Oral presentations and abstracts

Binary asteroids are of special importance in planetary science as they provide direct measurements of the body's bulk mass and density. The main way to discover these systems is by detecting their mutual events in the lightcurves. There are almost 400 asteroids with satellites known as of writing this. Gaia Data Release 2 (Gaia DR2) contains sparse disk-integrated brightness measurements for more than 14.000 asteroids spanned over 22 months of observations. We have studied these data to detect multiple asteroid system candidates. For this work we have used the inversion genetic algorithm which provides best fit solutions for asteroids' spin and shape parameters. In order to cope with the limited viewing geometries of a large majority of asteroids, we have upgraded the inversion algorithm to combine Gaia DR2 with other ground-based data such as the Lowell Observatory photometric database. In the near future we envisage a great increase on the number of multiple asteroid discovery by analysing the data of large sky surveys. Particularly interesting will be the analysis of Gaia DR3 (expected for H2 2021) which will contain data for more than 100.000 asteroids.

How to cite: Santana-Ros, T., Cellino, A., Campo-Bagatin, A., Benavidez, P., Alvarez-Candal, A., and Tanga, P.: Asteroid multiplicity detection in Gaia DR2, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-100, https://doi.org/10.5194/epsc2020-100, 2020.

Gaia DR2, validating the debiasing of asteroid astrometry by orbit improvement

The optimal exploitation of asteroid astrometry is seminal at many tasks such as the monitoring of impact risks by potentially hazardous asteroids, and the measurement of subtle dynamical effects. These can include, most notably, the Yarkovsky thermal recoil force or perturbations due to other asteroids.

The Gaia mission has published astrometry with very high accuracy for 14.099 asteroids in the Data Release 2 (DR2), and about 10 times more are coming in DR3 (end 2021). The level of accuracy of Gaia is unprecedented, reaching 1 mas or better for each epoch, but it deserves unprecedented care to be exploited.
 
In particular, most archival data (astrometry available at the Minor Planet Center) are the result of a calibration with respect to pre-Gaia catalogues, that are often affected by local systematic errors. Such errors have different possible sources. They can be the result of the tiling of the celestial sphere by a imaging device, whose field of view presents some residual distortion in its astrometric reduction. There can also be effects related to the coupling of two different catalogs, distant in time, used to derive proper motions. Eventually, the adopted reference frame can also introduce other effects.

As it has been documented several times in literature such systematic bias, that can vary on spatial scales of a few degrees or less, can also be function of other parameters, such as the magnitude range considered (different bias affect stars of different brightness). 

To take into account these effects and apply the required corrections, we developed a completely new bias correction computation around on the position of single asteroid observations, instead of the classical approach of computing corrections on fixed grid for each catalogue. Despite being much more time-consuming, our approach allows us to reach a full flexibility on effects related to the field of view size of single surveys, magnitude limit and also epoch-dependent variations. We also implement corrections to the reference frame rotation detected for bright stars (V<12) in Gaia DR2 (Lindegren 2020) necessary to obtain a full consistency.

After having completed the debiasing of astrometry archived at MPC for all asteroids in Gaia DR2, we have run an orbit improvement procedure for all of them, that also exploits a refined error model. We illustrate here the results of our processing, in particular investigating the improvement in the ephemeris uncertainty, and the perfomance of the debiasing.
 

How to cite: Tanga, P., Spoto, F., Joao, F., and Pedro, M.: Gaia DR2: orbit improvement based on new debiasing of asteroid astrometry, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-555, https://doi.org/10.5194/epsc2020-555, 2020.

The Kepler space telescope collected continuous photometry of several Jovian Trojan asteroids in the Solar System during its K2 mission. We extracted light curves 43 new targets from K2 Campaigns 11-19 using our own photometric package developed for moving objects in the Kepler images which, together with the 56 asteroids from Campaign 6, brings the total sample size up to 99 asteroids. We calculated rotational frequencies and amplitudes for each object and their distributions, and we derived statistics on the binary fraction and possible compositions of these asteroids. We find and excess of very slow rotators (>100 hours) and a possible dichotomy in the period distribution. When compared to other space-based photometric results, we find that the distribution of Hilda rotation periods detected with K2 shows the same possible dichotomy, but the large sample of main-belt asteroids measured with the TESS space telescope does not.

