Main belt asteroid (6478) Gault has been dynamically linked with two overlapping asteroid families: Phocaea, dominated by S-type asteroids, and Tamara, dominated by low-albedo C-types. This object has recently become an interesting case for study, after images obtained in late 2018 revealed that it was active and displaying a comet-like tail. Previous authors have proposed that the most likely scenarios to explain the observed activity on Gault were rotational excitation or merger of near-contact binaries. Here we use new photometric and spectroscopic data of Gault to determine its physical and compositional properties. Lightcurves derived from the photometric data showed little variation over three nights of observations, which prevented us from determining the rotation period of the asteroid. Using WISE observations of Gault and the near-Earth Asteroid Thermal Model (NEATM) we determined that this asteroid has a diameter $<$6 km. NIR spectroscopic data obtained with the Infrared Telescope Facility (IRTF) showed a spectrum similar to that of S-complex asteroids, and a surface composition consistent with H chondrite meteorites. These results favor a compositional affinity between Gault and asteroid (25) Phocaea, and rules out a compositional link with the Tamara family. From the spectroscopic data we found no evidence of fresh material that could have been exposed during the outburst episodes.
We present the results of short observational program for asteroid 6478 Gault with using of V and R Johnson filters realized at the Kyiv Comet Station during January-April 2019. Color indices and distribution of brightness in the comet-like tail were calculated. We made a comparative analysis of circumstances of the asteroid 6478 Gault activity with others morphologically similar active Main Belt asteroids.
We present near-infrared spectroscopy of the sporadically active asteroid (6478) Gault collected on the 3 m NASA/Infrared Telescope Facility observatory in late 2019 March/early April. Long-exposure imaging with the 0.5 m NEEMO T05 telescope and previously published data simultaneously monitored the asteroid activity, providing context for our measurements. We confirm Gault is a silicate-rich (Q- or S-type) object likely linked to the (25) Phocaea collisional family. The asteroid exhibits substantial spectral variability over the 0.75-2.45 $μ$m wavelength range, from unusual blue (s'=-13.5+/-1…
We present archival observations demonstrating that main belt asteroid (6478) Gault has an extensive history of comet-like activity. Outbursts have taken place during multiple epochs since 2013 and at distances extending as far as 2.68 au, nearly aphelion. (6478) Gault is a member of the predominately S-type (i.e., volatile-poor) Phocaea family; no other main belt object of this type has ever shown more than a single activity outburst. Furthermore, our data suggest that this is the longest duration of activity caused by a body spinning near the rotational breakup barrier. If activity is indeed…
Active asteroid (6478) Gault sheds mass independent of location along its orbit. Rotational instability is considered to induce the observed activities. If this is the case, because Gaults breakup event has not been detected, surface failure is likely, implying its surface materials are constantly ejected while its major body remains intact. Given this scenario, we first constrain Gaults bulk cohesive strength. We then characterize heliocentric trajectories of ejected particles over thousands of years. The results show that Gault may be sensitive to structural failure at the current spin perio…
Main-belt asteroid (6478) Gault was observed to show cometary features in early 2019. To investigate the cause, we conducted {\it BVR} observations at Xingming Observatory, China, from 2019 January to April. The two tails were formed around 2018 October 26--November 08, and 2018 December 29--2019 January 08, respectively, and consisted of dust grains of $\gtrsim$20 $μ$m to 3 mm in radius ejected at a speed of $0.15 \pm 0.05$ m s$^{-1}$ and following a broken power-law size distribution bending at grain radius $\sim$70 $μ$m (bulk density 1 g cm$^{-3}$ assumed). The total mass of dust within a $…
We present imaging and spectroscopic observations of 6478 Gault, a 6 km diameter inner main-belt asteroid currently exhibiting strong, comet-like characteristics. Three distinct tails indicate that ultra-slow dust (ejection speed 0.15+/-0.05 m/s) was emitted from Gault in separate episodes beginning UT 2018 October 28+/-5 (Tail A), UT 2018 December 31+/-5 (Tail B), and UT 2019 February 10+/-7, with durations of 10 to 20 days. With a mean particle radius 100 micron, the estimated masses of the tails are M_A = 2e7 kg, M_B = 3e6 kg and M_C = 3e5 kg, respectively, and the mass loss rates from the …
The $\sim$4 km diameter main belt asteroid 6478 Gault has ejected dust intermittently since at least 2013. The character of the emission, including its episodic nature and the low speed of the ejected particles ($V \sim $ 0.15 m s$^{-1}$), is most consistent with mass loss from a body rotating near rotational breakup. Owing to dust contamination of the nucleus signal, this conclusion has not yet been confirmed. To test this idea, we have obtained new images of Gault in August 2020, in the absence of dust. Our photometry shows a lightcurve having a very small amplitude (maximum $\sim 0.05$ mag)…
