2018 AG37
Farthest currently observable known object in the Solar System.
2018 AG37 is a distant trans-Neptunian object and centaur, discovered at a distance of 132.2 ± 1.5 AU (19.78 ± 0.22 billion km) from the Sun. This makes it the farthest currently observable known object in the Solar System. It was nicknamed "FarFarOut" to highlight its extreme distance.
The object was first imaged on 15 January 2018 by astronomers Scott Sheppard, David Tholen, and Chad Trujillo using the 8.2-meter Subaru Telescope at Maunakea Observatory, Hawaii, during a search for hypothetical planets beyond Neptune. It was not noticed until January 2019, when Sheppard reviewed the 2018 images after a weather delay postponed a lecture. In two images taken one day apart, he spotted a faint object of apparent magnitude 25.3 moving slowly against background stars and galaxies. Based on those two positions, Sheppard estimated its distance at roughly 140 AU, farther than 2018 VG18, which his team had announced a month earlier. In his rescheduled talk on 21 February 2019, Sheppard jokingly nicknamed it "FarFarOut" as a successor to "Farout," the nickname for 2018 VG18. He reobserved the object in March 2019 with the 6.5-meter Magellan-Baade telescope in Chile, and additional observations followed in May 2019 and January 2020 with the Subaru Telescope. These observations over two years established a tentative orbit, allowing the Minor Planet Center to confirm and announce the object in a press release by the Carnegie Institution for Science on 10 February 2021.
The object is officially known by the provisional designation 2018 AG37, which indicates its discovery date: the first half of January 2018, and that it is the 932nd object discovered in that half-month. It has not yet received a minor planet number due to its short observation arc and orbital uncertainty; it will become eligible for naming after its orbit is well-defined through multiple oppositions.
As of 2021, 2018 AG37 had been observed nine times over two years. Its extreme distance means it moves very slowly, so two years of data have not adequately determined its orbit, which has a condition code of 9 (highly uncertain). Several more years of observations are needed. Its distance, inclination, and longitude of the ascending node are reasonably known, but elements like eccentricity and mean anomaly are poorly constrained.
Quick Facts
- Minorplanet
- yes
- Discoverer
- S. S. Sheppard / D. J. Tholen / C. Trujillo
- Discovery Site
- Maunakea Obs.
- Discovered
- 15 January 2018
- Mpc Name
- 2018 AG · 37
- Mp Category
- SDO · TNO · distant · centaur
- Epoch
- 2019-Feb-26 (JD 2458540.5)
- Uncertainty
- 9
- Observation Arc
- 2.03 yr (740 days) using 11 observations
Facts from the source article.
Lore & Background
2018 AG37 was first imaged on 15 January 2018 during a survey for distant Solar System objects and the hypothetical Planet Nine, but it was not noticed until January 2019 when Sheppard reviewed the images. Based on two positions, he estimated its distance at roughly 140 AU, farther than the previous record-holder 2018 VG18. Sheppard jokingly nicknamed it 'FarFarOut' in a talk on 21 February 2019. Additional observations in March and May 2019 and January 2020 established a tentative orbit, and the confirmation was announced in a press release on 10 February 2021.
The object's orbit is highly uncertain due to a short observation arc of two years. Its nominal best-fit orbit gives a semi-major axis of 80.2±4.5 AU and eccentricity of 0.655±0.02, with perihelion near 27.6 AU and aphelion near 133 AU. It likely crosses Neptune's orbit and has experienced strong gravitational interactions with Neptune. Its size is not measured but is estimated between 400–600 km in diameter assuming an albedo of 0.10–0.25; Sheppard favors a smaller diameter due to a likely ice-rich, reflective surface. Johnston classifies it as a centaur and assumes a dark albedo of 0.058, which would make it the largest known centaur at about 790 km.
Reader's Guide
2018 AG37 is significant as the farthest currently observable object in the Solar System, surpassing all other known objects at the time of its discovery. Its nickname 'FarFarOut' highlights its record distance, succeeding 'Farout' for 2018 VG18. The object was discovered during a search for hypothetical planets beyond Neptune, and its elongated orbit and small perihelion distance indicate it has been scattered by Neptune's gravity, placing it among the scattered disc objects. Its orbit remains poorly determined due to its slow motion and short observation arc, requiring years of additional observations. The object's size is uncertain, with estimates ranging from 400 km to 790 km depending on assumed albedo. As of January 2024, it remains the farthest observed object in the Solar System, though many comets and trans-Neptunian objects have greater aphelion distances but are not currently observable.
Did You Know?
- 2018 AG37 was nicknamed 'FarFarOut' because it is even farther than the previous farthest known object 2018 VG18, nicknamed 'Farout'.
- It was discovered 132.2 ± 1.5 AU from the Sun, farther than any other currently observable known object in the Solar System.
- The object was first imaged on 15 January 2018 but was not noticed until January 2019 when Sheppard reviewed the images after a lecture delay due to weather.
- Its orbit is so uncertain that it has a condition code of 9, the highest uncertainty level.
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