# Astronomy:List of exoplanet extremes

Short description: None

The following are lists of extremes among the known exoplanets. The properties listed here are those for which values are known reliably.

On 31 March 2022, K2-2016-BLG-0005Lb was reported to be the most distant exoplanet found by Kepler to date.[1][2]

## Extremes from Earth's viewpoint

Title Planet Star Data Notes
Most distant discovered SWEEPS-11 / SWEEPS-04 SWEEPS J175902.67−291153.5 / SWEEPS J175853.92−291120.6 27,710 light-years[3] Several candidate extragalactic planets have been detected.

The most distant potentially habitable planet confirmed is Kepler-1606b, at 2,870 light-years distant,[4] although the unconfirmed planet KOI-5889.01 is over 5,000 light-years distant.

Least distant c, and d Proxima Centauri 4.25 light years Proxima Centauri b and d are the closest rocky exoplanets, b is the closest potentially habitable exoplanet known, and c is the closest mini-Neptune and potentially-ringed planet. As Proxima Centauri is the closest star to the Sun (and will stay so for the next 25,000 years), this is an absolute record.
Most distant directly visible CT Chamaeleontis b CT Chamaeleontis 622 light-years[5] The disputed planet candidate CVSO 30 c may be more distant, at 1,200 light-years.
Closest directly visible COCONUTS-2b COCONUTS-2 35.5 light-years[5] WISE 1217+1626 B is closer, but is generally considered a brown dwarf. Proxima Centauri c (confirmed in 2020 using archival Hubble data from 1995+) may have been directly imaged.[6]
Star with the brightest apparent magnitude with a planet Pollux b Pollux[7] Apparent magnitude is 1.14 Aldebaran (apparent magnitude 0.75–0.95) has a disputed planet candidate. The evidence of planets around Vega with an apparent magnitude of 0.03 is strongly suggested by circumstellar disks surrounding it.[8] (As of 2021), a candidate planet around Vega has been detected.[9]
Star with the faintest apparent magnitude with a planet MOA-bin-29Lb MOA-bin-29L Apparent magnitude is 44.61[5]
Largest angular distance separation from its host star COCONUTS-2b COCONUTS-2 594 arcseconds[10]

## Planetary characteristics

Title Planet Star Data Notes
Least massive PSR B1257+12 b PSR B1257+12 0.020±0.002 M[5] The extrasolar planetesimal WD 1145+017 b is less massive, at 0.00067 M.[10]
Most massive The candidate for the most massive planet is contentious, as it is difficult to distinguish between a highly massive planet and a brown dwarf (the border between them approximately from 13 to 80 MJ). So it is estimated the largest planets are approximately a dozen Jupiter masses.
Smallest radius Kepler-37b Kepler-37 0.296±0.037 R[5] The extrasolar planetesimals SDSS J1228+1040 b[11] and WD 1145+017 b are smaller.
Most dense Kepler-131c Kepler-131 77.7+55
−55
g/cm3[12]
Highly uncertain.
Least dense Kepler-51c, b and/or possibly d[13] Kepler-51[13] ~ 0.03 g/cm3[13] The densities of Kepler-51 b and c have been constrained to be below 0.05 g/cm3 (expected value 0.03 g/cm3 for each). The density of Kepler-51d is determined to be 0.046 ± 0.009 g/cm3.[13]
Hottest KELT-9b KELT-9 4050±180 K[5] The disputed planet candidate Kepler-70b may be hotter, at >7,000 K.[14]
Coldest OGLE-2016-BLG-1195L 31 K
Highest albedo Kepler-1658b Kepler-1658 0.758[15](geometric albedo)
Lowest albedo TrES-2b GSC 03549-02811 Geometric albedo < 1%[16] Best-fit model for albedo gives 0.04% (0.0004).[14]
Youngest Proplyd 133-353 Proplyd 133-353 The upper mass limit (13 Jupiter masses) may make this a brown dwarf.
Oldest WASP-183b WASP-183 14.9±1.7 Gyr[5] The estimated age of the universe is 13.8 billion years, within the margin of error. The disputed Kapteyn b is the oldest potentially habitable exoplanet at 11 Gyr.[17]