Asteroid (6478) Gault was discovered to exhibit a comet-like tail in observations from December 2018, becoming a new member of the so-called active asteroid population in the main asteroid belt. The aims are to investigate the grain properties of the dust ejected from asteroid (6478) Gault and to give insight into the activity mechanism(s). We use a Monte Carlo dust tail brightness code to retrieve the dates of dust ejection, the physical properties of the grains, and the total dust mass losses during each event. The code takes into account the brightness contribution of the asteroid itself. T…
We report dense lightcurve photometry, $BVR_{c}$ colors and phase - mag curve of (6478) Gault, an active asteroid with sporadic comet-like ejection of dust. We collected optical observations along the 2020 Jul-Nov months during which the asteroid appear always star-like, without any form of perceptible activity. We found complex lightcurves, with low amplitude around opposition and a bit higher amplitude far opposition, with a mean best rotation period of $2.46_{\pm 0.02}$ h. Shape changes were observed in the phased lightcurves after opposition, a probable indication of concavities and surfac…
We report on accurate $BVR_{c}$ observations of (6478) Gault, a 5-6 km diameter inner main-belt asteroid in the Phocaea family, notable for its sporadic, comet-like ejection of dust. This curious behavior has been mainly interpreted as reconfigurations after YORP spin-up, although merging of a contact binary system cannot be fully excluded. We collected optical observations along the 2019 March-April period, at orbital phase angles between $12^{\circ}-21^{\circ}$, to search for direct evidence of asteroid quick spinning rotation. A prevailing period value of $3.34 \pm 0.02$ hours is supported …
In December 2018, the main-belt asteroid (6478)~Gault was reported to display activity. Gault is an asteroid belonging to the Phocaea dynamical family and was not previously known to be active, nor was any other member of the Phocaea family. In this work we present the results of photometric and spectroscopic observations that commenced soon after the discovery of activity. We obtained observations over two apparitions to monitor its activity, rotation period, composition, and possible non-gravitational orbital evolution. We find that Gault has a rotation period of $P = 2.4929 \pm 0.0003$ hour…
We observed Episodically Active Asteroid (6478) Gault in 2020 with multiple telescopes in Asia and North America and have found that it is no longer active after its recent outbursts at the end of 2018 and start of 2019. The inactivity during this apparation allowed us to measure the absolute magnitude of Gault of H_r = 14.63 +/- 0.02, G_r = 0.21 +/- 0.02 from our secular phasecurve observations. In addition, we were able to constrain Gault's rotation period using time-series photometric lightcurves taken over 17 hours on multiple days in 2020 August, September and October. The photometric lig…
Main-belt asteroid (6478) Gault unexpectedly sprouted two tails in late 2018 and early 2019, identifying it as a new active asteroid. Here we present observations obtained by the 1.2-m Zwicky Transient Facility survey telescope that provide detailed time-series coverage of the onset and evolution of Gault's activity. Gault exhibited two brightening events, with the first one starting on 2018 Oct. 18$\pm5$ days and a second one starting on 2018 Dec. 24$\pm1$ days. The amounts of mass released are $2\times10^7$ kg and $1\times10^6$ kg, respectively. Based on photometric measurements, each event …
We present the results of photometric observations of active asteroid (6478) Gault performed at heliocentric distances from 2.46 to 2.30 au and geocentric distances from 1.79 to 1.42 au between January 15 and March 28, 2019. Observations were carried out at the 2.5-m telescope of SAI MSU (CMO) on January 15, 2019 and at the 1.3-m and 0.61-m telescopes (SPb) on February 6 and March 28, 2019, respectively. The direct images of the asteroid were obtained with the broad-band B, V and R filters. Comet-like structures were detected at all observation dates. Colour maps were built and colour variatio…
On 2019 January 5 a streamer associated with the 4--10 km main-belt asteroid (6478)~Gault was detected by the ATLAS sky survey, a rare discovery of activity around a main-belt asteroid. Archival data from ATLAS and Pan-STARRS1 show the trail in early December 2018, but not between 2010 and January 2018. The feature has significantly changed over one month, perfectly matching predictions of pure dust dynamical evolution and changes in observing geometry for a short release of dust around 2018 October 28. Follow-up observations with HST show a second narrow trail corresponding to a brief release…
The study of active asteroids has attracted a great deal of interest in recent years since the recognition of main-belt comets (which orbit in the main asteroid belt, but exhibit comet-like activity due to the sublimation of volatile ices) as a new class of comets in 2006, and the discovery of the first disrupted asteroids (which, unlike MBCs, exhibit comet-like activity due to a physical disruption such as an impact or rotational destabilization, not sublimation) in 2010. In this paper, I will briefly discuss key areas of interest in the study of active asteroids.
