Kappa1 Ceti
Encyclopedia
Kappa1 Ceti is a yellow dwarf
star
approximately 30 light-year
s away in the constellation
of Cetus
. The star was discovered to have a rapid rotation, roughly once every nine day
s. Though there are no extrasolar planet
s confirmed to be orbiting the star, Kappa1 Ceti is considered a good candidate to contain terrestrial planet
s (like the Earth
). The system is thought to be a binary star
, but has not been confirmed. The star should not be confused with the star (which is ten times as distant).
star
of the spectral type G5Ve. The star is thought to have roughly the same mass
as the Sun
, along with a similar radius
, but only 85 percent of the luminosity
. It is unclear whether the star is equal or is more enriched in elements heavier than hydrogen
, but it is determined that the star has between 98 and 240 percent of the Sun's abundance of iron
. Kappa1 Ceti is much younger than the Sun, and may only be around 800 million years old.
The rapid rotation rate of this star, approximately once every nine days, is indicative of a relatively youthful body several hundred million years in age. Due to starspots
, the star varies slightly over the approximately the same period. The variations in period are thought to be caused by differential rotation at various latitudes, similar to what happens on the surface of our Sun. The star spots on Kappa1 Ceti range in latitude from 10° to 75° The magnetic properties of this star make it "an excellent match for the Sun at a key point in the Earth's past".
According to recent hypotheses, unusually intense stellar flares from a solar twin star could be caused by the interaction of the magnetic field of a giant planet in tight orbit with that star's own magnetic field. Some Sun-like stars of spectral class F8 to G8 have been found to undergo enormous magnetic outbursts to produce so-called superflares (coronal mass ejections) that release between 100 and 10 million times more energy than the largest flares ever observed on the sun, making them brighten briefly by up to 20 times. In 1998, nine Solar twin stars (including Kappa1 Ceti) were observed to have produced superflares, on average, about once per century. None of these stars rotate particularly fast, have close binary companions, or are very young. Previously, such large flares had not been observed in Sol-type main sequence stars, although they are common in a group of dim main-sequence, reddish M dwarfs
known as flare star
s.
The space velocity components of this star are = . It is not known to be a member of a moving group of stars.
technique, the search for substellar companions has thus far failed to find a brown dwarf
or extrasolar planet
in the "hot zone
" orbit around Kappa1 Ceti. Given the regular eruption of superflares, however, it is unlikely that Earth-type life could survive for long on any inner terrestrial planet
. The distance from the star where an Earth-type planet (with liquid water
) would be stable is centered around 0.92 astronomical unit
s from the star (between the orbital distances of Earth
and Venus
in the Solar system
). At this distance, such a planet would have an orbital period of almost 324 day
s. Astronomers are hoping to use NASA
's Terrestrial Planet Finder
(TPF) and ESA's Darwin Mission to search for a terrestrial planet in the habitable zone
around Kappa1 Ceti.
Yellow dwarf
A G-type main-sequence star , often called a yellow dwarf, is a main-sequence star of spectral type G and luminosity class V. Such a star has about 0.8 to 1.2 solar masses and surface temperature of between 5,300 and 6,000 K., Tables VII, VIII...
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...
approximately 30 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 Cetus
Cetus
Cetus is a constellation. Its name refers to Cetus, a sea monster in Greek mythology, although it is often called 'the whale' today. Cetus is located in the region of the sky that contains other water-related constellations such as Aquarius, Pisces, and Eridanus.-Ecliptic:Although Cetus is not...
. The star was discovered to have a rapid rotation, roughly once every nine day
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...
s. Though there are no 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...
s confirmed to be orbiting the star, Kappa1 Ceti is considered a good candidate to contain 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 (like the 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 system is thought to be a binary star
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...
, but has not been confirmed. The star should not be confused with the star (which is ten times as distant).
Stellar components
Kappa1 Ceti is a yellow dwarfYellow dwarf
A G-type main-sequence star , often called a yellow dwarf, is a main-sequence star of spectral type G and luminosity class V. Such a star has about 0.8 to 1.2 solar masses and surface temperature of between 5,300 and 6,000 K., Tables VII, VIII...
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...
of the spectral type G5Ve. The star is thought to have roughly the same mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
as 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...
, along with 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...
, but only 85 percent of the luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
. It is unclear whether the star is equal or is more enriched in elements heavier than 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...
, but it is determined that the star has between 98 and 240 percent of the Sun's abundance of 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...
. Kappa1 Ceti is much younger than the Sun, and may only be around 800 million years old.
The rapid rotation rate of this star, approximately once every nine days, is indicative of a relatively youthful body several hundred million years in age. Due to starspots
Sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....
, the star varies slightly over the approximately the same period. The variations in period are thought to be caused by differential rotation at various latitudes, similar to what happens on the surface of our Sun. The star spots on Kappa1 Ceti range in latitude from 10° to 75° The magnetic properties of this star make it "an excellent match for the Sun at a key point in the Earth's past".
According to recent hypotheses, unusually intense stellar flares from a solar twin star could be caused by the interaction of the magnetic field of a giant planet in tight orbit with that star's own magnetic field. Some Sun-like stars of spectral class F8 to G8 have been found to undergo enormous magnetic outbursts to produce so-called superflares (coronal mass ejections) that release between 100 and 10 million times more energy than the largest flares ever observed on the sun, making them brighten briefly by up to 20 times. In 1998, nine Solar twin stars (including Kappa1 Ceti) were observed to have produced superflares, on average, about once per century. None of these stars rotate particularly fast, have close binary companions, or are very young. Previously, such large flares had not been observed in Sol-type main sequence stars, although they are common in a group of dim main-sequence, reddish M dwarfs
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
known as flare star
Flare star
A flare star is a variable star that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to magnetic reconnection in the atmospheres of the stars. The brightness increase is...
s.
The space velocity components of this star are = . It is not known to be a member of a moving group of stars.
Possible planetary system
Using the radial velocityRadial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
technique, the search for substellar companions has thus far failed to find a brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
or 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...
in the "hot zone
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
" orbit around Kappa1 Ceti. Given the regular eruption of superflares, however, it is unlikely that Earth-type life could survive for long on any inner 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...
. The distance from the star where an Earth-type planet (with liquid water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
) would be stable is centered around 0.92 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s from the star (between the orbital distances 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...
and Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
in the Solar system
Solar 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...
). At this distance, such a planet would have an orbital period of almost 324 day
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...
s. Astronomers are hoping to use NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Terrestrial Planet Finder
Terrestrial Planet Finder
The Terrestrial Planet Finder was a proposed project by NASA to construct a system of telescopes for detecting extrasolar terrestrial planets. TPF was postponed several times and finally cancelled...
(TPF) and ESA's Darwin Mission to search for a terrestrial planet in the habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...
around Kappa1 Ceti.