The total surface area of Earth is about . Of this, 70.8%, or , is below sea level and covered by ocean water. Below the ocean's surface are much of the continental shelf, mountains, volcanoes, oceanic trenches, submarine canyons, oceanic plateaus, abyssal plains, and a globe-spanning mid-ocean ridge system. The remaining 29.2%, or , not covered by water has terrain that varies greatly from place to place and consists of mountains, deserts, plains, plateaus, and other landforms. Tectonics and erosion, volcanic eruptions, flooding, weathering, glaciation, the growth of coral reefs, and meteorite impacts are among the processes that constantly reshape Earth's surface over geological time.The continental crust consists of lower density material such as the igneous rocks granite and andesite.
Surface
Earth
Earth | Surface
Of the total surface area of Earth about 70.8%, is below sea level an/d covered by ocean water. The pedosphere is the outermost layer of Earth's continental surface and is composed of soil and subject to soil formation processes. About 29% of Earth's surface is land and remaining 71% is covered with water About 29% of Earth's surface is land consisting of continents and islands. The remaining 71% is covered with water, mostly by oceans but also lakes, rivers and other fresh water, which together constitute the hydrosphere. 70.8% of its surface is below sea level and covered by ocean water. The remaining 29.2%, has terrain that varies greatly from place to place and consists of mountains, deserts, plains, plateaus, and other landforms.
what factor limits the number of eclipses each year
user
The alignment of the Sun, Moon and Earth.
assistant
what is this phenomena ?
user
A solar eclipse occurs when a portion of the Earth is engulfed in a shadow cast by the Moon which fully or partially blocks sunlight.
assistant
what are the different types of it ?
user
There are four types of solar eclipses.
assistant
what is their frequency ?
user
Between two and five solar eclipses occur every year.
assistant
what is their duration ?
user
The longest eclipse that has been calculated thus far is 7 minutes 29 seconds.
assistant
does it follow any path ?
user
Yes, the Moon's umbra moves rapidly from west to east across the Earth.
assistant
talk about the planet you mentioned above ?
user
It is the third planet from the Sun and the only astronomical object known to harbor life.
assistant
talk about its surface ?
user
Planet Earth is the third planet from the Sun. Planet Earth may also refer to:
Planet Earth (disambiguation) | Introduction
The following outline is provided as an overview of and topical guide to the planet Earth: Earth – third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to harbor life.
Outline of Earth | Introduction
Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consisting of continents and islands. The remaining 71% is covered with water, mostly by oceans but also lakes, rivers and other fresh water, which together constitute the hydrosphere. The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's outer layer is divided into several rigid tectonic plates that migrate across the surface over many millions of years. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates Earth's magnetic field, and a convecting mantle that drives plate tectonics.
Earth | Introduction
Earth is a planet in the Solar System, and the third planet from the Sun. Earth may also refer to:
Earth (disambiguation) | Introduction
Earth (1 AU from the Sun) is the largest and densest of the inner planets, the only one known to have current geological activity, and the only place where life is known to exist. Its liquid hydrosphere is unique among the terrestrial planets, and it is the only planet where plate tectonics has been observed. Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen. It has one natural satellite, the Moon, the only large satellite of a terrestrial planet in the Solar System.
Solar System | Earth
Earth is the only planet known to support life, and its natural features are the subject of many fields of scientific research. Within the solar system, it is third closest to the sun; it is the largest terrestrial planet and the fifth largest overall. Its most prominent climatic features are its two large polar regions, two relatively narrow temperate zones, and a wide equatorial tropical to subtropical region. Precipitation varies widely with location, from several metres of water per year to less than a millimetre. 71 percent of the Earth's surface is covered by salt-water oceans. The remainder consists of continents and islands, with most of the inhabited land in the Northern Hemisphere.
Nature | Earth
The Solar System, showing the Sun and the planets in the order of their position from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. (Pluto has since been reclassified as a dwarf planet by the International Astronomical Union, but it was considered a planet at the time the message was transmitted.) The Earth is the third planet from the Sun; its graphic is shifted up to identify it as the planet from which the signal was sent. Additionally, the human figure is shown just above the Earth graphic. In addition to showing position, the graphic provides a general, not-to-scale size reference of each planet and the Sun.
Arecibo message | Planets
In differentiated bodies, the surface is where the crust meets the planetary boundary layer. Anything below this is regarded as being sub-surface or sub-marine. Most bodies more massive than super-Earths, including stars and gas giants, as well as smaller gas dwarfs, transition contiguously between phases, including gas, liquid, and solid. As such, they are generally regarded as lacking surfaces. Planetary surfaces and surface life are of particular interest to humans as it is the primary habitat of the species, which has evolved to move over land and breathe air. Human space exploration and space colonization therefore focuses heavily on them.