In this note we have shown that a newly discovered comet P/2017 S5 (ATLAS), that moves around the Sun in an asteroid-like orbit, is a member of the Theobalda asteroid family.
Some asteroids eject dust, producing transient, comet-like comae and tails; these are the active asteroids. The causes of activity in this newly-identified population are many and varied. They include impact ejection and disruption, rotational instabilities, electrostatic repulsion, radiation pressure sweeping, dehydration stresses and thermal fracture, in addition to the sublimation of asteroidal ice. These processes were either unsuspected or thought to lie beyond the realm of observation before the discovery of asteroid activity. Scientific interest in the active asteroids lies in their pro…
We report on the results of a systematic search for associated asteroid families for all active asteroids known to date. We find that 10 out of 12 main-belt comets (MBCs) and 5 out of 7 disrupted asteroids are linked with known or candidate families, rates that have ~0.1% and ~6% probabilities, respectively, of occurring by chance, given an overall family association rate of 37% for asteroids in the inner solar system. We find previously unidentified family associations between 238P/Read and the candidate Gorchakov family, 311P/PANSTARRS and the candidate Behrens family, 324P/La Sagra and the …
The dust emission from active asteroids is likely driven by collisions, fast rotation, sublimation of embedded ice, and combinations of these. Characterising these processes leads to a better understanding of their respective influence on the evolution of the asteroid population. We study the role of fast rotation in the active asteroid 358P (P 2012/T1). We obtained two nights of deep imaging of 358P with SOAR/Goodman and VLT/FORS2. We derived the rotational light curve from time-resolved photometry and searched for large fragments and debris > 8 mm in a stacked, ultra-deep image. The nucleus …
We announce the discovery of activity, in the form of a distinct cometary tail, emerging from main-belt asteroid 2015 VA108. Activity was first identified by volunteers of the Citizen Science project Active Asteroids (a NASA Partner). We uncovered one additional image from the same observing run which also unambiguously shows 2015 VA108 with a tail oriented between the anti-solar and anti-motion vectors that are often correlated with activity orientation on sky. Both publicly available archival images were originally acquired UT 2015 October 11 with the Dark Energy Camera (DECam) on the Blanco…
The 1950 discovery of activity emanating from asteroid (4015) Wilson-Harrington prompted astronomers to realize comet-like activity is not limited to comets. Since then < 30 active asteroids have been discovered, yet they hold clues about fundamental physical and chemical processes in the solar system. Around half of the activity is attributed to sublimation, highlighting asteroids as a "volatile reservoir" - a dynamical group of minor planets that harbor volatiles. Centaurs, found between the orbits of Jupiter and Neptune, were first recognized in 1977 and represent another reservoir. Active …
We present archival observations of Main-belt asteroid (248370) 2005 QN173 (also designated 433P) that demonstrate this recently discovered active asteroid (a body with a dynamically asteroidal orbit displaying a tail or coma) has had at least one additional apparition of activity near perihelion during a prior orbit. We discovered evidence of this second activity epoch in an image captured 2016 July 22 with the Dark Energy Camera on the 4 meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile. As of this writing, (248370) 2005 QN173 is just the 8th active asteroid demo…
Small bodies in the solar system are conventionally classified into asteroids and comets. However, it is recently found that a small number of objects can exhibit properties of both asteroids and comets. Some are more consistent with asteroids despite episodic ejections and are labeled as "active asteroids", while some might be aging comets with depleting volatiles. Ejecta produced by active asteroids and/or dormant comets are potentially detectable as meteor showers at the Earth if they are in Earth-crossing orbits, allowing us to retrieve information about the historic activities of these ob…
