Disintegrating Inbound Long-period Comet C/2019 J2

Abstract

We present observations of the disintegrating long-period comet C/2019 J2 (Palomar) taken to determine the nature of the object and the cause of its demise.The data are consistent with break-up of a sub-kilometer nucleus into a debris cloud of mass ∼ 10 9 kg, peaking on UT 2019 May 24±12. This is ∼56 days before perihelion and at a heliocentric distance of ∼1.9 AU. We consider potential mechanisms of disintegration. Tidal disruption is ruled-out, because the comet has not passed within the Roche sphere of any planet. Impact disruption is implausible, because the comet orbit is highly inclined (inclination 105.1 • ) and disruption occurred far above the ecliptic, where asteroids are rare. The back-pressure generated by sublimation (0.02 to 0.4 N m −2 ) is orders of magnitude smaller than the reported compressive strength (30 to 150 N m −2 ) of cometary material and, therefore, is of no importance. The depletion of volatiles by sublimation occurs too slowly to render the nucleus inactive on the timescale of infall. However, we find that the e-folding timescale for spin-up of the nucleus by the action of sublimation torques is shorter than the infall time, provided the nucleus radius is r n < 0.4 km. Thus, the disintegration of C/2019 J2 is tentatively interpreted as the rotational disruption of a sub-kilometer nucleus caused by outgassing torques.

Initial Characterization of Interstellar Comet 2I/2019 Q4 (Borisov)

“…Sekanina and Kracht 2018). The nucleus of C/2019 J2, like that of Q4, had a radius of only a few hundred meters and was probably rotationally disrupted by torques from anisotropic outgassing (Jewitt and Luu 2019). Continued observations are encouraged to determine whether Q4 might undergo the same fate and, if so, whether it might leave behind a low activity remnant resembling 'Oumuamua.…”

“…Jewitt and Luu 2019), a distance essentially equal to the q = 2.0 AU perihelion distance of Q4. Disintegration is a common yet poorly quantified property of comets, especially those with small nuclei and perihelia (c.f Sekanina and Kracht 2018)…”

'Oumuamua as a Cometary Fractal Aggregate: the "Dust Bunny" Model

“…But this region is most likely not populated by dust particles alone. Comets are prone to fragmentation, particularly long-period comets (e.g., comet Hyakutake (Weaver et al (2001)), comet C/2019 J2 (Jewitt & Luu (2019b)), so we suspect that the inner coma must also contain many small, meter-to 10msize, fragments that often go undetected. For exam-ple, the numerous meter-size boulders strewn on the surface of comet Churyumov-Gerasimenko (Cambianica et al (2019)) may represent those fragments that failed to reach escape velocity.…”

“…Widely expected to be a comet, 'Oumuamua showed no sign of cometary activity (Jewitt et al (2017); Meech et al (2017)), but its orbit nevertheless exhibited nongravitational acceleration (Micheli et al (2018)). In contrast, 2I/Borisov is most definitely a comet, with cometary emission (Opitom et al (2019)), and optical colors similar to those of solar system comets (Jewitt & Luu (2019a); Fitzsimmons et al (2019); Guzik et al (2020)). The stark difference between the two interstellar bodies suggests that whereas Borisov is probably a comet formed in a planetary disk, 'Oumuamua's origin lies elsewhere.…”

Rotational Disruption of Nonspherical Cometary Dust Particles by Radiative Torques

“…Rotational disruption of bodies in different size regimes has been vigorously studied recently. For cometary objects, a particularly recent and interesting object was identified by Jewitt & Luu (2019) to be tentatively the victim of torques due to outgassing instead of tidal disruption. Similar rotational disruption mechanism for small dust grains due to radiative torques (Lazarian & Hoang 2007), or RATs, was recently proposed by Hoang et al (2019), provided large enough radiation intensities.…”