![hoptune](https://upload.wikimedia.org/wikipedia/commons/9/94/Hoptune.jpg)
A hot Neptune or Hoptune is a type of
giant planet
The giant planets constitute a diverse type of planet much larger than Earth. They are usually primarily composed of low-boiling-point materials (volatiles), rather than rock or other solid matter, but massive solid planets can also exist. Ther ...
with a
mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
similar to that of
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
or
Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
orbiting close to its star, normally within less than 1
AU. The first hot Neptune to be discovered with certainty was
Gliese 436 b
Gliese 436 b (sometimes called GJ 436 b) is a Neptune-sized exoplanet orbiting the red dwarf Gliese 436. It was the first hot Neptune discovered with certainty (in 2007) and was among the smallest-known transiting planets in mass and radius, un ...
in 2007, an exoplanet about 33 light years away. Recent observations have revealed a larger potential population of hot Neptunes in the Milky Way than was previously thought. Hot Neptunes may have formed either
in situ
''In situ'' (; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in ...
or ex situ.
General characteristics
Because of their close proximity to their parent stars, hot Neptunes have a much greater rate and chance of
transiting their star as seen from a farther outlying point, than planets of the same mass in larger orbits. This increases the chances of discovering them by
transit-based observation methods.
Transiting hot Neptunes include
Gliese 436 b
Gliese 436 b (sometimes called GJ 436 b) is a Neptune-sized exoplanet orbiting the red dwarf Gliese 436. It was the first hot Neptune discovered with certainty (in 2007) and was among the smallest-known transiting planets in mass and radius, un ...
and
HAT-P-11b
HAT-P-11b (or Kepler-3b) is an extrasolar planet orbiting the star HAT-P-11. It was discovered by the HATNet Project team in 2009 using the transit method, and submitted for publication on 2 January 2009.
This planet is located approximately ...
. Gliese 436 b (also known as GJ 436b) was the first hot Neptune to be discovered with certainty in 2007. The exoplanet
Dulcinea
Dulcinea del Toboso is a fictional character who is unseen in Miguel de Cervantes' novel ''Don Quijote''. Don Quijote believes he must have a lady, under the mistaken view that chivalry requires it.
As he does not have one, he invents her, mak ...
(or HD 160691 c) discovered in 2004 might also be a hot Neptune, but it has not been determined definitively. Another may be
Kepler-56b
Kepler-56b (KOI-1241.02) is a hot Neptune—a class of exoplanets—located roughly away. It is somewhat larger than Neptune and orbits its parent star Kepler-56 and was discovered in 2013 by the Kepler Space Telescope.
Planetary orbit
Keple ...
, which has a mass somewhat larger than
Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
's and orbits its star at 0.1 AU, closer than
Mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
orbits the sun.
The first theoretical study of how hot Neptunes could form was carried out in 2004.
If these planets formed ex situ, i.e., by migrating to their current locations while growing, they may contain large quantities of frozen
volatiles
Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances.
On planet Earth, the term ' ...
and
amorphous ice
Amorphous ice (non-crystalline or "vitreous" ice) is an amorphous solid form of water. Common ice is a crystalline material wherein the molecules are regularly arranged in a hexagonal lattice, whereas amorphous ice has a lack of long-range order ...
s. Otherwise, if they formed in situ, their inventory of heavy elements should be made entirely of
refractory materials
In materials science, a refractory material or refractory is a material that is resistant to Thermal decomposition, decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycr ...
.
Yet, regardless of the mode of formation, hot Neptunes should contain large fractions (by mass) of gases, primarily hydrogen and helium, which also account for most of their volume.
Ultra-hot Neptune
LTT 9779 b LTT is an initialism for the following:
* Libya Telecom & Technology
* Light the Torch, an American Rock Band formerly as Devil You Know
* Linux Trace Toolkit, for tracing computer program execution
* Lithuanian talonas, ISO 4217 code
*Lokmanya Til ...
is the first ultra-hot Neptune discovered with an orbital period of 19 hours and an atmospheric temperature of over 1700 degrees Celsius. Being so close to its star and with a mass around twice that of Neptune, its atmosphere should have evaporated into space so its existence requires an unusual explanation.
An Ultra-Hot Neptune in the Neptune desert
James S. Jenkins et al, 27 Sep 2020 A candidate planet around Vega
Vega is the brightest star in the northern constellation of Lyra. It has the Bayer designation α Lyrae, which is Latinised to Alpha Lyrae and abbreviated Alpha Lyr or α Lyr. This star is relatively close at only from the Sun, an ...
slightly more massive than Neptune was detected in 2021. It orbits Vega, an A-class star, every 2.43 days, and with a temperature of about 2500 degrees Celsius would be the second-hottest planet on record if confirmed.
See also
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References
Sources
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* A discussion of the "Detection of transits of the nearby hot Neptune GJ 436 b" paper.
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Types of planet
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