Lalande 21185 System

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Exoplanetary Scratchpad

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The Lalande 21185 system would be the closest planetary system to the Sun if we could confirm the existence of its two planets. It is also one of the earliest planets detected that still has a good chance to exist. The planets orbit far away from their dim Red Dwarf star, which makes one planet colder than Saturn and the other colder than Neptune despite being at a Saturn-like distance.

Lalande 21185 Web Pages

Lalande 21185 in the News

2 Planets Announced (1996)

Follow Ups on Announcements (1996-2005)

Atmospheric Water Detected

Lalande 21185 Fun Links

Lalande 21185 System Factoids

  • Fourth nearest star system to the Sun after Alpha Centauri, Barnard's Star and Wolf 359
  • One of the most luminous red dwarves near the Sun. Also a flare star.
  • If confirmed, this system would be the nearest known planetary system to Earth (8.25 ly vs. Epsilon Eridani's 10.5).
  • If the suspected planets turn out to be Brown Dwarves instead, then this would be the closest system to harbor a Brown Dwarve (vs Epsilon Indi's 11.8 ly)
  • Like Tau Ceti, it is thought to belong to the Milky Way's Thick Disk. As such, it is relatively old and travels at great velocities with respect to the Sun.
  • One of the first planetary systems hinted at having a solar-system like configuration. That is, giant planets occupying the outer star system.
  • Astrometric data available from 1930. Studied in high detail since 1988.
  • Dopplar Spectroscopy method unable to detect signs of planetary system. Perhaps the inclination is unfavorable to this method?
  • Water signature was detected in the system in 2002. It could be coming from planets or the star. Future observations should pinpoint the source.
  • A planet at 0.22 AU would receive equivelent radiation as the Earth does (accounting for infrared radiation).

Lalande 21185 Star Factoids

  • M2.1V spectral class
  • 46% Solar Mass, 46% Solar Diameter, 63% Solar Metalicity
  • A flare star
  • Older than the Sun, younger than 10 Billion Years old

Lalande 21185 b Factoids

  • Jupiter-sized planet orbiting at twice Earth's distance at sub-Saturn temperatures
  • Orbit takes 5.9 years. It should have been observed at high detail for multiple cycles (since 1988). It probably has not been confirmed yet because the stronger signature of the outer planet has not completed one 30 year cycle yet.
  • Notable for its very circular orbit (e = 0.0)

Lalande 21185 c Factoids

  • Possible large planet in a Saturn-like orbit at sub-Neptune-like temperatures.
  • The more massive (1.6 MJ) of the two planets and the first one hinted at. Dubbed 'c' because it and 'b' were announced at the same time and it was further from the star.
  • Orbit believed to take 30 years to complete, tugging on the motion of the star across the sky as it goes. When announced in 1996, accurate measurements had been taken for 8 years. 9 years have passed since then. It may be another 13 years before the planet completes one full orbit, confirming the existence and nature of the planet. Perhaps someone will photograph it before then?

Lalande d Factoids

  • Presense barely hinted at. The other two planets don't fully account for the star's wobble across the sky.
  • Further away than planet c to some degree.

Prince of the Red Dwarves

Lalande 21185 is the largest and brightest of the seven red dwarves within 10 light years of the Sun. The next brighter red dwarf further out is Lacaille 9352 (M0.5-1.5 Ve, 0.47 MS, 10.7ly). Lalande 21185 is also somewhat brighter than Gliese 876 , which has three confirmed planets (M3.5V, 0.27MS, 15.3 ly).

Red Dwarves Out to 10 Light Years (from Sol Station )
4.2 ly - Proxima Centauri (M5.5 Ve, 0.12 MS) - brown dwarf b?
6.0 ly - Barnard's Star (M3.8 Ve, 0.17 MS) - old star
7.8 ly - Wolf 359 (M5.8 Ve, 0.11 MS) - flare star
8.3 ly - Lalande 21185 (M2.1 Vne, 0.46 MS) - Flare & thick disk star; 3 planets?
8.7 ly - Luyten 726-8 A (M5.6 Ve, 0.1 MS) - flare Star
8.7 ly - UV Ceti (M6.0 Ve, 0.10 MS) - Flare star, a=5.5 AUs, e=0.62
9.7 ly - Ross 154 (M3.5 Ve, 0.17 MS) - flare star

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