Surface composition of mid-sized TNOs: searching for ammonia

Program lead: Aurélie Guilbert-Lepoutre

Program duration: 9 hours

This program will focus on constraining the surface composition of 2 Charon-like objects, i.e. mid-sized Transneptunian objects (TNOs) and in particular looking for possible presence of ammonia at their surface. The recent observations of the NASA/New Horizons probe have shown that Charon’s surface is possibly indicative of past cryovolcanic activity. Ammonia and ammonia hydrates, common antifreezes, have been detected in the spectra obtained both from the probe and ground-based facilities. We have selected 2 targets, Orcus and 2003 AZ84, with physical properties similar to Charon, for which past cryovolcanism could have been an interesting evolutionary path. Traces of volatiles such as ammonia and/or hydrates have been found in ground-based spectra of Orcus. We will further investigate this possibility, and open a new window into constraining the inventory of volatiles at the surface of Orcus by observing also the 3-5micron range, where fundamental absorption bands of C-H-, N-H- and O-H-bearing ices can be found. Recent occultation results suggest that 2003 AZ84 may have a canyon-like feature on its surface, similar to the large canyon seen on the surface of Charon. Given its other physical characteristics, this object is selected as our second target. Ground-based observations of this fainter TNO suggest that crystalline water ice may be the dominant volatile species present at its surface, though the presence of minor species cannot be constrained.

Observations and targets: