2017 OF201
Extreme TNO and dwarf planet candidate discovered in 2025.
2017 OF201 is an extreme trans-Neptunian object and dwarf planet candidate discovered in archived telescope images from 2011 to 2018 and announced in 2025. It is notable for its extremely large and elongated orbit, bringing it from 45 to 1,610 astronomical units from the Sun, and for being one of the brightest known Solar System objects without a directly measured size.
Quick Facts
- Minorplanet
- yes
- Discoverer
- Sihao Cheng, Jiaxuan Li, Eritas Yang
- Discovery Site
- Cerro Tololo Inter-American Observatory
- Discovered
- 23 July 2017
- Mpc Name
- 2017 OF · 201
- Mp Category
- TNO, SDO and eTNO
- Epoch
- 5 May 2025 / (JD 2460800.5)
- Uncertainty
- 3
- Observation Arc
- 14.11 yr (5,153 days) / (based on 25 observations)
- Earliest Precovery Date
- 21 Sep 2004
- Time Periastron
- 1930 November 13 ± 3 days
- Semimajor
- 840 AU
Facts from the source article.
Lore & Background
2017 OF201 was discovered by a team led by Sihao Cheng at the Institute for Advanced Study, along with Princeton University students Jiaxuan Li and Eritas Yang, in a search for trans-Neptunian objects in archived Dark Energy Camera Legacy Survey images, hoping to find the hypothetical Planet Nine. Cheng was inspired after attending a 2005 lecture by Michael E. Brown. The team found ten DECaLS detections from 2014–2018 and, following advice from Mike Alexandersen, nine additional detections in Canada–France–Hawaii Telescope images from 2011–2012. The Minor Planet Center gave it the provisional designation 2017 OF201 and announced it on 21 May 2025. Additional precovery observations were later found in Sloan Digital Sky Survey images from 2004 and 2009. The orbit of 2017 OF201 has a perihelion of 44.9 AU and aphelion of 1,610 AU, placing it near the boundary of the scattered disc and inner Oort cloud. Its orbit is shaped by both Neptune and the galactic tide. The object is not considered a sednoid because its perihelion is below 60 AU, allowing Neptune's gravity to influence its orbit. Its diameter is estimated at 500 to 900 km. It has a red color similar to Sedna and shows no brightness variability over 0.1 magnitudes, suggesting a nearly spherical shape. It has no known moons, and the Hubble Space Telescope is planned to image it in 2026.
Reader's Guide
2017 OF201 is significant as an extreme trans-Neptunian object whose orbit challenges the Planet Nine hypothesis. Its longitude of perihelion does not align with other extreme TNOs like Sedna, which have been hypothesized to cluster due to a distant massive planet. Simulations by Cheng's team suggest Planet Nine would eject 2017 OF201 from its current orbit within 100 million years, though the current orbit could be temporary. Cheng stated that the object's existence as an outlier could potentially challenge the Planet Nine hypothesis. Co-discoverer Konstantin Batygin argued the discovery means nothing because the orbit is influenced by Neptune. The team's simulations do not disprove Planet Nine, with Cheng still thinking it possible, Yang neutral, and Li initially thinking it 'kills Planet Nine' but later conceding it is '49 percent killed'. Astronomer Samantha Lawler stated that the original argument for Planet Nine is getting weaker. The discovery implies there are likely thousands of similar objects too distant and faint to be observed.
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