Abstract
Abstract Centaurs are small bodies orbiting in the giant planet region that were scattered inward from their source populations beyond Neptune. Some members of the population display comet-like activity during their transition through the solar system, the source of which is not well understood. The range of heliocentric distances where the active Centaurs have been observed and their median lifetime in the region suggest that this activity is driven neither by water-ice sublimation nor entirely by supervolatiles. Here we present an observational and thermodynamical study of 13 Centaurs discovered in the Pan-STARRS1 detection database aimed at identifying and characterizing active objects beyond the orbit of Jupiter. We find no evidence of activity associated with any of our targets at the time of their observations with the Gemini North telescope in 2017 and 2018, or in archival data from 2013 to 2019. Upper limits on the possible volatile and dust production rates from our targets are 1–2 orders of magnitude lower than production rates in some known comets and are in agreement with values measured for other inactive Centaurs. Our numerical integrations show that the orbits of six of our targets evolved interior to r ∼ 15 au over the past 100,000 yr, where several possible processes could trigger sublimation and outgassing, but their apparent inactivity indicates that either their dust production is below our detection limit or the objects are dormant. Only one Centaur in our sample—2014 PQ70—experienced a sudden decrease in semimajor axis and perihelion distance attributed to the onset of activity for some previously known inactive Centaurs, and therefore it is the most likely candidate for any future outburst. This object should be a target of high interest for any further observational monitoring.
Highlights
Centaurs are small bodies most commonly defined as having perihelia (q) and semimajor axes (a) between the orbits of Jupiter and Neptune, i.e., 5.2 AU < q, a < 30 AU (e.g. Jewitt 2009), which are migrating towards the inner Solar system from their source regions in trans-Neptunian space
Our investigation consisted of three steps: 1) analysis of images taken with Gemini-N to search for comet-like activity, 2) a search of archival images from the Dark Energy Camera (DECam) to look for traces of activity in the past, 3) thermal modeling to examine surface temperatures as a function of orbital parameters and object size to put upper limits on sublimative gas production from volatile species potentially present on the surface, and 4) numerical integrations to inspect the orbital histories of objects in our sample
SBP analysis is a powerful method for detecting faint coma, and by averaging the mean brightness values within a fixed distance from the Centaur nucleus we can increase our sensitivity to coma many-fold
Summary
Centaurs are small bodies most commonly defined as having perihelia (q) and semimajor axes (a) between the orbits of Jupiter and Neptune, i.e., 5.2 AU < q, a < 30 AU (e.g. Jewitt 2009), which are migrating towards the inner Solar system from their source regions in trans-Neptunian space. Due to the chaotic gravitational environment, the typical dynamical lifetime of a Centaur is only ∼10 Myr (Tiscareno and Malhotra 2003; Di Sisto and Brunini 2007) In this way, the Centaur population delivers useful clues of the pristine composition and physical properties of small trans-Neptunian objects (TNOs) beyond our current observational limits right to our doorstep. Most known Centaurs have spent the majority of their lifetime in region too warm to maintain surface supplies of super-volatile ices such as CO and CO2 (Jewitt 2009), for example if free CO ice was present on all Centaurs, we should observe Centaurs with comae well beyond the orbit of Neptune, just like in some long period comets Almost 27% of all active Centaurs has perihelia smaller than 6.5 AU, as can be seen on Figure 1
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