Epsilon Reticuli
Encyclopedia
Epsilon Reticuli (HD 27442) is a binary system
approximately 59 light-year
s away in the constellation
of Reticulum
. The primary star is an orange subgiant star, while the secondary star is a white dwarf
star. The primary star should be easily visible without optical aid under dark skies in the southern hemisphere. In 2000, an extrasolar planet
was confirmed to be orbiting the primary star in the system.
. Being a subgiant it is ceasing or has already ceased fusing
hydrogen
in its core. Soon the star will swell up and become a red giant
. Despite its advanced stage, it cannot be much older than the Sun.
The companion star, Epsilon Reticuli B, is a white dwarf
star located around 240 AU from Epsilon Reticuli A. It has a surface temperature between 9000 and 17000 K.
On December 11, 2000, a team of astronomers announced the discovery of a planet Epsilon Reticuli b
. With a minimum mass of 1.17 that of Jupiter
and a similar radius
, the planet moves around Epsilon Reticuli with an average separation of 1.16 AUs. The eccentricity of the planet is extremely low (at 0.06), and it completes an orbit every 418 days (or 1.13 years).
Stability analysis shows that the planet's Lagrangian point
s would be stable enough to host Earth-sized planets, though as yet no trojan planets have been detected in this system.
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
approximately 59 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Reticulum
Reticulum
Reticulum is a small, faint constellation in the southern sky. Its name is Latin for a small net, or reticle—a net of crosshairs at the focus of a telescope eyepiece that is used to measure star positions...
. The primary star is an orange subgiant star, while the secondary star is a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
star. The primary star should be easily visible without optical aid under dark skies in the southern hemisphere. In 2000, an extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
was confirmed to be orbiting the primary star in the system.
Star system
The primary star, Epsilon Reticuli A, is an orange subgiant 20% more massive than our SunSun
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...
. Being a subgiant it is ceasing or has already ceased fusing
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
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...
in its core. Soon the star will swell up and become a red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
. Despite its advanced stage, it cannot be much older than the Sun.
The companion star, Epsilon Reticuli B, is a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
star located around 240 AU from Epsilon Reticuli A. It has a surface temperature between 9000 and 17000 K.
Planetary system
Epsilon Reticuli b
Epsilon Reticuli b, sometimes designated Epsilon Reticuli Ab to distinguish from the white dwarf companion of the primary star Epsilon Reticuli, also known as HD 27442, was discovered on December 16, 2000 by the Anglo-Australian Planet Search Team using the highly successful radial velocity method...
. With a minimum mass of 1.17 that of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
and a similar radius
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
, the planet moves around Epsilon Reticuli with an average separation of 1.16 AUs. The eccentricity of the planet is extremely low (at 0.06), and it completes an orbit every 418 days (or 1.13 years).
Stability analysis shows that the planet's Lagrangian point
Lagrangian point
The Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects...
s would be stable enough to host Earth-sized planets, though as yet no trojan planets have been detected in this system.