HD 69830 / HR 3259

© ESO





Larger illustration.






Three Neptune-
to Uranus-sized
planets and an
asteroid belt
have been
detected around
HD 69830 (more).

Today, some astronomers prefer to refer to this star as HD 69830, as it is listed in the Henry Draper (1837-82) Catalogue with extension (HDE), a massive photographic stellar spectrum survey carried out by Annie Jump Cannon (1863-1941) and Edward Charles Pickering (1846-1919) from 1911 to 1915 under the sponsorship of a memorial fund created by Henry's wife, Anna Mary Palmer. As a relatively bright star in Earth's night sky, the star is also catalogued as Harvard Revised (HR) 3259, a numbering system derived from the 1908 Revised Harvard Photometry catalogue of stars visible to many Humans with the naked eye. The HR system has been preserved through its successor, the Yale Bright Star Catalogue -- revised and expanded through the hard work of E. Dorrit Hoffleit and others.

On the other hand, the star has an older designation as BD-12 2449 from a catalogue that was originally published in 1863 by Friedrich Wilhelm August Argelander (1799-1875) on the position and brightness of 324,198 stars between +90° and -2° declination that were measured over 11 years from Bonn, Germany with his assistants Eduard Schönfeld (1828-1891) and Aldalbert Krüger (1832-1896). The catalogue became famous as the Bonner Durchmusterung ("Bonn Survey") and is typically abbreviated as BD. It was later expanded and extended during the early 20th Century with the Cordoba (observed from Argentina) then the Cape Photographic Durchmusterung (observed from South Africa).

T. Pyle, JPL, Caltech, NASA




Larger illustration.




Warm dust detected around
HD 69830 was probably generated
by an asteroidal collision, like
that depicted at right center (more).

The Star

HD 69830 is a yellow-orange to orange-red, main sequence dwarf star of spectral and luminosity type G7.5-K0 V. The star has a mass of 86 +/- 3 percent of Sol's (Lovis et al, 2006), 87 to 89 percent of its diameter (Pasinetti-Fracassini et al, 2001; Johnson and Wright, 1983, page 663; and NASA Star and Exoplanet Database, derived from Kenneth R. Lang, 1980), and 45 percent of its bolometric ("total") luminosity (Beichman et al, 2005; and Arthur N. Cox, 2000). It appears to be slightly less abundant 89 to 93 percent in iron than Sol (Lovis et al, 2006; and Cayrel de Strobel et al, 2001). The star is around 87 to 93 percent as enriched as Sol in elements heavier than hydrogen (Valenti and Fischer, 2005; and Santos et al, 2004). While a recent age estimate indicates 7 +/- 3 billion years (Lovis et al, 2006), a prior estimate indicated only around half of Sol's 4.6 billion years. Useful catalogue numbers and designations for the star include: HR 3259, Gl 302, Hip 40693, HD 69830, BD-12 2449, SAO 154093, and LHS 245.

Robert Hurt, JPL,
Caltech, NASA




Larger illustration.




The zodiacal light
reflected by the warm
dust of HD 39830's
asteroidal collisions
would be around a
thousand times
brighter than what
is seen on Earth,
outshining the
Milky Way (more).

Asteroid Belt

In April 2005, astronomers (including Charles A. Beichman, Geoffrey Bryden, Thomas N. Gautier, Karl Stapelfeldt, Michael W. Werner, Karl Misselt, George H. Rieke, John Stansberry, and David E. Trilling) announced the probable discovery of an asteroid belt around this star with some 25 times the mass of the Main Asteroid Belt around Sol (press release from the Spitzer Space Telescope). The asteroids were detected by a ring of warm dust that is probably generated by asteroidal collisions every thousand years or so, although a less likely cause may be a "super-comet" of the size of Pluto that was perturbed into the warmer inner reaches of this star system and so is "boiling off dust" containing small silicate crystals (including bright green-colored forsterite) like those found in comet Hale-Bopp (more). The dust appears to lie within the equivalent of Venus' orbital distance in the Solar System, much closer to HD 69830 than Sol's Main Asteroid Belt, which lies between the orbits of Mars and Jupiter. However, like the Solar System where Jupiter acts as an "outer wall" by shepherding the outer asteroids of the main belt, a recently discovered (if unseen) planet that may exceed the mass of Neptune may be acting playing a similar role around HD 69830.