Planetary surface | Introduction
A planetary surface is where the solid (or liquid) material of the outer crust on certain types of astronomical objects contacts the atmosphere or outer space. Planetary surfaces are found on solid objects of planetary mass, including terrestrial planets (including Earth), dwarf planets, natural satellites, planetesimals and many other small Solar System bodies (SSSBs). The study of planetary surfaces is a field of planetary geology known as surface geology, but also a focus of a number of fields including planetary cartography, topography, geomorphology, atmospheric sciences, and astronomy. Land (or ground) is the term given to non-liquid planetary surfaces. The term "landing" is used to describe the collision of an object with a planetary surface and is usually at a velocity in which the object can remain intact and remain attached.
Planetary surface | Introduction
Earth is the third planet from the Sun with an approximate distance of , and is traveling nearly through outer space.
Location of Earth | Details
The total surface area of Earth is about . Of this, 70.8%, or , is below sea level and covered by ocean water. Below the ocean's surface are much of the continental shelf, mountains, volcanoes, oceanic trenches, submarine canyons, oceanic plateaus, abyssal plains, and a globe-spanning mid-ocean ridge system. The remaining 29.2%, or , not covered by water has terrain that varies greatly from place to place and consists of mountains, deserts, plains, plateaus, and other landforms. Tectonics and erosion, volcanic eruptions, flooding, weathering, glaciation, the growth of coral reefs, and meteorite impacts are among the processes that constantly reshape Earth's surface over geological time.The continental crust consists of lower density material such as the igneous rocks granite and andesite.
Earth | Surface
Planets like this in that system have been presumed "super-Earth".
HD 40307 f | Introduction
Normally, gas giants are considered to not have a surface, although they might have a solid core of rock or various types of ice, or a liquid core of metallic hydrogen. However, the core, if it exists, does not include enough of the planet's mass to be actually considered a surface. Some scientists consider the point at which the atmospheric pressure is equal to 1 bar, equivalent to the atmospheric pressure at Earth’s surface, to be the surface of the planet.
Planetary surface | Surface of gas giants
It has an equilibrium temperature of 256 K (-16.5 °C; 2.3 °F), highly similar to Earth's equilibrium temperature of 255 K (-18 °C; -1 °F), If the atmosphere is similar to Earth's, it would have an average surface temperature of 291 K (17.85 °C; 64.13 °F), slightly higher than Earth's.
KOI-4878.01 | Temperature
Surface liquid, while abundant on Earth (the largest body of surface liquid being the World Ocean) is rare elsewhere, a notable exception being Titan which has the largest known hydrocarbon lake system while surface water, abundant on Earth and essential to all known forms of life is thought only to exist as Seasonal flows on warm Martian slopes and in the habitable zones of other planetary systems. Volcanism can cause flows such as lava on the surface of geologically active bodies (the largest being the Amirani (volcano) flow on Io). Many of Earth's Igneous rocks are formed through processes rare elsewhere, such as the presence of volcanic magma and water.
Planetary surface | Rare surface occurrences
The planet has a "minimum" Earth mass of 3.6 ± 0.5, "minimum" surface gravity of about 1.4 g and assuming an atmosphere like Earth's despite its far greater mass, an estimated temperature of 298 K (24.85 °C or 76.73 °F) at the top of its atmosphere. The estimated temperature is noted to be similar to temperatures in Southern France, but various atmospheric conditions prevalent in the planet have to be analyzed to estimate the temperature of the surface. An estimated radius of 1.3 is possible based on its mass.
HD 85512 b | Mass, radius and temperature
An exoplanet with a larger volume than that of Earth, or with a more complex terrain, or with a larger surface covered with liquid water, could be more hospitable for life than Earth. Since the volume of a planet tends to be directly related to its mass, the more massive it is, the greater its gravitational pull, which can result in a denser atmosphere. Some studies indicate that there is a natural limit, set at R, below which nearly all planets are terrestrial, composed primarily of rock-iron-water mixtures. Generally, objects with a mass below 6 M are very likely to be of similar composition as Earth.
Superhabitable planet | Surface, size and composition
Planetary surfaces are found throughout the Solar System, from the inner terrestrial planets, to the asteroid belt, the natural satellites of the gas giant planets and beyond to the Trans-Neptunian objects. Surface conditions, temperatures and terrain vary significantly due to a number of factors including Albedo often generated by the surfaces itself. Measures of surface conditions include surface area, surface gravity, surface temperature and surface pressure. Surface stability may be affected by erosion through Aeolian processes, hydrology, subduction, volcanism, sediment or seismic activity. Some surfaces are dynamic while others remain unchanged for millions of years.
