Observations of Comets C/2007 D1 (LINEAR), C/2007 D3 (LINEAR), C/2010 G3 (WISE), C/2010 S1 (LINEAR), and C/2012 K6 (McNaught) at large heliocentric distances

TL;DR

This study observed five distant comets beyond 4 AU, finding no molecular emissions and attributing activity solely to dust, with implications for understanding comet activity mechanisms at large heliocentric distances.

Contribution

It provides new upper limits on gas production and nucleus sizes for distant comets, highlighting dust-driven activity at large heliocentric distances.

Findings

No molecular emissions detected in any comet.

Dust production is the main activity source at >4 AU.

Estimated nucleus radii range from 2 km to 28 km.

Abstract

Photometric and spectroscopic observations of five nearly parabolic comets with eccentricity larger than 0.99 at heliocentric distances greater than 4 AU were performed. No molecular emission was observed for any studied comet and the entire cometary activity in all cases was attributed to dust production. Upper limits of the gas production rates for the main neutral molecules in the cometary comae were calculated. The derived values of dust apparent magnitudes were used to estimate the upper limit of the geometric cross-section of cometary nuclei (upper limits of radii range from 2 km to 28 km). Due to the poor sublimation of water ice at these distances from the Sun, other mechanisms triggering activity in comets are discussed.