Appearance of extrasolar planets
Encyclopedia
The Sudarsky extrasolar planet classification system is a theoretical model-based classification system for predicting the appearance of extrasolar gas giant
planets based on their temperature. It was outlined by David Sudarsky
et al. in the paper Albedo and Reflection Spectra of Extrasolar Giant Planets and expanded on in Theoretical Spectra and Atmospheres of Extrasolar Giant Planets, published before any successful direct or indirect observation of an extrasolar planet atmosphere was made. It is a broad classification system with the goal of bringing some order to the likely rich variety of extrasolar gas giant planet atmospheres.
Gas giant planets are split into five classes (numbered using Roman numerals
) according to their modeled physical atmospheric properties. From our solar system: both planets eligible for the Sudarsky classification, Saturn and Jupiter, are Class I.
The appearance of planets that are not gas giants cannot be predicted by the Sudarsky system, for example terrestrial planet
s such as Earth
, HD 85512 b
(3.6 Earth mass
es) and OGLE-2005-BLG-390Lb
(5.5 Earth masses); or ice giant
s such as Uranus
(14 Earth masses) and Neptune
(17 Earth masses).
can apply for few of the extrasolar planets known; because most are wholly unlike any of our planets, for example the hot Jupiter
s.
Bodies which transit their star may be spectrographically mapped, for instance HD 189733 b
.
That planet has further been shown to be blue with an albedo
greater (brighter) than 0.14. Most transiting planets are hot Jupiters.
Speculation on the appearances of unseen extrasolar planets currently relies upon computational models of the likely atmosphere
of such a planet, for instance how the atmospheric temperature/pressure profile and composition would respond to varying degrees of insolation
.
Planets in this class have appearances dominated by ammonia
clouds. These planets are found in the outer regions of a planetary system
. They exist at temperatures less than about 150 kelvin
s (−120 degrees Celsius
/−190 degrees Fahrenheit
). The predicted Bond albedo
of a class I planet around a star
like the Sun
is 0.57, compared with a value of 0.343 for Jupiter and 0.342 for Saturn. The discrepancy can be partially accounted for by taking into account non-equilibrium condensates such as tholin
or phosphorus
, which are responsible for the coloured clouds in the Jovian atmosphere, and are not modelled in the calculations.
The temperatures for a class I planet require a cool star or else a distant perihelion for the planet's orbit. The former stars might be too dim for us even to know about them, and the latter orbits might be too unpronounced for notice until several observations of those orbits "years" (c.f. Kepler's Third Law). Superjovian planets would have enough mass to improve these observations; but a superjovian of comparable age to Jupiter will have more internal heat
ing than said planet, which could push it to a higher class.
As of 2000, the Sudarsky papers could assign no planets to class I except for Jupiter and Saturn. 55 Cancri d
could be a Class I planet.
. This type of planet is expected for planets with temperatures below around 250 K. Water clouds are more reflective than ammonia clouds, and the predicted Bond albedo of a class II planet around a sunlike star is 0.81. Even though the clouds on such a planet would be similar to those of Earth
, the atmosphere would still consist mainly of hydrogen
and hydrogen-rich molecules such as methane
.
The possible class II planets listed in Sudarsky's original paper includes 47 Ursae Majoris b
and Upsilon Andromedae d
(note that the true mass of Upsilon Andromedae d is significantly greater than was assumed).
and absorption by methane
in their atmospheres, appearing like Jovian-mass versions of Uranus
and Neptune
. Because of the lack of a reflective cloud layer, the Bond albedo is low, around 0.12 for a class III planet around a sunlike star. They exist in the inner regions of a planetary system, roughly corresponding to the location of Mercury
.
Exoplanets listed in Sudarsky's paper as being possible class III planets include Gliese 876 b
and Upsilon Andromedae c
. Above 700 K (800 °F, 430 °C), sulfides and chlorides might provide cirrus
-like clouds.
becomes the dominant carbon-carrying molecule in the planet's atmosphere (rather than methane
). Furthermore, the abundance of alkali metal
s, such as sodium
substantially increase, and spectral line
s of sodium
and potassium
are predicted to be prominent in the planet's spectrum
. These planets form cloud decks of silicate
s and iron
deep in their atmospheres, but this is not predicted to affect the spectrum of the planet. The Bond albedo of a class IV planet around a sunlike star is predicted to be very low, at 0.03 because of the strong absorption by alkali metals. Planets of classes IV and V are referred to as hot Jupiter
s.