Planetary surface | Distribution and conditions
It is argued that life requires terrestrial planets like Earth and as gas giants lack such a surface, that complex life cannot arise there. A planet that is too small cannot hold much atmosphere, making surface temperature low and variable and oceans impossible. A small planet will also tend to have a rough surface, with large mountains and deep canyons. The core will cool faster, and plate tectonics may be brief or entirely absent. A planet that is too large will retain too dense an atmosphere like Venus. Although Venus is similar in size and mass to Earth, its surface atmospheric pressure is 92 times that of Earth, and surface temperature of 735 K (462 °C; 863 °F).
Rare Earth hypothesis | A terrestrial planet of the right size
The table below lists Solar System bodies once considered to be planets.
Planet | Objects formerly considered "planets"
The Earth's terrain varies greatly from place to place. About 70.8% of the surface is covered by water, with much of the continental shelf below sea level. The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes, oceanic trenches, submarine canyons, oceanic plateaus, and abyssal plains. The remaining 29.2% not covered by water consists of mountains, deserts, plains, plateaus, and other geomorphologies. The planetary surface undergoes reshaping over geological time periods due to the effects of tectonics and erosion. The surface features built up or deformed through plate tectonics are subject to steady weathering from precipitation, thermal cycles, and chemical effects.
Geology of solar terrestrial planets | Earth
This is much older than any other known planet, and nearly three times as old as Earth. It has been undergoing many stages through its lifetime.
PSR B1620−26 b | Mass, orbit, and age
Consequently, "its atmosphere was ripped away from the planet by the solar wind. If you could stand on Mars today, you would find a landscape of lifeless desolation; very cold, and very dry."
A Beautiful Planet | Spaceship Earth
Earth is the only known planet with seas of liquid water on its surface, although Mars possesses ice caps and similar planets in other solar systems may have oceans. Earth's of sea contain about 97.2 percent of its known water and cover more than 70 percent of its surface. Another 2.15% of Earth's water is frozen, found in the sea ice covering the Arctic Ocean, the ice cap covering Antarctica and its adjacent seas, and various glaciers and surface deposits around the world. The remainder (about 0.65% of the whole) form underground reservoirs or various stages of the water cycle, containing the freshwater encountered and used by most terrestrial life: vapor in the air, the clouds it slowly forms, the rain falling from them, and the lakes and rivers spontaneously formed as its waters flow again and again to the sea.
Sea | Physical science
Brown estimates it is likely a dwarf planet based on its presumed size, calculated from its absolute magnitude (H) and assumed albedo.
(144897) 2004 UX10 | Introduction
(2014) speculated that the planet may lie outside the habitable zone and closer to a Venus-like world.
Tau Ceti e | Introduction
Its surface therefore most likely resembles a bare rock.
2015 TC25 | Introduction
This is the smaller world, with 0.76 Earth masses at 94% of its diameter, and 85% of its surface gravity. The mean surface temperature is only +5 °C. Because most of this chilly planet's water is locked in permafrost and glaciers, the atmosphere (which has a sea-level pressure of 0.7 bar, equivalent to about 3,650 m altitude on Earth) is not only thin but also uncomfortably dry. From the hemisphere where the companion world Genji can be seen it hangs in the sky as a globe of 6° 20' diameter, and when full gives over 320 times the light of the full Moon as seen from Earth.
Murasaki (novel) | Chujo
The planet has a mass about half that of Jupiter and orbits at a distance of 0.921 AU from the star with a period of 310.55 days. The planet may be located at a distance close enough to the star to receive a comparable amount of ultraviolet radiation as the Earth does from the Sun. However, it is too close to the star to be able to support liquid water at its surface. Furthermore, given its mass, the planet is likely to be a gas giant with no solid surface.
Mu Arae d | Characteristics
The world of Ptolus is called Praemal. 80% of its surface is covered with water, and it is currently in an ice age. The planet has two visible moons, and allegedly a third that disappeared eons ago.
Ptolus | World
found this planet in 2002 by using the telescope in Anglo-Australian Observatory.
HD 196050 b | Introduction
Most planets known to humans are either gaseous Jovian planets or solid terrestrial planets. Terrestrial planets include Mercury, Venus, Earth, and Mars. These inner planets have a rocky surface with metal interiors. The Jovian planets consist of Jupiter, Saturn, Uranus, and Neptune. While these planets are larger, their only land surface is a small rocky core surrounded by a large, thick atmosphere. The gas giants, Jupiter and Saturn, are thought to have surface layers composed of liquid hydrogen rather than solid land; however, their planetary geology is not well understood. The possibility of Uranus and Neptune (the ice giants) possessing hot, highly compressed, supercritical water under their thick atmospheres has been hypothesised.
