X-shooter search for outgassing from main belt comet P/2012 T1 (Pan-STARRS)^⋆

¹ Planetary and Space Sciences, School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
e-mail: Colin.Snodgrass@open.ac.uk
² European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago, Chile
³ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast, BT7 1NN, UK

Received: 28 April 2017
Accepted: 17 June 2017

Abstract

Context. Main belt comets are a recently identified population of minor bodies with stable asteroid-like orbits but cometary appearances. Sublimation of water ice is the most likely mechanism for their recurrent activity (i.e. dust tails and dust comae), although there has been no direct detection of gas. These peculiar objects could hold the key to the origin of water on Earth.

Aims. In this paper we present a search for the gas responsible for lifting dust from P/2012 T1 (Pan-STARRS), and review previous attempts at such measurements. To date such searches have mainly been indirect, looking for the common cometary gas CN rather than gasses related to water itself.

Methods. We use the VLT and X-shooter to search for emission from OH in the UV, a direct dissociation product of water.

Results. We do not detect any emission lines, and place an upper limit on water production rate from P/2012 T1 of 8−9 × 10²⁵ molecules s^-1. This is similar to limits derived from observations using the Herschel space telescope.

Conclusions. We conclude that the best current facilities are incapable of detecting water emission at the exceptionally low levels required to produce the observed activity in main belt comets.