MLO 4 / HR 6426 / Gl 667 ABC
MLO 4 / HR 6426 / Gl 667 ABC |
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© Torben Krogh & Mogens Winther,
(Amtsgymnasiet and EUC Syd Gallery,
student photo used with permission)
MLO 4 AB are orange-red dwarf
stars, like Epsilon
Eridani at left
center of meteor. (See a 2MASS
Survey
image
of MLO 4 from the
NASA Exoplanet
Archive.)
System Summary
Martin Kormmesser,
ESO
Larger and
jumbo illustrations.
Three, possibly four,
super-Earths
have been detected in the habitable
zone around Star C
(more), view of
daytime sky from planet "d"
as imagined by Kormmesser.
On June 25, 2013, astronomers announced the Gliese 667 C has at least six planets (possibly seven) and confirmed that at least three (possibly four) super-Earths (possibly four) orbit within the habitable zone around the star (ESO news release; and Anglada-Escude et al, 2013).
ESO
Larger and
jumbo illustrations.
Six, possibly seven, planets
have been detected around
Star C
(more).
On December 17, 2012, an astronomer submitted a preprint with new analysis of available radial-velocity data supporting the existence of five planetary candidates around Gliese 667 C. Two planetary candidates were previous detected with orbital periods of 7.2 and 28.1 days ("b" and "c'), while three additional orbital periods of 30.8, 38.8, and 91.3 days ("d," "e," and "f") are also likely to be associated with planetary companions around Gliese 667 C. If confirmed as planets, the 28.1-, 30.8-, and 38.8-day periods would be associated with objects orbiting in the "central portion of the habitable zone, while the 91.3 day orbits lies partly within the habitable zone." The minimum masses for b, c, d, e, and f are 5.4, 4.8, 3.1, 2.4, and 5.4 Earth-masses, respectively. If confirmed, planetary candiate "e" with a 38.8-day period with 2.4 Earth-masses is the lowest mass extra-Solar planet detected in a star's habitable zone to day (Philip C. Gregory, 2012).
System Summary
This triple star system is located about 22.7 light-years (ly) away from our Sun, Sol, at the southwestern central part (17:18:57.2-34:59:23.3, ICRS 2000.0) of Constellation Scorpius, the Scorpion -- west of the Butterfly Cluster and northwest of Lesath (Upsilon Scorpii) and Shaula (Lamda Scorpii). It is composed of close binary Stars A and B and a more distant Star C, but a fourth stellar companion D is not gravitationally bound. According to Robert Thorburn Ayton Innes (1861-1933), Stars A and B were first noted as a binary by astronomers at the old Melbourne Observatory (MLO) in Australia in 1867 and so was the system was catalogued MLO (or Melb or Mlb) 4 (Bob Argle, Web Deep-Sky Society, July 2007).
Guillem Anglada-Escudé,
CIS
Larger illustration of planet "c" only.
MLO 4 C, orbiting Stars A and B,
appears to have at least two
super-Earths,
and one ("c") in
the star's habitable zone
(more).
Planetary candidates have been found around Star C. On October 19, 2009, a team of astronomers using the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph with the European Southern Observatory's (ESO) 3.6-meter telescope announced the discovery of a potential super-Earth "b" with at least 5.7 Earth-masses in a tight orbit (~0.05 AUs) around Star C at an ESO/CAUP conference on extra-Solar planets in Porto, Portugal -- ESO press release and more below). Beginning with a pre-print submitted on November 21, 2011 and a Carnegie Institution for Science news release on February 2, 2012, two teams of astronomers revealed the finding of a second, even smaller potential super-Earth "c" with around 4.5 (but possibly as little as 3.4) but as much as 9 Earth-masses in a potentially habitable-zone orbit (~0.12 AUs) completed in 28.15 days around Star C, with evidence of another super-Earth "d?" with a period of 75 days and a gas giant "e?" in outer orbits (Carnegie news release; UCSC news release; Anglada-Escudé et al, 2012; Lisa Grossman, New Scientist, February 2, 2012; Nancy Atkinson, Universe Today, February 2, 2012; Bonfils et al, 2011; and Delfosse et al, 2011, in prep -- more below). (See animations of the orbits of Stars A and B and their potentially habitable zones and of planetary and potentially habitable zone orbits of Star C, with tables of basic orbital and physical characteristics.)