The excess of slow rotators corroborates with an outward origin, with synchronized binaries migrating inwareds from the Kuiper belt, and some of them dissociating along the way, creating very slowly rotating single objects. Both a low critical density limit and comparison with strengthless ellipsoid models indicate that none of the objects exceed the density of icy objects, further strengthening an inward migration scenario.

We estimate a binary fraction of at least 21% based on the number of high-amplitude, long-period objects, in agreement with earlier results. Large photometric amplitudes are prevalent over the entire period range, and we cannot fit all objects with a strengtless model in rotational equilibrium.

We highlight a few individual objects as well. (99306) 2001 SC101 is the only asteroid observed in to Campaigns, from different sides of the Sun, and we find clear differences in the light curve shape. (13062) Podarkes is the principal body of a proposed small family: we detect a rotation period of 245 hr which puts it into the very slow rotator group. Finally, we present the first continuous light curve of (11351) Leucus, one of the targets of the Lucy spacecraft, and confirm that it also rotates exceedingly slowly, with a period of 445 hr.

How to cite: Kalup, C., Molnár, L., Kiss, C., Szabó, G. M., and Pál, A.: Slow rotators and binary candidates among the Jovian Trojans with K2, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-855, https://doi.org/10.5194/epsc2020-855, 2020.

Due to their faintness light curves of transneptunian objects (TNOs) in most cases are difficult to obtain, and therefore the number of TNOs with known rotational properties (at least rotation period) are rather limited. As it was shown for other small body populations, long-term, 1-3-month monitoring of small bodies revealed many targets with long rotation periods. These measurements significantly increased the number of slow rotators (P > 24h) for Jovian Trojans (Szabó et al., 2017), Hildas (Szabó et al., 2020) and Centaurs (Marton et al., 2020) using Kepler/K2 measurements, and also for main belt asteroids (Pál et al., 2020) using the TESS space telescope. Here we report on Kepler/K2 measurements of 70 TNOs, collected over the whole length of the K2 mission, in Campaigns 3-19. Our data notably increases the number of TNOs with known rotational properties. We compare these characteristics with those of other small body populations in the Solar system.

Figure 1: Light curve of (50000) Quaoar obtained from the K2 measurements, folded with the canonical P = 8.84 h period (Ortiz et al., 2003, left), and with the newly determined P = 8.88h rotation period (right). 

References: 

- Marton, G., et al., 2020, Icarus, 345, 113721 
- Ortiz, J.L., et al., 2003, A&A, 409, L13
- Pál, A., et al., 2020, ApJS, 247, 26 
- Szabó, Gy. et al., 2017, A&A, 599, A44 
- Szabó, Gy. et al., 2020, ApJS, 247, 34

How to cite: Kiss, C., Kecskeméthy, V., Szakáts, R., Pál, A., Molnár, L., Sárneczky, K., Vinkó, J., Szabó, R., Szabó, G. M., Marton, G., and Kiss, L. L.: Rotational properites of transneptunian objects from the K2 mission, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-536, https://doi.org/10.5194/epsc2020-536, 2020.

We identified 125 individual light curves of Hilda asteroids observed by the K2 mission. We found that despite of the mixed taxonomies, the Hilda group highly resembles the Trojans in the distribution of rotation periods and amplitudes, and even the LR group (mostly C- and X-type) Hildas follow this rule. Contrary to the Main Belt, the Hilda group lacks the very fast rotators. The ratio of extremely slow rotators (P > 100 hr) is a surprising 18%, which is unique in the solar system. The occurrence rate of asteroids with multiple periods (4%) and asteroids with three maxima in the light curves (5%) can be signs of a high rate of binarity, which we can estimate as 25% within the Hilda group. 

Based on our extraction of 10 thousand full asteroid light curves from the first year observations by TESS (P\'al et al. 2020) we can compare the distribution of rotation period and shape asphericity in the most populated asteroid families overall in the Main Belt. We reveal internal structure of some asteroid families in respect to rotation statistics and signs of rotation properties evolving with age.