55 Cancri b
was listed as a class IV planet.
HD 209458 b
at 1300 K (1000 °C) would be another such planet, with a geometric albedo of, within error limits, zero; and in 2001, NASA witnessed atmospheric sodium in its transit - but less than predicted. This star hosts an upper cloud deck absorbing so much heat that below it is a relatively cool stratosphere
. The composition of this dark cloud, in the models, is assumed to be titanium/vanadium oxide (sometimes abbreviated "TiVO"), by analogy with M class dwarf stars, but its true composition is unknown as of yet; it could well be as per Sudarsky.
HD 189733 b
, with measured temperatures 920-1200 K (650-930 °C), also qualifies as class IV. However it has in late 2007 been measured as deep blue, with an albedo over 0.14 (possibly due to the brighter glow of its "hot spot"). No stratosphere has been conclusively proven for it as yet.
TrES-2
was measured with the lowest albedo, and therefore listed as Class IV.
and iron
cloud decks are predicted to lie high up in the atmosphere. The predicted Bond albedo of a class V planet around a sunlike star is 0.55, thanks to reflection by the cloud decks. At such temperatures, the planet may glow red from thermal radiation. For stars of visual magnitude under 4.50 in our sky, such planets are theoretically visible to our instruments. Examples of such planets might include 51 Pegasi b
. HAT-P-11b
and those other gas giant exoplanets found by the Kepler telescope might be possible class V planets.
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
planets based on their temperature. It was outlined by David Sudarsky
David Sudarsky
David Sudarsky is an astrophysicist at the University of Arizona. He is primarily known for producing the first extrasolar planet classification system, which is based on a series of theoretical gas giant planet atmosphere models...
et al. in the paper Albedo and Reflection Spectra of Extrasolar Giant Planets and expanded on in Theoretical Spectra and Atmospheres of Extrasolar Giant Planets, published before any successful direct or indirect observation of an extrasolar planet atmosphere was made. It is a broad classification system with the goal of bringing some order to the likely rich variety of extrasolar gas giant planet atmospheres.
Gas giant planets are split into five classes (numbered using Roman numerals
Roman numerals
The numeral system of ancient Rome, or Roman numerals, uses combinations of letters from the Latin alphabet to signify values. The numbers 1 to 10 can be expressed in Roman numerals as:...
) according to their modeled physical atmospheric properties. From our solar system: both planets eligible for the Sudarsky classification, Saturn and Jupiter, are Class I.
The appearance of planets that are not gas giants cannot be predicted by the Sudarsky system, for example terrestrial planet
Terrestrial planet
A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun...
s such as Earth
Earth
Earth is the third planet from the Sun, and 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...
, HD 85512 b
HD 85512 b
HD 85512 b is an extrasolar planet orbiting the K-type star Gliese 370 approximately 36 light-years away in the constellation of Vela ....
(3.6 Earth mass
Earth mass
Earth mass is the unit of mass equal to that of the Earth. 1 M⊕ = 5.9722 × 1024 kg. Earth mass is often used to describe masses of rocky terrestrial planets....
es) and OGLE-2005-BLG-390Lb
OGLE-2005-BLG-390Lb
OGLE-2005-BLG-390Lb is a 'super-Earth' extrasolar planet orbiting the star OGLE-2005-BLG-390L, which is situated 21,500 ± 3,300 light years away from Earth, near the center of the Milky Way galaxy...
(5.5 Earth masses); or ice giant
Ice giant
Ice Giant or Ice giants may refer to:* A type of gas giant composed largely of materials less volatile than hydrogen and helium* The frost giants of Norse mythology, see also Hrimthurs...
s such as Uranus
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. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
(14 Earth masses) and Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
(17 Earth masses).
Background
The appearance of extrasolar planets is largely unknown because of the difficulty in making direct observations of extrasolar planets. In addition, analogies with planets in our solar systemSolar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
can apply for few of the extrasolar planets known; because most are wholly unlike any of our planets, for example the hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
s.
Bodies which transit their star may be spectrographically mapped, for instance HD 189733 b
HD 189733 b
HD 189733 b is an extrasolar planet approximately 63 light-years away in the constellation of Vulpecula . The planet was discovered orbiting the star HD 189733 on October 5, 2005, when astronomers in France observed the planet transiting across the face of the star. The planet is classified as a...
.
That planet has further been shown to be blue with an albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
greater (brighter) than 0.14. Most transiting planets are hot Jupiters.
