Venus
Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, gravity, and bulk composition (Venus is both the closest planet to Earth and the planet closest in size to Earth). However, it has also been shown to be very different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet's surface is 92 times that of Earth's. Physical characteristics Venus is one of the four terrestrial planets in the Solar System, meaning that, like Earth, it is a rocky body. Geography The Venusian surface was a subject of speculation until some of its secrets were revealed by planetary science in the 20th century. Most Venusian surface features are named after historical and mythological women.[26] Exceptions are Maxwell Montes, named after James Clerk Maxwell, and highland regions Alpha Regio, Beta Regio and Ovda Regio. Surface geology
Magnetosphere
Mars
Animation of Mars' rotation from the vantage of an observer who moves south, then north, to hover over both poles, showing the planet's major topographic features. Mars is currently host to five functioning spacecraft: three in orbit – the Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter – and two on the surface – Mars Exploration Rover Opportunity and the Mars Science Laboratory Curiosity. Defunct spacecraft on the surface include MER-A Spirit and several other inert landers and rovers such as the Phoenix lander, which completed its mission in 2008. Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Physical characteristics Size comparison of Earth and Mars. Internal structure Surface geology During the Solar System's formation, Mars was created as the result of a stochastic process of run-away accretion out of the protoplanetary disk that orbited the Sun. This Mars rock revealed its bluish-gray interior to Mars Science Laboratory[40] Soil
Orbit and rotation
Earth
Earth is the third planet from the Sun. It is the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the world or the Blue Planet.[23] Earth formed approximately 4.54 billion years ago, and life appeared on its surface within its first billion years.[24] Earth's biosphere then significantly altered the atmospheric and other basic physical conditions, which enabled the proliferation of organisms as well as the formation of the ozone layer, which together with Earth's magnetic field blocked harmful solar radiation, and permitted formerly ocean-confined life to move safely to land.[25] The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist. Name and etymology In general English usage, the name earth can be capitalized or spelled in lowercase interchangeably, either when used absolutely or prefixed with "the" (i.e. Heat
Formation and migration
Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both are of different chemical composition than the larger gas giants Jupiter and Saturn. For this reason, astronomers sometimes place them in a separate category called "ice giants". Uranus's atmosphere, although similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, contains more "ices" such as water, ammonia, and methane, along with traces of hydrocarbons.[12] It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (−224.2 °C), and has a complex, layered cloud structure, with water thought to make up the lowest clouds, and methane the uppermost layer of clouds.[12] In contrast, the interior of Uranus is mainly composed of ices and rock.[11] History Discovery The power I had on when I first saw the comet was 227. Naming Name Axial tilt
Observation
Mercury (planet)
Mercury is gravitationally locked and rotates in a way that is unique in the Solar System. As seen relative to the fixed stars, it rotates exactly three times for every two revolutions[b] it makes around its orbit.[13] As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two years. Because Mercury's orbit lies within Earth's orbit (as does Venus's), it can appear in Earth's sky in the morning or the evening, but not in the middle of the night. Internal structure Internal structure of Mercury: 1. Mercury's density can be used to infer details of its inner structure. Mercury's core has a higher iron content than that of any other major planet in the Solar System, and several theories have been proposed to explain this. Alternatively, Mercury may have formed from the solar nebula before the Sun's energy output had stabilized. Surface geology
Saturn
Saturn's interior is probably composed of a core of iron, nickel and rock (silicon and oxygen compounds), surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium and an outer gaseous layer.[15] The planet exhibits a pale yellow hue due to ammonia crystals in its upper atmosphere. Electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than Earth's magnetic field but has a magnetic moment 580 times that of the Earth due to Saturn's larger body radius. Saturn's magnetic field strength is around one-twentieth the strength of Jupiter's.[16] The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h (1,100 mph), faster than on Jupiter, but not as fast as those on Neptune.[17] Physical characteristics Composite image roughly comparing the sizes of Saturn and Earth Atmosphere
Jupiter
Structure Jupiter is composed primarily of gaseous and liquid matter. It is the largest of four gas giants as well as the largest planet in the Solar System with a diameter of 142,984 km (88,846 mi) at its equator. The density of Jupiter, 1.326 g/cm3, is the second highest of the gas giants, but lower than for any of the four terrestrial planets. Composition Jupiter's upper atmosphere is composed of about 88–92% hydrogen and 8–12% helium by percent volume or fraction of gas molecules. Based on spectroscopy, Saturn is thought to be similar in composition to Jupiter, but the other gas giants Uranus and Neptune have relatively much less hydrogen and helium.[21] Because of the lack of atmospheric entry probes, high-quality abundance numbers of the heavier elements are lacking for the outer planets beyond Jupiter. Mass Jupiter's diameter is one order of magnitude smaller (×0.10045) than the Sun, and one order of magnitude larger (×10.9733) than the Earth. Internal structure Atmosphere Cloud layers
