Planetary and Space Science 126 (2016) 8–23 Contents lists available at ScienceDirect Planetary and Space Science journal homepage: www.elsevier.com/locate/pss Comet C/2011 J2 (LINEAR) nucleus splitting: Dynamical and structural analysis Federico Manzini a,b,n, Virginio Oldani a,b, Masatoshi Hirabayashi c, Raoul Behrend d, Roberto Crippa a,b, Paolo Ochner e, José Pablo Navarro Pina f, Roberto Haver g, Alexander Baransky h, Eric Bryssinck i, Andras Dan a,b, Josè De Queiroz j, Eric Frappa k, Maylis Lavayssiere l a Stazione Astronomica – Stazione Astronomica di Sozzago, 28060 Sozzago, Italy b FOAM13, Osservatorio di Tradate, Tradate, Italy c Earth, Atmospheric and Planetary Science, Purdue University, West Lafayette, IN 47907-2051, USA d Geneva Observatory, Geneva, Switzerland e INAF Astronomical Observatory of Padova, Italy f Asociacion Astronomica de Mula, Murcia, Spain g Osservatorio di Frasso Sabino, Italy h Astronomical Observatory of Kyiv University, Ukraine i BRIXIIS Observatory, Kruibeke, Belgium j Sternwarte Mirasteilas, Falera, Switzerland k Saint-Etienne Planetarium, France l Observatoire de Dax, France article info abstract Article history: After the discovery of the breakup event of comet C/2011 J2 in August 2014, we followed the primary Received 7 February 2016 body and the main fragment B for about 120 days in the context of a wide international collaboration. Received in revised form From the analysis of all published magnitude estimates we calculated the comet's absolute magni- 24 March 2016 tude H¼10.4, and its photometric index n¼1.7. We also calculated a water production of only 110 kg/s at Accepted 18 April 2016 the perihelion. These values are typical of a low-activity, long-period or new comet. Available online 20 April 2016 Analysis of the motion of fragment B over the observation period showed that the first breakout event Keywords: likely occurred between 12 July and 30 July 2014. Nucleus B remained persistently visible throughout the Comets 4-month observation period. Comet C/2011 J2 (LINEAR) The projected separation velocity of nucleus B from the parent body was 4.22 m/s at the time of the Spin axis breakup and 12.7 m/s at the end of the observation period, suggesting that nucleus B was subjected to a Rotation ¼ : ∙ À 7 = 2 Break-up constant deceleration a 6 87 10 m s . The spin period of the main nucleus was estimated as 4.56 h70.05 h by photometric analysis. The structural analysis of the comet showed a cohesive strength of the nucleus greater than 0.9 kPa; assuming a bulk density of 500 kg/m3, with a rotation period of 4.56 h the cometary nucleus might have failed structurally, especially if the body was elongated. These results suggest that the nucleus of comet C/2011 J2 has an elongated shape, with a ratio of the semi-minor axis to the semi-major axis βo0:675; the semi-major axis of the pristine nucleus could be larger than 8 km. From this study, we propose that rotational disruption, possibly combined with sublimation pressure, was a reasonable explanation for the breakup event in comet C/2011 J2. & 2016 Elsevier Ltd. All rights reserved. 1. Introduction Progressive fragmentation is one of the main events leading to n Corresponding author at: Stazione Astronomica, Cascina Guascona, 28060 complete disintegration of cometary nuclei and to their extinction Sozzago, Novara, Italy. Tel.: þ39 03408077664. (Sekanina, 1982, 2005). E-mail address: [email protected] (F. Manzini). http://dx.doi.org/10.1016/j.pss.2016.04.004 0032-0633/& 2016 Elsevier Ltd. All rights reserved. F. Manzini et al. / Planetary and Space Science 126 (2016) 8–23 9 In the case of comets that closely approach the Sun, fragmen- Given the scarcity of data in the literature on the fragmentation tation is often preceded by significant nucleus erosion, and may be of distant comets, we investigated the multiple fragmentation of associated with activity outbursts, with appearance of inner coma this comet and the evolution of the companion nuclei over the features (Sekanina et al., 2002). However, although some objects first months following the first breakup event, with the aim of such as 133P/Elst–Pizarro (Hsieh et al., 2010) may show similar better understanding the possible causes that could have led to the activities, this is not usually the case for more distant comets that detachment of the fragments and to identify the physical para- are considered to be less influenced by solar radiation. Evidence of meters typical of this cometary nucleus. nucleus splitting in such cases is usually provided through the detection of one or more secondary components (a fragment or companion) arising from the same parent body and usually mov- 2. Comet C/2011 J2 (LINEAR): discovery and evolution of its