C/2015 V2 (Johnson)

Lore & Background

C/2015 V2 (Johnson) was discovered on 3 November 2015 by Jess Johnson using a 0.68-meter Schmidt–Cassegrain telescope at an apparent magnitude of 17.1. Its incoming orbit had a semimajor axis of 59,200 AU (0.936 ly), but after leaving the Solar System it will follow a hyperbolic trajectory with an eccentricity of 1.0009. The comet was expected to be visible with binoculars in late May 2017 in the Northern Hemisphere at magnitude 6 to 7, but it was fainter than predicted, reaching a magnitude of 7.1 on June 21.

The comet was characterized by very low activity, resembling a manx comet. When it was 2.83 AU from the Sun, it showed no emission from C2, C3, or CN—typical cometary spectral features—but these emissions were detected when it reached 2.3 AU from the Sun. The SWAN instrument on SOHO measured its water production near perihelion at 10^29 molecules per second. Infrared spectroscopy indicated a rotational temperature warmer than predicted, suggesting an icy grainy halo. Polarimetric imaging revealed fan-shaped fine jets in the direction opposite the Sun.

Reader's Guide

C/2015 V2 (Johnson) is significant as a non-periodic comet that exhibited unusually low activity, fitting the classification of a manx comet. Its discovery by Jess Johnson at the Catalina Sky Survey on 3 November 2015 highlights the role of survey programs in detecting faint objects. The comet's behavior—being fainter than predicted and showing delayed emergence of typical cometary emissions (C2, C3, CN) only when closer to the Sun—provides insight into the composition and outgassing processes of such low-activity comets. The water production rate measured by SOHO's SWAN instrument and the warm rotational temperature inferred from infrared spectroscopy suggest a complex icy grain halo. The polarimetric detection of fan-shaped jets opposite the Sun adds to the understanding of dust and gas dynamics. Its hyperbolic exit trajectory (eccentricity 1.0009) confirms it will leave the Solar System permanently. The comet's legacy lies in its contribution to the study of manx comets and the variability of cometary activity.

Did You Know?

• The comet was discovered at an apparent magnitude of 17.1 using a 0.68-meter Schmidt–Cassegrain telescope.
• It showed no emission from C2, C3, or CN at 2.83 AU from the Sun, but these emissions appeared at 2.3 AU.
• Its water production near perihelion was measured at 10^29 molecules per second by the SWAN instrument on SOHO.
• The comet's effective radius is estimated at 1.7±0.138 km based on an absolute nuclear magnitude of 16.127±0.176.