Epsilon Eridani System

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Exoplanetary Scratchpad

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Nearest single non-red dwarf star to the Sun and the second nearest system with a confirmed planet. The planet is a very elliptical Jupiter-like world. It also has two asteroid belts and a kuiper belt, with evidence of planets in between.

The Epsilon Eridani System is the second nearest confirmed system containing at least one planet (for more than a decade it was the nearest). It has always been a specially watched star because it is also the nearest single star system (excluding dim red dwarves). At one point, it was said to be the home of Spock's world Vulcan (although it seems to have been moved to 40 Eridani). The station Babylon 5 was also said to be near Epsilon Eridani.

Planet b is one of the longest period planets yet detected. Its eccentric orbit swings it inwards to where it is too hot for ammonia clouds to form and then back outwards to become nearly as cold as Saturn. Its mass is reported in some places to be about 15% less than Jupiter's, in others, it is 20% greater than Jupiter. Despite being listed as confirmed, the fact it orbits a very chromospherically active star causes some astronomers to not be convinced of its existence, including Marcy et al.

Epsilon Eridani Web Pages

Epsilon Eridani System Artwork

Planet b compared to other Eccentric Ammonia Giants

Dual Phase Ammonia/Water Cloud Jupiters

  • Mu Ara - Hot Super Earth, Water/Sulfur Cloud Jupiter, and Ammonia/Water Cloud Jupiter (115 - 219 K, e = 0.57, 3.1 MJ) around a Yellow Dwarf
  • 14 Herculis - Ammonia/Water Cloud Jupiter (120 - 170 K, e = 0.338, 4.74 MJ) around an Orange Dwarf
  • HD 30177 - Ammonia/Water Cloud Jupiter (121 - 165 K, e = 0.3, 9.17 MJ) around a Yellow Dwarf
  • HD 33636 - Ammonia/Water Cloud Jupiter (110 - 199 K, e = 0.53, 9.28 MJ) around a Yellow Dwarf
  • Gliese 777 - Ammonia/Water Cloud Jupiter (96 - 162 K, e = 0.48, 1.33 MJ, 4.8 au) around a Yellow Subgiant
  • Epsilon Eridani - Ammonia/Water Cloud Jupiter (89 - 181 K, e = 0.608, 0.86 MJ) and Ice Giant? and Kuiper Belt around an Orange Dwarf

Single Phase Eccentric Ammonia Cloud Giants

  • 55 Cancri - Hot Superearth, Clarified Jovian, Single Phase Eccentric Clarified Jovian, and Single Phase Eccentric Water Cloud Jovian (87 - 122 K, e = 0.327, 3.912 MJ)

  • Epsilon Eridani b can get colder than any other confirmed exoplanet other than after 55 Cancri d.
  • Epsilon Eridani b was the 2nd Eccentric Ammonia Giant discovered (after 14 Herculis b in 1998)
  • Epsilon Eridani b has the highest eccentricity of all known Ammonia Giants

Epsilon Eridani in the News

Radio Search for Intelligent Life (1960)

Early Indications of Planets and Dust Disk (1973-1997) (1992)

Discovery of Dust Ring (1998)

Follow-Ups on Dust Disk (1998-2005) (2004) - confirmation of extended disk

Discovery of Epsilon Eridani b (2000)

Follow-Ups on Planet b (2000-2005) (2005) - influence on dust disk

Nature of the Star (2001-2005) (2003) - chemical abundances

Search for Habitable Planets (2000-2004) (2004)

Detection of Water? (2002) (2002) - no water masers

Announcement of Epsilon Eridani c (2002)

Continued Search for Dust Disk Planets (2002-2005) - Interior Planet (2005)

Planet b's Effects on Disk Detected (2005)

Dust disk rotating (2005-2006) (2006)

Coronagraphic Search Fails (2006) (2006)

Spitzer Searches for Dust Disk Planets (2006)

Hubble Finds Planet b Coplanar with Belt(2006)

Perihelion Detection Attempt (2007) (2007) - Visible Light Detection Fails

Contains Ingredients for Live? (2007)

Triple Ring System Found(Nov 2008)

Fun Links

Epsilon Eridani System and Star Factoids

  • Nearest Single Naked-Eye Star to Sun
  • Significantly younger than the Sun
  • Chromospherically active
  • Less massive and simmer than the Sun, a type K Orange Dwarf
  • Due to size of it Kuiper Belt, it is surmised that any inner rocky planets would be undergoing an epoch of heavy bombardment
  • Slightly metal deficient

Epsilon Eridani b (planet) Factoids

  • Second nearest confirmed exoplanet.
  • Period is 6.85 years
  • Semi-Major Axis = 1.88 +/- 0.20 AU;
  • Periastron = 1.36 AU; Apastron = 5.44 AU
  • inclination = 30.1 deg (Coplanar with dust belt)
  • Eccentric Ammonia Giant. Likely loses its Ammonia Clouds and hydro-carbon stains (leaving only white water clouds) near periastron and gains an obscuring haze during apastron.
  • Second Eccentric Ammonia Giant discovered.
  • Can get colder than any other exoplanet confirmed other than 55 Cancri d.
  • Most eccentric known Ammonia Cloud Jovian
  • Nearest Ammonia Cloud Jovian outside of solar system.
  • Discovery disputed by Marcy et. al (2002), but accepted by most the rest of the astronomical community
  • Its minimum mass is 0.85 MJ.
  • Actual mass is 1.55 MJ +/- 0.24 based on Astrometrics [1].
  • Its proximity makes this planet a prime target for direct observation.
  • Periastron is in March of 2007 [2]. Will be brightest in reflected light near periastron. Attempt to detect planet visibly failed.
  • Maximum mass is 4-6 MJ due to failure of Coronagraphic search to detect a point source for it in 2006[3].Certainly not a brown dwarf.
  • Any moons might have liquid water when nearest to star, but be frozen solid when furthest.

Suspected Planets

Several suspected planets have been theorized at different times by various means throughout its history. It can get confusing trying to name these planets, since they could all be called "planet b" or "planet c" depending on when they were "detected". I'm going to name them by their proposers and "roles" to try to sort it all out.

  • Van de Kamp's Planet (1974, 1988) Using astrometrics, Peter Van de Kamp proposes a 25 year period (7.7 au) planet with 6 Jupiter Masses. Discredited but suggested again by Campell using doppler-shift and radial-velocity analysis (3-5 Jupiters, e=0.5). The idea of a planet was revived when indications arrived that Epsilon Eridani may have a planetary disk in 1983.
  • Loiu's Interior Planet (1999) The absense of dust within 35 au of the planet required a Jupiter-mass planet interior to the dust ring. Liou and Zook in 1999 placed it just inside the ring at 30 au.
  • Ozernoi's Clump Planet (1999-2000) Planet first proposed by Liou and Zook to explain the assymetrical clump of dust particles appearing in the dust belt. In 2000, Ozernoi produced models giving it a mass of 0.2 Jupiters masses and orbit between 55 and 60 AUs, and an eccentricity of 0.0.
  • Cochran's Planet b (1999, 2000)First reported (1999), then retracted by Marcy et. al due to high chromospheric activity that could be periodic. After gathering data from several sources, Cochran published the planet after showing no 6.8 year cycles in stellar activity. It has 0.8 Jupiter mass, is a 3.3 au, and e=0.6. Could this also be Van de Kamp's planet? The planet is too close to the star to be responsible for any patterns seen in the Dust Belt though.
  • Hypothetical Habitable Planet(s) (2002) Jones et. al demonstrates that a terrestrial planet could survive in the Habitable Zone (0.47-0.91 au) due to Planet b's large distance from the star.
  • Quillin's Dust Sculpting Planet c (2002) Computer simulations of patterns in dust disk reveal likely planet with 0.1 Jupiter Masses orbiting at 40 AU with e=0.3.
  • Deller's Interior Planet (2005) Building on Quillin's 2002 model (and discrediting Ozernoi's model because it didn't demonstrate the assymetries observed in the "clump"), Deller et all (2005) moved the Jupiter mass planet proposed by Liou responsible for clearing particles inside the dust disk inwards (it was too close to Quillin's planet) to between 10-18 au. Future modeling should help refine its properties.
  • Benedict's Outer Radial Planet (2006) 25 years of radial velocity data suggests a Jupiter-mass planet with a period in excess of 50 years which is possibly responsible for the inner dust cavity [4].


Other Nearby Stars Similar to Epsilon Eridani

Here is a list of all bright single stars within 20 light years, courtesy of Sol Station (source = ). Epsilon Eridani is the nearest one to have confirmed planet(s):

10.5 ly - Epsilon Eridani (K2V, 10.5 ly, 0.85 MS) - Planets?, dust disk
11.8 ly - Epsilon Indi(K IV-V, 0.77 MS) - Has two brown dwarves
11.9 ly - Tau Ceti(G8 VP, 0.82 MS) - Dust Disk, old star
15.9 ly - Groombridge 1618(K7.vne, 0.64 MS)
16.7 ly - Altair- (A7 V-IV, 1.7 MS) - Subgiant?, NSV 24910, dust
18.8 ly - Sigma Draconis(K0 V, 0.89 MS) - Alsafi
19.8 ly - 82 Eridani(G5 V, 0.97 MS) - old, spec. double?, three planets and a cold dust disk 
19.9 ly - Delta Pavonis (G5-8 V-IV, 1.1 MS) - Subgiant?

Map of Epsilon Eridani System

Assuming all the planets suggested to exist do so, here is what the Epsilon Eridani system would look like:

0.0 au - Epsilon Eridani
0.47-0.91 au - Rocky planet(s) in restricted Habitable Zone (hypothetical)
1.29-5.3 au - Cochran's Planet b (confirmed, controversial) (0.85 MJ)
7.7 au - Van de Kamp's Planet (status?) (4 MJ, e=0.5)
10-18 au - Deller's Interior Planet (needs refinement)
30.0 au - Loui's Interior Planet (disproven?)
35.0 au - Inner Edge of Main Dust Belt
40 au - Quillin's Dust Sculpting Planet c (likely) (0.1 MJ) (e=0.3)
55-60 au - Ozernoi's Clump Planet (disproven?) (0.2 MJ)
60.0 au - Peak of Dust Belt (assymetrical)
75.0 au - Outer Edge of Main Dust Belt
105 au - Outer Edge of observed Dust Disk

IRAS Fab Four Debris Disk Stars

Epsilon Eridani is one of the "Fab Four" ( ) stars found to contain a debris disk by IRAS. These include:

Planet Candiates Closer Than Epsilon Eridani

For now, Epsilon Eridani is definitely the second closest system to the Sun (10.5 ly) to have confirmed planets. But there are some unconfirmed planets that are nearer. There are also some disproven planets that would have been nearer, around some nearby Red Dwarf stars. And of course, there is Alpha Centauri B, which like Epsilon Eridani is an Orange Dwarf star but not a solitary star instead it's a member of a multiple star system. It hosts the nearest confirmed planetary system to the Sun (4.4 ly), to date.

Confirmed Planetary Systems Closer than Epsilon Eridani

4.4 ly - Alpha Centauri System

Unconfirmed Planetary Systems Closer than Epsilon Eridani

8.3 ly - Lalande 21185 System

Disproven Planetary Systems Closer than Epsilon Eridani

4.2 ly - Proxima Centauri System
6.0 ly - Barnard's Star System

Stars Closer Than Epsilon Eridani

Here is a list of stars closer than Epsilon Eridani. If a system ever knocks Epsilon Eridani's "closest system with confirmed planets" down to third place, it would have to be one of these systems (unless there's a planet around a faint, as yet undiscovered Red Dwarf or Brown Dwarf or completely free-floating):

4.2 ly - Alpha Centauri / Proxima Centauri (disproven planet) & marginal candidate
4.4 ly - Alpha Centauri / Alpha Centauri B hosts one confirmed planet (for the record, now the title holder for closest)
6.0 ly - Barnard's Star (disproven planet)
7.8 ly - Wolf 359 (Starfleet ship graveyard thanks to Borg)
8.3 ly - Lalande 21185 (unconfirmed planets)
8.6 ly - Sirius
8.7 ly - Luyten 726-8
9.7 ly - Ross 154
10.3 ly - Ross 248

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