2017 OF201

Last updated

2017 OF201
2017 OF201 CFHT 2011-08-31 annotated.gif
2017 OF201 imaged by the Canada–France–Hawaii Telescope on 31 August 2011
Discovery [1]
Discovered by Sihao Cheng, Jiaxuan Li, Eritas Yang
Discovery site Cerro Tololo Inter-American Observatory
Discovery date23 July 2017 (date of first observation) [2]
Designations
2017 OF201
TNO, SDO and eTNO
Orbital characteristics   (barycentric)
Epoch 5 May 2025
(JD 2460800.5)
Uncertainty parameter 3
Observation arc 14.11 yr (5,153 days)
(using 25 observations) [2]
Earliest precovery date21 Sep 2004 [2]
Aphelion 1612 AU [3]
1632±14 AU [1]
1693±6 AU (heliocentric) [a]
Perihelion 44.9 AU [1] [4]
840 AU [1]
Eccentricity 0.946
23800 years [3]
24300 years [1]
26000±1300 yr (heliocentric) [a]
1.3°
0° 38m 7.8s / day
Inclination 16.21°
328.7°
13 November 1930 ± 3 days [4]
338.2°
Physical characteristics
≈700 km (est. at 0.15 albedo) [1]
560 to 850 km (for albedo 0.10–0.25) [5]
0.15 (predicted) [1]
BV = 0.99±0.11 [1]
gr = 0.77±0.11
rz = 0.80±0.07
22.8 [1]
3.49±0.45 [6]

    2017 OF201 is an extreme trans-Neptunian object and dwarf planet candidate, estimated to be around 500 to 900 kilometres (300 to 600 miles) in diameter. It was announced in 2025 by Sihao Cheng, Jiaxuan Li, and Eritas Yang, who discovered the object in archived telescope images from 2011 to 2018. With an absolute magnitude of between 3 and 4, 2017 OF201 is one of the brightest known objects in the Solar System that does not have a directly measured size. The orbit of 2017 OF201 is extremely large and elongated, bringing it from 45 to 1,610 astronomical units (0.00071 to 0.02546  ly ) away from the Sun.

    Contents

    2017 OF201 has not yet been imaged by high-resolution telescopes, so it has no known moons. The Hubble Space Telescope is planned to image it in 2026, which should determine if it has significantly sized moons. [7]

    Discovery

    The path of 2017 OF201 in the sky from 2012 to 2018. Black circles mark the time and location of 2017 OF201 when it was imaged by DECaLS and CFHT (inset images shown). 2017 OF201 discovery Cheng et al. 2025 Fig 1.png
    The path of 2017 OF201 in the sky from 2012 to 2018. Black circles mark the time and location of 2017 OF201 when it was imaged by DECaLS and CFHT (inset images shown).

    2017 OF201 was discovered by a team at the Institute for Advanced Study led by Sihao Cheng and two Princeton University students, Jiaxuan Li, and Eritas Yang, in a search for trans-Neptunian objects (TNOs) in archived Dark Energy Camera Legacy Survey (DECaLS) images in the hope of finding the hypothetical Planet Nine. [8] [9] [10] [11] [1] Cheng claimed that he became inspired to survey the deep solar system after attending a 2005 lecture by Dr. Michael E. Brown, the discoverer of Eris and Sedna and co-author of the Planet Nine hypothesis, at California Institute of Technology. [9] Cheng's team were able to find ten DECaLS detections of 2017 OF201 from 2014 to 2018, which allowed them to determine that this TNO had an unusually distant and eccentric orbit. [1] Following the advice of Mike Alexandersen of the Minor Planet Center, Cheng's team found nine additional detections of 2017 OF201 in archived Canada–France–Hawaii Telescope (CFHT) images from 2011 and 2012, which further improved calculations of 2017 OF201's orbit. [1] Cheng's team attempted to search for 2017 OF201 in more archived images from the Subaru and Gemini North telescopes, but were unable to find any detections. [1]

    Cheng's team reported their DECaLS and CFHT detections to the Minor Planet Center, which gave the TNO its provisional designation 2017 OF201 and announced it to the public on 21 May 2025. [12] Following the announcement, the institutions of Cheng's team published a press release and a paper detailing the discovery of 2017 OF201. [10] [11] Additional precovery observations of 2017 OF201 were later found in Sloan Digital Sky Survey images from 2004 and 2009. [2]

