Editing Epsilon Eridani (section)

==== Planet b (AEgir) ====
{{main|Epsilon Eridani b}}
[[Extrasolar planet#Nomenclature|Referred to]] as [[Epsilon Eridani b|Epsilon Eridani&nbsp;b]], this planet was announced in 2000, but the discovery remained controversial over roughly the next two decades. A comprehensive study in 2008 called the detection "tentative" and described the proposed planet as "long suspected but still unconfirmed".<ref name=apj690_2_1522 /> Many astronomers believed the evidence is sufficiently compelling that they regard the discovery as confirmed.<ref name=aaa488_2_771 /><ref name=arxiv1011_4882 /><ref name=aaa499_2_L13 /><ref name=apj688_1_583 /> The discovery was questioned in 2013 because a search program at [[La Silla Observatory]] did not confirm it exists.<ref name="aa552_A78_62" /> Further studies since 2018 have gradually reaffirmed the planet's existence through a combination of radial velocity and astrometry.<ref name="MawetHirsch2019"/><ref name="MakarovZacharias2021"/><ref name="Llop-Sayson2021"/><ref name="Benedict2022"/><ref name="Feng2023"/>

[[File:Epsilon Eridani b.jpg|thumb|left|Artist's impression of Epsilon Eridani&nbsp;b orbiting within a zone that has been cleared of dust. Around the planet are conjectured rings and moons.|alt=At left is a shadowed, spherical red object encircled by a ring, with a smaller crescent at lower centre portraying a moon. To the right is a luminous source bisected by a line representing a debris disk.]]

Published sources remain in disagreement as to the planet's basic parameters. Recent values for its orbital period range from 7.3 to 7.6 years,<ref name="Feng2023"/> estimates of the size of its elliptical orbit—the [[semimajor axis]]—range from 3.38 au to 3.53 au,<ref name=cne2008 /><ref name=apj646_505 /> and approximations of its [[orbital eccentricity]] range from 0.055 to 0.26.<ref name="Feng2023"/>

Initially, the planet's mass was unknown, but a lower limit could be estimated based on the orbital displacement of Epsilon Eridani. Only the component of the displacement along the line of sight to Earth was known, which yields a value for the formula [[Stellar rotation#Measurement|''m''&nbsp;sin&nbsp;''i'']], where ''m'' is the mass of the planet and ''i'' is the [[orbital inclination]]. Estimates for the value of {{nowrap|''m'' sin ''i''}} ranged from 0.60 [[Jupiter mass]]es to 1.06 Jupiter masses,<ref name=cne2008 /><ref name=apj646_505 /> which sets the lower limit for the mass of the planet (because the [[sine]] function has a maximum value of 1). Taking {{nowrap|''m'' sin ''i''}} in the middle of that range at 0.78, and estimating the inclination at 30° as was suggested by [[Hubble Space Telescope|Hubble]] astrometry, this yields a value of {{nowrap|1.55 ± 0.24}} Jupiter masses for the planet's mass.<ref name=aj132_2206 /> More recent astrometric studies have found lower masses, ranging from 0.63 to 0.78 Jupiter masses.<ref name="Feng2023"/>

Of all the measured parameters for this planet, the value for orbital eccentricity is the most uncertain. The eccentricity of 0.7 suggested by some older studies<ref name=aj132_2206 /> is inconsistent with the presence of the proposed asteroid belt at a distance of 3&nbsp;au. If the eccentricity was this high, the planet would pass through the asteroid belt and clear it out within about ten thousand years. If the belt has existed for longer than this period, which appears likely, it imposes an upper limit on Epsilon Eridani&nbsp;b's eccentricity of about 0.10–0.15.<ref name=aaa499_2_L13 /><ref name=spitzer20081027 /> If the dust disk is instead being generated from the outer debris disk, rather than from collisions in an asteroid belt, then no constraints on the planet's orbital eccentricity are needed to explain the dust distribution.<ref name=arxiv1011_4882 />