Active Asteroid Research Articles

Research of the family associations of active asteroids in the main belt

ABSTRACT We apply the Hierarchical Clustering method (HCM) and Selective Backward Integration method (BIM) to search for associated families and young families for all main-belt active asteroids (MBAAs) known to date. We find four newly candidate sub-groups of known families, which include the candidate Brueghel family associated with 176P/LINEAR, the candidate 324P group associated with 324P/La Sagra, the candidate G1 group associated with P/2016 G1, and the candidate Tutenchamun family associated with (62412) 2000 SY178. Additionally, we identify three entirely new candidate families, the Interamnia family associated with P/2021 A5, the candidate 457P group associated with 457P/Lemmon-PANSTARRS, and the candidate Scheila family associated with (596) Scheila. We also reveal two newly identified family associations with known families between 259P/Garradd and the Adeona family, P/2019 A4 and the Jones family. All main-belt comets (MBCs) are likely associated with young and primitive families. Some unstable MBCs, which cannot be identified using HCM, may still originate from young and primitive families. However, due to dynamic diffusion, they cannot be conclusively linked to current families. Impact-disrupted asteroids could be linked with young families and they may change their original spectrum under the impact activity. Rotational fission of young and primitive asteroids might be a useful mechanism for facilitating the exposure of subsurface ice, and therefore triggering sublimation-driven activity. Rapid rotation and sublimation activity mechanisms are likely coupled. Therefore, further research should be made on such fast rotational asteroids that are located in primitive families.

New Active Jupiter Family Comet 2008 QZ44: a Discovery with Citizen Science

We report our discovery of cometary activity in the form of a diffuse tail associated with minor planet 2008 QZ44 during two previous orbits: 2008 and 2017. This finding was prompted in part by Active Asteroids, our Zooniverse-hosted NASA Partner Citizen Science program. Participants flagged two UT 2017 July 12 Dark Energy Camera images of 2008 QZ44 as active. Independently, our team identified activity in nine Canada-France-Hawaii Telescope MegaPrime images from UT 2008 November 20. During both apparitions 2008 QZ44 was near its perihelion passage. 2008 QZ44 has a Tisserand parameter with respect to Jupiter of 2.821, placing it in the Jupiter-family comet (JFC) class, and our dynamical integrations confirm this classification. JFCs contain primordial material that informs us about solar system evolution, and help us map the present-day volatile distribution. We note that 2008 QZ44 has previously been classified as a quasi-Hilda comet candidate.

Cometary Activity Discovered on Vacationing Centaur 2019 OE31

We have detected cometary activity on minor planet 2019 OE31 through both the Active Asteroids Citizen Science program and an independent archival search. Before 2013, 2019 OE31 was on a Centaur orbit, between the orbits of Jupiter and Neptune. Centaurs are objects in transition from the outer solar system to the inner solar system. They play a vital role in the understanding of the Kuiper Belt and comets. In 2013 October, following a close encounter with Jupiter, 2019 OE31 moved to an orbit entirely interior to that of Jupiter. This reduced orbital distance and, hence, increased temperature is likely the cause of the observed activity. Through a suite of orbital dynamics simulations, we find that 2019 OE31 will experience many more similar encounters and is statistically likely to return to a Centaur orbit, potentially within the next 80 yr, from its current “vacation.”

Citizen Science Discovery of a Recurrently Active Jupiter-Family Comet: (551023) 2012 UQ192

We have discovered evidence of cometary activity originating from (551023) 2012 UQ192 (alternately designated 2019 SN40), which we dynamically classify as a Jupiter Family Comet (JFC). JFCs have eccentric Jupiter-crossing orbits and originate in the Kuiper Belt. Analysis of these objects can provide vital information about minor planets in the outer solar system, such as the distribution of volatiles within the solar system. Activity on 2012 UQ192 was first recognized by volunteers on our NASA Partner Citizen Science project Active Asteroids. Through our own examination of archival image data, we found a total of ∼30 images presenting strong evidence of activity near perihelion during two separate orbits. 2012 UQ192 is notable as we found it to be recurrently active. When 2012 UQ192 approaches its perihelion passage in 2027 September, we predict it will reactivate and will be a prime subject for follow-up observations.

New Active Quasi-Hilda Asteroid 2004 CV50: A Citizen Science Discovery

We report that minor planet 2004 CV50 displayed cometary activity in the form of a short, diffuse tail, first identified by volunteers of the Citizen Science program Active Asteroids, a NASA Partner program hosted on the Zooniverse online platform. The activity is present in three images, from UT 2020 February 15 and UT 2020 March 14, that were acquired with the Dark Energy Camera on the Blanco 4 m telescope at the Cerro-Tololo Inter-American Observatory in Chile. We find that 2004 CV50 is most likely an active quasi-Hilda object rather than an active asteroid, despite 2004 CV50 having a Tisserand parameter with respect to Jupiter of 3.06.