    Orbit

    Orbit diagram of 2017 OF201 (red) compared to other extreme TNOs. The right plot shows the orientation (longitude of perihelion) and average distance (semi-major axis) of extreme TNO orbits, with 2017 OF201 plotted in red. 2017 OF201 orbit Cheng et al. 2025 Fig 2.png
    Orbit diagram of 2017 OF201 (red) compared to other extreme TNOs. The right plot shows the orientation (longitude of perihelion) and average distance (semi-major axis) of extreme TNO orbits, with 2017 OF201 plotted in red.

    2017 OF201 orbits far beyond Neptune at an average distance (semi-major axis) of 840 astronomical units (AU), taking around 24,000 years to complete an orbit around the Sun. [1] 2017 OF201 has an extremely elongated orbit with an eccentricity of 0.95, which together with its large orbital distance makes it an extreme trans-Neptunian object. [1] 2017 OF201 has an orbital inclination of 16.2° with respect to the ecliptic. It last passed perihelion in mid-November 1930. [4] As of 2025, its current distance from the Sun is 90.5 AU, making it one of the most distant Solar System objects observed. [1] Because of 2017 OF201's extremely distant and eccentric orbit, it is only visible to Earth during perihelion, which spans less than 1% of its orbit. [13] Co-discoverer Eritas Yang stated that the discovery of 2017 OF201 means that there are likely thousands of similar objects that are currently too distant and faint from Earth to be observed. [13]

    The orbit of 2017 OF201 has a perihelion distance of 44.9 AU and aphelion distance of 1,610 AU (0.0255 light-years ), which places this object near the estimated boundary of the scattered disc region and the inner Oort cloud. [1] As a result, the orbit of 2017 OF201 is shaped by both Neptune and the galactic tide over billions of years. [1] [13] Specifically, 2017 OF201 is thought to have been gravitationally scattered into a high semi-major axis and low perihelion orbit by Neptune first, and then galactic tides and stellar encounters raised its perihelion. [1] Yang has not stated which planetary body the team thinks scattered 2017 OF201, and argued that it might have been scattered multiple times. [14] Specifically, Yang stated the team believes that 2017 OF201 had been scattered into the Oort cloud by some "large planet" and something from the Oort cloud ejected it again into its current orbit. [15] In terms of semi-major axis and eccentricity, the orbit of 2017 OF201 is similar to that of extreme TNO 2013 SY99 . [1]

    Implications for the Planet Nine hypothesis

    The orientation or longitude of perihelion of 2017 OF201's orbit does not align with other extreme TNOs like Sedna, whose orbits are thought to be clustered because of the gravitational influence of a distant massive planet, dubbed Planet Nine. [14] Simulations run by Cheng's team suggest that Planet Nine would have ejected 2017 OF201 from its current orbit within 100 million years, though 2017 OF201's current orbit could be a temporary state. [9] [1] [11] Cheng stated, "the existence of 2017 OF201 as an outlier to [TNOs] clustering could potentially challenge [the Planet Nine] hypothesis." [16] Konstantin Batygin, the co-author of the Planet Nine hypothesis, argued that the discovery of 2017 OF201 means nothing in relation to the hypothesis because the object's orbit is significantly influenced by Neptune. [13] Cheng, however, notes that 2017 OF201 "is right at the boundary between being stable and unstable." [13] Nevertheless, Cheng's team agree that their simulations do not disprove Planet Nine. [9] In an interview with The New York Times , Cheng "still thought Planet Nine was possible" while Yang "was neutral on Planet Nine’s existence." [9] Li initially thought "OK, this kills Planet Nine" upon seeing 2017 OF201's orbit, but later conceded that the results were not definitive, jokingly stating that "it's 49 percent killed." [9] Yang also reiterated that the discovery of 2017 OF201 means it is likely there are many more similar objects in similar orbits that just have not been detected yet. [14] In response to the discovery, astronomer Samantha Lawler from the University of Regina stated that "the original argument for Planet Nine is getting weaker and weaker". [8]

