SAFARI: Searching Asteroids for Activity Revealing Indicators

Abstract

Active asteroids behave dynamically like asteroids but display comet-like comae. These objects are poorly understood, with only about 30 identified to date. We have conducted one of the deepest systematic searches for asteroid activity by making use of deep images from the Dark Energy Camera (DECam) ideally suited to the task. We looked for activity indicators amongst 11,703 unique asteroids extracted from 35,640 images. We detected three previously-identified active asteroids ((62412), (1) Ceres and (779) Nina), though only (62412) showed signs of activity. Our activity occurrence rate of 1 in 11,703 is consistent with the prevailing 1 in 10,000 activity occurrence rate estimate. Our proof of concept demonstrates 1) our novel informatics approach can locate active asteroids and 2) DECam data are well-suited to the search for active asteroids.

Six Years of Sustained Activity in (6478) Gault

“…Active asteroids like (6478) Gault (Figure 1, this work) are dynamically asteroidal objects but they uncharacteristically manifest cometary features such as tails or comae (Hsieh & Jewitt 2006a). With only ∼20 known to date (see Table 1 of Chandler et al 2018), active asteroids remain poorly understood, yet they promise insight into solar system volatile disposition and, concomitantly, the origin of water on Earth (Hsieh & Jewitt 2006b).…”

“…Thermally induced activity is thought to increase with decreasing heliocentric distance; that is, the closer a body is to the Sun, the more likely an outburst is to occur. Active asteroids are more likely to exhibit activity during perihelion passage (see Table 1 of Chandler et al 2018). Notable exceptions where activity was discovered at distances far from perihelion include 311P/PanSTARRS ) and (493) Griseldis (Tholen et al 2015).…”

Cometary Activity Discovered on a Distant Centaur: A Nonaqueous Sublimation Mechanism

“…serendipitously imaged by the instrument can be searched. We identified Centaurs in our own proprietary database cataloging the NSFs National Optical-Infrared Astronomy Research Laboratory (NSFs OIR Lab, formerly NOAO) public DECam archive following the methodology outlined in Chandler et al (2018). Our general approach was to correlate image celestial coordi-nate and temporal data with object ephemeris services such as NASA JPL Horizons (Giorgini et al 1996) and IMCCE SkyBot (Berthier et al (2006); see also the acknowledgements).…”

“…After (4) downloading the data, we (5) checked each chip for the presence of the Centaur to ensure the object was visible and free of imaging complications (e.g., gaps between chips, scattered light from bright stars, cosmic rays). Finally, we (6) adhered to the routine outlined in Chandler et al (2018) where, following image file retrieval of 2014 OG 392 from the archive, we extracted Flexible Image Transport System (FITS) and Portable Network Graphics (PNG) thumbnails (480×480 pixel images). We subjected these thumbnails to image processing techniques in order to assist by-eye analysis.…”

“…To ascertain potential heliocentric distance effects we made use of a simple metric (Chandler et al 2018), % T →q , which describes how close to perihelion (q) an object's distance (d) is relative to its aphelion distance (Q):…”