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Lalande 21185





Lalande 21185
The fourth nearest star system to the Sun after Alpha Centauri, Barnard's Star, and Wolf 359. Lalande 21185 is located in the southeastern corner of Ursa Major, northwest of Alula Borealis (Nu UMa). It is about three times too faint to be seen with the unaided eye.

Although Lalande 21185 is almost 200 times dimmer than the Sun, it is among the brightest red dwarfs in the solar neighborhood. Moving perpendicular to the galactic plane at a high velocity of 47 km/s, Lalande 21185 appears to belong to the Galaxy's thick disk population and to be considerably older than the Sun. It has both a high radial velocity, of 86 km/s toward the Sun, and a high tangential velocity (proper motion) of 57 km/s. The former is bringing the star 0.028 light-year closer to us each century and to a closest approach of about 4.6 light-years in 22,000 A.D.

After analyzing 50 years of astrometric observations of the star, George Gatewood and colleagues of the Allegheny Observatory suggested (1996) that Lalande 21185 is orbited by two Jupiter-like planets, a and b, though the evidence for b is weaker than that for a.1 There is also the possibility of a third, more remote object. If confirmed, these planets would be the nearest known extrasolar worlds to the Sun and the first to be discovered by astrometry. However, their existence has been questioned by researchers who have monitored Lalande 21185 by the radial velocity method and found no evidence of unseen companions. Thus Gatewood's claim is now in serious doubt.


Host star
Distance 8.29 light-years (2.54 parsecs)
Spectral type M2.1Ve
Apparent magnitude 7.47
Absolute magnitude 10.46
Luminosity (Sun=1) 0.0016
Position R.A. 11h 03m 20.2s; Dec. +35° 58' 11"
Mass (Sun=1) 0.45
Other designations HD 95735, BD +36 2147, G 119-052, PLX 2576, GJ 411, LHS 37, MCC 594, SAO 62377, LTT 12960, LFT 756, HIP 54035


Planets (to be confirmed and in doubt)
  a b
Mass (Jupiter=1) 0.9 1.6 ?
Semimajor axis 2.5 AU 10 AU ?
Orbital period 5.8 years 30 years ?
Discovery 1996, Gatewood et al, Allegheny Observatory 1996, Gatewood et al, Allegheny Observatory
Method of discovery astrometry astrometry


Lalande 21185 in fiction

In Star Light, a novel by Hal Clement, Lalande 21185 is orbited by a planet called Dhrawn, which has an extremely high gravitational pull.

In the fictional universe of Star Trek, on several occasions in the year 2364, viewscreen readouts aboard the starship USS Enterprise-D show the location of Lalande 21185 in the form of charts from the Enterprise library computer. (TNG: "The Naked Now", "The Last Outpost", "Conspiracy"). [From Memory Alpha.]


Reference

  1. Gatewood, G. D. "Lalande 21185," Bulletin of the Aerican Astronomical Society, 28, 885 (1996).

Related entry

   • nearest stars


Related categories

   • NOTABLE STARS
   • EXTRASOLAR PLANETS AND SUBSTELLAR OBJECTS