How to cite: Szabo, G., Kiss, C., Szakáts, R., Pál, A., Molnár, L., Sárneczky, K., Vinkó, J., Szabó, R., Marton, G., and Kiss, L.: Rotation properties in the Hilda and Main-Belt asteroid families observed by K2 and TESS, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-810, https://doi.org/10.5194/epsc2020-810, 2020.

By analyzing the full-frame images acquired during the first year of the TESS mission, rotation characteristics of nearly ten thousand light curves of bright asteroids were determined with a good accuracy. The continuation of this space-borne mission with its second year on the Northern Hemisphere is just ending by the summer of 2020, allowing us to extend the database. In this presentation we report the results of the initial analysis of the new data set, focusing on the similarities and differences in observational artefacts (and constraints) and the recent development of the processing pipeline. 

How to cite: Pál, A., Szakáts, R., and Kiss, C.: Towards the second data release of TESS asteroid photometry, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-697, https://doi.org/10.5194/epsc2020-697, 2020.

In recent years, the observed orbital geometry of extreme trans-Neptunian objects (TNOs) has provided tantalizing evidence predicting the existence of an as-yet undiscovered “Planet Nine.” Combined with orbit stability models, these observations permit a detailed prediction of Planet Nine's properties, with a shrinking parameter space as more of these rare objects are discovered. I will present the first results from a new survey utilizing light curve data from the Transiting Exoplanet Survey Satellite (TESS) to search for TNOs at distances 70-800 au, with a magnitude limit V~22. This survey leverages an innovative new pipeline designed to extract the locations, magnitudes, and 27-day orbital arcs of undiscovered outer solar system objects, including both Planet Nine and the population of extreme trans-Neptunian objects pertinent to the Planet Nine theory, using a blind shift-stacking search along all plausible outer solar system orbits. Together with the extensive sky coverage of the TESS survey, this search will place stringent constraints upon the as-yet undiscovered TNO population, with great potential to either discover Planet Nine or almost entirely rule out its existence.

How to cite: Rice, M. and Laughlin, G.: Surveying the Trans-Neptunian Solar System with TESS, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-420, https://doi.org/10.5194/epsc2020-420, 2020.

The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) spacecraft was reactivated in December 2013 and since then has been conducting an all-sky survey at 3.4 and 4.6 microns to discover and characterize asteroids and comets that come close to the Earth.  NEOWISE employs an automated pipeline for the detection of moving objects, recording their astrometry and photometry and reporting positions to the Minor Planet Center for archiving.  However, there are a subset of near-Earth objects that are not found by the automated system due to rates of motion or acceleration outside the pipeline limits, an insufficient number of detections, or confusion with background sources.  Because NEOWISE archives every full-frame image obtained during the survey, detections of these objects can be recovered by manually searching the expected positions for coincident sources.

We have performed searches for near-Earth objects in the NEOWISE archives from 2013 to 2019, recovering detections for over 400 objects and enabling fitting of their diameters and albedos (Masiero et al. 2018, Masiero et al. 2020).  This builds on earlier work that searched the data from the cryogenic phase of the original WISE mission (Mainzer et al. 2014).  Objects found through this technique tend to be smaller than those detected by the automated processing. The distribution of albedos for these objects is skewed to high reflectivities, as is expected for a population that is optically-selected.

Here we present the results of our searches along with the physical properties of the recovered objects.  We also will discuss the reasons these objects were missed by the automated processing, and what the observed physical property distribution implies about any remaining objects still waiting to be found in the data.

How to cite: Masiero, J., Mainzer, A., Cutri, R., Grav, T., and Wright, E.: Physical properties of near-Earth asteroids manually recovered from NEOWISE data, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-333, https://doi.org/10.5194/epsc2020-333, 2020.

The Herschel Space Observatory had two imaging instruments, working in the far-infrared and submillimetre regimes: the PACS cameras at 70/100 and 160 μm and the SPIRE photometers at 250, 350 and 500 μm. Small solar system bodies, especially main belt asteroids were serendipitously present in the field of view mainly in large scan maps. We identified these objects with the original aim to mark the affected sources in the Herschel PACS and SPIRE Point Source Catalogues. In our present study we extracted flux densities in the PACS bands for asteroids above the detection limit, either using  existing standard data products from the Herschel Science Archive, or re-reducing the PACS maps in the co-moving frame of the target. We obtained ~600 new flux density values for 270 asteroids, a significant increase in the number of Herschel asteroid observations. These new flux densities will be included in the Small Bodies: Near and Far (SBNAF) Infrared Database (Szakáts et al., 2020). The fluxes obtained from Herschel are excellent for radiometric studies to get the object's size, albedo and maybe also thermal properties, when combined with other measurements (Alí-Lagoa et al., 2020).

