Comet C/2017 E4 (Lovejoy) is definitively a returning, long-periodic comet, actual MPC orbit points to original orbit with period 11603 years and semimajor axis 512 AU. The photometric behavior also points to a returning comet. When it was discovered it shows a very low activity and absolute magnitude below the Bortle survival limit. However it seems that comet was brightening fast and the activity level increased very fast. There was 2 very small outbursts recorded by observers and after second one, comet stopped fast brightening phase and entered calm phase instead.
However quick analysis of photometric parameters shows that even with smaller rate, the activity of comet is still increasing as comet approaching closer to Sun with pretty normal rate for most of comets. Therefore comet looks healthy now and also actual photometric parameters placing comet above Bortle survival limit:
H0 =12.69 mag, n =12.61 [ -40 ,-20.5 ]
H0 =9.04 mag, n =3.34 [ -20.5 ,-13 ]
Actual astrometry of comet shows good result for both orbits with non-gravitational parameters and without. Orbit with them giving A1 = 2.32E-07, A2 = -1.82E-07. For actual activity level of comet, this corresponding to nucleus with maximal mass 1E+07 to 5E+07 tons. With average comet nucleus density this means spherical nucleus with diameter between 400 – 600 meters.
Small activity level, non calm photometric behavior and possible non gravitational forces definitively points to a small comet with sub-km sized nucleus. Because it is returning comet, it doesn’t necessarily means, the comet can totally disintegrate, even the risk is very high. If it will disintegrate, there is a high possibility, this comet can be a smaller fragment of different comet, which may return in a different time.