Land | Extraterrestrial land
As Soter noted in his article, "how are we to quantify the degree of roundness that distinguishes a planet? Does gravity dominate such a body if its shape deviates from a spheroid by 10 percent or by 1 percent? Nature provides no unoccupied gap between round and nonround shapes, so any boundary would be an arbitrary choice." Furthermore, the point at which an object's mass compresses it into an ellipsoid varies depending on the chemical makeup of the object. Objects made of ices, such as Enceladus and Miranda, assume that state more easily than those made of rock, such as Vesta and Pallas.
Definition of planet | Hydrostatic equilibrium
The Earth is a ball in space perpetually intercepting a cylinder of parallel energy rays from the sun. (Think of a tennis ball being held in the wind.) The angle of any earthly site to the solar beam is determined by The change due to date is the most difficult to visualize. The Earth’s axis is steady but "tilted": the plane that includes the Earth’s equator, which is perpendicular to the axis, is not parallel to the plane that includes the center of the sun and the center of the Earth, called the ecliptic. Think of the Earth as a car on a Ferris wheel.
Heliodon | Scientific background
The Arizonan astronomer Rory Barnes's mathematical model, in 2009, found that "Planet b’s orbit must be more than 15◦ from face-on"; however it cannot be much more.
HD 40307 b | Orbit and mass
Planets like this in that system have been presumed "super-Earth". However planets b, c, and d are presumed to have migrated in from outer orbits; and planet b is predicted a sub-Neptune. It is likely that this planet formed even further out. Whether it is a sub-Neptune, a super-Venus or even a super-Mercury is unknown.
HD 40307 e | Introduction
This figure represents about 12 percent of Earth's total surface. The Space Radar Laboratory obtained radar images of approximately 25 percent of the planet's land surfaces.
STS-59 | 19 April
Depending on composition the two planets may be around the same size, or HD 154345 b may be larger. This planet may also harbor a system of moons and rings.
HD 154345 b | Characteristics
One of these, discovered by Fresnel, is called wave surface by mathematicians. The surface of the reflector of a telescope is a paraboloid of revolution.
Surface | In the physical sciences
However, since it is probably an ocean planet or Mini-Neptune, it is likely larger.
HD 219134 g | Introduction
Humans have only directly explored the surface of Earth and the Moon. The vast distances and complexities of space makes direct exploration of even near-Earth objects dangerous and expensive. As such, all other exploration has been indirect via space probes.
Planetary surface | Introduction
The outermost planet orbits at a distance similar to the distance of Venus to the Sun and is situated well in the system's liquid water habitable zone.
HD 40307 | Planetary system
The estimated period of this planet if the orbit is face-on is about 50 years.
HR 8799 e | Description
In 2008, it was considered to be a dwarf planet based on its lightcurve amplitude and the assumption that it was larger than in diameter. Because is a member of the Haumea family, it is assumed to have an albedo of around 0.7, which would result in a diameter of about .
(55636) 2002 TX300 | Size
Due to the harsh conditions on the surface, little of the planet has been explored; in addition to the fact that life as currently understood may not necessarily be the same in other parts of the universe, the extent of the tenacity of life on Earth itself has not yet been shown. Creatures known as extremophiles exist on Earth, preferring extreme habitats. Thermophiles and hyperthermophiles thrive at temperatures reaching above the boiling point of water, acidophiles thrive at a pH level of 3 or below, polyextremophiles can survive a varied number of extreme conditions, and many other types of extremophiles exist on Earth.
Atmosphere of Venus | Possibility of life
A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. Surface may also refer to:
Surface (disambiguation) | Introduction
This planet was discovered on June 13, 2002 by Tinney, Butler, and Marcy "et al." using the Doppler spectroscopy from the Anglo-Australian Telescope.
HD 30177 b | Introduction
Several possible classifications for terrestrial planets have been proposed:
Terrestrial planet | Types
Earth's crust is continually recycled by subduction at the boundaries of tectonic plates, and has an average age of about 100 million years, while Venus' surface is estimated to be about 500 million years old. Venusian craters range from to in diameter. There are no craters smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed down so much by the atmosphere that they do not create an impact crater.
