2M1207b is a
planetary-mass object orbiting the
brown dwarf
Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...
2M1207, in the constellation
Centaurus
Centaurus () is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one ...
, approximately 170
light-year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...
s from Earth.
It is one of the first candidate
exoplanet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...
s to be directly observed (by
infrared
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
imaging). It was discovered in April 2004 by the
Very Large Telescope (VLT) at the
Paranal Observatory in
Chile
Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...
by a team from the
European Southern Observatory led by Gaël Chauvin.
It is believed to be from 5 to 6 times the
mass
Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...
of
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
and may orbit 2M1207 at a distance roughly as far from the brown dwarf as
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...
is from the
Sun.
The object is a very hot
gas giant
A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranu ...
; the estimated surface
temperature
Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
is roughly 1200
K (930 °C or 1700 °F),
mostly due to gravitational contraction.
Its
mass
Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...
is well below the calculated limit for
deuterium fusion in brown dwarfs, which is 13
Jupiter masses. The projected
distance
Distance is a numerical or occasionally qualitative measurement of how far apart objects, points, people, or ideas are. In physics or everyday usage, distance may refer to a physical length or an estimation based on other criteria (e.g. "two co ...
between 2M1207b and its primary is around 40
AU (similar to the mean distance between
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...
and the
Sun).
[Estimated observed projected separation from observed angular separation and estimated distance.] Its
infrared
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
spectrum indicates the presence of
water
Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
molecules in its atmosphere.
The object is not a likely candidate to support
life
Life, also known as biota, refers to matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes. It is defined descriptively by the capacity for homeostasis, Structure#Biological, organisation, met ...
, either on its surface or on any
satellite
A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...
s.
Discovery and identification

2M1207b is around 100 times fainter in the sky than its companion. It was first spotted as a "faint reddish speck of light" in 2004 by the
VLT. After the initial observation, there was some question as to whether the objects might be merely an
optical double, but subsequent observations by the ''
Hubble Space Telescope
The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...
'' and the VLT have shown that the objects move together and are therefore presumably a
binary system.
An initial
photometric estimate for the distance to 2M1207b was 70
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, and ...
s.
In December 2005, American astronomer
Eric Mamajek reported a more accurate distance () to 2M1207b using the
moving-cluster method. Recent trigonometric
parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
results have confirmed this moving-cluster distance, leading to a distance estimate of 52.75 parsecs or 172 ± 3
light years.
Properties
Estimates for the mass, size, and temperature of 2M1207b are still uncertain. Although spectroscopic evidence is consistent with a mass of 8 ± 2 Jupiter masses and a surface temperature of 1600 ± 100
kelvin
The kelvin (symbol: K) is the base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K. By de ...
s, theoretical models for such an object predict a
luminosity
Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...
10 times greater than observed. Because of this, lower estimates for the mass and temperature have been proposed. Alternatively, 2M1207b might be dimmed by a surrounding disk of dust and gas.
As an unlikely possibility, Mamajek and Michael Meyer have suggested that the planet is actually much smaller, but is radiating away heat generated by a recent collision.
JWST observations of 2M1207B with
NIRSpec did not detect any
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
(CH
4) and only weak
carbon monoxide
Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...
(CO) in the atmosphere of this object. The best-fit models show stronger methane and carbon monoxide bands than observed. A weaker methane band is a sign for
nonequilibrium chemistry for young low-mass objects. The weakness of carbon monoxide could be attributed to other effects, such as temperature gradient or cloud thickness. The researchers used cloudless models that show some inconsistency with the temperature and absorption of methane and carbon monoxide, which might be resolved in the future with models that include
clouds.
The JWST observations were also able to detect emission of hydrogen (
Paschen transitions) and the
Helium
Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
I triplet at 1.083 μm. This is a sign of active
accretion from a small
circumstellar disk or
circumplanetary disk.
For now this disk remains undetected, but it might be detected in future observations by JWST at longer wavelengths.
Status as an exoplanet
Although the mass of 2M1207b is less than that required for deuterium fusion to occur, some 13 times the mass of Jupiter, and the image of 2M1207b has been widely hailed as the first direct image of an exoplanet, it may be questioned whether 2M1207b is actually a planet. , the
International Astronomical Union
The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...
's (IAU) official definition of an exoplanet requires that the mass ratio of the orbiting object to the central object be below the
L4/L5 instability, which is given by the equation M/M
central < 2/(25+) ≈ 1/25.
The mass ratio of 2M1207b and 2M1207 is approximately 0.22, which exceeds the L4/L5 instability threshold and therefore means 2M1207b does not qualify as an exoplanet under the IAU's definition.
Some other
definitions of the term ''planet'' require a planet to have formed in the same way as the planets in the
Solar System
The Solar SystemCapitalization 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 "Sola ...
did, by secondary accretion in a
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 not be considered an accretion disk; while the two are sim ...
.
With such a definition, if 2M1207b formed by direct
gravitational collapse of a gaseous
nebula
A nebula (; or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral, or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regions, such as in the Pillars of Creation in ...
, it would be a
sub-brown dwarf rather than a planet. A similar debate exists regarding the identity of
GQ Lupi b, also first imaged in 2004.
On the other hand, the discovery of marginal cases like
Cha 110913-773444—a free-floating, planetary-mass object—raises the question of whether distinction by formation is a reliable dividing line between stars/brown dwarfs and planets.
In 2006, the IAU's Working Group on Extrasolar Planets described 2M1207b as a "possible planetary-mass companion to a brown dwarf."
See also
*
Extrasolar moon
*
HD 172555
*
Rogue planet
References
External links
ESO Press Release 12/05:Yes, it is the Image of an Exoplanet BBC: Planet 'seen' around distant sun*
ttp://www.space.com/scienceastronomy/planet_photo_040910.html Space.com article on the discovery*
"A Giant Planet Candidate Near a Young Brown Dwarf" (PDF)from the
European Southern Observatory.
Space.com: Fresh Debate over First Photo of Extrasolar Planet"A Moving Cluster Distance to the Exoplanet 2M1207 B in the TW Hydrae Association""The Planetary Mass Companion 2MASS 1207-3932B: Temperature, Mass, and Evidence for an Edge-on Disk"
Catalog views: Aladin Lite
DSS colorDSS near IRsDSS red (high res)
{{Centaurus
b
Centaurus
TW Hydrae association
Giant planets
Exoplanets discovered in 2004
Exoplanets detected by direct imaging