Asteroid (3200) Phaethon is an active near-Earth asteroid and the parent body of the Geminid Meteor Shower. Because of its small perihelion distance, Phaethon's surface reaches temperatures sufficient to destabilize hydrated materials. We conducted rotationally resolved spectroscopic observations of this asteroid, mostly covering the northern hemisphere and the equatorial region, beyond 2.5-micron to search for evidence of hydration on its surface. Here we show that the observed part of Phaethon does not exhibit the 3-micron hydrated mineral absorption (within 2-sigma). These observations sugg…
Thermal infrared emission and thermophysical modeling techniques are powerful tools in deciphering the surface properties of asteroids. The near-Earth asteroid (3200) Phaethon is an active asteroid with a very small perihelion distance and is likely the source of the Geminid meteor shower. We estimate and interpret the thermal inertia of this extraordinary asteroid using observations that span ten distinct sightings. The variation in thermal inertia over these sightings is inconsistent with the expected temperature-dependent thermal inertia theorized from radiative heat transfer within the reg…
We present a dynamical analysis of the fragmented active asteroid 331P/Gibbs. Using archival images taken by the Hubble Space Telescope from 2015 to 2018, we measured the astrometry of the primary and the three brightest (presumably the largest) components. Conventional orbit determination revealed a high-degree of orbital similarity between the components. We then applied a fragmentation model to fit the astrometry, obtaining key parameters including the fragmentation epochs and separation velocities. Our best-fit models show that Fragment B separated from the primary body at a speed of $\sim…
We revisited a mass ejection phenomenon that occurred in asteroid P/2010 A2 in terms of the dynamical properties of the dust particles and large fragments. We constructed a model assuming anisotropic ejection within a solid cone-shaped jet and succeeded in reproducing the time-variant features in archival observational images over ~3 years from 2010 January to 2012 October. When we assumed that the dust particles and fragments were ejected in the same direction from a point where no object had been detected in any observations, the anisotropic model can explain all of the observations includin…
The recently discovered near-Earth asteroid 2021 PH27 has the shortest orbital period of all known asteroids. It cannot be excluded that 2021 PH27 is also an active asteroid, as (3200) Phaethon. We intend to estimate the consequences of this hypothesis, although testing is difficult with ground-based observations during perihelion passages, due to low solar elongation. Assuming a surface activity similar to that of Phaethon, an increase in brightness of about 1.4 mag can be estimated. Since it is an asteroid with a MOID of $0.014660 \pm 0.000034$ AU with Venus, 2021 PH27 could be the equivalen…
For the first time, spectral signs of subtle coma activity were observed simultaneously on four main-belt primitive asteroids (145) Adeona, (704) Interamnia, (779) Nina, and (1474) Beira around their perihelion distances in September 2012, which were interpreted as manifestations of the sublimation of H2O ice in/under the surface matter (Busarev et al., 2015a, 2015b). We confirm the phenomenon for Nina when it approached perihelion in September 2016. At the same time, based on results of spectral observations of near-Earth asteroid (162173) Ryugu (Vilas, 2008) being a target of Japan's Hayabus…
Some asteroids eject dust, unexpectedly producing transient, comet-like comae and tails. First ascribed to the sublimation of near-surface water ice, mass losing asteroids (also called "main-belt comets") can in fact be driven by a surprising diversity of mechanisms. In this paper, we consider eleven dynamical asteroids losing mass, in nine of which the ejected material is spatially resolved. We address mechanisms for producing mass loss including rotational instability, impact ejection, electrostatic repulsion, radiation pressure sweeping, dehydration stresses and thermal fracture, in additio…
We present the physical and dynamical properties of the recently discovered active asteroid (248370) 2005 QN173 (aka 433P). From our observations, we derived two possible rotation period solutions of 2.7 and 4.1 hours. The corresponding light curve amplitudes computed after correcting for the effect of coma are 0.28 and 0.58 mag, respectively. Both period solutions are shorter than the critical rotation limit computed for a strengthless triaxial ellipsoid, suggesting that rotation mass shedding should at least partly be responsible for the observed activity. We confirm that the activity level …
