C/2017 E4 (Lovejoy) – time of death

In a previous post I note a high risk of disintegration of this comet, in fact, when the post was made, the nucleus disintegration was already done. The images of Jean-Fran├žois Soulier show a great loss of gas coma between 8. and 9. April. It seems to be the time, when solid nucleus of this comet cease to exist.

Date of disintegration is independently confirmed by Terry Lovejoy with astrometric measures, as after 8. April, the residuals starting to systematically grows.

Residuals of comet C/2017 E4 plotted by Terry Lovejoy

So what exactly happened with this comet? I already suggest that nucleus size of this comet must be very small with diameter between 400 – 600 meters. Also the light curve shows a extremely chaotic behaviour as comet shows strong brightening and two small outbursts. There can be hardly established any stable parameters for this comet brightening. This behaviour is very common for small fragments of larger comets, for example, see comparison with comet C/1988 A1 and its smaller fragment designated as C/1996 Q1 here. We can see, that behaviour of comet Lovejoy is extremely similar to that of comet Tabur (C/1996 Q1).

So what happened to the nucleus? We already know that small fragments are very fragile, for example fragments of comet 73P/Schwassmann-Wachmann never exist longer than 1-2 returns. Also the fragments are very small. The size and fragility causing the photometric curve instability as the brightness more depends on a very random events (when a part of nucleus is detached) than distance from Sun. We can imagine that volatiles and ices are something as a “glue” for large boulders, but small sized nucleus loosing them relatively fast. In time when nucleus loose all the glue, there is not much more gases to refill gaseous coma and the brightness will start to decline. In same time, the absence of glue cause boulders to separate into inactive swarm of debris. Many of them collapse into thin dust, creating a large cloud dust. One emission of different sized dust grain in same time is knows as a synchronic feature – a line of dust that is aligned in one direction from original nucleus, where most heavy dust remains closely behind, while most thin dust moving far away on the line. Synchronic feature can be observerd a long time after nucleus cease to exist.

Brightness evolution from COBS data plotting magnitude data corrected for geocentric distance (real activity level) against log of heliocentric distance. It is apparent that after initial fast brightening, the comet calmed down and then a nucleus disruption occurred around distance 0.59 AU from Sun

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