How to cite: Szakáts, R., Kiss, C., Farkas-Takács, A., Marton, G., Müller, T., and Pál, A.: Far-infrared flux densities of main belt asteroids from serendipitous Herschel/PACS observations, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-727, https://doi.org/10.5194/epsc2020-727, 2020.

The Io Volcano Observer (IVO) [1] is a NASA Discovery mission currently under Phase A study [2]. Its primary goal is a thorough investigation of Io (e.g., [3]), the innermost of Jupiter's Galilean moons and the most volcanically active body in the Solar system. The strategy consists of the observation of Io mainly during ten targeted flybys [4] between August 2033 and April 2037. At this time, IVO will orbit Jupiter on highly eccentric orbits with periods between 78 and 260 days, a minimum Jupiter altitude of ~340000 km, apoapsis distances between 10 and 23 million kilometers, and an orbit inclination of ~45°. Among the remote-sensing and field-and-particle instruments, there are also a narrow-angle camera (NAC; clear aperture of ~15 cm; pixel field-of-view of 10 µrad) and an infrared mapping instrument (TMAP).

The irregular moons of Jupiter [5] are a group of Solar system objects which is poorly studied. With 71 currently known objects ranging in size from ~150 x 120 km  (Himalia) down to ~2 km, they are the largest sub-group of Jovian moons with respect to quantity. Irregular moons are believed to be remnants from catastrophic collisions of progenitor objects suspected to have been trapped by Jupiter in the early history of the Solar system. Many details and characteristics, including their region of origin and their relationship to other small bodies, are not known [6].

The first irregular-moon inventory by a spacecraft orbiting the host planet was successfully performed within the Saturn system by the Cassini spacecraft [7] [8]. Especially in the second half of the mission, approximately one or two days per orbit were used to observe Saturn's irregular moons, resulting in more than 200 observations of these objects. Since Saturn's irregulars were between 4 and >30 million kilometers away from Cassini (except for the targeted Phoebe flyby in June 2004), the objects appear smaller than a pixel in the imaging data. From photometric time series observations, lightcurves were extracted. These lightcurves allowed determination of 24 previously unknown rotation periods and 13 pole solutions, shape models, and phase curves. No such inventory has been done so far at Jupiter, Uranus, or Neptune systems.

Irregular moons are difficult to observe from Earth using small and mid-sized telescopes because of their small sizes (most diameters are below 10 km) and thus faint appearance (most are darker than 23rd magnitude). In addition, there is a significant straylight problem from bright Jupiter. Furthermore, since they are quite numerous, thorough inventories are not possible because there are not enough large telescopes available.

With a spacecraft like Cassini or IVO orbiting close to these objects, the situation improves fundamentally. No large telescopes are needed anymore because the objects appear much brighter, and because the angular distances to the planet are large. In addition, the long orbits of IVO offer plenty of uninterrupted observation time over many hours and days. In addition, a large phase-angle range as well as out-of-orbit plane observations are possible, adding crucial information that is not possible to achieve from Earth.

Similar to the campaign with Cassini at Saturn, the major scientific goal of IVO's observations of irregular moons is to determine fundamental physical properties such as rotation periods, pole directions, sizes, and brightnesses as a function of illumination conditions (phase curves), as well as to provide constraints on object shapes (convex-shape models). This campaign would address many of the fundamental research goals formulated for small Solar system bodies by NASA's Small Bodies Assessment Group [9] [10]. These goals include the role of the irregulars in Solar system formation and dynamical evolution; a more complete understanding of the census, architecture, physical properties (size, shape, mass, density, porosity, spin rate, etc.), surfaces, surface alteration processes, and nature of interiors, as well as relationships to other bodies, events, and processes. With IVO, fundamental remote-sensing data can be obtained to move closer to achieving these goals. Since IVO's orbits are very long, this mission provides an ideal platform for a detailed survey campaign of these intriguing bodies. Performing coordinated observations with other missions (like ESA's JUICE), or combining observations with laboratory measurements (as proposed in the IVO mission as well) will improve the overall value and interpretation of the collected data.

