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Exoplanetary Scratchpad

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Ran (Epsilon Eridani) is the nearest single non-red dwarf star to the Sun, also known as HD 195019, Gl 144, and HR 1084. It is a member of the Ursa Major star association and close encounters to other stars is relatively common. One of the first stars found to have a dust disk, with several potential planets suspected in the gaps early on, and later on of the earliest nearest system with confirmed planets. Has an inner asteroid belt at 3 AU, Jovian planet AEger at 3.4 AU, outer asteroid belt at 20 AU, and Kuiper Belt at 35-100 AU. A planet is proposed to be just outside the outer asteroid belt, and another just before the Kuiper belt.Because the star is very chromospherically active, doubts were cast on planet's b's existence. Hubble then confirmed its existence with astrometrics and found to be orbiting in the plane of the dust disks, which supported the theory that planets are born from dust disks and yielded a precise mass of 1.5 MJ. The planet b was originally thought to be extremely eccentric (2-10 AU), but later discovery of the inner asteroid belt suggests it is more moderately eccentric so as not to cross the belt. It could still have high eccentricity if the outer belt was being fed with material from the outer belt though. Dinosaur-killing sized impacts would be frequent on any Earth-like planets, about once every 2 million years. One of 5 PICTURE-C targets selected for sub-orbital coronograph observation. One of the first 20 exoplanet systems allowed to be given common names by the IAU. Star is named after a Norse goddess of the seas, while the planet after her husband, god of the ocean. A common sci fi system, including the original home of Star Trek Vulcans (though this moved to 40 Eridani) and Babylon 5.

My Thoughts[]

So, do we have a good idea what its real eccentricity is? Can't we determine that for sure with the 2.5 year's we've observed it since discovery and from before? I didn't realize eccentricity was something the dopplar technique would have difficulty with. I'm hoping for low eccentricity, since studies say high eccentricity planets tend not to have any neighbors. Do these other planets between the belt exist? Being the closest single sun-like (non-Red Dwarf) star is a distinction, so the makeup of this system is important.


It is in the "River" constellation. It was first suspected by a Canadian team, and discovered by an American who has an observatory in Germany and confirmed with Hubble.

Ziyu/Cheng - Named for a type of Jade that appears in the middle of a river and the sound that a type of ornament makes.

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)[]

Discovery of Dust Ring (1998)[]

Follow-Ups on Dust Disk (1998-2005)[]

Discovery of Epsilon Eridani b (2000)[]

Follow-Ups on Planet b (2000-2005)[]

Nature of the Star (2001-2005)[]

Search for Habitable Planets (2000-2004)[]

Detection of Water? (2002)[]

Announcement of Epsilon Eridani c (2002)[]

Continued Search for Dust Disk Planets (2002-2005)[]

Planet b's Effects on Disk Detected (2005)[]

Dust disk rotating (2005-2006)[]

Coronagraphic Search Fails (2006)[]

Spitzer Searches for Dust Disk Planets (2006)[]

Hubble Finds Planet b Coplanar with Belt(2006)[]

Perihelion Detection Attempt (2007)[]

Contains Ingredients for Live? (2007)[]

Triple Ring System Found(Nov 2008)[]

Planet b Extreme Eccentricity Conflicts With Inner Asteroid Belt (2009)[]

Inner Belt Could Be Fed From Outer Belt (2010)[]

Selected As PICTURE-C Suborbital Coronograph Target (Mar 2015)[]

See Vega System, Alsafi System, Epsilon Eridani System, Altair System, Tau Ceti System

One of the Top 20 Exoplanetary Systems First Up For Naming (May 2015)[]

Asteroid Belts Confirmed (2017)[]

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[]

  • 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 one of the five stars to have confirmed planet(s):

10.5 ly - Epsilon Eridani (K2V, 10.5 ly, 0.85 MS) - Dust disk and Jupiter
11.8 ly - Epsilon Indi (K IV-V, 0.77 MS) - Has two brown dwarves and a super-Jupiter
11.9 ly - Tau Ceti (G8 VP, 0.82 MS) - Old star, dust disk and four planets
15.9 ly - Groombridge 1618 (K7.vne, 0.64 MS) - Unconfirmed planet
16.7 ly - Altair - (A7 V-IV, 1.7 MS) - Subgiant?, NSV 24910, inside dust cloud
18.8 ly - Sigma Draconis (K0 V, 0.89 MS) - Alsafi - Unconfirmed planet
19.8 ly - 82 Eridani (G5 V, 0.97 MS) - spec. double? Old star, dust disk and four planets
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[]

Epsilon Eridani was once believed to be the closest system to the Sun (10.5 ly) to have confirmed planets. But over the years, as radial velocity precision steadily improved, there were planets confirmed to be closer than that. And, it is the nearest star, Proxima Centauri (4.2 ly), that hosts this planet. However, Epsilon Eridani still wins the prize for the nearest star system with a Jupiter sized gas giant.

In the past there were also some disproven planets that would have been nearer. These are all Red Dwarf stars. Here they are

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. Some of these systems broke Epsilon Eridani's "closest system with confirmed planet" record that was held for more than a decade, though none as yet has been discovered with a planet as large as Epsilon Eridani b. Proxima Centauri, the smallest star of the Alpha Centauri system, is the record holder for the closest planet (unless there are nearer planets around a faint, as yet undiscovered Red Dwarf, Brown Dwarf or is completely free-floating):

4.2 ly - Alpha Centauri / Proxima Centauri (two, one confirmed and one unconfirmed, planets)
6.0 ly - Barnard's Star (one unconfirmed planet)
6.5 ly - Luhman 16 (binary brown-dwarf)(one disproven planet)
7.3 ly - WISE 0855−0714 (coldest sub-brown dwarf known)
7.8 ly - Wolf 359 (one unconfirmed planet)(Starfleet ship graveyard thanks to Borg)
8.3 ly - Lalande 21185 (two confirmed planets)
8.6 ly - Sirius
8.7 ly - Luyten 726-8
9.7 ly - Ross 154
10.3 ly - Ross 248

See Also[]