HD 69830 d is an

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

likely orbiting within the habitable zone of the star HD 69830, the outermost of three such planets discovered in the system. It is located approximately 40.7

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s (12.49

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, or km) 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

Puppis Puppis is a constellation in the southern sky. Puppis, the Latin translation of "poop deck", was originally part of an over-large constellation Argo Navis (the ship of Jason and the Argonauts), which centuries after its initial description, was ...

. The exoplanet was found by using the

radial velocity method Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in t ...

, from radial-velocity measurements via observation of

Doppler shift The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

s in the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

of the planet's parent star.

Characteristics

Mass, radius and temperature

HD 69830 d is an

ice giant An ice giant is a giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. There are two ice giants in the Solar System: Uranus and Neptune. In astrophysics and planetary science t ...

, with a mass and radius near that of the planets

Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...

and

Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...

, but smaller than that of the gas giants

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 mass more than two and a half times that of all the other planets in the Solar System combined, but ...

and

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

. Its temperature is , close to that of Earth. The radius is not known, however given its mass of 17 , which is around that of the planet Neptune, it likely has a radius of around 4 . In other terms, it is basically a warmer version of Neptune.

Host star

The planet orbits a ( G-type) star named HD 69830, orbited by total of three planets, of which HD 69830 d has the longest orbital period. The star has a mass of 0.86 and a radius of 0.90 . It has a surface temperature of 5394 K and is 10.6 billion 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. 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 li ...

, or how bright it appears from Earth's perspective, is 5.47. Therefore, HD 69830 is visible to the naked eye.

Orbit

The planet's orbit has a low

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...

, like most of 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 "Solar S ...

. The

semimajor axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the longe ...

of the orbit is only 0.63 AU, similar to that of

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...

. However, its star is less massive and energetic than the

(with a luminosity of 0.62 ), thereby putting the planet within its

habitable zone In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kas ...

Habitability

HD 69830 d likely resides in the

of its parent star. The exoplanet, with an estimated mass of 17 , is too massive to likely be rocky, and because of this the planet itself is not habitable. Hypothetically, large enough moons, with a sufficient atmosphere and pressure, may be able to support liquid water and potentially life. For a stable orbit the ratio between the moon's

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

''P''_s around its primary and that of the primary around its star ''P''_p must be < 1/9, e.g. if a planet takes 90 days to orbit its star, the maximum stable orbit for a moon of that planet is less than 10 days. Simulations suggest that a moon with an orbital period less than about 45 to 60 days will remain safely bound to a massive giant planet or

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

that orbits 1 AU from a Sun-like star. In the case of HD 69830 d, this would be around 22 days in order to have a stable orbit. Tidal effects could also allow the moon to sustain

plate tectonics Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

, which would cause volcanic activity to regulate the moon's temperature and create a geodynamo effect which would give the satellite a strong

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

. To support an Earth-like atmosphere for about 4.6 billion years (the age of the Earth), the moon would have to have a Mars-like density and at least a mass of 0.07 . One way to decrease loss from

sputtering In physics, sputtering is a phenomenon in which microscopic particles of a solid material are ejected from its surface, after the material is itself bombarded by energetic particles of a plasma or gas. It occurs naturally in outer space, and can ...

is for the moon to have a strong

that can deflect

stellar wind A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. D ...

and radiation belts. NASA's Galileo's measurements hints large moons can have magnetic fields; it found that

's moon Ganymede has its own magnetosphere, even though its mass is only 0.025 .

Discovery

HD 69830 d was discovered in 2006 with the

HARPS The High Accuracy Radial Velocity Planet Searcher (HARPS) is a high-precision echelle planet-finding spectrograph installed in 2002 on the ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003. H ...

echelle spectrograph An echelle grating (from French ''échelle'', meaning "ladder") is a type of diffraction grating characterised by a relatively low groove density, but a groove shape which is optimized for use at high incidence angles and therefore in high diffract ...

installed on the

European Southern Observatory The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 mem ...

3.6-meter telescope at

La Silla Observatory La Silla Observatory is an astronomy, astronomical observatory in Chile with three telescopes built and operated by the European Southern Observatory (ESO). Several other telescopes are located at the site and are partly maintained by ESO. The obse ...

, Chile.

In popular culture

In the ''Halo'' video game series, a moon of HD 69830 d is the homeworld of the Kig-Yar ("Jackal") species, a member species of the enemy, the Covenant Empire.

References

External links

SST: Signs of Alien Asteroid Belt

* ttp://www.spacedaily.com/reports/Trio_Of_Neptunes_And_Their_Belt.html SpaceDaily: Trio Of Neptunes And Their Belt (May 18, 2006) {{Sky, 08, 18, 23.9, -, 12, 37, 55.0, 41 HD 69830 Exoplanets discovered in 2006 Exoplanets detected by radial velocity Giant planets in the habitable zone Ice giants