Recurring Activity Discovered on Quasi-Hilda 2009 DQ118

We have discovered two epochs of activity on quasi-Hilda 2009 DQ118. Small bodies that display comet-like activity, such as active asteroids and active quasi-Hildas, are important for understanding the distribution of water and other volatiles throughout the solar system. Through our NASA Partner Citizen Science project, Active Asteroids, volunteers classified archival images of 2009 DQ118 as displaying comet-like activity. By performing an in-depth archival image search, we found over 20 images from UT 2016 March 8–9 with clear signs of a comet-like tail. We then carried out follow-up observations of 2009 DQ118 using the 3.5 m Astrophysical Research Consortium Telescope at Apache Point Observatory, Sunspot, New Mexico, USA and the 6.5 m Magellan Baade Telescope at Las Campanas Observatory, Chile. These images revealed a second epoch of activity associated with the UT 2023 April 22 perihelion passage of 2009 DQ118. We performed photometric analysis of the tail and find that it had a similar apparent length and surface brightness during both epochs. We also explored the orbital history and future of 2009 DQ118 through dynamical simulations. These simulations show that 2009 DQ118 is currently a quasi-Hilda and that it frequently experiences close encounters with Jupiter. We find that 2009 DQ118 is currently on the boundary between asteroidal and cometary orbits. Additionally, it has likely been a Jupiter family comet or Centaur for much of the past 10 kyr and will be in these same regions for the majority of the next 10 kyr. Since both detected epochs of activity occurred near perihelion, the observed activity is consistent with sublimation of volatile ices. 2009 DQ118 is currently observable until ∼mid-October 2023. Further observations would help to characterize the observed activity.

Search for Signs of Sublimation-Driven Dust Activity of Primitive-Type Asteroids Near Perihelion

—In December 2021 to February 2022, the UBVRI photometry of 29 primitive-type asteroids of the Main Belt, being near the perihelion distances, was carried out at the 0.6-meter RC600 semiautomatic telescope of the Caucasus Mountain Observatory (CMO) of the Sternberg Astronomical Institute, Moscow State University. These observations, as well as the data processing and analysis, were aimed at searching for supposed sublimation-driven dust activity on asteroids under maximal subsolar temperatures. Among the tasks to be accomplished was the comparison of the physical and dynamic parameters of active and inactive asteroids. The main result is that substantial spectral signs of quasi-simultaneous sublimation-driven dust activity were detected on six primitive-type asteroids of the Main Belt—145 Adeona, 302 Clarissa, 322 Phaeo, 435 Ella, 690 Wratislavia, and 779 Nina (on 302 Clarissa, 322 Phaeo, 435 Ella, and 690 Wratislavia—for the first time). These six asteroids represent ~21% of all bodies included in the observation program. Probable spectral manifestations of activity at a lower intensity level were detected for the first time on five more asteroids—424 Gratia, 751 Faina, 762 Pulcova, 778 Theobalda, and 859 Bouzaréah. On 145 Adeona and 779 Nina, sublimation-driven dust activity near perihelion was registered for the third time for the last ten years; this time interval corresponds to about three orbital periods of these asteroids around the Sun. We consider the circumstances due to which five of the listed asteroids possess families. General processes and conditions that could and/or can influence the portion of primitive-type asteroids that quasi-simultaneously show signs of sublimation-driven dust activity are discussed.

Active Asteroid 311P/PanSTARRS: Rotational Instability as the Origin of its Multitails?

The active asteroid 311P/PanSTARRS is one of the two targets of the planned Chinese asteroid exploration mission Tianwen-2. During 2013, 311P experienced several mass-loss events and exhibited multiple comet-like tails. Here we analyze the morphology and surface brightness of the tails to investigate the dust environment around the nucleus and the mechanism of activities. We enhance the features of the tails using image processing techniques to obtain information about the morphologies of the tails, and fit the processed images with syndyne–synchrone diagrams. The fitting results give estimations of the upper limits of the durations (2–8 days) of eruptions and the dust size ranges (0.006 –38.9 mm) in the tails. The results of surface photometry performed for each dust tail show that the brightness distribution index of each tail ranged from approximately −1.81 to 0 and the dust size distribution indices of 311P's tails ranged from −2.29 to −1.45. The quantity of particles in each tail ranged from 0.5 to 8 × 106 kg, which leads to a total dust-loss quantity of 3.0 × 107 kg and a mass-loss rate of 1.59 kg s−1. Sublimation, continuous impacts, or tidal forces of planets are excluded as explanations for 311P’s activities, and rotational instability remains a possible activation cause without strong evidence against it.