Luis Calçada,
ESO
Larger and
jumbo illustrations.
Sunset on planetary candidate "c"
with binary stars A and B in the
darkening sky
(more), as imagined
by Calçada.
As a relatively bright star in Earth's night sky, Star A also is catalogued as Harvard Revised (HR) 6426, 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 -- updated and expanded through the hard work of E. Dorrit Hoffleit (1907 - 2007) and others. In addition, HR 6426 is listed as HD 156384 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. However, many astronomers now refer to this star by its designation as Gliese (or Gl or expanded GJ) 667 in the famous Gliese Catalogue of Nearby Stars (CNS, now ARICNS database) of Wilhelm Gliese (1915-93), who was a longtime astronomer at the Astronomiches Rechen-Institut at Heidelberg (even when it was at Berlin). (More discussion on star names and catalogue numbers is available from Alan MacRobert at Sky and Telescope and from Professor James B. Kaler's Star Names.)
Habitable Zones around the Stars
As MLO 4 A and B are like distant cousins of Sol, some wonder whether Earth-type planets might be in orbit around either star, although astronomers would find it very difficult to detect such small planets in inner orbits using present methods. In order to be warmed sufficiently have liquid water at the surface, an Earth-type rocky planet around Star A would have to have an orbital distance around between 0.78 to 1.04 AU, with a period lasting around six months. Such a planet around Star B would be located within less than 0.5 AU and a period of less than a couple of months.
For an even cooler and dimmer red dwarf star like Star C, the water zone probably would be located between 0.1 and 0.28 AUs with a period of with less than two months (Anglada-Escude et al, 2013, Figure 15; and Anglada-Escudé et al, 2012, Figure 3). At such a close distance, a planet would probably be tidally locked -- with one side in perpetual day. In any case, the light emitted by red dwarfs may be too red in color for Earth-type plant life to perform photosynthesis efficiently. (See animations of the orbits of Stars A and B and their potentially habitable zones and of the planetary and potentially habitable zone orbits of Star C, with tables of basic orbital and physical characteristics.)
This star is an orange-red dwarf star of spectral and luminosity type K3-4 V (NASA Star and Exoplanet Database). This star have around 71 to 75 percent of Sol's mass (NASA Star and Exoplanet Database, derived from David F. Gary, 1992), around 76 percent of its diameter (Pasinetti-Fracassini et al, 2001), and about 12 percent of its visual and over 32 percent of its bolometric luminosity (NASA Star and Exoplanet Database, derived from Kenneth R. Lang, 1980). It appears to be less enriched than Sol in elements heavier than hydrogen ("metals") with only about 26 percent of Sol's abundance of iron (Cayrel de Strobel et al, 1991, page 301). It is a New Suspected Variable star designated NSV 8482 (with an amplitude of 0.04). Useful star catalogue numbers for MLO 4 A include: HR 6426*, Gl 667 A, Hip 84709, HD 156384, CD-34 11626 A, CP-34 6803, SAO 208670, LHS 442, LTT 6888, LFT 1336, LPM 638, and UGPMF 433.
According to the Sixth Catalog of Visual Orbits of Binary Stars, Stars A and B have an average separation of 12.6 AUs (a semi-major axis of 1.81" at a HIPPARCOS distance estimate of 20.74 ly) in a highly eccentric orbit (e= 0.58). The orbital period takes 42.15 years to complete and is inclined 128° from the perspective of an observer on Earth (Staffan Soderhjelm, 1999; Baize and Petit, 1989, page 509; Roland Wielen, 1962, page 604; and W.P. Hirst, 1950, page 458; and 1947). In turn, Stars A and B have been separated from Star C by 56 to 213 AUs (8 to 30.5") from 1889 to 1948 at an orbital inclination of 139° -- to 215 AUs (30.8") at an inclination of 136°; calculations published in 2012 suggest a minimum separation of 230 AUs (Anglada-Escudé et al, 2012) (See an animation of the orbits of Stars A and B and their potentially habitable zones, with a table of basic orbital and physical characteristics.)