## Orbital characteristics

Title Planet Star Data Notes
Longest orbital period
(Longest year)
COCONUTS-2b COCONUTS-2 1,100,000 years[18] 2MASS J2126–8140 previously held this record at ~900,000 years.
Shortest orbital period
(Shortest year)
SWIFT J1756.9-2508 b SWIFT J1756.9-2508 48 minutes, 56.5 seconds[19] K2-137b has the shortest orbit around a main-sequence star (an M dwarf) at 4.31 hours.[20]
Most eccentric orbit HD 20782 b[21] HD 20782 0.956±0.004 [22] Record among confirmed planets. The disproven planet candidate at VB 10 was thought to have a higher eccentricity of 0.98.[23]
Largest orbit around a single star COCONUTS-2b COCONUTS-2 7506+5205
−2060
astronomical unit|AU
[5]
Projected separation of 6471 AU.[18] Next largest are 2MASS J2126–8140 with 6900 AU and HD 106906 b[24] with ~738 AU.
Smallest orbit WD 1202-024 B WD 1202-024 0.0021 AU
Smallest orbit around binary star Kepler-47b 0.2877+0.0014
−0.0011
astronomical unit|AU
[5]
[25]
Smallest ratio of semi-major axis of a planet orbit to binary star orbit Kepler-16b 3.14 ± 0.01 [26]
Largest orbit around binary star DT Virginis c DT Virginis 1,168 AU Star system is also known as Ross 458 AB. The planet was eventually confirmed to be below deuterium burning limit but its formation origin is unknown.
Largest orbit around a single star in a multiple star system ROXs 12 b ROXs 12 210±20 astronomical unit|AU[5]
Largest distance between binary stars with a circumbinary planet FW Tauri b FW Tauri AB ≈11 AU FW Tauri AB b orbits at a distance of 150-300 AU.[27]
Closest orbit between stars with a planet orbiting one of the stars OGLE-2013-BLG-0341LBb OGLE-2013-BLG-0341LB ~12–17 AU
(10 or 14 AU projected distance)[28]
OGLE-2013-BLG-0341L b's semi-major axis is 0.7 AU.[28]
Smallest semi-major axis difference between consecutive planets Kepler-70b and Kepler-70c[14] Kepler-70 0.0016 AU (about 240,000 km) During closest approach, Kepler-70c would appear 5 times the size of the Moon in Kepler-70b's sky.
Smallest semi-major axis ratio between consecutive planets Kepler-36b and Kepler-36c Kepler-36 11% Kepler-36b and c have semi-major axes of 0.1153 AU and 0.1283 AU respectively, c is 11% further from star than b.

## Stellar characteristics

Title Planet Star Data Notes
Highest metallicity HD 126614 Ab +0.56 dex Located in a triple star system.
Lowest metallicity K2-344b K2-344 −0.95±0.02 dex[5] BD+20°2457 may be the lowest metallicity planet host ([Fe/H]=−1.00), however the proposed planetary system is dynamically unstable.[29] Kapteyn's Star may also be the lowest metallicity planet host ([Fe/H]=−0.99±0.04), but its planets are most likely artifacts of stellar activity and rotation.[30]

Planets were announced around even the extremely low metallicity stars HIP 13044 and HIP 11952, however these claims have since been disproven.[31]

Highest stellar mass Mu2 Scorpii b Mu2 Scorpii 9.1±5.6 M[32] M51-ULS-1b, listed as a candidate planet with 4 sigma confidence, may be the planet with the highest-mass host star. The host is a massive O-class supergiant and a black hole orbiting each other at 0.8 AU, with a combined system mass of >60 solar masses. The planet is a Saturn sized (0.72 Jupiter radii) object orbiting the black-hole/supergiant binary at 10 AU. The host stars giving off a combined 1 million solar luminosities, the planet receives the equivalent irradiation of 51 Pegasi b, which orbits its star at 0.045 AU. M51-ULS-1b would also be one of the youngest planets ever discovered, with a system age of <10 million years according to evolutionary models.[33]

Because M51-ULS-1b requires further confirmation, the object V921 Sco b, a 60 Jupiter mass object orbiting a 20 solar mass 30,000K Herbig Haro B0IV class subgiant at 835 AU, may actually be the record holder. Despite the large distance, V921 Sco b receives a comparable amount of irradiation as Mars, owing to the large mass and luminosity of the host star. At 20 solar masses, V921 Sco is the most massive object to host a substellar object. Normally, V921 Sco b would be considered a brown dwarf, but given the high mass of the host star, and the growing studies that confirm the correlation of more massive planets around more massive stars, this object could be considered a planet. Hatzes and Rauer quote an upper limit of 60 Jupiter masses for a core-accretion formation of high mass gas giants, which is how heavy this object is. Furthermore, the Extrasolar Planets Encyclopedia lists objects up to 60 Jupiter masses as planets if they orbit stars.[34]

b Centauri has a mass of 6 solar masses.

The stars R126 and R66 in the Large Magellanic Cloud have masses of 70 and 30 solar masses and have dust discs but no planets have been detected yet.

