HD 28185 b
Encyclopedia
HD 28185 b is an extrasolar planet
approximately 138 light-year
s away from Earth in the constellation
of Eridanus
. The planet was discovered orbiting the Sun-like star
HD 28185 in April 2001 as a part of the CORALIE survey for southern extrasolar planets, and its existence was independently confirmed by the Magellan Planet Search Survey in 2008. HD 28185 b orbits its sun in a circular orbit that is at the inner edge of its star's habitable zone
.
of its parent star caused by the gravitational attraction of the planet. This was achieved by measuring the Doppler shift of the star's spectrum
. In 2001 it was announced that HD 28185 exhibited a wobble along the line-of-sight with a period of 383 days, with an amplitude
indicating a minimum mass
5.72 times that of Jupiter
.
planets, the orbit of HD 28185 b has a low eccentricity, comparable to that of Mars
in our solar system
. The orbit lies entirely within its star's habitable zone.
The amplitude of the radial velocity oscillations means that the planet has a mass at least 5.7 times that of Jupiter in our solar system. However, the radial velocity method only yields a minimum value on the planet's mass, depending on the orbital inclination
to our line-of-sight
. Therefore, the true mass
of the planet may be much greater than this lower limit.
with no solid surface. Since the planet has only been detected indirectly through observations of the star, properties such as its radius
, composition, and temperature
are unknown.
Since HD 28185 b orbits in its star's habitable zone, some have speculated on the possibility of life on worlds in the HD 28185 system. While it is unknown whether gas giants can support life, simulations of tidal interactions suggest that HD 28185 b could harbor Earth-mass satellites
in orbit around it for many billions of years. Such moons, if they exist, may be able to provide a habitable
environment, though it is unclear whether such satellites would form in the first place. Additionally, a small planet in one of the gas giant's Trojan points could survive in a habitable orbit for long periods. In addition, the high mass of HD 28185 b of over six Jupiter masses actually makes either of these scenarios more likely than if the planet was about Jupiter's mass or less.
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...
approximately 138 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 from Earth 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 Eridanus
Eridanus (constellation)
Eridanus is a constellation. It is represented as a river; its name is the Ancient Greek name for the Po River. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations. It is the sixth largest of the modern...
. The planet was discovered orbiting the Sun-like 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...
HD 28185 in April 2001 as a part of the CORALIE survey for southern extrasolar planets, and its existence was independently confirmed by the Magellan Planet Search Survey in 2008. HD 28185 b orbits its sun in a circular orbit that is at the inner edge of its star's 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...
.
Discovery
Like the majority of known extrasolar planets, HD 28185 b was discovered by detecting small periodic variations in 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...
of its parent star caused by the gravitational attraction of the planet. This was achieved by measuring the Doppler shift of the star's spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
. In 2001 it was announced that HD 28185 exhibited a wobble along the line-of-sight with a period of 383 days, with an amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
indicating a minimum mass
Minimum mass
In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars and binary systems, nebulae, and black holes. Minimum mass is a widely cited statistic for extrasolar planets...
5.72 times 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,...
.
Orbit and mass
HD 28185 b takes 1.04 years to orbit its parent star. Unlike most known long-periodOrbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
planets, the orbit of HD 28185 b has a low eccentricity, comparable to that of Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
in our 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...
. The orbit lies entirely within its star's habitable zone.
The amplitude of the radial velocity oscillations means that the planet has a mass at least 5.7 times that of Jupiter in our solar system. However, the radial velocity method only yields a minimum value on the planet's mass, depending on the orbital inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
to our line-of-sight
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
. Therefore, the true mass
True mass
The term true mass is synonymous with the term mass, but is used in astronomy to differentiate the measured mass of a planet from the lower limit of mass usually obtained from radial velocity techniques...
of the planet may be much greater than this lower limit.
Characteristics
Given the planet's high mass, it is most likely to be a gas giantGas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
with no solid surface. Since the planet has only been detected indirectly through observations of the star, properties such as its 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...
, composition, and temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
are unknown.
Since HD 28185 b orbits in its star's habitable zone, some have speculated on the possibility of life on worlds in the HD 28185 system. While it is unknown whether gas giants can support life, simulations of tidal interactions suggest that HD 28185 b could harbor Earth-mass satellites
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
in orbit around it for many billions of years. Such moons, if they exist, may be able to provide a habitable
Planetary habitability
Planetary habitability is the measure of a planet's or a natural satellite's potential to sustain life. Life may develop directly on a planet or satellite or be transferred to it from another body, a theoretical process known as panspermia...
environment, though it is unclear whether such satellites would form in the first place. Additionally, a small planet in one of the gas giant's Trojan points could survive in a habitable orbit for long periods. In addition, the high mass of HD 28185 b of over six Jupiter masses actually makes either of these scenarios more likely than if the planet was about Jupiter's mass or less.