450P/LONEOS

Lore & Background

The comet was discovered as an 18th-magnitude object on CCD images taken by Brian A. Skiff as part of the Lowell Observatory's LONEOS program. The LONEOS images showed the object with a stellar-like appearance, but its motion prompted Skiff to request additional observations. H. R. Miller (Perkins Observatory) and J. Young (Table Mountain Observatory) later found a coma about 4 arcseconds in diameter and a very faint tail about 10 arcseconds in length, confirming its cometary nature. At the time its cometary activity was detected, 450P/LONEOS (then known as P/2004 A1) was about 5.54 AU from the Sun. The first orbital calculations were published on the Minor Planet Center's website on 13 January 2004, alongside precovery images from Kitt Peak Observatory dating back to 18 December 2003.

The comet was successfully recovered from observations taken by the Gemini North Observatory in August 2022, where it was noted to be 4.5 magnitudes fainter than previously predicted. It received its official numerical designation (450P) alongside 8 other comets in February 2023. Orbital calculations indicated that it made a close encounter with Saturn in 1992, coming within 0.031 AU of the giant planet, which decreased its semimajor axis by 5.2 AU. A long-term orbital investigation indicated that this is likely its first sojourn to the inner Solar System as it transitions from a centaur into a Jupiter-family comet. On 11 July 2026, the comet approached Jupiter at a distance of 0.5 AU, further sending it into a closer orbit around the Sun.

A 2011 study revealed that based on its measured dust activity, the nucleus may be between 0.5 km and 3.5 km in radius. At the time it was in an inactive state between 2019 and 2024, further observations from both the Gemini Observatory and the James Webb Space Telescope revised this to roughly 1.8±0.5 km. Its asymmetrical coma and anti-tail during its 2004 apparition extended up to 150,000 km in the solar direction. During its 2022 apparition, it had a low dust production rate of about ~4.8 kg/s, primarily driven by CO2 outgassing from amorphous water ice crystallization at temperatures between 140–160 K.

Reader's Guide

450P/LONEOS holds significance as a comet that has undergone a dramatic orbital transformation due to a close encounter with Saturn in 1992, which reduced its semimajor axis by 5.2 AU and likely brought it into the inner Solar System for the first time. This transition from a centaur to a Jupiter-family comet makes it a valuable object for studying the dynamical evolution of small bodies. Its recovery in 2022, 4.5 magnitudes fainter than predicted, and subsequent observations by the Gemini Observatory and the James Webb Space Telescope provided refined estimates of its nucleus size (1.8±0.5 km) and revealed that its low dust production is driven by CO2 outgassing rather than water. The comet's 2026 approach to Jupiter will further alter its orbit, offering a rare opportunity to observe the ongoing reshaping of a comet's trajectory. Its legacy includes being one of the comets discovered by the LONEOS program and serving as a case study for the physical and orbital changes that occur as centaurs evolve into Jupiter-family comets.

Did You Know?

• 450P/LONEOS was discovered as an 18th-magnitude object by Brian A. Skiff as part of the LONEOS program.
• Its nucleus size was revised to roughly 1.8±0.5 km based on observations from the Gemini Observatory and the James Webb Space Telescope.
• During its 2022 apparition, its dust production was primarily driven by CO2 outgassing at temperatures between 140–160 K.