K2-33b (also known by its EPIC designation ''EPIC 205117205.01'') is a very young
super-Neptune exoplanet, orbiting the
pre-main-sequence star
A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence. Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope of ...
K2-33. It was discovered by
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
's ''
Kepler
Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...
'' spacecraft on its "Second Light" mission. It is located about 456
light-years (140
parsec
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...
s) away from
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
in the constellation of
Scorpius
Scorpius is a zodiac constellation located in the Southern celestial hemisphere, where it sits near the center of the Milky Way, between Libra to the west and Sagittarius to the east. Scorpius is an ancient constellation that pre-dates the Gr ...
. The exoplanet was found by using the
transit method
Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty o ...
, in which the dimming effect that a planet causes as it crosses in front of its star is measured.
Among known exoplanets, K2-33b is considered extremely young − a mere 9.3 million years old. Only one other exoplanet is younger, with an age of 2 Myr (
V830 Tau b
V830 Tauri is a T Tauri star located away from the Sun in the constellation Taurus. This star is very young, with an age of only 2 million years, compared to the Sun's age, which is 4.6 billion years. Typical for a young stars, it exhibi ...
).
Physical characteristics
Mass, radius, and temperature
K2-33b is a
super-Neptune, an exoplanet that has a mass and radius larger than that of
Neptune. It has an
equilibrium temperature
The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is ...
of . It has a radius of 5.04 . While the exoplanet's mass hasn't been constrained yet, upper estimates place a mass of 3.6 .
Atmosphere
By 2022, the atmosphere of K2-33b was found to be hazy, without any noticeable molecular bands in transmission spectrum. Given the planetary radius and temperature, atmosphere is likely to contain an abundant
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
and dense
tholin
Tholins (after the Greek (') "hazy" or "muddy"; from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon ...
haze.
Host star
The planet orbits an (
M-type)
pre-main-sequence star
A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence. Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope of ...
named
K2-33. The star has a mass of 0.54 and a radius of 1.05 . It has a surface temperature of 3540
K and is 9.3 million years old. In comparison, the
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
is 4.6 billion years old and has a surface temperature of 5778 K. It has about the same amount of metals as the Sun, with a
metallicity (
e/H of 0. Its luminosity () is 15% that of the Sun.
The star's
apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
, or how bright it appears from Earth's perspective, is 14.3. Therefore, it is too dim to be seen with the naked eye.
Orbit
K2-33b orbits its host star with an orbital period of 5.424 days at a distance of 0.049 AU (compared to the distance of
Mercury from the Sun, which is about 0.38
AU). The planet likely receives about 125 times as much
sunlight that Earth does from the Sun.
Age and formation
![K2-33b](https://upload.wikimedia.org/wikipedia/commons/8/81/K2-33b.jpg)
The planet is best known for its remarkably young age, which is estimated to be about 9.3 million years.
Given this age, the planetary system most likely formed back near the end of the
Miocene
The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
epoch of the Earth's history. Observations made on the planet confirmed that it was in fact a fully formed exoplanet, not just a
protoplanet
A protoplanet is a large planetary embryo that originated within a protoplanetary disc and has undergone internal melting to produce a differentiated interior. Protoplanets are thought to form out of kilometer-sized planetesimals that gravitation ...
that was still in the stages of developing. The mass and radius of the exoplanet further help constrain this statement.
K2-33b is the youngest confirmed transiting exoplanet. There are relatively few other exoplanets discovered to date with an age this young, all of which are non-transiting (with some that were detected around the hot
A-type and
B-type star
A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type star ...
s, such as
HD 95086 and
HIP 78530, however these could just be brown dwarfs due to their mass). The
hot Jupiter
Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere tem ...
exoplanet
V830 Tau b
V830 Tauri is a T Tauri star located away from the Sun in the constellation Taurus. This star is very young, with an age of only 2 million years, compared to the Sun's age, which is 4.6 billion years. Typical for a young stars, it exhibi ...
, published in the same issue of the journal
Nature
Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...
as the discovery of K2-33b, is the youngest known exoplanet with an age of around 2 million years (around the time that humans evolved on Earth).
The discoveries of K2-33b and
V830 Tau b
V830 Tauri is a T Tauri star located away from the Sun in the constellation Taurus. This star is very young, with an age of only 2 million years, compared to the Sun's age, which is 4.6 billion years. Typical for a young stars, it exhibi ...
are most notable for explaining how close-in planets form, an open question in the field of exoplanets since the discovery of the first exoplanet,
51 Pegasi b
51 Pegasi b, officially named Dimidium , and formerly unofficially dubbed Bellerophon , is an extrasolar planet approximately away in the constellation of Pegasus. It was the first exoplanet to be discovered orbiting a main-sequence star, th ...
, in 1995. Given the young ages of these exoplanets, several theories of
planetary migration
Planetary migration occurs when a planet or other body in orbit around a star interacts with a disk of gas or planetesimals, resulting in the alteration of its orbital parameters, especially its semi-major axis. Planetary migration is the most li ...
can be ruled out because they take too long to form close-in planets. The most plausible formation scenario for K2-33b is that it formed further away from its star, then migrated inwards through the
protoplanetary disk
A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, be ...
, although it remains a possibility that the planet formed in place.
Trevor David of
Caltech
The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...
in Pasadena stated on the discovery of the exoplanet "The question we are answering is: Did those planets take a long time to get into those hot orbits, or could they have been there from a very early stage? We are saying, at least in this one case, that they can indeed be there at a very early stage."
Understanding the young ages of such exoplanets may eventually help to lead scientists on how planetary formation works and provide some clues on the origin of the
Solar System
The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
and other such planetary systems discovered.
Discovery
In 2014,
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
's
''Kepler'' spacecraft began its "Second Light" mission, after
two of its reactor wheels had failed the previous year, ending the primary mission. From 23 August to 13 November 2014, the spacecraft collected data from the core of
Upper Scorpius, which included K2-33.
The exoplanet was simultaneously discovered by two independent research groups, one led by astronomers from the
California Institute of Technology
The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...
and the other led by astronomers from the
University of Texas at Austin
The University of Texas at Austin (UT Austin, UT, or Texas) is a public research university in Austin, Texas. It was founded in 1883 and is the oldest institution in the University of Texas System. With 40,916 undergraduate students, 11,07 ...
.
The star was studied on days in late January, February, and March 2016. The observations were made with the Immersion Grating Infrared Spectrometer (IGRINS) on the 2.7-m
Harlan J. Smith Telescope at the
McDonald Observatory
McDonald Observatory is an astronomical observatory located near unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Locke in the Davis Mountains of West Texas, with additional faci ...
.
After observing the respective transits, which for K2-33b occurred roughly every 5 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic 5-day transits. The discovery was announced on 20 June 2016 in an announcement made by NASA.
See also
*
V830 Tau b
V830 Tauri is a T Tauri star located away from the Sun in the constellation Taurus. This star is very young, with an age of only 2 million years, compared to the Sun's age, which is 4.6 billion years. Typical for a young stars, it exhibi ...
References
External links
NASA – Kepler Mission
NASA – Kepler Discoveries – Summary Table
NASA – K2-33bat
The NASA Exoplanet Archive.
NASA – K2-33bat
The Exoplanet Data Explorer.
NASA – K2-33bat
The Extrasolar Planets Encyclopaedia.
{{Sky, 16, 10, 14.74, -, 19, 19, 09.4
Exoplanets discovered in 2016
Transiting exoplanets
Hot Jupiters
33
Scorpius (constellation)