Speculation on the appearances of unseen extrasolar planets currently relies upon computational models of the likely atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
of such a planet, for instance how the atmospheric temperature/pressure profile and composition would respond to varying degrees of insolation
Insolation
Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...
.
Class I: Ammonia clouds
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
clouds. These planets are found in the outer regions of a planetary system
Planetary system
A planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...
. They exist at temperatures less than about 150 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s (−120 degrees Celsius
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
/−190 degrees Fahrenheit
Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...
). The predicted Bond albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
of a class I planet around a star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
like the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
is 0.57, compared with a value of 0.343 for Jupiter and 0.342 for Saturn. The discrepancy can be partially accounted for by taking into account non-equilibrium condensates such as tholin
Tholin
Tholin [after the ancient Greek word meaning "not clear"] is a heteropolymer molecule formed by solar ultraviolet irradiation of simple organic compounds such as methane or ethane. Tholins do not form naturally on modern-day Earth, but are found in great abundance on the surface of icy bodies in...
or phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, which are responsible for the coloured clouds in the Jovian atmosphere, and are not modelled in the calculations.
The temperatures for a class I planet require a cool star or else a distant perihelion for the planet's orbit. The former stars might be too dim for us even to know about them, and the latter orbits might be too unpronounced for notice until several observations of those orbits "years" (c.f. Kepler's Third Law). Superjovian planets would have enough mass to improve these observations; but a superjovian of comparable age to Jupiter will have more internal heat
Internal heat
Internal heat is the heat source from the interior of celestial objects, such as planets, brown dwarfs, and stars, caused by gravity, nuclear fusion and decaying radioactive materials. The amount of internal heating depends on mass; the more massive the object, the more internal heat it has...
ing than said planet, which could push it to a higher class.
As of 2000, the Sudarsky papers could assign no planets to class I except for Jupiter and Saturn. 55 Cancri d
55 Cancri d
55 Cancri d is an extrasolar planet in a long-period orbit around the Sun-like star 55 Cancri A. Located at a similar distance from its star as Jupiter is from our Sun, it is the fifth and outermost known planet in its planetary system...
could be a Class I planet.
Class II: Water clouds
Planets in class II are too warm to form ammonia clouds: instead their clouds are made up of water vaporWater vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...
. This type of planet is expected for planets with temperatures below around 250 K. Water clouds are more reflective than ammonia clouds, and the predicted Bond albedo of a class II planet around a sunlike star is 0.81. Even though the clouds on such a planet would be similar to those of Earth
Earth
Earth is the third planet from the Sun, and 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...
, the atmosphere would still consist mainly of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and hydrogen-rich molecules such as methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
.
The possible class II planets listed in Sudarsky's original paper includes 47 Ursae Majoris b
47 Ursae Majoris b
47 Ursae Majoris b is an extrasolar planet approximately 46 light-years from Earth in the constellation of Ursa Major. The planet was discovered located in a long-period orbit around the star 47 Ursae Majoris in January 1996 and as of 2011 is the innermost of three known planets in its planetary...
and Upsilon Andromedae d
Upsilon Andromedae d
Upsilon Andromedae d is an extrasolar planet orbiting the Sun-like star Upsilon Andromedae A. Its discovery in April 1999 by Geoffrey Marcy and R. Paul Butler made Upsilon Andromedae the first star to be known to host a multiple-planet planetary system...
(note that the true mass of Upsilon Andromedae d is significantly greater than was assumed).
Class III: Cloudless
Planets with equilibrium temperatures between about 350 K (170 °F, 80 °C) and 800 K (980 °F, 530 °C) do not form global cloud cover, as they lack suitable chemicals in the atmosphere to form clouds. These planets would appear as featureless blue globes because of Rayleigh scatteringRayleigh scattering
Rayleigh scattering, named after the British physicist Lord Rayleigh, is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. The particles may be individual atoms or molecules. It can occur when light travels through...
and absorption by methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
in their atmospheres, appearing like Jovian-mass versions of Uranus
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. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
and Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
. Because of the lack of a reflective cloud layer, the Bond albedo is low, around 0.12 for a class III planet around a sunlike star. They exist in the inner regions of a planetary system, roughly corresponding to the location of Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
.
