Editing Vega (section)

==Possible planetary system==
{{OrbitboxPlanet begin
| name = Vega
| table_ref = <ref name="Hurt2021"/><ref name=Su2024/>
}}
{{OrbitboxPlanet hypothetical
| exoplanet = b
| mass_earth = {{Val|21.9|5.1|p=≥}} 
| period = {{Val|2.42977|0.00016|fmt=none}} 
| semimajor = {{Val|0.04555|0.00053|fmt=none}}
| eccentricity = {{Val|0.25|0.15}}
}}
{{OrbitboxPlanet disk
| disk = Hot dust
| periapsis = 
| apoapsis = ≤0.2
| inclination = 
}}
{{OrbitboxPlanet hypothetical
| exoplanet =
| mass_earth = 20
| semimajor = ~2–5
}}
{{OrbitboxPlanet disk
| disk = Inner Disk
| periapsis = (3-5)
| apoapsis = 78
| inclination = 7-8
}}
{{OrbitboxPlanet hypothetical
| exoplanet =
| mass_earth = <6
| semimajor = ~65
}}
{{OrbitboxPlanet disk
| disk = Outer Disk
| periapsis = 78
| apoapsis = 170
| inclination = 9-11
}}
{{OrbitboxPlanet disk
| disk = Halo
| periapsis = 
| apoapsis = <250
| inclination = 
}}
{{Orbitbox end}}
[[File:Imaging of the Vega Debris System using JWST MIRI - figure 1.png|thumb|The debris disk around Vega with JWST [[Mid-Infrared Instrument|MIRI]] (all images) and ALMA (contours lower right image). Image published by Su et al.<ref name=Su2024/>]]

=== Infrared excess ===
One of the early results from the [[Infrared Astronomy Satellite]] (IRAS) was the discovery of [[infrared excess|excess infrared flux]] coming from Vega, beyond what would be expected from the star alone. This excess was measured at [[wavelength]]s of 25, 60 and {{val|100|ul=μm}}, and came from within an angular radius of {{val|10|u=arcseconds}} ({{val|10|u="}}) centered on the star. At the measured distance of Vega, this corresponded to an actual radius of {{val|80|ul=astronomical units}} (AU), where an AU is the average radius of the Earth's orbit around the Sun. It was proposed that this radiation came from a field of orbiting particles with a dimension on the order of a millimetre, as anything smaller would eventually be removed from the system by radiation pressure or drawn into the star by means of [[Poynting–Robertson effect|Poynting–Robertson drag]].<ref name="apj285_808"/> The latter is the result of radiation pressure creating an effective force that opposes the orbital motion of a dust particle, causing it to spiral inward. This effect is most pronounced for tiny particles that are closer to the star.<ref name="mnras_97_423"/>

Subsequent measurements of Vega at {{val|193|u=μm}} showed a lower than expected flux for the hypothesized particles, suggesting that they must instead be on the order of {{val|100|u=μm}} or less. To maintain this amount of dust in orbit around Vega, a continual source of replenishment would be required. A proposed mechanism for maintaining the dust was a disk of coalesced bodies that were in the process of collapsing to form a planet.<ref name=apj285_808/> Models fitted to the dust distribution around Vega indicate that it is a 120-astronomical-unit-radius circular disk viewed from nearly pole-on. In addition, there is a hole in the center of the disk with a radius of no less than {{val|80|u=AU}}.<ref name=mnras314_4_702/>

Following the discovery of an infrared excess around Vega, other stars have been found that display a similar anomaly that is attributable to dust emission. As of 2002, about 400 of these stars have been found, and they have come to be termed "Vega-like" or "Vega-excess" stars. It is believed that these may provide clues to the origin of the [[Solar System]].<ref name=apj124_1_514/>

