A Review of Cometary Outbursts at Large Heliocentric Distances

First Results from TESS Observations of Comet 46P/Wirtanen

“…Outbursts have been observed in comets for over a century (e.g., Hughes 1990;Filonenko & Churyumov 2006). A number of proposals have been put forth as trigger mechanisms (Hughes 1991;Gronkowski & Weso lowski 2016), though it is generally believed that a single explanation is insufficient to account for all cases. Similarly, little is known about the physical processes that govern the behavior of the ejecta during the initial stages of the event.…”

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

“…To explain the cometary activity at large heliocentric distances a few mechanisms (see, e.g., review by Meech and Svoren, 2004;Gronkowski 2005) have been proposed. The most popular sources of the energy required to explain the activity are: the sublimation of more volatile compounds like CO or CO 2 (Houpis and Mendis, 1981; Prialnik and Bar-Nun, 1992; Hughes, 1992), the transition phase between amorphous and crystalline water ice (Prialnik, 1992;Gronkowski and Smela, 1998;De Sanctis et al, 2002), polymerisation of HCN (Rettig et al, 1992), and the annealing of amorphous water ice (Meech et al 2009). Observations of distant comets by different methods (e.g., photometry, spectroscopy, and polarimetry) can be used to determine the sizes of cometary nuclei (Svoren, 1983), to study the brightness evolution and dust composition of cometary comae (Meech et al, 2009), as well as to detect gas emissions above the reflected solar continuum (Larson, 1980;Cochran et al, 1980Cochran et al, , 1982 To enlarge the set of the comets studied at relatively large heliocentric distances, in Sects.…”

“…To explain the cometary activity at large heliocentric distances a few mechanisms (see, e.g., review by Meech and Svoren, 2004;Gronkowski 2005) have been proposed. The most popular sources of the energy required to explain the activity are: the sublimation of more volatile compounds like CO or CO 2 (Houpis and Mendis, 1981; Prialnik and Bar-Nun, 1992; Hughes, 1992), the transition phase between amorphous and crystalline water ice (Prialnik, 1992;Gronkowski and Smela, 1998;De Sanctis et al, 2002), polymerisation of HCN (Rettig et al, 1992), and the annealing of amorphous water ice (Meech et al 2009).…”

Evolution of mobile phases in cometary interiors

“…Only the permeability and cohesive strength of the outer refractory layer will limit the pressure achievable beneath the surface, and only the incident solar flux will limit the temperatures achievable; for example, surface temperatures at the equator of order 400 K have been estimated for near-Earth asteroids such as (162173) Ryugu (Busareva et al 2018). Eventual rupture of the cemented dust layer to release a water-based slurry can account for the mud-bath-like features attributed to flow of fluidised material observed in association with ruptures on cometary surfaces (Thomas et al 2015), structures consistent with conduits for liquid flow (Auger et al 2015), and for the very high-volume eruptions observed in some comets at considerable distances from the sun (Gronkowski & Wesołowski 2016;West, Hainaut & Smette 1991). For example, observation of the post-perihelion eruption of 67P/Churyumov-Gerasimenko at a distance of 3.32 AU has indicated that there must be a mechanism for significant energy storage well beneath the surface of the cometary nucleus (Agarwal et al 2017).…”