Exoplanets listed in Sudarsky's paper as being possible class III planets include Gliese 876 b
Gliese 876 b
Gliese 876 b is an extrasolar planet orbiting the red dwarf star Gliese 876. It completes one orbit in approximately 61 days. Discovered in June 1998, Gliese 876 b was the first planet to be discovered orbiting a red dwarf star.- Discovery :...
and Upsilon Andromedae c
Upsilon Andromedae c
Upsilon Andromedae c is an extrasolar planet or star orbiting the Sun-like star Upsilon Andromedae A every 241.2 days. Its discovery in April 1999 by Geoffrey Marcy and R. Paul Butler made Upsilon Andromedae the first known star to host a multiple-planet planetary system...
. Above 700 K (800 °F, 430 °C), sulfides and chlorides might provide cirrus
Cirrus cloud
Cirrus clouds are atmospheric clouds generally characterized by thin, wispy strands, giving them their name from the Latin word cirrus meaning a ringlet or curling lock of hair...
-like clouds.
Class IV: Alkali metals
Above 900 K (630 °C/1160 °F), carbon monoxideCarbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
becomes the dominant carbon-carrying molecule in the planet's atmosphere (rather than methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
). Furthermore, the abundance of alkali metal
Alkali metal
The alkali metals are a series of chemical elements in the periodic table. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, along with hydrogen. The alkali metals are lithium , sodium , potassium , rubidium , caesium , and francium...
s, such as sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
substantially increase, and spectral line
Spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...
s of sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
are predicted to be prominent in the planet's spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
. These planets form cloud decks of silicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
s and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
deep in their atmospheres, but this is not predicted to affect the spectrum of the planet. The Bond albedo of a class IV planet around a sunlike star is predicted to be very low, at 0.03 because of the strong absorption by alkali metals. Planets of classes IV and V are referred to as hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
s.
55 Cancri b
55 Cancri b
55 Cancri b is an extrasolar planet orbiting the Sun-like star 55 Cancri A every 14.65 days. It is the second planet in order of distance from its star, and is an example of a hot Jupiter. Discovered in 1996 by Geoffrey Marcy and R...
was listed as a class IV planet.
HD 209458 b
HD 209458 b
HD 209458 b is an extrasolar planet that orbits the Solar analog star HD 209458 in the constellation Pegasus, some 150 light-years from Earth's solar system, with evidence of water vapor....
at 1300 K (1000 °C) would be another such planet, with a geometric albedo of, within error limits, zero; and in 2001, NASA witnessed atmospheric sodium in its transit - but less than predicted. This star hosts an upper cloud deck absorbing so much heat that below it is a relatively cool stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
. The composition of this dark cloud, in the models, is assumed to be titanium/vanadium oxide (sometimes abbreviated "TiVO"), by analogy with M class dwarf stars, but its true composition is unknown as of yet; it could well be as per Sudarsky.
HD 189733 b
HD 189733 b
HD 189733 b is an extrasolar planet approximately 63 light-years away in the constellation of Vulpecula . The planet was discovered orbiting the star HD 189733 on October 5, 2005, when astronomers in France observed the planet transiting across the face of the star. The planet is classified as a...
, with measured temperatures 920-1200 K (650-930 °C), also qualifies as class IV. However it has in late 2007 been measured as deep blue, with an albedo over 0.14 (possibly due to the brighter glow of its "hot spot"). No stratosphere has been conclusively proven for it as yet.
TrES-2
TrES-2
TrES-2b is an extrasolar planet orbiting the star GSC 03549-02811 located 718 light years away from our solar system. The planet has been identified in 2011 as the darkest known exoplanet, reflecting less than 1% of any light that hits it. The planet's mass and radius indicate that it is a gas...
was measured with the lowest albedo, and therefore listed as Class IV.
Class V: Silicate clouds
On the very hottest gas giants, with temperatures above 1400 K (2100 °F, 1100 °C) or cooler planets with lower gravity than Jupiter, the silicateSilicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
cloud decks are predicted to lie high up in the atmosphere. The predicted Bond albedo of a class V planet around a sunlike star is 0.55, thanks to reflection by the cloud decks. At such temperatures, the planet may glow red from thermal radiation. For stars of visual magnitude under 4.50 in our sky, such planets are theoretically visible to our instruments. Examples of such planets might include 51 Pegasi b
51 Pegasi b
51 Pegasi b , sometimes though unofficially named Bellerophon, is an extrasolar planet approximately 50 light-years away in the constellation of Pegasus...
. HAT-P-11b
HAT-P-11b
HAT-P-11b is an extrasolar planet orbiting the star HAT-P-11. This planet was discovered by the transit method and submitted for publication on January 2, 2009....
and those other gas giant exoplanets found by the Kepler telescope might be possible class V planets.