This star is an orange-red dwarf star of spectral and luminosity type K5 V (NASA Star and Exoplanet Database). This star may have around 65 percent of Sol's mass, 70 percent of its diameter (Pasinetti-Fracassini et al, 2001), and five percent of its visual luminosity. Useful star catalogue numbers for MLO 4 B include: Gl 667 B.
NASA -- larger image
MLO 4 C is a dim red dwarf star, like Gliese
623 A (M2.5V) and B (M5.8Ve) at lower right.
Currently separated from Stars A and B by at least 230 AUs, MLO 4 C is a red dwarf star of spectral and luminosity type M1.5-2.5 V (Anglada-Escudé et al, 2012; NASA Star and Exoplanet Database; and Hawley et al, 1996). This star may have around 31 to 38 percent of Sol's mass (Anglada-Escudé et al, 2012), 42 percent of its diameter (Pasinetti-Fracassini et al, 2001), and just over 3/1,000th of its visual luminosity. Assuming to have the same metallicity as Stars A and B with around 26 percent of Sol's metallicity, it appears to be a main sequence stars of two to 10 billion years old (Anglada-Escudé et al, 2012). Useful star catalogue numbers for MLO 4 C include: Gl 667 C, and LHS 443.
A Planetary System around C
On June 25, 2013, astronomers announced the Gliese 667 C has at least six planets (possibly seven) and confirmed that at least three (possibly four) super-Earths (possibly four) orbit within the habitable zone around the star (ESO news release; and Anglada-Escude et al, 2013).
ESO
Larger and
jumbo illustrations.
Six, possibly seven, planets
have been detected around
Star C
(more).
On December 17, 2012, an astronomer submitted a preprint with new analysis of available radial-velocity data supporting the existence of five planetary candidates around Gliese 667 C. Two planetary candidates were previously detected with orbital periods of 7.2 and 28.1 days ("b" and "c'), while three additional orbital periods of 30.8, 38.8, and 91.3 days ("d," "e," and "f") are also likely to be associated with planetary companions around Gliese 667 C. If confirmed as planets, the 28.1-, 30.8-, and 38.8-day periods would be associated with objects orbiting in the "central portion of the habitable zone, while the 91.3 day orbits lies partly within the habitable zone." The minimum masses for b, c, d, e, and f are 5.4, 4.8, 3.1, 2.4, and 5.4 Earth-masses, respectively. If confirmed, planetary candiate "e" with a 38.8-day period with 2.4 Earth-masses is the lowest mass extra-Solar planet detected in a star's habitable zone to day (Philip C. Gregory, 2012).
---------------------------------------------- [Guide] -- [Larger] ----------------------------------------------
| Orbital Distance (a=AUs) | Orbital Period (P=years) | Orbital Eccentricity (e) | Orbital Inclination (i=degrees) | Mass (Earths) | Diameter (Earths) | Density (Earths) | Surface Gravity (Earths) | Metallicity (Solar) | |
| MLO 4 C | 0.0 | ... | ... | ... | 125,000 | 46 | ... | ... | ... |
|---|---|---|---|---|---|---|---|---|---|
| Planet "b" | 0.050 | 0.020 | 0.13 | ? | =>5.6 | >1<4 | ... | ... | ... |
| Planet "h?" | 0.089 | 0.046 | 0.06 | ? | =>1.1 | ~1 | ... | ... | ... |
| Inner H.Z. Edge? | 0.10-0.12 | <0.05 | 0 | ? | ... | ... | ... | ... | ... |
| Planet "c" | 0.125 | 0.077 | 0.02 | ? | =>3.8 | >1<4 | ... | ... | ... |
| Planet "d/f" | 0.156 | 0.107 | 0.03 | ? | =>2.7 | >1<4 | ... | ... | ... |
| Planet "e" | 0.213 | 0.170 | 0.02 | ? | =>2.7 | >1<4 | ... | ... | ... |
| Planet "f/d" | 0.276 | 0.251 | 0.03 | ? | =>5.1 | >1<4 | ... | ... | |
| Outer H.Z. Edge? | 0.23-0.28 | <0.27 | 0 | ? | ... | ... | ... | ... | ... |
| Planet "g" | 0.549 | 0.702 | 0.08 | ? | =>4.6 | >1<4 | ... | ... |
Planet "b" -
On October 19, 2009, a team of astronomers using the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph with the European Southern Observatory's (ESO) 3.6-meter telescope announced the discovery of a planetary candidate "b" revised in 2013 to at least 5.6 Earth-masses orbiting only around 0.05 AU from Star C (Anglada-Escudé et al, 2012; Bonfils et al, 2011; Delfosse et al, 2011, in prep; and ESO/CAUP conference on extra-Solar planets in Porto, Portugal). The super-Earth's tight orbit is completed in around 7.2 days (Bonfils et al, 2011; Delfosse et al, 2011, in prep; and ESO press release).