Fig. 1: Range (red line) and phase angle (green) of Jupiter as seen from IVO during the orbit tour.

Fig. 2: Range, phase angle, and apparent magnitude of Jovian irregular moon Sinope (J9; ø ~ 35 km) as seen from IVO. This plot illustrates the potential of IVO observations of irregular moons. Sinope is the irregular moons where IVO comes closest in the current orbit tour. On 27 Dec 2033, the minimum distance will be 690000 km. In the IVO-NAC, the size of Sinope will be ~6 pxl at this time.

References:

[1] https://ivo.lpl.arizona.edu/

[2] https://www.nasa.gov/press-release/nasa-selects-four-possible-missions-to-study-the-secrets-of-the-solar-system

[3] McEwen, A.S., de Kleer, K., Park, R. (2019): Does Io Have a Magma Ocean? eos.org. https://eos.org/features/does-io-have-a-magma-ocean

[4] https://youtu.be/7AO4CDwIXv0

[5] https://sites.google.com/carnegiescience.edu/sheppard/moons/jupitermoons

[6] Nicholson, P.D., Ćuk, M., Sheppard, S.S., Nesvorný, D., Johnson, T.V. (2008): Irregular satellites of the giant planets. In: The Solar System Beyond Neptune (Barucci, M.A. et al., eds.), Space Science Series, The University of Arizona Press, 411-424.

[7] Denk, T., Mottola, S., Tosi, F., Bottke, W.F., Hamilton, D.P. (2018): The Irregular Satellites of Saturn. In: Enceladus and the Icy Moons of Saturn (Schenk, P.M., Clark, R.N., Howett, C.J.A., Verbiscer, A.J., Waite, J.H., editors), Space Science Series, The University of Arizona Press, 409-434. doi:10.2458/azu_uapress_9780816537075-ch020.

[8] Denk, T., Mottola, S. (2019): Studies of Irregular Satellites: I. Lightcurves and Rotation Periods of 25 Saturnian Moons from Cassini Observations. Icarus 322, 80-103. doi:10.1016/j.icarus.2018.12.040.

[9] SBAG (2016): Goals and Objectives for the Exploration and Investigation of the Solar System’s Small Bodies. Version 1, 04 Mar 2016, 41 pp. https://www.lpi.usra.edu/sbag/goals/SBAG_GoalsDoc_ver.1.2.2016.pdf

[10] SBAG (2020): Goals and Objectives for the Exploration and Investigation of the Solar System's Small Bodies. Version 2, 19 Feb 2020, 47 pp. https://www.lpi.usra.edu/sbag/goals/SBAG_Goals_Document_2020.pdf

How to cite: Denk, T., McEwen, A., Helbert, J., and IVO Team, T.: Survey of Irregular Jovian Moons with IVO, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-767, https://doi.org/10.5194/epsc2020-767, 2020.

The Twinkle Space Mission is a space-based observatory that has been conceived to measure the atmospheric composition of exoplanets, stars and solar system objects. The satellite is based on a high-heritage platform and will carry a 0.45 m telescope with a visible and infrared spectrograph providing simultaneous wavelength coverage from 0.5 - 4.5 μm. The spacecraft will be launched into a Sun-synchronous low-Earth polar orbit and will operate in this highly stable thermal environment for a baseline lifetime of seven years.

Twinkle’s rapid pointing and non-sidereal tracking capabilities will enable the observation of a diverse array of Solar System objects, including asteroids and comets. Twinkle aims to provide a visible and near-infrared spectroscopic population study of asteroids and comets to study their surface composition and monitor activity. Its wavelength coverage and position above the atmosphere will make it particularly well-suited for studying hydration features that are obscured by telluric lines from the ground as well as searching for other spectral signatures such as organics, silicates and CO₂.

Twinkle is available for researchers around the globe in two ways:

1) joining its collaborative multi-year survey programme, which will observe hundreds of exoplanets and solar system objects; and

2) accessing dedicated telescope time on the spacecraft, which they can schedule for any combination of science cases.