© ESO






Larger illustration.







The middle and
outermost planets
act as "shepherds"
around HD 69830's
asteroid belt (more).

By July 2006, the astronomers (including Carey M. Lisse, Charles A. Beichman, Geoffrey Bryden, and Mark C. Wyatt) were able to detect debris derived from the break up of a P or D-type, outer Main-Belt asteroid lacking in carbonaceous and iron-rich materials with a diameter of around some 30 kilometers (19 miles). In the Solar System, there are numerous large, P and D-type asteroids near Jupiter's orbit (e.g., the Hildas and Trojans), which have been disrupted to produce "debris-disk like structures" (Lisse el al, 2007). The debris belt detected is located around one AU from HD 69830, "coincident" with the 2:1 and 5:2 mean motion resonances of the outermost of three Neptune-sized planets also discovered in early 2006 (more below).

Planetary System

On May 17, 2006, a team of astronomers (Christophe Lovis, Michel Mayor, Francisco Pepe, Didier Queloz, Stephane Udry, Nuno C. Santos, Yann Alibert, Willy Benz, Christoph Mordasini, François Bouchy, Alexandre C. M. Correia, Jacques Laskar, Jean-Loup Bertaux, and Jean-Pierre Sivan) using the ESO's HARPS spectrograph announced the discovery of three planets ("b", "c", and "d") with minimum masses of 10.5, 12.1, and 18.4 times that of Earth orbiting HD 69830 (ESO press release and Nature abstract). The three planets have orbital distances of 0.0785, 0.186, and 0.63 AUs, periods of 8.67, 31.6 and 197 days (where the longest exceeds half a Earth-year), and eccentricities of 0.1 ± 0.04, 0.13 ± 0.06, and 0.07 ± 0.07, respectively. The previously discovered asteroid belt appears to lie between the orbits of the middle and outermost most planets discovered. (The ESO has developed animations of these planetary orbits around HD 69830.) As of early 2005, no planet with more than half of Jupiter's mass has been detected within 3 AUs of HD 69830 (Beichman et al, 2005).

© Yann Alibert, C. Vaillant, ESO



Larger illustration.




The mass and orbits of the
three planets indicate that
none has an Earth-like
planetary surface (more).

Theoretical simulations indicate that innermost planet is rocky and very hot, that the middle one is rocky with gas, and that outermost planet is likely to have a rocky core that may be surrounded by a highly pressurized water layer as well as a massive outer gas envelope. The outermost planet appears to be located near the inner edge of the habitable zone, where surface liquid water may exist. Although this planet does not appear Earth-like due to its Neptune-like mass, some astronomers speculate that it may have moons suitable for Earth-type life. (More information and links are available from the Extrasolar Planets Encyclopaedia.)

For an Earth-type planet around HD 69830 to have liquid water at its surface, it would need a stable orbit centered around 0.75 AU -- between the orbital distances of Venus and Earth in the Solar System, with an orbital period around 259 days. However, the presence of planet "d" (which may exceed the mass of Neptune and is shepherding the star's inferred asteroid belt within the orbital distance of Venus the Solar System) would probably perturb the orbit of such a hypothetical Earth-mass planet. Life on such a planet would also be under a relatively high frequency of asteroid impacts, than is Earth at present. Astronomers would find it very difficult to detect an Earth-sized planet around this star using present methods. (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)

The following table includes all star systems known to be located within 10 light-years (ly), plus more bright stars within 10 to 20 ly, of HD 69830.