Lowest stellar mass (main sequence) OGLE-2016-BLG-1195Lb OGLE-2016-BLG-1195L 0.078+0.016
−0.012
M
[5]
Could also be OGLE-2015-BLG-1771L, at 0.077+0.119
−0.044
M
.[5]
Lowest stellar mass (brown dwarf) 2MASS J1119-1137 B 2MASS J1119–1137 A 0.0033 M The system 2MASS J1119-1137 AB is a pair of binary rogue planets approximately 3.7 Jupiter masses each.[35]
Largest stellar radius HD 240237 b HD 240237 71.23±17.07 R[5] HD 81817 is larger, at 83.8±7.8 R,[5] but its substellar companion is most likely a brown dwarf or red dwarf. R Leonis (299 or 320-350 R)[36][37] has a candidate planet. It is a Mira variable.
Smallest stellar radius (main sequence star) Teegarden's Star b and c Teegarden's Star 0.107±0.004 R[5] VB 10 (0.102 R)[38] has a disproven planet candidate.
Smallest stellar radius (brown dwarf) 2M 0746+20 b[39] 2M 0746+20 0.089 (± 0.003) R Planet's mass is very uncertain at 30.0 (± 25.0) Mjup.
Smallest stellar radius (stellar remnant) PSR J1719-1438 b[40] PSR J1719-1438 0.04 R
Oldest star WASP-183b WASP-183 14.9±1.7 Gyr[5] The estimated age of the universe is 13.8 billion years, within the margin of error.
Hottest star with a planet NN Serpentis planets NN Serpentis 57,000 K[5]
Hottest main-sequence star with a planet b Centauri b b Centauri V921 Scorpii b orbits a hotter star, at 30,000 K. Its host star is a 20 solar mass B0IV class subgiant.[34] However, at 60 Jupiter masses, it is not considered a planet under most definitions.

The candidate planet M51-ULS-1b's supergiant primary is an O5 class supergiant with an estimated surface temperature of 40,000K, but as the star is a supergiant, does not count as on the main-sequence.

Coolest star with a planet TRAPPIST-1b, c, d, e, f, g, and h. TRAPPIST-1 2,511 K Technically Oph 162225-240515, CFBDSIR 1458+10, and WISE 1217+1626 are cooler, but are classified as brown dwarfs.

## System characteristics

Title System(s) Planet(s) Star(s) Notes
System with most planets Kepler-90 8 1
System with most planets in habitable zone TRAPPIST-1 7 1 Four planets in this system (d, e, f and g) orbit within the habitable zone.[41]
System with most stars Kepler-64 PH1b (Kepler-64b) 4 PH1b has a circumbinary orbit.
Multiplanetary system with smallest mean semi-major axis (planets are nearest to their star) Kepler-42 b, c, d 1 Kepler-42 b, c, and d have a semimajor axis of only 0.0116, 0.006, and 0.0154 AU, respectively.

Kepler-70 b, c, and d (all unconfirmed and disputed) have a semimajor axis of only 0.006, 0.0076, and ~0.0065 AU, respectively.

Multiplanetary system with largest mean semi-major axis (planets are farthest from their star) TYC 8998-760-1 b, c 1 TYC 8998-760-1 b and c have a semimajor axis of 162 and 320 AU, respectively.[5]
Multiplanetary system with smallest range of semi-major axis (smallest difference between the star's nearest planet and its farthest planet) Kepler-42 b, c, d 1 Kepler-42 b, c, and d have a semimajor axis of only 0.0116, 0.006, and 0.0154 AU, respectively. The separation between closest and furthest is only 0.0094 AU.

Kepler-70 b, c, and d (all unconfirmed and disputed) have a semimajor axis of only 0.006, 0.0076, and ~0.0065 AU, respectively. The separation between closest and furthest is only 0.0016 AU.

Multiplanetary system with largest range of semi-major axis (largest difference between the star's nearest planet and its farthest planet) TYC 8998-760-1 b, c 1 TYC 8998-760-1 b and c have a semimajor axis of 162 and 320 AU, respectively.[5] The separation between closest and furthest is 158 AU.
System with smallest total planetary mass Kepler-444 b, c, d, e, f 3 The planets in the Kepler-444 system have radii of 0.4, 0.497, 0.53, 0.546, and 0.741 Earth radii respectively. Due to their size and proximity to Kepler-444, these must be rocky planets, with masses close to that of Mars. For comparison, Mars has a mass of 0.105 Earth masses and a radius of 0.53 Earth radii.
System with largest total planetary mass Nu Ophiuchi b, c 1 Nu Ophiuchi b and c have masses of 22.206 and 24.662 Jupiter masses, respectively.[5] They may be brown dwarfs.
Multiplanetary system with smallest mean planetary mass Kepler-444 b, c, d, e, f 3 The planets in the Kepler-444 system have radii of 0.4, 0.497, 0.53, 0.546, and 0.741 Earth radii respectively. Due to their size and proximity to Kepler-444, these must be rocky planets, with masses close to that of Mars. For comparison, Mars has a mass of 0.105 Earth masses and a radius of 0.53 Earth radii.
Multiplanetary system with largest mean planetary mass Nu Ophiuchi b, c 1 Nu Ophiuchi b and c have masses of 22.206 and 24.662 Jupiter masses, respectively.[5] They may be brown dwarfs.
Exo-multiplanetary system with smallest range in planetary mass, log scale (smallest proportional difference between the most and least massive planets) Teegarden's Star b, c 1 Teegarden b and c are estimated to have masses of 1.05 and 1.11 Earth masses, respectively.
Exo-multiplanetary system with largest range in planetary mass, log scale (largest proportional difference between the most and least massive planets) Kepler-37 b, d 1 Mercury and Jupiter have a mass ratio of 5,750 to 1. Kepler-37 d and b may have a mass ratio between 500 and 1000, and Gliese 676 c and d have a mass ratio of 491.

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