Sizes of main-belt asteroids by combining shape models and Keck adaptive optics observations

Non-resolved thermal infrared observations enable studies of thermal and physical properties of asteroids via thermo-physical models provided the shape and rotational properties of the target are well determined. We used calibration-programme Herschel PACS data (70, 100, 160 μm) and state-of-the-art shape models derived from adaptive-optics observations and/or optical light curves to constrain for the first time the thermal inertia of twelve large main-belt asteroids. We also modelled previously well-characterised targets such as (1) Ceres or (4) Vesta as they constitute important benchmarks. Using the scale as a free parameter, most targets required a re-scaling ~5% consistent with what would be expected given the absolute calibration error bars. This constitutes a good cross-validation of the scaled shape models, although some targets required larger re-scaling to reproduce the IR data. We obtained low thermal inertias typical of large main belt asteroids studied before, which continues to give support to the notion that these surfaces are covered by fine-grained insulating regolith. Although the wavelengths at which PACS observed are longwards of the emission peak for main-belt asteroids, they proved to be extremely valuable to constrain size and thermal inertia and not too sensitive to surface roughness. Finally, we also propose a graphical approach to help examine how different values of the exponent used for scaling the thermal inertia as a function of heliocentric distance (i.e. temperature) affect our interpretation of the results.

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Binary asteroid (31) Euphrosyne: ice-rich and nearly spherical

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038372 ◽

2020 ◽

Vol 641 ◽

pp. A80

Author(s):

B. Yang ◽

J. Hanuš ◽

B. Carry ◽

P. Vernazza ◽

M. Brož ◽

...

Keyword(s):

Adaptive Optics ◽

Family Formation ◽

Large Fraction ◽

Imaging Study ◽

Spherical Shape ◽

Hydrostatic Equilibrium ◽

Main Belt ◽

Binary Asteroid ◽

Water Ice ◽

The Impact

Aims. Asteroid (31) Euphrosyne is one of the biggest objects in the asteroid main belt and it is also the largest member of its namesake family. The Euphrosyne family occupies a highly inclined region in the outer main belt and contains a remarkably large number of members, which is interpreted as an outcome of a disruptive cratering event. Methods. The goals of this adaptive-optics imaging study are threefold: to characterize the shape of Euphrosyne, to constrain its density, and to search for the large craters that may be associated with the family formation event. Results. We obtained disk-resolved images of Euphrosyne using SPHERE/ZIMPOL at the ESO 8.2 m VLT as part of our large program (ID: 199.C-0074, PI: Vernazza). We reconstructed its 3D shape via the ADAM shape modeling algorithm based on the SPHERE images and the available light curves of this asteroid. We analyzed the dynamics of the satellite with the Genoid meta-heuristic algorithm. Finally, we studied the shape of Euphrosyne using hydrostatic equilibrium models. Conclusions. Our SPHERE observations show that Euphrosyne has a nearly spherical shape with the sphericity index of 0.9888 and its surface lacks large impact craters. Euphrosyne’s diameter is 268 ± 6 km, making it one of the top ten largest main belt asteroids. We detected a satellite of Euphrosyne – S/2019 (31) 1 – that is about 4 km across, on a circular orbit. The mass determined from the orbit of the satellite together with the volume computed from the shape model imply a density of 1665 ± 242 kg m−3, suggesting that Euphrosyne probably contains a large fraction of water ice in its interior. We find that the spherical shape of Euphrosyne is a result of the reaccumulation process following the impact, as in the case of (10) Hygiea. However, our shape analysis reveals that, contrary to Hygiea, the axis ratios of Euphrosyne significantly differ from those suggested by fluid hydrostatic equilibrium following reaccumulation.

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Physical parameters of selected Gaia mass asteroids

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936380 ◽

2020 ◽

Vol 638 ◽

pp. A11

Author(s):

E. Podlewska-Gaca ◽

A. Marciniak ◽

V. Alí-Lagoa ◽

P. Bartczak ◽

T. G. Müller ◽

...

Keyword(s):