Geology of solar terrestrial planets | Venus
These may be characterized as the orbital definition and the geophysical definition. The issue of a clear definition for "planet" came to a head in January 2005 with the discovery of the trans-Neptunian object Eris, a body more massive than the smallest then-accepted planet, Pluto. In its August 2006 response, the International Astronomical Union (IAU), recognised by astronomers as the world body responsible for resolving issues of nomenclature, released its decision on the matter during a meeting in Prague. This definition, which applies only to the Solar System (though exoplanets had been addressed in 2003), states that a planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has "cleared its neighbourhood" of smaller objects approaching its orbit.
Definition of planet | Introduction
A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and – acconding to the International Astronomical Union but not all planetary scientists – has cleared its neighbouring region of planetesimals. The term "planet" is ancient, with ties to history, astrology, science, mythology, and religion. Apart from Earth itself, five planets in the Solar System are often visible to the naked eye. These were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects.
Planet | Introduction
This planet is at a pre-modern, even barbaric stage of civilization, but may here and there have remarkable technologies that hint at a more advanced past. There is no obligation for the physical properties or biology of the alien planet to follow any scientific understanding of the potential conditions of habitable worlds; in general, the conditions will be earth-like, but with variations such as a different-colored sun or different numbers of moons. A lower gravity may be invoked to explain such things as large flying animals or people, or the superhuman strength of the hero, but will otherwise be ignored.
Sword and planet | Form
From a geological perspective, the optimal mass of a planet is about 2 M, so it must have a radius that keeps the density of the Earth among 1.2 and 1.3R. The average depth of the oceans also affects the habitability of a planet. The shallow areas of the sea, given the amount of light and heat they receive, usually are more comfortable for aquatic species, so it is likely that exoplanets with a lower average depth are more suitable for life. More massive exoplanets would tend to have a regular surface gravity, which can mean shallower—and more hospitable—ocean basins.
Superhabitable planet | Surface, size and composition
(See List of smallest exoplanets.)
Geophysical definition of 'planet' | Applicability to exoplanets
These are best explained by an unseen planet with a semimajor axis of about 60-80 au. An additional planet with a semimajor axis of 30 au and with a large pitch angle compared to the disk (likely higher inclination) could explain the emptiness of the inner dusty disk.
AB Aurigae | Planetary system
Temperature must also be considered as Venus and the planets of Alpha Centauri B (discovered in 2012), Kepler-20 (discovered in 2011), COROT-7 (discovered in 2009) and the three planets of Kepler-42 (all discovered in 2011) are very hot, and Mars, Ganymede and Titan are frigid worlds, resulting also in wide variety of surface and atmospheric conditions. The masses of the Solar System's moons are a tiny fraction of that of Earth whereas the masses of extrasolar planets are very difficult to accurately measure. However discoveries of Earth-sized terrestrial planets are important as they may indicate the probable frequency and distribution of Earth-like planets.
Earth analog | Size
Encyclopedic facts about the Earth and the Solar System.
Charlie Brown's Super Book of Questions and Answers | Volume Two: About the Earth and Space – from Plants to Planets! (Sept 1977)
Defining an exact surface for an object such as the Sun is made difficult by the diffuse nature of matter which constitutes the Sun at distances far from the stellar core. An often used definition for the surface of a star is based on the path that photons take. Inside a star, photons travel by random walk, constantly interacting with matter, and the surface of the star is defined as the point at which photons encounter little resistance from the matter in the stellar atmosphere, or in other words, when photons stream freely. The light which constitutes the cosmic microwave background comes from the surface of last scattering.
Free streaming | Use in defining surfaces
Surface mineral deposits such as olivine and hematite discovered on Mars by lunar rovers provide direct evidence of past stable water on the surface of Mars. Apart from water, many other abundant surface materials are unique to Earth in the Solar System as they are not only organic but have formed due to the presence of life – these include carbonate hardgrounds, limestone, vegetation and artificial structures although the latter is present due to probe exploration (see also List of artificial objects on extra-terrestrial surfaces).
Planetary surface | Rare surface occurrences
This planet was typical as it was discovered spectroscopically using the radial velocity method.
HD 167042 b | Introduction
An ocean world, ocean planet, water world, aquaplanet or panthalassic planet is a type of terrestrial planet that contains a substantial amount of water either at its surface or within a subsurface ocean. The term "ocean world" is also used sometimes for astronomical bodies with an ocean composed of a different fluid, such as lava (the case of Io), ammonia (in a eutectic mixture with water, as is likely the case of Titan's inner ocean) or hydrocarbons like on Titan's surface (which could be the most abundant kind of exosea). Earth is the only astronomical object known to have bodies of liquid water on its surface, although several exoplanets have been found with the right conditions to support liquid water.
Ocean world | Introduction
The size of has been measured by the Herschel Space Telescope to be . It is likely a dwarf planet.