===Debris disks===
By 2005, the [[Spitzer Space Telescope]] had produced high-resolution infrared images of the dust around Vega. It was shown to extend out to 43″ ({{val|330|u=AU}}) at a wavelength of {{val|24|u=μm}}, 70″ ({{val|543|u=AU}}) at {{val|70|u=μm}} and {{val|105|u="}} ({{val|815|u=AU}}) at {{val|160|u=μm}}. These much wider disks were found to be circular and free of clumps, with dust particles ranging from 1–{{val|50|u=μm}} in size. The estimated total mass of this dust is 3{{e|-3}} times the [[mass of the Earth]] (around 7.5 times more massive than the [[asteroid belt]]). Production of the dust would require collisions between asteroids in a population corresponding to the [[Kuiper Belt]] around the Sun. Thus the dust is more likely created by a [[debris disk]] around Vega, rather than from a [[protoplanetary disk]] as was earlier thought.<ref name=apj628_1_487/>

[[Image:Massive Smash-Up at Vega.jpg|thumb|Artist's concept of a recent massive collision of [[dwarf planet]]-sized objects that may have contributed to the dust ring around Vega]]

The inner boundary of the debris disk was estimated at {{val|11|2|u="}}, or 70–{{val|100|u=AU}}. The disk of dust is produced as radiation pressure from Vega pushes debris from collisions of larger objects outward. However, continuous production of the amount of dust observed over the course of Vega's lifetime would require an enormous starting mass—estimated as hundreds of times the [[mass of Jupiter]]. Hence it is more likely to have been produced as the result of a relatively recent breakup of a moderate-sized (or larger) comet or asteroid, which then further fragmented as the result of collisions between the smaller components and other bodies. This dusty disk would be relatively young on the time scale of the star's age, and it will eventually be removed unless other collision events supply more dust.<ref name=apj628_1_487/>

Observations, first with the [[Palomar Testbed Interferometer]] by [[David Ciardi]] and [[Gerard van Belle]] in 2001<ref name=apj559_1_237/> and then later confirmed with the [[CHARA array]] at Mt. Wilson in 2006 and the [[Infrared Optical Telescope Array]] at Mt. Hopkins in 2011,<ref name=aaa534_1_237/> revealed evidence for an inner dust band around Vega. Originating within {{val|8|u=AU}} of the star, this [[exozodiacal dust]] may be evidence of dynamical perturbations within the system.<ref name=aaa452_1_237/> This may be caused by an intense bombardment of [[comet]]s or [[meteor]]s, and may be evidence for the existence of a planetary system.<ref name=girault_rime_2006/>

The disk was also observed with [[Atacama Large Millimeter Array|ALMA]] in 2020,<ref name="Matrà2020"/> the [[Large Millimeter Telescope|LMT]] in 2022<ref name="Marshall2022"/> and with [[Hubble Space Telescope|Hubble]] STIS<ref name=Wolff2024/> and [[James Webb Space Telescope|JWST]] MIRI in 2024.<ref name=Su2024/> The ALMA image did resolve the outer disk for the first time.<ref name="Matrà2020"/> The Hubble observation is the first image of the disk in scattered light and found an outer halo made up of small dust grains.<ref name=Wolff2024/> JWST observations also detected the Halo, the outer disk and for the first time the inner disk. The infrared observations also showed a gap at 60 AU for the first time. The dust interior of the outer disk is consistent with dust being dragged by the [[Poynting-Robertson effect]]. The inner edge of the inner disk is hidden behind the [[coronagraph]], but it was inferred to be 3-5 AU from photometry. The star is also surrounded by hot infrared excess, located at the sub-AU region, leaving a second gap between the inner disk and the hot dust around the star. This hot infrared excess lies within about 0.2 AU or closer and is made up of small grains, like [[graphite]] and [[Iron oxide|iron]] and [[manganese]] oxides, which was previously verified.<ref name=Su2024/>

===Possible planets===
Observations from the [[James Clerk Maxwell Telescope]] in 1997 revealed an "elongated bright central region" that peaked at 9″ ({{val|70|u=AU}}) to the northeast of Vega. This was hypothesized as either a perturbation of the dust disk by a [[extrasolar planet|planet]] or else an orbiting object that was surrounded by dust. However, images by the [[Keck telescope]] had ruled out a companion down to magnitude 16, which would correspond to a body with more than 12 times the mass of Jupiter.<ref name=nature392_6678_788/> Astronomers at the [[Joint Astronomy Centre]] in Hawaii and at [[UCLA]] suggested that the image may indicate a planetary system still undergoing formation.<ref name=jac19980421/>