Search for Signs of Sublimation-Driven Dust Activity of Primitive-Type Asteroids Near Perihelion

In December 2021 to February 2022, the UBVRI photometry of 29 primitive-type asteroids of the Main Belt, being near the perihelion distances, was carried out at the 0.6-meter RC600 semiautomatic telescope of the Caucasus Mountain Observatory (CMO) of the Sternberg Astronomical Institute, Moscow State University. These observations, as well as the data processing and analysis, were aimed at searching for supposed sublimation-driven dust activity on asteroids under maximal subsolar temperatures. Among the tasks to be accomplished was the comparison of the physical and dynamic parameters of active and inactive asteroids. The main result is that substantial spectral signs of quasi-simultaneous sublimation-driven dust activity were detected on six primitive-type asteroids of the Main Belt—145 Adeona, 302 Clarissa, 322 Phaeo, 435 Ella, 690 Wratislavia, and 779 Nina (on 302 Clarissa, 322 Phaeo, 435 Ella, and 690 Wratislavia—for the first time). These six asteroids represent ~21% of all bodies included in the observation program. Probable spectral manifestations of activity at a lower intensity level were detected for the first time on five more asteroids— 424 Gratia, 751 Faina, 762 Pulcova, 778 Theobalda, and 859 Bouzaréah. On 145 Adeona and 779 Nina, sublimation-driven dust activity near perihelion was registered for the third time for the last ten years; this time interval corresponds to about three orbital periods of these asteroids around the Sun. We consider the circumstances due to which five of the listed asteroids possess families. General processes and conditions that could and/or can influence the portion of primitive-type asteroids that quasi-simultaneously show signs of sublimation-driven dust activity are discussed.

A nanolander for a space mission to an active asteroid in the main belt

A nanolander (CALICUT) with a total mass of about 10 kg was proposed in response to the CNSA (China National Space Administration) Announcement of Opportunity (AO) for an Asteroid Exploration Mission (AEM) by a joint European-Chinese team to operate on an active asteroid in the main belt. CALICUT is a further development of the MASCOT lander that flew on the Hayabusa2 mission to asteroid Ryugu. The nanolander was designed with mobility and autonomy capabilities. It will be able to operate for at least 6 weeks to measure the physical, morphological and compositional properties of the target. The data can be used to derive answers to scientific questions, such as what drives activity on active asteroids, and identify similarities and differences between inactive asteroids and classical comets. CALICUT carries a payload of four scientific instruments with a total mass of about 2 kg to provide unique measurements that can only be done directly on the surface.

Multiscale Stamps for Real-time Classification of Alert Streams

In recent years, automatic classifiers of image cutouts (also called “stamps”) have been shown to be key for fast supernova discovery. The Vera C. Rubin Observatory will distribute about ten million alerts with their respective stamps each night, enabling the discovery of approximately one million supernovae each year. A growing source of confusion for these classifiers is the presence of satellite glints, sequences of point-like sources produced by rotating satellites or debris. The currently planned Rubin stamps will have a size smaller than the typical separation between these point sources. Thus, a larger field-of-view stamp could enable the automatic identification of these sources. However, the distribution of larger stamps would be limited by network bandwidth restrictions. We evaluate the impact of using image stamps of different angular sizes and resolutions for the fast classification of events (active galactic nuclei, asteroids, bogus, satellites, supernovae, and variable stars), using data from the Zwicky Transient Facility. We compare four scenarios: three with the same number of pixels (small field of view with high resolution, large field of view with low resolution, and a multiscale proposal) and a scenario with the full stamp that has a larger field of view and higher resolution. Compared to small field-of-view stamps, our multiscale strategy reduces misclassifications of satellites as asteroids or supernovae, performing on par with high-resolution stamps that are 15 times heavier. We encourage Rubin and its Science Collaborations to consider the benefits of implementing multiscale stamps as a possible update to the alert specification.