2002 XV93 | Physical characteristics
Planet "d" would receive a similar amount of ultraviolet to the Earth and thus lies in the ultraviolet habitable zone. However, it would be too hot for any moons to support surface liquid water.
Mu Arae | System architecture and habitability
The next planet is also described by a single word. That word is "Ugh!"
The Waitabits | Plot
It is currently at 35.8 AU from the Sun, near its perihelion.
(230965) 2004 XA192 | Introduction
Determining the roundness of a body requires measurements across multiple chords (and even that is not enough to determine whether it is actually in equilibrium), but exoplanet detection techniques provide only the planet's mass, the ratio of its cross-sectional area to that of the host star, or its relative brightness. One small exoplanet, Kepler-1520b, has a mass of less than 0.02 times that of the Earth, and analogy to objects within the Solar system suggests that this may not be enough for a rocky body to be a planet. Another, WD 1145+017 b, is only 0.0007 Earth masses, while SDSS J1228+1040 b may be only 0.01 Earth radii in size, well below the upper equilibrium limit for icy bodies in the Solar system.
Geophysical definition of 'planet' | Applicability to exoplanets
(Smaller planets will lose any atmosphere they gain through various escape mechanisms.)
Planet | Formation
This is a partial list of artificial objects left on extraterrestrial surfaces.
List of artificial objects on extraterrestrial surfaces | Introduction
The most common planetary surface material in the Solar System appears to be water ice. Surface ice is found as close to the Sun as Mercury but is more abundant beyond Mars. Other surfaces include solid matter in combinations of rock, regolith and frozen chemical elements and chemical compounds. In general, ice predominates planetary surfaces beyond the frost line, while closer to the sun, rock and regolith predominate. Minerals and hydrates may also be present in smaller quantities on many planetary surfaces.
Planetary surface | Surface materials
It is 3.3 billion years old, younger than the Sun, making its planets about 3,000,000,000 years old (3 Gyr). It has a temperature of 6,210 K, making it appear bright yellowish-white.
Kepler-89e | Physical properties
The planet's equilibrium temperature is calculated to be , similar to that of Mercury. It receives about 4.7 times the stellar insolation of Earth.
HD 219134 d | Mass, radius, and temperature
For example, the surface of the Earth resembles (ideally) a two-dimensional sphere, and latitude and longitude provide two-dimensional coordinates on it (except at the poles and along the 180th meridian). The concept of surface is widely used in physics, engineering, computer graphics, and many other disciplines, primarily in representing the surfaces of physical objects. For example, in analyzing the aerodynamic properties of an airplane, the central consideration is the flow of air along its surface.
Surface (topology) | In general
A survey for objects beyond the Kuiper Cliff by Scott Sheppard, Chadwick Trujillo and David Tholen gives a diameter of 250 kilometers assuming a moderate albedo of 0.10. Johnston's archive estimates a diameter of 280 kilometers based on an assumed albedo of 0.09, while American astronomer Michael Brown, calculates a diameter of 266 kilometers, using an estimated albedo of 0.08 and an absolute magnitude of 6.3. This is approximately half the size of , which is estimated at around , roughly a quarter the size of Pluto. On his website, Brown lists this object as a "possible" dwarf planet (200–400 km), which is the category with the lowest certainty in his 5-class taxonomic system.
2013 FQ28 | Physical characteristics
TRAPPIST-1b is very close in both mass, radius and gravity to Earth. It has a radius of 1.121 , a mass of 1.02 , and about 81% Earth's surface gravity. However, the density of the planet indicates that it is not entirely rocky. With a density of 3.98 g/cm, about ≤5% of its mass must be water, likely in the form of a thick Venus-like atmosphere due to its high stellar flux being nearly 4 times higher than Earth's. The planet's extremely thick atmosphere has likely risen its temperature far above its equilibrium temperature of . Its surface temperature is estimated to be between and , potentially as high as .
TRAPPIST-1b | Mass, radius, and temperature
Some water may be retained at the poles and there may be occasional rainstorms, but for the most part the planet would be a dry desert with large dunefields covering its equator, and a few salt flats on what was once the ocean floor, similar to the ones in the Atacama Desert in Chile. With no water to serve as a lubricant, plate tectonics would very likely stop and the most visible signs of geological activity would be shield volcanoes located above mantle hotspots. In these arid conditions the planet may retain some microbial and possibly even multicellular life. Most of these microbes will be halophiles and life could find refuge in the atmosphere as has been proposed to have happened on Venus.
