 Color composite image ofC/2014 UN271 by theHubble Space Telescope on 28 March 2022 | |
| Discovery[1] | |
|---|---|
| Discovered by |
|
| Discovery date | 20 October 2014 (first discovery image) |
| Designations | |
| Orbital characteristics (barycentric)[4] | |
| Epoch | |
| Observation arc | 14.84 yr (5,419 days) |
| Earliestprecovery date | 15 November 2010[3] |
| Orbit type | Oort cloud |
| Aphelion | ≈ 42,000 AU (inbound) ≈ 60,000 AU (outbound) |
| Perihelion | 10.9502 AU (1.64 billion km)[6][c] |
| Semi-major axis | ≈ 21,000 AU (inbound) ≈ 30,000 AU (outbound) |
| Eccentricity | 0.99948 (inbound) 0.99963 (outbound) |
| Orbital period | ≈ 3.04 million yr (inbound) ≈ 5.14 million yr (outbound) |
| Inclination | 95.466° (inbound) 95.460° (outbound) |
| 190.003° (inbound) 190.009° (outbound) | |
| Argument of periapsis | 326.280° (inbound) 326.246° (outbound) |
| Next perihelion | ≈ 23 January 2031[d] |
| TJupiter | –0.390[7] |
| JupiterMOID | 6.137 AU[7] |
| Physical characteristics | |
| Dimensions | a/b =1.26±0.11[8] |
Mean diameter | 119±15[e] to137±17 km[10] |
| 20.6±0.2 d[8] | |
| 0.033±0.009 to0.044±0.012[f] | |
| Absolute magnitude (H) | 8.63±0.11 (nucleus only)[9] |
| Comet total magnitude (M1) | 6.2±0.9[7] |
C/2014 UN271 (Bernardinelli–Bernstein), simply known asC/2014 UN271 orComet Bernardinelli–Bernstein (nicknamedBB),[3] is a largeOort cloudcomet discovered by astronomersPedro Bernardinelli andGary Bernstein in archival images from theDark Energy Survey.[11][2] When first imaged in October 2014, the object was 29 AU (4.3 billion km; 2.7 billion mi) from the Sun, almost as far asNeptune's orbit and the greatest distance at which a comet has been discovered.[12] With anucleus diameter of at least 100 km (62 mi), it is the largest Oort cloud comet known. It is approaching the Sun and will reach itsperihelion of 10.9 AU (just outside ofSaturn's orbit) in January 2031.[7] It will not be visible to the naked eye because it will not enter theinner Solar System.[g]
C/2014 UN271 was discovered by astronomers Pedro Bernardinelli and Gary Bernstein in analgorithm-assisted search for slowly-movingtrans-Neptunian objects, in archival images from theDark Energy Survey (DES) atCerro Tololo Inter-American Observatory.[13] It was detected at the 22ndapparent magnitude in 42 DES images spanning 10 October 2014 to 26 November 2018.[3] The longobservation arc by the DES images revealed that the object was on a near-parabolic trajectory inbound towards the Solar System, implying a cometary origin from theOort cloud, despite the object's apparently asteroidal (point-like) appearance in the images.[14][15] When first imaged by the DES, the object was located in thesouthernconstellationSculptor, inside the orbit ofNeptune at a distance of 29.0 AU (4.3 billion km; 2.7 billion mi) from the Sun.[16][2] The object's relatively high brightness from its distance indicated that its diameter must be on the order of 100 km (62 mi)—an exceptionally large size for an object of cometary origin.[3]
The discovery was announced by theMinor Planet Center on 19 June 2021, and the object was given theminor planetprovisional designation2014 UN271.[11][h] The object attracted significant attention from astronomers worldwide: astronomers made follow-up observations and found severalprecoveries within days of the announcement.[1][14] The earliest precovery observations of2014 UN271 were obtained fromParanal Observatory'sVISTA survey images taken on 15 November 2010, when the object was 34.1 AU (5.1 billion km; 3.2 billion mi) from the Sun.[3]
Cometary activity in2014 UN271 was first reported on 22 June 2021, byTim Lister atLas Cumbres Observatory's telescope inSutherland, South Africa and byLuca Buzzi at theSkyGems Remote Telescope in Namibia. The comet was found to be onemagnitude brighter than predicted in their observations, with a slightly asymmetriccoma up to 15arcseconds in width.[18][1] At that time, the comet's distance from the Sun was 20.2 AU (3.0 billion km; 1.9 billion mi).[18] The detection of cometary activity was confirmed by the Minor Planet Center and the comet was formallynamedC/2014 UN271 (Bernardinelli–Bernstein) on 24 June 2021.[1][i]
Analysis of archival images fromNASA'sTransiting Exoplanet Survey Satellite (TESS) show thatC/2014 UN271 had an extensive, diffuse coma at least 43 arcseconds wide in observations as early as September 2018, when it was 23.8 AU (3.6 billion km) from the Sun.[3][20] Between the 2018 and 2020 TESS observation epochs, the comet's brightness had significantly increased by 1.5 magnitudes, likely as a result of continuous activity rather than a spontaneous outburst.[3][21]