Luis Calçada,
ESO
Large and
jumbo illustrations.
A planet with at least 5.6
Earth-masses has been found
in orbit around MLO 4 C at an
orbital distance of only 0.05
AUs (more
info and
video).
Planet "h?" - On June 25, 2013, astronomers announced the Gliese 667 C has at least six planets, but possibly seven including a new planetary candidate designated "h?". At at least 1.1 Earth-mass, this potential planet would be the smallest planet yet detected around Star C. With a semi-major axis around 0.0893 AUs and an orbital eccentricity of 0.03, it takes just under 17 days to complete an orbit around Star C. Its orbital distance averages near the inner edge of the hypothesized habitable zone of Star C and so could have liquid water on its surface assuming favorable planetary characteristics such as sufficient coverage by reflective clouds and atmospheric composition (ESO news release; and Anglada-Escude et al, 2013).
Guillem Anglada-Escudé,
CIS
Larger illustration of planet "c" only.
MLO 4 C, orbiting Stars A and B,
appears to have at least two
super-Earths,
with one ("c") in
the star's habitable zone
(more).
Planet "c" - Beginning with a pre-print submitted on November 21, 2011 and a Carnegie Institution for Science news release on February 2, 2012, two teams of astronomers revealed astronomers revealed the finding of a second, even smaller potential super-Earth "c" with at at least 3.8 (2013 update) Earth-masses in a potentially habitable-zone orbit (0.125 AUs) with an eccentricity of 0.03, which is completed in 28.1 days, with evidence of another super-Earth "d?" with 5.7 Earth-masses and a period of 75 days as well as a gas giant "e?" in outer orbits. Planet c's average orbital distance of around 0.12 AU places it within the inner edge of Star's potentially habitable zone, where the planet could support liquid water on its surface given a sufficiently favorable atmosphere. According to the astronomers, this planetary "candidate receives about 90% of the light received by Earth in our Solar System" (Carnegie news release; UCSC news release; Philip C. Gregory, 2012; and Anglada-Escudé et al, 2012; Lisa Grossman, New Scientist, February 2, 2012; Nancy Atkinson, Universe Today, February 2, 2012; Bonfils et al, 2011; Delfosse et al, 2011; and Anglada-Escude et al, 2013 -- more below).
Guillem Anglada-Escudé,
CIS
Larger diagram.
Like Gliese 581 g, Gliese 667 C-c is
believed to be a super-Earth that orbits
Gliese 667 C within the red dwarf
star's habitable zone
(more).
Planet "d" or "f" - This planet has alternative designations, depending on the astronomers cited. On December 17, 2012, an astronomer submitted a preprint with new analysis of available radial-velocity data supporting the existence of five planetary candidates around Gliese 667 C. In addition to the two previously discovered planets with orbital periods of 7.2 and 28.1 days ("b" and "c'), three additional planets with orbital periods of 30.8, 38.8, and 91.3 days ("d," "e," and "f") were also detected around Gliese 667 C. Planet "d", with a 30.8-day period was found to be one of three orbiting in the "central portion of the habitable zone" (Philip C. Gregory, 2012).
Martin Kormmesser,
ESO
Larger and
jumbo illustrations.