Future of Earth | Loss of oceans
From this information it can be inferred that the outer radius of the Amerind tier (and hence the radius of the monolith Thayaphaeawoed) is approximately 4000 km. The next tier down (Okeanos) consists of a circular ocean girdling the monolith Thayaphaeawoed, approximately 480 kilometers wide, and a circular beach and forest. The edge of the Okeanos tier is easily reached by foot from the beach in less than a day. It follows that the outer radius of the lowest (largest) tier of the planet is approximately 4500 km. This disagrees with the quote above, since, in order to have a surface area equal to that of the water surface of Earth, the world of tiers would require a radius of approximately 10,700 km.
World of Tiers | Alofmethbin
In December 2004, it was found to have a long-period 1.78 M giant planet in orbit around it.
HD 89307 | Planetary system
Scientists at the University of Warwick determined that it has winds of up to blowing from the day side to the night side. NASA released a brightness map of the surface temperature of HD 189733 b; it is the first map ever published of an extra-solar planet.
HD 189733 b | Map of the planet
De stellis (on the stars) 12. De cursu planetarum (on the course of the planets) 13. De ordine eorum (on their arrangement) For example, chapter 3, 'Quid sit mundus' ('what the world is') runs: Mundus est universitas omnis, quæ constat ex cœlo et terra, quatuor elementis in speciem orbis absoluti globata: igne, quo sidera lucent; aere, quo cuncta viventia spirant: aquis, quæ terram cingendo et penetrando communiunt: atque ipsa terra, quæ mundi media atque ima, librata volubili circa eam universitate pendet immobilis. The world is the whole of everything, which is constituted by the sky and the land, the four elements in the form of a completely rounded sphere: fire, by which the stars shine; air, which all living things breathe; waters, which surround the land, encircling and penetrating; and the land itself, which is the middle and core of the world, hanging unmoving, with everything turning in equilibrium around it.
De natura rerum (Bede) | Contents
The concept of the habitable zone (or Liquid Water Zone) defining a region where water can exist on the surface, is based on the properties of both the Earth and Sun. Under this model, Earth orbits roughly at the centre of this zone or in the "Goldilocks" position. Earth is the only planet currently confirmed by humankind to possess large bodies of surface water. Venus is on the hot side of the zone while Mars is on the cold side. Neither are known to have persistent surface water, though evidence exists that Mars did have in its ancient past, and it is speculated that the same was the case for Venus.
Earth analog | Surface water and hydrological cycle
Such a planet would probably have an iron- or steel-rich core like the known terrestrial planets. Surrounding that would be molten silicon carbide and titanium carbide. Above that, a layer of carbon in the form of graphite, possibly with a kilometers-thick substratum of diamond if there is sufficient pressure. During volcanic eruptions, it is possible that diamonds from the interior could come up to the surface, resulting in mountains of diamonds and silicon carbides. The surface would contain frozen or liquid hydrocarbons (e.g. tar and methane) and carbon monoxide. A weather cycle is theoretically possible on carbon planets with an atmosphere, provided that the average surface temperature is below 77 °C.
Carbon planet | Definition
Mike Brown's website, using a radiometrically determined diameter of , lists it as a possible dwarf planet.
(15874) 1996 TL66 | Introduction
If there has been no activity for 3 billion years, it will not be possible to destroy the surface by terrestrial contamination, so can be treated as Category I. Otherwise, the category may need to be reassessed.
Planetary protection | Other objects
Its mass is roughly half that of the planet Mercury. The smallest known planet orbiting a main-sequence star other than the Sun is Kepler-37b, with a mass (and radius) slightly higher than that of the Moon.
Planet | Mass
"HD 189733 A" has one known planet, designated HD 189733 b, a gaseous giant 13% larger than Jupiter close enough to complete an orbit every two days. Using spectrometry it was found in 2007 that this planet contains significant amounts of water vapour. This planet is the second extrasolar planet where definitive evidence for water has been found. The chemical signature of water vapour was detected in the atmosphere of this planet. Although HD 189733b with atmospheric temperatures rising above is far from being habitable, this finding increases the likelihood that water, an essential component of life, would be found on a more Earth-like planet in the future.
HD 189733 | Planetary system
Although unconfirmed, there is 98.6% probability that this planet does exist. The National Science Foundation announced on 29 September the discovery of a fourth super-Earth (Gliese 581g) orbiting within the Gliese 581 planetary system. The planet has a minimum mass 3.1 times that of Earth and a nearly circular orbit at 0.146 AU with a period of 36.6 days, placing it in the middle of the habitable zone where liquid water could exist and midway between the planets c and d. It was discovered using the radial velocity method by scientists at the University of California at Santa Cruz and the Carnegie Institution of Washington.
