Barnards Star Planetary System

Barnards Planetary System

System Summary

This dim star is the second closest to Sol after Alpha Centauri 3. It is located about 6.0 light-years away in the northernmost part (17:57:48.5+04:41:36.2, ICRS 2000.0) of Constellation Ophiuchus, the Serpent Holder -- west of Cebalrai or Kelb al Rai (Beta Ophiuchi). The star was named after its discoverer, noted astronomer Edward Emerson Barnard (1857-1923), who found in 1916 that the star has the largest known proper motion of all known stars (10.3 arcseconds per year). This high apparent speed is the result of its proximity to Sol as well as actual speed of travel through interstellar space. In fact, Barnard's Star is approaching Sol rapidly at 140 kilometers per second (87 miles/second) and will get as close as 3.8 light-years (ly) around 11,800 CE. Like other red dwarfs, however, it is not visible to the naked eye.

The Star

A very cool and dim, main sequence red dwarf (M3.8 Ve), Barnard's Star may have less than 17 percent of Sol's mass (RECONS estimate), 15 percent of its diameter (Ochsenbein and Halbwachs, 1982, page 529), around 4/10,000th of its luminosity, and between 10 and 32 percent of its abundance of elements heavier than hydrogen -- "metallicity" (John E. Gizis, 1997, page 820). According to calculations by Dr. Sten Odenwald, substituting Barnard's Star for Sol would give the Earth such a dim and very red Sun that it would only be 100 times brighter than the Full Moon, and so the planet would freeze solid at the surface.

Unlike Sol, Barnard's appears to be an old disk star that formed before the galaxy became much enriched with heavy elements (Monet et al, 1992, page 655). While the star may already be around 10 billion years old, it may last another another 40 billion years or more before cooling into a black dwarf. A small star spot that was shrinking in size may have been observed on Barnard's recently with the Hubble Space Telescope (Benedict et al, 1998). Barnard's is a New Suspected Variable star designated NSV 9910. Some other useful star catalogue numbers include: Gl 699, Hip 87937, BD+04 3561a, LHS 57, LTT 15309, LFT 1385, G 140-24, Vys/McC 799, and Munich 15040.

Interstellar Card
A Planetary System

Astronomers have long sought to find perturbations ("wobbles") in this star's motion that could be due to planet-sized companions. During the late 1960s, Peter van de Kamp (1901-1995) announced the detection of possibly two coplanar and corevolving planets, whose estimated masses were fine-tuned in 1982 to be about 0.7 and 0.5 of Jupiter's mass with orbital periods of 12 and 20 years, respectively, in "approximately" circular orbits based on astrometric positions obtained from 1938 to 1981 (van de Kamp, 1982). Until his death in 1995, Van de Kamp devoted most of his life (at at Sproul Observatory at (Swarthmore College) to analyzing over 2,000 plates of Barnard's Star that he and his students had taken from 1938 through 1981.

Neither planet was ever verified, however, and more recent observations with the Hubble Space Telescope have failed to yield supporting evidence for a large Jupiter or brown dwarf sized object (Schroeder et al, 2000). Some astronomers suspected that van de Kamp's data were distorted by the cleaning and remounting of the telescope lens at Sproul, 25 years after he began his observations. In 1995, George G. Gatewood (director of the University of Pittsburgh's Allegheny Observatory) suggested that, while brown dwarfs exceeding Jupiter's mass by more than 10 times could not exist around Barnard's Star, planets having a mass smaller than Jupiter's may possibly be present. (For more information about the search for planets around Barnard's through astrometric perturbation methods, go to George Bell's summary of Barnard's Star and van de Kamp's Planets.)

In order to be warmed sufficiently have liquid water at the surface, an Earth-type rocky planet would have to be located very close to such a cool and dim red dwarf star like Barnard's, at around 1/50th the Earth-Sun distance (or 0.02 AU). At distance, such a planet would probably be tidally locked -- with one side in perpetual day -- and race around the star in only about 2.6 days. Some have suggested that any rocky planets that formed around Barnard's are likely to be sparse in the heavier elements of the atomic table, and that there may be a greater probability of gas giants made mostly of hydrogen and helium in cold, outer orbits.