ing in close orbits. fragmentation Several fragmentation mechanisms have been proposed to explain splitting of cometary nuclei: tidal disruption, rotational 2.1. Description of discovery of the comet forces, thermal stress, internal gas pressure and impacts by other solar system bodies (Davidsson, 1999, 2001; Altenhoff et al., 2009; Comet C/2011 J2 was discovered on 4 May 2011 by M. Blythe, G. Boehnhardt, 2004). Davidsson (1999, 2001) established simple, Spitz, R. Brungard, J. Paige, P. Festler, T. McVey, and A. Valdivia with useful criteria for disruption of rotating bodies that plastically the LINEAR 1-m f/2.15 reflector (Williams, 2011). It brightened at deform and that are affected by tidal forces from larger objects, an apparent magnitude of 19.7 at the time of discovery. considering them to be either spheres or biaxial ellipsoids. This comet was successively found on earlier images taken on However, while tidal disruption has been generally accepted as 10 and 25 March 2011 with the Catalina Sky Survey 0.68-m the most likely mechanism for the splitting of comet P/Shoe- Schmidt camera by A.D. Grauer et al. (Williams, 2011). maker–Levy 9 (Weaver et al., 1997) and 16P/Brooks 2 (Sekanina The orbital elements of this comet (http://ssd.jpl.nasa.gov/hor and Yeomans, 1985), none of the other scenarios were ideally izons.cgi) give an eccentricity of 1.00051, a perihelion transit on 25 detected. Although for comet 73P/SW3 disruption of the parent December 2013 (JD 2456651.802176393) and a perihelion distance body due to a large centrifugal force was proposed following the q¼3.44 AU from the Sun. finding of a fast rotation of the nucleus, it cannot be considered as A widely accepted definition of “dynamically new” comets a proof of this scenario; in fact, the perihelion distance of the (Oort and Schmidt, 1951; Kresak, 1977; Marsden and Williams, À À comet at the time of the splitting was less than 1 AU, and the 1997; Oort, 1990) states that their 1/ao1 Â 10 4 AU 1, which is nucleus was already showing highly active (Sekanina, 2005; Dra- equivalent to a410,000 AU. In the case of comet C/2011 J2, the hus et al., 2010). orbital parameters provide a value for a of 6800 AU; thus, it can The difficulty in identifying the exact mechanism of the split- be considered a long-period comet and close to those defined as ting may come from the fact that the most important parameters dynamically new. of cometary nuclei (such as internal structure, size and rotation) There are no reports that provide particular phenomena related used in these models were not well known, and the available to this comet after its discovery. observations did not allow to ascertain the actual sequence of events, as most of the secondary components of a split comet 2.2. Description of discovery of fragmentation vanish with time, or become too faint to be detected even with the largest telescopes. On 27 August 2014 a 18th magnitude fragment was detected by In this paper, we study comet C/2011 J2 (LINEAR), which has F. Manzini, V. Oldani, A. Dan, R. Crippa and R. Behrend with the recently incurred multiple splitting events at a considerable dis- 0.4 m reflector at the SAS Observatory 0.8 arcsec east and tance from the Sun (r44 AU). This event appeared very interest- 7.5 arcsec north of the main, brighter nuclear condensation (Green, ing, as at this distance no significant heating from solar radiation is 2014)(Fig. 1). expected, such as to trigger phenomena that could lead to a Astrometry of the main nucleus and of the secondary compo- fragmentation of the nucleus. nent was reported in preliminary studies (Green, 2014; Williams, Fig. 1. Discovery of the splitting of comet C/2011 J2. Image of the discovery of nucleus B (27 August 2014), resulting from a total exposure time of 40 minutes as sum of single frames. The coma of the main nucleus appears evenly diffuse, almost circular, with a diameter of 50 arcsec. Fragment B was at a 7.6 arcsec distance from the primary nucleus, corresponding to about 19,700 km. A faint tail develops at PA 20°. Left: original image. Right: same image in false colors to enhance the tail and the coma. North is up, East left; a 30 arcsec-wide line is shown for reference. Stars are trailed due to the telescope tracking the comet. Images taken with the 0.4-m Cassegrain telescope at the Stazione Astronomica di Sozzago (Italy). 10 F. Manzini et al. / Planetary and Space Science 126 (2016) 8–23 2014c, 2014d, 2014e; Spahr and Williams, 2014). The secondary additional images of the comet, taken prior to the discovery of the component was named C/2011 J2-B. splitting and in which the fragment was already detectable, were At the time of discovery of the fragmentation, the comet was at successively retrieved.