Comets can exhibit non-gravitational accelerations caused by recoil forces due to anisotropic mass loss. So might active asteroids. We present an astrometric investigation of 18 active asteroids in search of non-gravitational acceleration. Statistically significant (signal-to-noise ratio (SNR) $> 3$) detections are obtained in three objects: 313P/Gibbs, 324P/La Sagra and (3200) Phaethon. The strongest and most convincing detection ($>$7$σ$ in each of three orthogonal components of the acceleration), is for the $\sim$1 km diameter nucleus of 324P/La Sagra. A 4.5$σ$ detection of the transverse c…
We present Hubble Space Telescope observations of active asteroid P/2020 O1 taken to examine its development for a year after perihelion. We find that the mass loss peaks <~1 kg/s in 2020 August and then declines to nearly zero over four months. Long-duration mass loss (~180 days) is consistent with a sublimation origin, indicating that this object is likely an ice-bearing main-belt comet. Equilibrium sublimation of water ice from an area as small as 1580 m^2 can supply the observed mass loss. Time-series photometry shows tentative evidence for extremely rapid rotation (double-peaked period < …
We report on the catastrophic disintegration of P/2016 G1 (PANSTARRS), an active asteroid, in April 2016. Deep images over three months show that object is constituted by a central concentration of fragments surrounded by an elongated coma, and presents previously unreported sharp arc-like and a narrow linear features. The morphology and evolution of these characteristics independently point toward a brief event on 2016 March 6. The arc and the linear feature can be reproduced by large particles on a ring, moving at ~2.5 m/s. The expansion of the ring defines a cone with a ~40deg half-opening.…
The JAXA/ISAS spacecraft DESTINY$^+$ will be launched to the active asteroid (3200) Phaethon in 2022. Among the proposed core payload is the DESTINY+ Dust Analyzer (DDA) which is an upgrade of the Cosmic Dust Analyzer flown on the Cassini spacecraft to Saturn (Srama et al. 2011). We use two up-to-date computer models, the ESA Interplanetary Meteoroid Engineering Model (IMEM, Dikarev et al. 2005), and the interstellar dust module of the Interplanetary Meteoroid environment for EXploration model (IMEX; Sterken2013 et al., Strub et al. 2019) to study the detection conditions and fluences of inter…
It is well known that some Main Belt asteroids show comet-like features. A representative example is the first known Main Belt comet 133P/(7968) Elst-Pizarro. If the mechanisms causing this activity are too weak to develop visually evident comae or tails, the objects stay unnoticed. We are presenting a novel way to search for active asteroids, based on looking for objects with deviations from their expected brightnesses in a database. Just by using the MPCAT-OBS Observation Archive we have found five new candidate objects that possibly show a type of comet-like activity, and the already known …
While having a comet-like appearance, P/2012 F5 (Gibbs) has an orbit native to the Main Asteroid Belt, and physically is a km-sized asteroid which recently (mid 2011) experienced an impulsive mass ejection event. Here we report new observations of this object obtained with the Keck II telescope on UT 2014 August 26. The data show previously undetected 200-m scale fragments of the main nucleus, and reveal a rapid nucleus spin with a rotation period of 3.24 $\pm$ 0.01 hr. The existence of large fragments and the fast nucleus spin are both consistent with rotational instability and partial disrup…
We present initial observations of the newly-discovered active asteroid 313P/Gibbs (formerly P/2014 S4), taken to characterize its nucleus and comet-like activity. The central object has a radius $\sim$0.5 km (geometric albedo 0.05 assumed). We find no evidence for secondary nuclei and set (with qualifications) an upper limit to the radii of such objects near 25 m, assuming the same albedo. Both aperture photometry and a morphological analysis of the ejected dust show that mass-loss is continuous at rates $\sim$0.2 to 0.4 kg s$^{-1}$, inconsistent with an impact origin. Large dust particles, w…