Determining the nature of the planet has not been straightforward; a 2002 paper hypothesizes that the clumps are caused by a roughly [[Eccentric Jupiter|Jupiter-mass planet on an eccentric orbit]]. Dust would collect in orbits that have [[Orbital resonance|mean-motion resonances]] with this planet—where their orbital periods form integer fractions with the period of the planet—producing the resulting clumpiness.<ref name=apj569_2_L115/>

In 2003, it was hypothesized that these clumps could be caused by a roughly [[Neptune]]-mass planet having [[planetary migration|migrated]] from 40 to {{val|65|ul=AU}} over 56&nbsp;million&nbsp;years,<ref name=apj598_2_1321/> an orbit large enough to allow the formation of smaller [[rocky planet]]s closer to Vega. The migration of this planet would likely require gravitational interaction with a second, higher-mass planet in a smaller orbit.<ref name=roe20031201/>

Using a [[coronagraph]] on the [[Subaru Telescope]] in Hawaii in 2005, astronomers were able to further constrain the size of a planet orbiting Vega to no more than 5–10 times the mass of Jupiter.<ref name=apj652_2_1729/> The issue of possible clumps in the debris disc was revisited in 2007 using newer, more sensitive instrumentation on the [[Plateau de Bure Interferometer]]. The observations showed that the debris ring is smooth and symmetric. No evidence was found of the blobs reported earlier, casting doubts on the hypothesized giant planet.<ref name=aaa531/> The smooth structure has been confirmed in follow-up observations by Hughes et al. (2012)<ref name="hughes2012"/> and the [[Herschel Space Telescope]].<ref name="sibthorpe2010"/>

Although a planet has yet to be directly observed around Vega, the presence of a planetary system cannot yet be ruled out. Thus there could be smaller, [[terrestrial planet]]s orbiting closer to the star. The [[inclination]] of planetary orbits around Vega is likely to be closely aligned to the [[equator]]ial plane of this star.<ref name=pasp97_180/>

From the perspective of an observer on a hypothetical planet around Vega, the Sun would appear as a faint 4.3-magnitude star in the [[Columba (constellation)|Columba]] constellation.<ref group="note" name="coord"/>

In 2021, a paper analyzing 10 years of spectra of Vega detected a candidate 2.43-day signal around Vega, statistically estimated to have only a 1% chance of being a false positive.<ref name="Hurt2021"/> Considering the amplitude of the signal, the authors estimated a minimum mass of {{val|21.9|5.1}} Earth masses, but considering the very oblique rotation of Vega itself of only 6.2° from Earth's perspective, the planet may be aligned to this plane as well, giving it an actual mass of {{val|203|47}} Earth masses.<ref name="Hurt2021"/> The researchers also detected a faint {{val|196.4|1.6|1.9}}-day signal which could translate to {{val|80|21}} Earth masses ({{val|740|190}} at 6.2° inclination) but is too faint to claim as a real signal with available data.<ref name="Hurt2021"/>

Observations of the disk with JWST MIRI did find a very circular face-on disk. The morphology indicate that there is no planet more massive than [[Saturn]] beyond 10 AU. The disk has a gap at around 60 AU. Gap-opening planets are inferred for disks around other stars and the team tests this idea for Vega by running simulations. The simulations have shown that a planet with <6 {{earth mass}} at 65 AU would introduce interior asymetric structures that are not seen in the disk of Vega. Any gap-opening planet would need to be less massive. Additionally the inner edge of the inner disk was inferred to be 3-5 AU. Vega shows also evidence for hot infrared excess at the sub-AU region. The inner boundary of the warm debris might indicate that there is a [[Neptune]]-mass planet inside, [[shepherd moon|shepherding]] it.<ref name=Su2024/>