Super-Earth | 2010
, provisional designation , is a trans-Neptunian object of the scattered disc orbiting in the outermost region of the Solar System. The Spitzer Space Telescope has estimated this object to be about in diameter, but 2012 estimates from the Herschel Space Observatory estimate the diameter as closer to . It is not a detached object, since its perihelion (closest approach to the Sun) is under the influence of Neptune. Light-curve-amplitude analysis suggests that it is a spheroid. Tancredi presents "in the form of a decision tree, the set of questions to be considered in order to classify an object as an icy 'dwarf planet'." They find that is very probably a dwarf planet.
(15874) 1996 TL66 | Introduction
Genji is a Super-Earth but only moderately so: it has 2.8 times the mass and 1.36 times the diameter of Earth, and 1.5 times Earth's gravity. The side of the planet that constantly faces its companion world Chujo ("Moonside") is mostly land, the other hemisphere ("Starside") is mostly ocean. The mean surface temperature is +20 °C, slightly warmer than Earth. Although humans in good condition can physically accommodate to the high gravity, the sea level air pressure of 3.1 bars which results from this gravity (as per the barometric formula) requires artificial decompression for safe breathing. Only at 5,800 meters (an altitude found on this planet only in the form of a few small highlands that are cold and arid) the atmospheric pressure drops to Earth-standard 1 bar.
Murasaki (novel) | Genji
Despite its Earth-like composition, the planet's equilibrium temperature is around , far too hot for liquid water or life. Depending on the amount of cloud cover in the atmosphere of HD 219134 b, the actual temperature may be somewhat lower, but nowhere near the range for liquid water.
HD 219134 b | Mass, radius and temperature
says, 'I once took the moon to be (or saw the moon as) a planet, but I was mistaken.' Copernicus obliquely refers to Earth as a planet in "De Revolutionibus" when he says, "Having thus assumed the motions which I ascribe to the Earth later on in the volume, by long and intense study I finally found that if the motions of the other planets are correlated with the orbiting of the earth..." Galileo also asserts that Earth is a planet in the "Dialogue Concerning the Two Chief World Systems": "[T]he Earth, no less than the moon or any other planet, is to be numbered among the natural bodies that move circularly."
Definition of planet | Earth
, is 46.5 AU from the Sun. It will reach perihelion, its closest point to the Sun, in 2122. At nearly 800 km in diameter, it is approximately tied (to within measurement uncertainties) as the largest unnamed object in the Solar System and is also tied as the largest known planetoid without a moon.
(307261) 2002 MS4 | Introduction
However, this provides an unrealistic picture of the surface temperature of the planet. Earth's equilibrium temperature is 255 K ; it is Earth's greenhouse gases that raise its surface temperatures to the levels we experience. If TRAPPIST-1e has a thick atmosphere, its surface could be much warmer than its equilibrium temperature.
TRAPPIST-1e | Mass, radius, and temperature
In 2017, it was found that the planet likely hosts an atmosphere.
HD 219134 b | Introduction
It is possible that a planet in this system may have been scattered and ended up being accreted by the star, which may account for the large surface metallicity.
HD 12661 | Properties
With a generically estimated diameter of , is a possible dwarf planet.
(82075) 2000 YW134 | Classifications
The elevation of the land surface varies from the low point of at the Dead Sea, to a maximum altitude of at the top of Mount Everest. The mean height of land above sea level is about . The pedosphere is the outermost layer of Earth's continental surface and is composed of soil and subject to soil formation processes. The total arable land is 10.9% of the land surface, with 1.3% being permanent cropland. Close to 40% of Earth's land surface is used for agriculture, or an estimated of cropland and of pastureland.
Earth | Surface
The planet is estimated to be about five times Earth's mass (5.5 ). Some astronomers have speculated that it may have a rocky core like Earth, with a thin atmosphere. Its distance from the star, and the star's relatively low temperature, means that the planet's likely surface temperature is around , making it one of the coldest known. If it is a rocky world, this temperature would make it likely that the surface would be made of frozen volatiles, substances which would be liquids or gases on Earth: water, ammonia, methane and nitrogen would all be frozen solid. If it is "not" a rocky planet, it would more closely resemble an icy gas planet like Uranus, although much smaller.
OGLE-2005-BLG-390Lb | Mass, radius and temperature
Its surface is estimated to be about 500 million years old, so it would not be expected to show evidence of plate tectonics.
Atmosphere of Venus | Evolution
It was later found to be a gas giant.
Terrestrial planet | Extrasolar terrestrial planets
At the age of 4.46 billion years, it has 1.25 times the mass of the Sun and is radiating 61.7 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,370 K.
HD 143787 | Introduction