Reexamination of other telescope datasets have also identified a diffuse and distinctly asymmetric coma in DES images beginning from 2017 (at 25.1 AU) andPan-STARRS 1 images beginning from 2019 (at 22.6 AU).C/2014 UN271's coma brightness has been growing exponentially since 2017, while the comet's overall brightness had remained steady in 2014–2018, hinting that activity may have well begun prior to the comet's discovery at 29.0 AU.[3][20] The observation of cometary activity from such large heliocentric distances is rare: as of 2025[update] only five other comets,Comet Hale–Bopp (27.2 AU outbound),[22]C/2010 U3 (Boattini) (25.8 AU inbound),C/2017 K2 (PanSTARRS) (24.0 AU inbound),C/2019 E3 (ATLAS) (23.0 AU inbound),[23] andC/2025 D1 (Gröller) (~21 AU inbound)[24] have been observed to exhibit activity at heliocentric distances greater than 20 AU.[3][21] As of 2022[update],C/2014 UN271 holds the record for the greatest distance at which a comet has been discovered in the Solar System.[12]
C/2014 UN271 was observed by theHubble Space Telescope in January,[25][9] March, July, August, and October 2022.[26]
On 9 September 2021, an apparent outburst ofC/2014 UN271 was detected at Las Cumbres Observatory, as reported on 14 September. It brightened by 0.65 magnitudes compared to images taken earlier that day, and reached an apparent magnitude of 18.9. Calculations based on this brightening indicate that 10 to 100 million kg (11 to 110 thousand short tons) of dust was ejected during the outburst.[27] At the time, the comet was 19.9 AU (3.0 billion km; 1.8 billion mi) from the Sun.[28] The comet's brightness subsequently faded back down to the 19th magnitude by December 2021.[29]
Rigorous computations ofC/2014 UN271's orbit andephemeris have identified few potentialoccultation events by the comet from 2021–2025, during which the comet would pass in front of a bright star and briefly block out the star's light.[30] Observing these occultation events would allow for opportunities to make precise measurements of the comet's size and position, as well as search for surrounding dust and possible satellites.[31] The first attempt at observing one of those occultations was made from Australia and New Zealand on 19 September 2021, but was unsuccessful due to poor weather conditions.[30]
With a currentdeclination of−47° below thecelestial equator,C/2014 UN271 is best seen from the Southern hemisphere. The evolution of its cometary activity will soon be monitored by the upcomingVera C. Rubin Observatory starting 2023.[2][15][32] Once at perihelion, the comet is not expected to get brighter thanPluto (mag 13–16) and is more likely to reach the brightness of Pluto's moonCharon (mag 16.8) as the comet does not enter theinner Solar System where comets become notably more active.[33][34][35] Even if it reaches the magnitude of Pluto, it will require about a200 mm telescope to be visually seen.[36]
Radiothermal emission measurements by theAtacama Large Millimeter Array (ALMA) in 2021 estimate a maximum diameter of 137 ± 17 km (85 ± 11 mi) forC/2014 UN271'snucleus, assuming negligible contamination of the nucleus's thermal emission by an unseen dust coma.[10] The ALMA measurements have not ruled out the possibility of a dust coma contaminating up to 24% of the nucleus's thermal emission, so the actual diameter may well be smaller.[9]Hubble Space Telescope observations confirmedC/2014 UN271's large size in 2022, placing a lower limit diameter of 119 ± 15 km (74 ± 9 mi) for the maximum possible dust coma contamination.[9]
Even at its minimum estimated diameter,C/2014 UN271 is the largest Oort cloud comet discovered, being more than 50 times larger than a typical comet which is less than 2 km (1.2 mi) in diameter. The previous largest knownlong-period comet wasC/2002 VQ94 (LINEAR) with a diameter of 96 km (60 mi),[37] followed byComet Hale–Bopp at 74 km (46 mi).[10][32][j] The only known comet larger thanC/2014 UN271 is theactivecentaur95P/Chiron, which has a diameter of approximately 215 km (134 mi).[10]
While the mass and densityC/2014 UN271 have not yet been measured,[3] a rough estimate by NASA places its mass at 450 quadrillion kg (500 trillion short tons), about 100,000 times greater than that of a typical comet.[39]