I will present an overview of Twinkle’s capabilities and discuss the broad range of targets the mission could observe, demonstrating the huge scientific potential of the spacecraft.

How to cite: Edwards, B., Tessenyi, M., Savini, G., Tinetti, G., Stotesbury, I., Archer, R., Joshua, M., Wilcock, B., Windred, P., and Tennyson, J.: Twinkle: a low-Earth orbit, visible and infrared observatory for exoplanet and solar system spectroscopy, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-701, https://doi.org/10.5194/epsc2020-701, 2020.

The All-Sky Automated Survey for Supernovae (ASAS-SN) currently
operates 24 small-aperture telescopes distributed around the globe to
automatically survey the entire visible sky every night down to about
g~18 mag. Between 2013 and 2018, the survey used a V filter with
limiting magnitude V~17. Although primarily hunting for supernovae and
other transients, asteroids are common intruders in the ASAS-SN's
images. Here we present efforts to analyze the sparsely sampled V-band
photometry extracted from the ASAS-SN images for >10,000 asteroids
that get brighter than V~17 mag. The data span years 2013-2018 and
sample up to 7 consequent apparitions for each asteroid. We provide
details about the photometry extraction and calibration, photometry
accuracy, and various statistics such as the typical number of data
points per asteroid as a function of the brightness. Finally, we
analyze the photometric data with the lightcurve inversion method and
derive rotation periods, spin axis directions, and shapes for a sample
of studied asteroids. We discuss the typical amount of data sufficient
for a successful shape model determination. We compare derived
physical properties with those available in the literature to
illustrate the reliability of the ASAS-SN photometry.

How to cite: Hanus, J., Pejcha, O., and Shappee, B.: V band photometry of asteroids from the All-Sky Automated Survey for Supernovae, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-585, https://doi.org/10.5194/epsc2020-585, 2020.

References: Bolin, et al. 2020, Minor Planet Electronic Circulars, 2020-A99., Bellm et al. 2019, PASP, 131, 6., Blagorodnova et al 2018, PASP, 130, 985., Coughlin et al. 2019, MNRAS, 485, 1412-1419., DeMeo et al. 2009, Icarus, 202, 160-180., DeMeo et al. 2014, Nature, 505, 629-634.

Figure 1. Left panel: Orbital configuration of 2020 AV₂ (black line), Earth (blue line) and Venus (Red line at the time of its discovery looking from above the orbital plane of the inner Solar System. The orbits of 2019 AQ₃ and 2020 LF₆ are plotted for reference. Right panel: Visible wavelength reflectance spectrum taken of 2020 AV₂ with the LRIS instrument on Keck I on 2020 January 23 plotted as blue dots. The spectrum has been normalized to unity at 550 nm indicated by the black cross. The 1 σ uncertainties are indicated by the error bars on the datapoints. The spectral range of S, V and C-type asteroids from the Bus-DeMeo asteroid taxonomic catalog (DeMeo et al. 2009) are over-plotted with the S-type spectrum most closely resembling the spectra of 2020 AV₂.

How to cite: Bolin, B., Ip, W.-H., Masci, F., and Helou, G.: The Discovery and Characterization of the First Inner-Venus Asteroid, 2020 AV2, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-482, https://doi.org/10.5194/epsc2020-482, 2020.

The inner main belt asteroid (4) Vesta, with a diameter of about 525 km, is the largest differentiated asteroid showing a basaltic crust [1]. The collisional family of Vesta includes more than 15,000 known members [2] and it is considered the main source of basaltic material.  The results found by the Dawn mission support the hypothesis that this family is a result of cratering events. They revealed two remnant craters, Rheasilvia (the young crater retention age of this basin indicates that it was formed ≈ 1 Gy) and Veneneia (the crater counts suggest an age of 2.1 ± 0.2 Gyr ago) with diameters of 500 ± 25 and 400 ± 25 km respectively [3].

The discovery of V-types which can't be associated dynamically with the Vesta family shows that the basaltic material is common through the inner Solar System and suggests that other differentiated parent bodies once existed.  Furthermore, by using the data provided by the OSIRIS-REx instruments, [4] reported the presence of meter-scale exogenic boulders on the surface of (101955) Bennu which shows the spectral signature of basaltic material.