Three, possibly four,
super-Earths
have been detected in the habitable
zone around Star C
(more), view of
daytime sky from planet "d"
as imagined by Kormmesser.
On June 25, 2013, astronomers announced the Gliese 667 C has at least six planets, of which "f" (or "d") is a super-Earth-class planet in Star C's habitable zone, with at least 2.7 Earth-masses. With a semi-major axis around 0.156 AU and an orbital eccentricity of 0.02, the planet completes its orbit around Star in just over 39 days. Its orbital distance of 0.156 AU is near the middle of the hypothesized habitable zone of Star C and so could have liquid water on its surface assuming favorable planetary characteristics such as sufficient coverage by reflective clouds and atmospheric composition (ESO news release; and Anglada-Escude et al, 2013).
Planet "e" - Like planet d/f, this super-Earth-class planet in Star C's habitable zone also has at least 2.7 Earth-masses. With a semi-major axis around 0.213 AU and an orbital eccentricity of 0.02, the planet completes its orbit around Star in 62.2 days. As its orbit is also is with the hypothesized habitable zone of Star C, planet e also may have liquid water on its surface assuming favorable planetary characteristics such as sufficient coverage by reflective clouds and atmospheric composition (ESO news release; and Anglada-Escude et al, 2013; and Philip C. Gregory, 2012).
Planet "f" or "d" - This planet has alternative designations, depending on the astronomers cited. Like its planetary neighbors d/f and e, this super-Earth-class planet in Star C's habitable zone has at least 5.1 Earth-masses. With a semi-major axis around 0.276 AU and an orbital eccentricity of 0.03, the planet completes its orbit around Star in 91.6 days. As its orbit is also just within the hypothesized habitable zone of Star C, planet e also may have liquid water on its surface assuming favorable planetary characteristics such as sufficient coverage by reflective clouds and atmospheric composition (ESO news release; and Anglada-Escude et al, 2013; and Philip C. Gregory, 2012).
Planet "g" - This planet is the outermost planet object detected around Star C thus far. Lying outside Star C;s habitable zone, it is a super-Earth-class planet with least 4.6 Earth-masses. With a semi-major axis around 0.549 AU and an orbital eccentricity of 0.03, the planet completes its orbit around Star in 256.2 days (ESO news release; and Anglada-Escude et al, 2013; and Philip C. Gregory, 2012).
Closest Neighbors
The following star systems are located within 10 light-years of MLO 4.
| Star System | Spectra & Luminosity | Distance (light-years) |
| CD-32 13297 | M2 V | 3.5 |
| 36 Ophiuchi 3? | K0-1 Ve K1-5 Ve K5-6 Ve | 4.5 |
| CD-44 11909 | M3.5-5 V | 7.1 |
| CD-37 10765 AB | M3-4 V M5 V | 7.2 |
| HR 6416 AB | G8-K0 V M0 V | 7.9 |
| CD-40 9712 | M0-3 V | 8.6 |
| CD-46 11540 | M2.5-3 V | 8.8 |
| L 205-128 | M3.5-5 V | 9.0 |
| G 154-44 | M4.5 V | 9.7 |
| L 347-14 | M4.5 V | 9.7 |
Other Information
Up-to-date technical summaries on these stars can be found at: Jean Schneider's Extrasolar Planet Encyclopaedia entry for GJ 667C; the Astronomiches Rechen-Institut at Heidelberg's ARICNS Star A, Star B, and Star C; and the NASA Exoplanet Archive. Additional information may be available at Roger Wilcox's Internet Stellar Database.
According to one legend, Orion (the Hunter) boasted that he could kill all the animals which alarmed, Gaea, the Goddess of Earth. Hence, she ordered a giant scorpion to sting Orion to death, which it managed to do at Orion's heel (marked by the star Rigel). For more information on stars and other objects in this Constellation and an illustration, go to Christine Kronberg's Scorpius. For another illustration, see David Haworth's Scorpius.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.
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Note: Special thanks to Spike Valance for notifying us of the discovery of planetary candidate "c" around Star C in this system and to Andrew Tribick on the corrected, average semi-major of planet "c" around Star C. © 1998-2013 Sol Company. All Rights Reserved. |
