Most inner main-belt asteroids are primitive rock and metal bodies in orbit about the Sun between Mars and Jupiter. Disruption, through high-velocity collisions or rotational spin-up, is believed to be the primary mechanism for the production and destruction of small asteroids and a contributor to dust in the Sun's zodiacal cloud, while analogous collisions around other stars feed dust to their debris disks. Unfortunately, direct evidence about the mechanism or rate of disruption is lacking, owing to the rarity of the events. Here we report observations of P/2010 A2, a previously unknown inner-belt asteroid with a peculiar, comet-like morphology. The data reveal a nucleus of diameter approximately 120 metres with an associated tail of millimetre-sized dust particles. We conclude that it is most probably the remnant of a recent asteroidal disruption in February/March 2009, evolving slowly under the action of solar radiation pressure, in agreement with independent work.

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Interstellar comets penetrating through the Solar System had been anticipated for decades 1,2 . The discovery of asteroidal-looking 'Oumuamua 3,4 was thus a huge surprise and a puzzle. Furthermore, the physical properties of the 'first scout' turned out to be impossible to reconcile with Solar System objects 4-6 , challenging our view of interstellar minor bodies 7,8 . Here, we report the identification and early characterization of a new interstellar object, which has an evidently cometary appearance. The body was discovered by Gennady Borisov on 30 August 2019 UT and subsequently identified as hyperbolic by our data mining code in publicly available astrometric data. The initial orbital solution implies a very high hyperbolic excess speed of ~32 km s −1 , consistent with 'Oumuamua 9 and theoretical predictions 2,7 . Images taken on 10 and 13 September 2019 UT with the William Herschel Telescope and Gemini North Telescope show an extended coma and a faint, broad tail. We measure a slightly reddish colour with a g′-r′ colour index of 0.66 ± 0.01 mag, compatible with Solar System comets. The observed morphology is also unremarkable and best explained by dust with a power-law sizedistribution index of -3.7 ± 1.8 and a low ejection speed (44 ± 14 m s −1 for β = 1 particles, where β is the ratio of the solar gravitational attraction to the solar radiation pressure).The nucleus is probably ~1 km in radius, again a common value among Solar System comets, and has a negligible chance of experiencing rotational disruption. Based on these early characteristics, and putting its hyperbolic orbit aside, 2I/Borisov appears indistinguishable from the native Solar System comets.

We show that 'Oumuamua's excited spin could be in a high energy LAM state, which implies that its shape could be far from the highly elongated shape found in previous studies. CLEAN and ANOVA algorithms are used to analyze 'Oumuamua's lightcurve using 818 observations over 29.3 days. Two fundamental periodicities are found at frequencies (2.77±0.11) and (6.42±0.18) cycles/day, corresponding to (8.67±0.34) h and (3.74±0.11) h, respectively. The phased data show that the lightcurve does not repeat in a simple manner, but approximately shows a double minimum at 2.77 cycles/day and a single minimum at 6.42 cycles/day. This is characteristic of an excited spin state. 'Oumuamua could be spinning in either the long (LAM) or short (SAM) axis mode. For both, the long axis precesses around the total angular momentum vector with an average period of (8.67±0.34) h. For the three LAMs we have found, the possible rotation periods around the long axis are 6.58, 13.15, or 54.48 h, with 54.48 h being the most likely. 'Oumuamua may also be nutating with respective periods of half of these values. We have also found two possible SAM states where 'Oumuamua oscillates around the long axis with possible periods at 13.15 and 54.48 h, the latter as the most likely. In this case any nutation will occur with the same periods. Determination of the spin state, the amplitude of the nutation, the direction of the TAMV, and the average total spin period may be possible with a direct model fit to the lightcurve. We find that 'Oumuamua is "cigar-shaped", if close to its lowest rotational energy, and an extremely oblate spheroid if close to its highest energy state for its total angular momentum.

One of the least understood properties of comets is the compositional structure of their nuclei, which can either be homogeneous or heterogeneous. The nucleus structure can be conveniently studied at millimeter wavelengths, using velocity-resolved spectral time series of the emission lines, obtained simultaneously for multiple molecules as the body rotates. Using this technique, we investigated the sources of CH 3 OH and HCN in comet 103P/Hartley 2, the target of NASA's EPOXI mission, which had an exceptionally favorable apparition in late 2010. Our monitoring with the IRAM 30 m telescope shows short-term variability of the spectral lines caused by nucleus rotation. The varying production rates generate changes in brightness by a factor of 4 for HCN and by a factor of 2 for CH 3 OH, and they are remarkably well correlated in time. With the addition of the velocity information from the line profiles, we identify the main sources of outgassing: two jets, oppositely directed in a radial sense, and icy grains, injected into the coma primarily through one of the jets. The mixing ratio of CH 3 OH and HCN is dramatically different in the two jets, which evidently shows large-scale chemical heterogeneity of the nucleus. We propose a network of identities linking the two jets with * Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).Note. -∆t is the time coverage of the measurement; other symbols and units are the same as defined and used throughout the paper.The errors on TmBdv and on the resulting Q include the uncertainty of the telescope pointing, and therefore are partly correlated in the simultaneous measurements of CH3OH and HCN, unlike the errors on subsequent data points. The errors on v0 and Trot are free of the pointing contribution and therefore are fully independent, both in time and between the molecules.