In this context, we aim to determine the distribution of basaltic asteroids based on large surveys data. We estimate their unbias distribution which provides us with an approximate calculation for the total volume of basaltic material present in the Main Belt. We compare this volume with the ejected volume from Vesta's Rheasilvia crater and find that the majority of this material has been lost or fragmented to smaller sized that go beyond detection capabilities.

For our work, we used the latest observations provided by VISTA -VHS survey  which observed the  southern hemisphere sky using four filters, Y, J, H, and Ks. The V-type candidates are selected using the following constraints  (Y − J) − (Y −J)err ≥ 0.45 and (J − Ks) + (J − Ks)err ≤ 0.35 were selected [5, 6]. 

In order to classify the asteroids according to HED typologies we used the K-Nearest Neighbor (KNN) algorithm. For the training set we selected the spectra of HED meteorites from the RELAB database. This set contains a number of 243 meteorites spectra out of which 42 are howardites, 160 eucrites and 41 are diogenites. The classification using the KNN algorithm shows that the majority of the basaltic candidates present an eucritic (≈ 39 %) and howarditic (≈ 37 %) type lithology while diogenitic material is less commmon with ≈ 24 %.

The majority of the basaltic candidates (≈95%) are located in the inner main belt while only ≈4 % and ≈ 1 % are located in the middle respectively outer main belt (Fig.1). However, we note that ~33% of these asteroids are linked with the Vesta family and a large fraction of them (64%) are not associated with any other collisional family [6]. There are only 14 bodies associated with other families, including four belonging to (15) Eunomia family, four to (135) Hertha family.

Fig. 1 The orbital distribution of the V-type candidates [6]. The fugitives are V-type asteroids with a < 2.3 A.U. (were a is the semi-major axis) and similar e (eccentricity) and i (inclination) as the Vesta family; the low inclination V-types are asteroids having i ≤ 6 deg. and 2.3 < a < 2.5 A.U. The remaining asteroids in the inner main belt are named inner-other (IO). The midlle main belt (MMB) are asteroids with 2.5 < a < 2.82. The  outer main belt (OMB) are asteroids with a > 2.82 A.U. The location of the most representative resonances with Jupiter are shown.

The data allow to find the unbiased distribution of basaltic asteroids across the main asteroid belt. The total unbiased volume for vestoids with the effective diameter of 0.5 - 8 km is V_Vestoids = 6.24 ± 0.54 x 10⁴ km³.  For comparison, [3] estimated that the minimum volume of excavated material from Rheasilvia is above ∼1 x 10⁶ km³ . Part of it, was retained on the surface and assuming an average ejecta thickness of 5 km over a range of 100 km they roughly estimated the volume of ejecta on the surface as 5 x 10⁵ km³. This shows that at least 80% of the ejected basaltic material from (4) Vesta is missing or is not yet detected because it is fragmented in sizes  smaller than ~1 km [6].

Acknowledgements

The article is based on observations acquired with VISTA. The observations were obtained as part of the VISTA Hemisphere Survey, ESO Program, 179.A-2010 (PI: McMahon). The work of J.A.M. and part of the work of M.P. was supported by a grant of the Romanian National Authority for Scientific Research – UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0371. M.P., J.dL., and J.L. acknowledge support from the AYA2015- 67772-R (MINECO, Spain). M.P. and J.dL. also acknowledge financial support from projects SEV-2015-0548 and AYA2017- 89090-P (Spanish MINECO).

References

[1] McCord T. B., Adams J. B., Johnson T. V., 1970, Science, 168, 1445

[2] Nesvorny D., Bro ´ z M., Carruba V., 2015, in Asteroids, IV, Michel P., DeMeo ˇ F. E., Bottke W. F., eds, Identification and Dynamical Properties of Asteroid Families. Univ. Arizona Press, Tucson, AZ, p. 297

[3] Schenk P. et al., 2012, Science, 336, 694

[4] DellaGiustina et al., 2020, A&A, 637, L4

[5] Licandro J., Popescu M., Morate D., de Leon J., 2017, ´ A&A, 600, A126

[6] Mansour et al 2020, MNRAS, 491, 5966-5979

How to cite: Mansour, J. A., Popescu, M., Licandro, J., and de Leon, J.: Basaltic material across the Main Asteroid Belt, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-368, https://doi.org/10.5194/epsc2020-368, 2020.