We report on the characterisation of the dust activity and dynamical evolution of two faint active asteroids, P/2019 A4, and P/2021 A5, observed with the 10.4m GTC using both imaging and spectroscopy. Asteroid P/2019 A4 activity is found to be linked to an impulsive event occurring some $\pm$10 days around perihelion, probably due to a collision or a rotational disruption. Its orbit is stable over 100 Myr timescales. Dust tail models reveal a short-term burst producing (2.0$\pm$0.7)$\times$10$^6$ kg of dust for maximum particle radius rmax=1 cm. The spectrum of P/2019 A4 is featureless, and sl…
Some active asteroids have been proposed to be the result of impact events. Because active asteroids are generally discovered serendipitously only after their tail formation, the process of the impact ejecta evolving into a tail has never been directly observed. NASA's Double Asteroid Redirection Test (DART) mission, apart from having successfully changed the orbital period of Dimorphos, demonstrated the activation process of an asteroid from an impact under precisely known impact conditions. Here we report the observations of the DART impact ejecta with the Hubble Space Telescope (HST) from i…
Observations of active asteroid P/2017 S5 when near perihelion reveal the ejection of large (0.1 to 10 mm) particles at 0.2 to 2 m/s speeds, with estimated mass-loss rates of a few kg/s. The protracted nature of the mass loss (continuous over 150 days) is compatible with a sublimation origin, meaning that this object is likely an ice-bearing main-belt comet. Equilibrium sublimation of exposed water ice covering as little as 0.1 sq. km can match the data. Observations a year after perihelion show the object in an inactive state from which we deduce a nucleus effective radius 450(+100/-60) m (al…
Active asteroids show (typically transient) cometary activity, driven by a range of processes. A sub-set, sometimes called main-belt comets, may be driven by sublimation and so could be useful for tracing the present-day distribution of asteroid ice. Object P/2018 P3 has a Tisserand parameter 3.096 but a high eccentricity 0.415, placing it within the dynamical boundary between asteroids and comets. We aim to determine the cause of activity (sublimation or something else) and assess the dynamical stability of P3, in order to better constrain the intrinsic ice content in the main belt. We obtain…
We examine the motions of large fragments at the head of the dust tail of active asteroid P/2010 A2. In previous work we showed that these fragments were ejected from the primary nucleus in early 2009, either following a hypervelocity impact or by rotationally induced break-up. Here, we follow their positions through a series of Hubble Space Telescope images taken during the first half of 2010. The orbital evolution of each fragment allows us to constrain its velocity relative to the main nucleus after leaving its sphere of gravitational influence. We find that the fragments constituting a pro…
We present the discovery of activity emanating from main-belt asteroid 2015 FW412, a finding stemming from the Citizen Science project Active Asteroids, a NASA Partner program. We identified a pronounced tail originating from 2015 FW412 and oriented in the anti-motion direction in archival Blanco 4-m (Cerro Tololo Inter-American Observatory, Chile) Dark Energy Camera (DECam) images from UT 2015 April 13, 18, 19, 21 and 22. Activity occurred near perihelion, consistent with the main-belt comets (MBCs), an active asteroid subset known for sublimation-driven activity in the main asteroid belt; th…
We present the results of a search for the reactivation of active asteroid 176P/LINEAR during its 2011 perihelion passage using deep optical observations obtained before, during, and after that perihelion passage. Deep composite images of 176P constructed from data obtained between June 2011 and December 2011 show no visible signs of activity, while photometric measurements of the object during this period also show no significant brightness enhancements similar to that observed for 176P between November 2005 and December 2005 when it was previously observed to be active. An azimuthal search f…
We present a photometric and astrometric study of the split active asteroid P/2016 J1 (PANSTARRS). The two components (hereafter J1-A and J1-B) separated either $\sim$1500 days (2012 May to June) or 2300 days (2010 April) prior to the current epoch, with a separation speed $V_{\mathrm{sep}} = 0.70 \pm 0.02$ m s$^{-1}$ for the former scenario, or $0.83 \pm 0.06$ m s$^{-1}$ for the latter. Keck photometry reveals that the two fragments have similar, Sun-like colors which are comparable to the colors of primitive C- and G-type asteroids. With a nominal comet-like albedo, $p_{R} = 0.04$, the effec…