Without its coma, the nucleus ofC/2014 UN271 has a visual (V-band)absolute magnitude of8.63±0.11, which is calculated from its distance and apparent magnitude.[9] Given the minimum estimated diameter (119 km) and absolute magnitude, the nucleus is calculated to have a very low visualgeometric albedo up to4.4%±1.2%, meaning that it reflects only4.4%±1.2% of visible light—making its surface darker thancoal.[39] For the maximum estimated diameter (137 km), the minimum albedo of the nucleus would be3.3%±0.9%.[9]C/2014 UN271's low albedo is characteristic of small comet nuclei from both short- and long-period populations, suggesting a lack of correlation between albedo, nucleus size, and orbit type in Solar System comets.[10] The low albedos of cometary nuclei are generally attributed to the deposition ofcarbon,organic compounds, andsulfides produced bycosmic raysdissociating molecules on the nucleus's surface.[10][40]
Optical observations ofC/2014 UN271 during its inbound passage show that its nucleus appears more reflective at longer wavelengths, indicating a moderately red color similar to (albeit slightly less red than) most long-period comets.[3][10] The albedo and color ofC/2014 UN271's nucleus are expected to change over time due to cometary activity, especially after perihelion passage when temperatures decrease; its nucleus is massive enough to gravitationally recapturedeposited icy ejecta back onto its surface, similar to what has been observed on Comet Hale–Bopp after its perihelion.[10]
Therotation period of2014 UN271's nucleus is disputed, as some studies found no significant rotational periodicity in itslight curve. Continuous observations by TESS in 2018 and 2020 did not detect any periodicity, placing an upper limit of 0.3 magnitudes for the nucleus'samplitude of variability.[41][21] In 2021, Bernardinelli and collaborators from the DES analyzed various ground-based telescope datasets from 2018 and earlier, finding an apparent nucleus variability of 0.2 magnitudes, but no periodicity due to sparse data. Bernardinelli et al. do not rule out other factors such as small dust outbursts that may contribute to this apparent variability, leaving room for the possibility that the nucleus's true rotational variability may be even less than 0.2 magnitudes.[3] In April 2022, astronomers Ignacio Ferrin and A. Ferrero reported a nucleus rotation period of20.6±0.2 days, based on an analysis of2014 UN271's long-term light curve behavior in observations from the Minor Planet Center's database.[8] Ferrin and Ferrero found a nucleus light curve amplitude of0.5±0.1 magnitudes, incongruous with findings by TESS and Bernardinelli et al.[8]
The exponential brightening ofC/2014 UN271's coma at 20–25 AU is consistent with it being generated bysublimatingcarbon dioxide (CO2) orammonia (NH3) ices from the nucleus's surface.[3] Less abundantsupervolatile substances such ascarbon monoxide (CO) are likely present inC/2014 UN271 and may additionally contribute to its distant activity, but their emissions remain yet to be detected.[3] InfraredNEOWISE observations from November 2020 did not detect any CO gas emission fromC/2014 UN271 at 20.9 AU, placing an upper limit COoutgassing rate at about ten times that of Comet Hale–Bopp at the same heliocentric distance.[21]
Analysis ofC/2014 UN271's coma shape in TESS images from 2018–2020 suggests that the coma is composed of submillimeter-sizeddust grains ejected at low speeds around 10 m/s (33 ft/s), indicating that the comet had become active 2 to 10 years prior to 2018.[21][9] Based on the coma's brightness in Hubble observations from January 2022,C/2014 UN271 is losing mass at a rate of roughly 1,000 kg/s (1.1 short ton/s) at 20 AU, similar to Comet Hale–Bopp at this distance.[9]
C/2014 UN271 came from the Oort cloud and has been inside of the orbit of Neptune (29.9 AU) since March 2014 and passed inside the orbit ofUranus (18.3 AU) in September 2022.[k][16][42] Thetime of perihelion has been well-known since June 2021.[6] The current3-sigma uncertainty in the comet's distance from the Sun is ±20,000 km.[16]