    Physical characteristics

    The diameter of 2017 OF201 has not been measured with observational techniques, but it can be estimated from its brightness by assuming it has the same geometric albedo as other large scattered disc objects like 2017 OF201. [1] Cheng, Li, and Yang estimate that 2017 OF201 is most likely 700 km in diameter, with a predicted albedo of 0.15. [1] This places 2017 OF201 within the diameter range of possible dwarf planets. [11] [13] For reference, Pluto is 2,377 km (1,477 mi) in diameter [11] and Ceres is 939 km (583 mi) in diameter. [13]

    Observations of 2017 OF201 in different light filters show that it has a red color similar to Sedna. [1] 2017 OF201 is slightly redder than the average color of TNOs on scattered disc and detached orbits. [1] The brightness of 2017 OF201 does not show variability over 0.1 magnitudes, indicating its shape is likely close to spherical. [1]

    See also

    Notes

    1. 1 2 Given the orbital eccentricity of this object, different epochs can generate quite different heliocentric unperturbed two-body best-fit solutions to the orbital period. For objects at such high eccentricity, the Solar System's barycenter (Sun+Jupiter) generates solutions that are more stable than heliocentric solutions. For example, at epoch 2028-May-01 the heliocentric solution shows aphelion at 1534 AU.

    References

    1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Cheng, Sihao; Li, Jiaxuan; Yang, Eritas (May 2025). "Discovery of a dwarf planet candidate in an extremely wide orbit: 2017 OF201". arXiv: 2505.15806 [astro-ph.EP].
    2. 1 2 3 4 "2017 OF201". Minor Planet Center. Retrieved 1 June 2025.
    3. 1 2 Horizons output. "Barycentric Osculating Orbital Elements for 2017 OF201". Solution using the Solar System Barycenter. Ephemeris Type:Elements and Center:@0
    4. 1 2 3 "Perihelion in November 1930" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons . Retrieved 7 July 2025.
    5. "Asteroid Size Estimator". Center for Near Earth Object Studies. Jet Propulsion Laboratory. Retrieved 20 August 2025.
    6. "JPL Small-Body Database Lookup: (2017 OF201)" (2018-10-31 last obs.). Jet Propulsion Laboratory . Retrieved 1 June 2025.
    7. Proudfoot, Benjamin (August 2025). "A Search For The Moons of Mid-Sized TNOs". Mikulski Archive for Space Telescopes. Space Telescope Science Institute: HST Proposal 18010. Cycle 33. Retrieved 17 August 2025.
    8. 1 2 Lawler, Daniel. "The hunt for mysterious 'Planet Nine' offers up a surprise". Phys.org . Retrieved 17 July 2025.
    9. 1 2 3 4 5 6 Chang, Kenneth (29 May 2025). "Scientists Say They've Found a Dwarf Planet Very Far From the Sun". The New York Times . Archived from the original on 31 May 2025. Retrieved 1 June 2025.
    10. 1 2 "Princeton Astronomers Discover Extraordinary Distant Object at Solar System's Edge". web.astro.princeton.edu (Press release). Princeton University. 22 May 2025. Retrieved 1 June 2025.
    11. 1 2 3 4 5 "An Extreme Cousin for Pluto? Possible Dwarf Planet Discovered at Solar System's Edge". www.ias.edu (Press release). Institute for Advanced Study. 22 May 2025. Retrieved 23 May 2025.
    12. "MPEC 2025-K47 : 2017 OF201". Minor Planet Electronic Circulars. Minor Planet Center. 21 May 2025. Retrieved 1 June 2025.
    13. 1 2 3 4 5 6 7 Chandler, David L. (27 May 2025). "Another Dwarf Planet In Our Solar System?". Sky & Telescope . Retrieved 1 June 2025.
    14. 1 2 3 "Astronomers Discover Dwarf Planet Candidate on 25,000-Year Orbit". sci.news. 27 May 2025. Retrieved 15 July 2025.
    15. Carter, Jamie. "New Pluto-Like Planet Discovered In Solar System — What To Know". Forbes . Retrieved 17 July 2025.
    16. Dunham, Will (30 May 2025). "Possible new dwarf planet spotted near the edge of the solar system". Reuters . Retrieved 15 July 2025.