Simulated Gravity Field Estimation for the Main Belt Comet 133P/Elst-Pizarro Based on a Satellite-to-satellite Tracking Mode

Most asteroids and comets are formed in the early stages of the solar system and therefore contain a wealth of information about their birth. The asteroid exploration mission planned in the coming years by China will likely target the celestial body named 133P/Elst-Pizarro (estimated diameter of about 4 km). The orbit of this asteroid stays within the asteroid belt, but nevertheless, it displays a comet-like dust tail. In this study, we used differential tracking data between two simulated probes and the data from an Earth station to estimate 133P gravity field model. This observation mode is similar to how the gravity field was estimated for large celestial objects in the GRAIL and GRACE missions, but here the object is the very small 133P asteroid. We compared the estimated gravity fields obtained for 133P from the satellite-to-satellite combined with the Earth-based two-way range-rate observation mode, with only the Earth-based two-way range rate mode. The results show that the accuracy of the low-degree (4 degree and order) estimate of the gravity field is improved by one order of magnitude by using the satellite-to-satellite combined with the Earth-based two-way range-rate observation mode with respect to the Earth-only tracking. Furthermore, another order of magnitude improvement in the gravity field solution is gained by decreasing the orbit altitude from 12 to 8 km.

A Jupiter-family Comet Discovery via Citizen Science: 2005 XR132

We report the discovery of cometary activity associated with minor planet 2005 XR132, a finding facilitated by our NASA Partner program Active Asteroids, hosted on the Zooniverse online Citizen Science platform. Volunteers identified activity in a Dark Energy Camera image of 2005 XR132 from UT 2021 March 26, and our own investigation uncovered additional images of activity in Zwicky Transient Facility data spanning UT 2021 January 3 through March 31. 2005 XR132 has a semimajor axis a = 3.760 au, eccentricity e = 0.432, inclination i = 14.°474, and a Tisserand parameter with respect to Jupiter of T J = 2.869, and thus is dynamically classified as a Jupiter-family comet.

Splitting of Long-period Comet C/2018 F4 (PANSTARRS)

Long-period comet C/2018 F4 (PANSTARRS) was observed to show duplicity of its inner region in 2020 September, suggestive of a splitting event. We here present analyses of our observations of the comet taken from the LCO Outbursting Objects Key project and the University of Hawaii 2.2 m telescope after the discovery of the splitting. The two fragments Components A and B, estimated to be ∼60 m to 4 km in radius, remained highly similar to each other in terms of brightness, color, and dust morphology throughout our observing campaign from 2020 September to 2021 December. Our fragmentation model yielded that the two components split at a relative speed of 3.00 ± 0.18 m s−1 in 2020 late April, implying a specific energy change of J kg−1, and that Component B was subjected to a stronger nongravitational acceleration than Component A in both the radial and normal directions of the orbit. The obtained splitting time is broadly consistent with the result from the dust morphology analysis, which further suggested that the dominant dust grains were millimeter-sized and ejected at a speed of ∼2 m s−1. We postulate that the pre-split nucleus of the comet consisted of two lobes resembling that of 67P, or that the comet used to be a binary system like main-belt comet 288P. Regardless, we highlight the possibility of using observations of split comets as a feasible manner to study the bilobate shape or binarity fraction of cometary nuclei.

Cometary Activity on Quasi-Hilda Object 2018 CZ16

We present the discovery of activity originating from quasi-Hilda Object 2018 CZ16, a finding stemming from the Citizen Science project Active Asteroids. For 2018 CZ16 we identified a broad (∼60°) but short (∼5″) tail in archival Blanco 4 m data from Cerro Tololo Inter-American Observatory, Chile, (CTIO) Dark Energy Camera images from UT 2018 May 15, 17 and 18. Activity occurred 2 months prior to perihelion, consistent with sublimation-driven activity.

New Active Asteroid (588045) 2007 FZ18

We present evidence that, on UT 2018 February 15, main-belt asteroid (588045) 2007 FZ18 displayed cometary activity in the form of two tails, one each in the anti-solar and anti-motion directions. Activity was first identified by volunteers of the NASA Partner program Active Asteroids, a Citizen Science program hosted on the Zooniverse platform, in an image acquired with the Dark Energy Camera on the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory in Chile. Notably, (588045) 2007 FZ18 is inbound toward perihelion, so telescope observations are timely to detect a possible second activity outburst.

