"ice giants" to emphasise this distinction. Traces of methane in the outermost areas in part account for the world's blue appearance.In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptune's atmosphere has visible and active weather patterns. For example, in the time of the Voyager 2 flyby in 1989, the world's southern hemisphere had a Great Dark Spot comparable to the Great Red Spot. These weather patterns are driven by the strongest sustained winds of almost any planet in the Solar System, with recorded wind speeds as high as 2,100 km/h (580 m/s; 1,300 mph). Due to its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures in its cloud tops approaching 55 K (−218 °C; −361 °F). Temperatures in the world's centre are approximately 5,400 K (5,100 °C; 9,300 °F). Neptune has a faint and fragmented ring system (labelled"arcs"), which was discovered in 1984, then afterwards confirmed by Voyager 2.

Source: Wikipedia
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Mercury

Mercury

Diameter (km)4.879,4
Distance to sun (km)57910000
Equator (km)15329
Temperature-173

Mercury is the first planet from the Sun and the smallest in the Solar System. In English, it is named after the Roman god Mercurius (Mercury), 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. The surface of Mercury is heavily cratered, as a result of countless impact events that have accumulated over billions of years. Its largest crater, Caloris Planitia, has a diameter of 1,550 km (960 mi) and one-third the diameter of the planet (4,880 km or 3,030 mi). Similarly to the Earth's Moon, Mercury's surface displays an expansive rupes system generated from thrust faults and bright ray systems formed by impact event remnants. Mercury's sidereal year (88.0 Earth days) and sidereal day (58.65 Earth days) are in a 3:2 ratio. This relationship is called spin–orbit resonance, and sidereal here means 'relative to the stars'. Consequently, one solar day (sunrise to sunrise) on Mercury lasts for around 176 Earth days: twice the planet's sidereal year. This means that one side of Mercury will remain in sunlight for one Mercurian year of 88 Earth days; while during the next orbit, that side will be in darkness all the time until the next sunrise after another 88 Earth days.



Combined with its high orbital eccentricity, the planet's surface has widely varying sunlight intensity and temperature, with the equatorial regions ranging from −170 °C (−270 °F) at night to 420 °C (790 °F) during sunlight. Due to the very small axial tilt, the planet's poles are permanently shadowed. This strongly suggests that water ice could be present in the craters. Above the planet's surface is an extremely tenuous exosphere and a faint magnetic field that is strong enough to deflect solar winds. Mercury has no natural satellite. As of the early 2020s, many broad details of Mercury's geological history are still under investigation or pending data from space probes. Like other planets in the Solar System, Mercury was formed approximately 4.5 billion years ago. Its mantle is highly homogeneous, which suggests that Mercury had a magma ocean early in its history, like the Moon. According to current models, Mercury may have a solid silicate crust and mantle overlying a solid outer core, a deeper liquid core layer, and a solid inner core. There are many competing hypotheses about Mercury's origins and development, some of which incorporate collision with planetesimals and rock vaporization.

Source: Wikipedia

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