Previously unknown asteroid P/2010 A2 rose to prominence in 2010 by forming a transient, comet-like tail consisting of ejected dust. The observed dust production was interpreted as either the result of a hypervelocity impact with a smaller body or of a rotational disruption. We have re-observed this object, finding that large particles remain a full orbital period after the initial outburst. In the intervening years, particles smaller than ~3 mm in radius have been dispersed by radiation pressure, leaving only larger particles in the trail. Since the total mass is dominated by the largest part…
From 1996 to 2015 sixteen main belt asteroids were discovered exhibiting cometary activity (less than one per year), all of them during searches at the telescope. In this work we will explore another way to discover them. We reduced 192016 magnitude observations of 165 asteroids of the Themis family, using data from the astrometric-photometric database of the Minor Planet Center, MPCOBS, and measuring the absolute magnitudes from the phase plots. 25 objects of 165 (15.2%), exhibited bumps or enhancements in brightness that might indicate low level cometary activity. Since activity repeats at t…
We describe active asteroid 331P/Gibbs (2012 F5) using archival Hubble Space Telescope data taken between 2015 and 2018. 331P is an outer main-belt active asteroid with a long-lived debris trail that formed in 2011. Embedded in the debris trail we identify 19 fragments with radii between 0.04 and 0.11 km (albedo 0.05 assumed) containing about 1 percent of the mass of the primary nucleus. The largest shows a photometric range (1.5 magnitudes), a V-shaped minimum and a two-peaked lightcurve period near 9 hours, consistent with a symmetric contact binary (Drahus and Waniak 2016). Less convincing …
In this work we characterize the recently discovered active main belt object P/2012 F5 (Gibbs), which was discovered with a dust trail > 7' in length in the outer main belt, 7 months prior to aphelion. We use optical imaging obtained on UT 2012 March 27 to analyze the central condensation and the long trail. We find nuclear B-band and R-band apparent magnitudes of 20.96 and 19.93 mag, respectively, which give an upper limit on the radius of the nucleus of 2.1 km. The geometric cross-section of material in the trail was ~ 4 x 10^8 m^2, corresponding to a dust mass of ~ 5 x 10^7 kg. Analysis of …
The unique inner-belt asteroid 311P/PANSTARRS (formerly P/2013 P5) is notable for its sporadic, comet-like ejection of dust in nine distinct epochs spread over $\sim$250 days in 2013. This curious behavior has been interpreted as the product of localized, equator-ward landsliding from the surface of an asteroid rotating at the brink of instability. We obtained new Hubble Space Telescope observations to directly measure the nucleus and to search for evidence of its rapid rotation. However, instead of providing photometric evidence for rapid nucleus rotation, our data set a lower limit to the li…
We report new observations of the active asteroid P/2010 A2 taken when it made its closest approach to the Earth (1.06 au in 2017 January) after its first discovery in 2010. Despite a crucial role of the rotational period in clarifying its ejection mechanism, the rotational property of P/2010 A2 has not yet been studied due to the extreme faintness of this tiny object ($\sim$120 m in diameter). Taking advantage of the best observing geometry since the discovery, we succeed in obtaining the rotational light curve of the largest fragment with Gemini/GMOS-N. We find that (1) the largest fragment …
Dynamically different groups of comets and active asteroids with orbits at 2 - 5 a. u. show dust activity in varying degrees and forms. Photometric study and comparison of physical parameters can help to classify mechanisms and nature of the activity for such objects. We present new observations using broadband photometry of 15 active objects in the main asteroid belt and surrounding regions obtained during 2012 - 2016. The study aims to compare the physical properties of main-belt comets (MBCs), quasi-Hilda comets (QHCs), and active asteroids (AAs). The observations were carried out with the …