We have searched a 2010 archival data set from the Canada-France-Hawaii Telescope for very small (km-scale) irregular moons of Jupiter in order to constrain the size distribution of these moons down to radii of ~400m, discovering 53 objects which are moving with Jupiter-like on-sky rates and are nearly certainly irregular moons. The four brightest detections, and seven in total, were all then linked to known jovian moons. Extrapolating our characterized detections (those down to magnitude m_r=25.7) to the entire retrograde circum-jovian population, we estimate the population of radius > 0.4km moons to be 600 (within a factor of 2).  At the faintest magnitudes we find a relatively shallow luminosity function of exponential index α = 0.29 ± 0.15, corresponding to a differential diameter power law of index q ≈ 2.5.

How to cite: Ashton, E., Beaudoin, M., and Gladman, B.: Six hundred 1-km retrograde jovian irregular moons, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-158, https://doi.org/10.5194/epsc2020-158, 2020.

Introduction: The Solar System group of the Instituto de Astrofisica de Canarias (IAC) is member of a consortium of astronomical observatories leaded by Deimos Space S.L.U, that presented a proposal to the ESA ITT no. AO/1-9591/18/D/MR “P3-NEO-I - Observational support from collaborating observatories”. The objective of this project is to provide ESA with the support of several observatories contributing to the follow-up of relevant objects for orbit computation and physical characterization.
We lead the Spectroscopic Observations Work Package (WP) that aim to increase the sample of near-Earth Objects (NEOs) with known spectral properties. This is crucial for understanding the origin and the evolution of NEOs and their potential threat. 
In this work we will present the preliminary results of this spectroscopic program

Aims of the program:  the main objective of the WP is to obtain a significant number of visible or near-infrared spectra of NEOs in order to increase the current number of objects with spectra available in any of these wavelengths; to obtain complementary visible/near-infrared spectra of NEOs that already have near-infrared/visible spectral information available; and to enhance the European contribution to the NEO research, in particular to the composition of NEOs, which represents a great opportunity to answer fundamental questions about their origin, properties, evolution and future potential threat. 
Additionally, we observe objects of interest of the Near-Earth Object Human Space Flight Accessible Targets Study (NHATS) and the Arecibo Planetary Radar Science Group.

The observations:  Spectroscopic observations using 2m-class or larger telescopes in the “El Roque de los Muchachos” Observatory (ORM, La Palma, Spain) started late April 2019. Data have been obtained in different runs almost every month. We used the 2.5m Nordic Optical Telescope (NOT), the 2.5m Isaac Neton Telescope (INT), the 3.5 6m Telescopio Nazionale Galileo (TNG), and world’s largest optical telescope, the 10.4m GranTeCan (GTC). 
Data with the 2.5m NOT was obtained on  8 different nights (Apr. 24, May 5, June 6, July 18, July 19, Oct. 18, Dec. 2, 2019, and Jan. 11, 2020). A total of 26 spectra of 25 different objects were obtained and reduced (Fig. 1). 
Additional data was obtained during one observing run (2019-10-01) with the 3.56m TNG (2 asteroids ), two observing runs with 2.5m INT (3 objects) and one observing run with the 10.4m GTC (5 objects).

Fig. 1 – Example of visible spectra of two of the NEAs (437316 and 99248) observed with ALFOSC spectrograph attached to the 2.5m NOT on Jan. 11, 2020.

Data base and analysis: We will make this database available at the Small Bodies Node of the NASA Planetary Data System (PDS) in the near future. This will include the spectral classification obtained using the procedures of the M4AST tool (http://m4ast.imcce.fr/index.php/index/analyze) described in detail by [1].

References: [1] Popescu, M., Birlan,M., & Nedelcu, D. A. 2012,A&A, 544, A130

How to cite: Licandro, J., Popescu, M., Oscoz, A., de Leon, J., Zamora, O., and Monelli, M.: The participation of the IAC in the ESA-SSA P3NEOI program. , Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-203, https://doi.org/10.5194/epsc2020-203, 2020.