Temporal evolution of the dynamical environment around asteroid (101955) Bennu

In this work the changing dynamical environment about asteroid (101955) Bennu, one of the most accurately modeled asteroids to date, is analyzed. This is done through the analysis of the evolving equilibrium points and corresponding dynamical ridge lines about this body, as a function of the asteroid’s spin rate. This is motivated by the measurement of an accelerating YORP effect on Bennu, causing its spin rate to increase over time with a doubling time on the order of 2 Myr. This study looks at the changes in the dynamical environment about Bennu over times ranging from 1 Myr in the past to 500 kyr in the future. Over this time interval several changes in this environment occur due to pairs of equilibria coming into and out of existence and changing stability properties of these equilibria. As a result of these bifurcations, if Bennu’s shape is assumed to be fixed, the number of equilibria increases from a minimum of four (1 Myr in the past), to eight (at the current epoch), to a maximum of 12 (430.6 kyr in the future). After this point, the number of equilibria will decrease as equilibria annihilate with each other. Several equilibria have undergone stability changes and in the future several will cross the surface of the asteroid. Criteria for mathematically detecting all of these transitions were developed and are presented in this work. It is also found that simulated particles initially at rest on the Bennu surface will be lofted when Bennu reaches a rotation period of 3.4304 hr, which will occur within the next 400 kyr. At this point we show that Bennu may appear as an active asteroid.

Spectroscopic identification of water emission from a main-belt comet.

Main-belt comets are small Solar System bodies located in the asteroid belt that repeatedly exhibit comet-like activity (that is, dust comae or tails) during their perihelion passages, strongly indicating ice sublimation1,2. Although the existence of main-belt comets implies the presence of extant water ice in the asteroid belt, no gas has been detected around these objects despite intense scrutiny with the world's largest telescopes3. Here we present James Webb Space Telescope observations that clearly show that main-belt comet 238P/Read has a coma of water vapour, but lacks a significant CO2 gas coma. Our findings demonstrate that the activity of comet Read is driven by water-ice sublimation, and implies that main-belt comets are fundamentally different from the general cometary population. Whether or not comet Read experienced different formation circumstances or evolutionary history, it is unlikely to be a recent asteroid belt interloper from the outer Solar System. On the basis of these results, main-belt comets appear to represent a sample of volatile material that is currently unrepresented in observations of classical comets and the meteoritic record, making them important for understanding the early Solar System's volatile inventory and its subsequent evolution.

Secular Light Curves of main-belt comets 133P/Elst-Pizarro, 176P/LINEAR, 288P/(300163) and 433P/(248370)

Among the main-belt comets (MBCs) that have been discovered, 133P/Elst-Pizarro, 176P/LINEAR, 288P/(300163) and 433P/(248370) do not have obvious coma, and the amplitudes of their Secular Light Curves (SLCs) are less than 3 mag. Through the SLCs, we can better understand the activity status and decay process of these four low-level active MBCs, and then understand the activity evolution of the MBCs. To get the SLCs of these four MBCs, we collected 2,962 observations (span 5–6 apparitions) and used improved methods (subtract the opposition and aspect angle effects). According to the SLCs and related parameters, we get the following conclusions: (1) 133P/Elst-Pizarro and 176P/LINEAR had activity decay characteristics. For 133P/Elst-Pizarro, the amplitude of SLC was 2.4 mag in 1996+2001 perihelion passages, but changed to 1.2 mag in 2007+2013 perihelion passages. The time TOFF and distance ROFF at the turn off point of activity changed significantly, from TOFF=388±20 d and ROFF=3.04±0.02 au (1996+2001) to TOFF=230±13 d and ROFF=2.81±0.02 au (2007+2013). For 176P/LINEAR, the amplitude of SLC during 2005 perihelion passage was 0.37 mag, while during 2011, 2017 and 2022 perihelion passages, it did not show activity. (2) 133P/Elst-Pizarro and 176P/LINEAR had the aspect angle effect. That could mean the nuclei of 133P/Elst-Pizarro and 176P/LINEAR have large obliquity and axis ratio. (3) The equinox of 133P/Elst-Pizarro was close to perihelion (Δt=45d, anomaly=12°) and 176P reaches the solstice near perihelion (Δt=69d, anomaly=18°). (4) 288P/(300163) had a large asymmetry parameter ROFF/RON, which means that the sublimation takes place in depth, not just in the surface. (5) It can also be seen from SLC that 433P/(248370) had been active since 2010 perihelion passage, which was earlier than previously reported in 2016. But, SLC of 433P did not show activity near the perihelion in 2005. 433P had photometric anomaly (∼ 0.5 mag), from Δt = 94 to 138 d or R = 2.425 to 2.481 au in 2021 perihelion passage. (6) The PAGE and TAGE of four comets were determined.

On the Prospects for Estimating the Properties of Particles in an Active Asteroid Exosphere by Features in the UV and Visible Reflectance Spectra

On the Prospects for Estimating the Properties of Particles in an Active Asteroid Exosphere by Features in the UV and Visible Reflectance Spectra