The inbound and outboundorbital period of an Oort cloud comet are never exactly the same as the orbit changes as a result of planetaryperturbations. For an Oort cloud comet an orbit defined while inside of the planetary region can produce results that are misleading. Therefore, the inbound and outbound orbits should be computed before entering the planetary region and after leaving the planetary region. With anobservation arc of several years using dozens of observations, the orbit ofC/2014 UN271 is securely known.[l] Its incoming orbit in 1600, as calculated byJPL Horizons, has a semimajor axis of 20,000 AU (0.3 ly).[4] This indicates thatC/2014 UN271 was at its furthest distance, or aphelion, of 40,000 AU (0.6 ly) in the Oort cloud around 1.4 million years ago.[4][a][m] It will come toperihelion (closest approach to the Sun) around 23 January 2031 at a distance of 10.95 AU (1.6 billion km; 1.0 billion mi),[6] just outside the aphelion ofSaturn's orbit (10.1 AU).[6][42] It will make its closest approach to Earth around 5 April 2031 at a distance of 10.1 AU (1.5 billion km; 0.94 billion mi).[43] It will cross theecliptic plane on 8 August 2033 when it is outbound12.0 AU from the Sun.[44] Its outbound orbital period will be approximately 5 million years with an aphelion distance of about 60,000 AU (0.9 ly).[4] The object is only very loosely bound to the Sun and subject toperturbations by thegalactic tide while in the Oort cloud.[45]
Large, long-period comets such asC/2014 UN271 are rarely found due to a phenomenon known asfading: comets on bound orbits around the Sun periodically lose mass and volatile content to activity in each perihelion passage, resulting in a gradual diminishing in size, brightness, and activity as they age.[46][32] This adds further evidence toC/2014 UN271 being a dynamically new comet.[46]
| Comet | Inbound Epoch 1600 Barycentric Aphelion (AU) | Outbound Epoch 2500 Barycentric Aphelion (AU) | Reference |
|---|---|---|---|
| C/1980 E1 (Bowell) | 74,000 | hyperbolic | Horizons |
| C/1999 F1 (Catalina) | 55,000 | 66,000 | Horizons |
| C/2000 W1 (Utsunomiya–Jones) | 69,000 | 1,700 | Horizons |
| C/2003 A2 (Gleason) | 47,000 | 15,000 | Horizons |
| C/2006 P1 (McNaught) | 67,000 | 4,100 | Horizons |
| C/2010 U3 (Boattini) | 34,000 | 9,900 | Horizons |
| C/2011 L4 (PanSTARRS) | 68,000 | 4,500 | Horizons |
| Comet ISON | hyperbolic | hyperbolic | Horizons |
| C/2013 A1 (Siding Spring) | 52,000 | 13,000 | Horizons |
| C/2013 US10 (Catalina) | 38,000 | hyperbolic | Horizons |
| C/2014 UN271 (Bernardinelli–Bernstein) | 40,000 | 60,000 | Horizons |
| C/2017 K2 (PanSTARRS) | 46,000 | 1,400 | Horizons |
| C/2017 T2 (PanSTARRS) | 74,000 | 2,900 | Horizons |
| C/2019 E3 (ATLAS) | 67,000 | 34,000 | Horizons |
As of 2022[update] there are no mission proposals toC/2014 UN271, nor are there any upcoming missions that can be retargeted to the comet. TheEuropean Space Agency's upcomingComet Interceptor mission, which will launch in 2029 and make aflyby of a long-period comet within Earth's orbit, will not be able to reachC/2014 UN271 due to its large perihelion distance.[47]
According to a 2021 study by theInitiative for Interstellar Studies, a future flyby mission with a direct, low-energy trajectory toC/2014 UN271 can have yearly optimal launch windows between September and October throughout 2022–2029, for a maximumdelta-v of 12 km/s at Earth. In all scenarios, the spacecraft would optimally arrive toC/2014 UN271 at a relative velocity of 12–14 km/s by August 2033, when the comet crosses the ecliptic plane at 11.9 AU from the Sun.[48][49] For instance a mission similar toNew Horizons (with the same launch vehicle but no Jupiter encounter) could reachC/2014 UN271 by August 2033 if launched in October 2029. Alternatively, a flyby trajectory toC/2014 UN271 using a combinedgravity assist andOberth maneuver at Jupiter can have feasible launch dates from 2020–2027 and 2034–2037. A launch within the latter window could utilize an Earth flyby to Jupiter after completing a 1:1 Earthresonant orbit, which would significantly reduce thecharacteristic energy at Earth launch and allow for target arrival above the ecliptic.[48] A flyby trajectory using consecutive gravity assists and orbital resonances from the inner planets is also possible, but the most optimal encounter combinations provide launch dates up to 2028, for a late 2033 arrival time.[48]
Arendezvous trajectory toC/2014 UN271 has been considered, although the comet's nearly-perpendicular orbit renders any direct rendezvous trajectory from the ecliptic unfeasible.[49] Nonetheless, a rendezvous withC/2014 UN271 can be performed with a Jupiter gravity assist after the comet has crossed the ecliptic, with optimal launch dates in 2030–2034 and flight durations around 14–15 years.[48]
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