122P/de Vico

Lore & Background

The comet was first observed in 1846, reaching magnitude 5 in mid March and last seen in May. Its elliptical orbit suggested a return between 1919 and 1925, but it was not detected then. Later calculations predicted a return around 1995 or 1996. On 17 September 1995, Japanese astronomers Yuji Nakamura, Masaaki Tanaka, and Shougo Utsunomiya spotted an apparently new comet of magnitude 7, independently found within 24 hours by Tsutomu Seki and Don Machholz. Brian G. Marsden, Gareth V. Williams and others identified it as the rediscovery of de Vico's lost comet. By late September it reached magnitude 5.5, visible by naked eye, and peaked at magnitude 5.1 in early October before fading. Its tail was reported up to seven degrees long. The comet was also observed by the Ulysses spacecraft and last detected on 25 June 1996.

Spectroscopic observations from McDonald Observatory in October 1995 detected emissions of carbon (C2 and C3), cyanogen (CN), hydrocarbon (CH), and amide (NH2), plus traces of carbon disulfide (CS2), but no nitrogen (N+2) ions. Its N14/N15 ratio was about half that of Earth's atmosphere, differing from other comets. Independent observations from Bisei Astronomical Observatory found it one of the most gas-rich comets known, with a gas-to-dust ratio ten times higher than 1P/Halley, comparable to 23P/Brorsen–Metcalf. Daniel Kirkwood in 1884 suggested it calved off comet 12P/Pons–Brooks centuries prior, and later linked their capture to a shared aphelion near Neptune in 991 CE. In 1979, Ichiro Hasegawa tentatively identified a comet observed in May 1391 as a previous apparition of 122P.

Reader's Guide

122P/de Vico's significance lies in its history as a lost comet recovered after nearly 150 years, demonstrating the value of persistent orbital calculations. Its recovery in 1995 by multiple independent observers highlighted the collaborative nature of modern comet discovery. The comet's chemical composition, particularly its low N14/N15 ratio and absence of N+2 ions, suggests an unknown parent compound for cyanogen, challenging models of cometary chemistry. Its extremely high gas-to-dust ratio, ten times that of 1P/Halley, makes it a benchmark for gas-rich comets. The potential detection of its dust trail by the Ulysses and Pioneer Venus Orbiter spacecraft, causing distortions in the interplanetary magnetic field, hints at possible meteor showers on Venus. Kirkwood's hypothesis that it split from 12P/Pons–Brooks adds a historical dimension to its origin. Its next perihelion in October 2069 and a close approach to Uranus in 2153 ensure continued interest for future observations.

Did You Know?

• It was recovered in September 1995 by Japanese astronomers Yuji Nakamura, Masaaki Tanaka, and Shougo Utsunomiya.
• Its gas-to-dust ratio is ten times higher than that of 1P/Halley.
• The comet's next perihelion is predicted for 14–21 October 2069.