Thermal Inertia ◽

Physical Property ◽

Physical Parameters ◽

Good Precision ◽

Main Belt ◽

Shape Models ◽

Solar System Bodies ◽

Fundamental Physical Property ◽

Thermophysical Modeling ◽

The Masses

Context. Thanks to the Gaia mission, it will be possible to determine the masses of approximately hundreds of large main belt asteroids with very good precision. We currently have diameter estimates for all of them that can be used to compute their volume and hence their density. However, some of those diameters are still based on simple thermal models, which can occasionally lead to volume uncertainties as high as 20–30%. Aims. The aim of this paper is to determine the 3D shape models and compute the volumes for 13 main belt asteroids that were selected from those targets for which Gaia will provide the mass with an accuracy of better than 10%. Methods. We used the genetic Shaping Asteroids with Genetic Evolution (SAGE) algorithm to fit disk-integrated, dense photometric lightcurves and obtain detailed asteroid shape models. These models were scaled by fitting them to available stellar occultation and/or thermal infrared observations. Results. We determine the spin and shape models for 13 main belt asteroids using the SAGE algorithm. Occultation fitting enables us to confirm main shape features and the spin state, while thermophysical modeling leads to more precise diameters as well as estimates of thermal inertia values. Conclusions. We calculated the volume of our sample of main-belt asteroids for which the Gaia satellite will provide precise mass determinations. From our volumes, it will then be possible to more accurately compute the bulk density, which is a fundamental physical property needed to understand the formation and evolution processes of small Solar System bodies.

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The impact crater at the origin of the Julia family detected with VLT/SPHERE?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833477 ◽

2018 ◽

Vol 618 ◽

pp. A154 ◽

Cited By ~ 16

Author(s):

P. Vernazza ◽

M. Brož ◽

A. Drouard ◽

J. Hanuš ◽

M. Viikinkoski ◽

...

Keyword(s):

Numerical Simulations ◽

Adaptive Optics ◽

Impact Crater ◽

Large Fraction ◽

Family Studies ◽

High Angular Resolution ◽

Main Belt ◽

3D Shape ◽

The Family ◽

The Impact

Context. The vast majority of the geophysical and geological constraints (e.g., internal structure, cratering history) for main-belt asteroids have so far been obtained via dedicated interplanetary missions (e.g., ESA Rosetta, NASA Dawn). The high angular resolution of SPHERE/ZIMPOL, the new-generation visible adaptive-optics camera at ESO VLT, implies that these science objectives can now be investigated from the ground for a large fraction of D ≥ 100 km main-belt asteroids. The sharp images acquired by this instrument can be used to accurately constrain the shape and thus volume of these bodies (hence density when combined with mass estimates) and to characterize the distribution and topography of D ≥ 30 km craters across their surfaces. Aims. Here, via several complementary approaches, we evaluated the recently proposed hypothesis that the S-type asteroid (89) Julia is the parent body of a small compact asteroid family that formed via a cratering collisional event. Methods. We observed (89) Julia with VLT/SPHERE/ZIMPOL throughout its rotation, derived its 3D shape, and performed a reconnaissance and characterization of the largest craters. We also performed numerical simulations to first confirm the existence of the Julia family and to determine its age and the size of the impact crater at its origin. Finally, we utilized the images/3D shape in an attempt to identify the origin location of the small collisional family. Results. On the one hand, our VLT/SPHERE observations reveal the presence of a large crater (D ~ 75 km) in Julia’s southern hemisphere. On the other hand, our numerical simulations suggest that (89) Julia was impacted 30–120 Myrs ago by a D ~ 8 km asteroid, thereby creating a D ≥ 60 km impact crater at the surface of Julia. Given the small size of the impactor, the obliquity of Julia and the particular orientation of the family in the (a,i) space, the imaged impact crater is likely to be the origin of the family. Conclusions. New doors into ground-based asteroid exploration, namely, geophysics and geology, are being opened thanks to the unique capabilities of VLT/SPHERE. Also, the present work may represent the beginning of a new era of asteroid-family studies. In the fields of geophysics, geology, and asteroid family studies, the future will only get brighter with the forthcoming arrival of 30–40 m class telescopes like ELT, TMT, and GMT.

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Shape, size and multiplicity of main-belt asteroidsI. Keck Adaptive Optics survey

Icarus ◽

10.1016/j.icarus.2006.06.001 ◽

2006 ◽

Vol 185 (1) ◽

pp. 39-63 ◽

Cited By ~ 72

Author(s):

F MARCHIS ◽

M KAASALAINEN ◽

E HOM ◽

J BERTHIER ◽

J ENRIQUEZ ◽

...

Keyword(s):

Adaptive Optics ◽

Main Belt

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Volume uncertainty of (7) Iris shape models from disc-resolved images

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3153 ◽

2020 ◽

Vol 499 (3) ◽

pp. 4545-4560

Author(s):

G Dudziński ◽

E Podlewska-Gaca ◽

P Bartczak ◽

S Benseguane ◽

M Ferrais ◽

...

Keyword(s):

Adaptive Optics ◽

Angular Resolution ◽

The Body ◽

High Angular Resolution ◽

Shape Modelling ◽

Shape Models ◽

Uncertainty Calculation ◽

Substantial Error ◽

Error Bars ◽

Inversion Techniques

ABSTRACT High angular resolution disc-resolved images of (7) Iris collected by VLT/SPHERE instrument are allowed for the detailed shape modelling of this large asteroid revealing its surface features. If (7) Iris did not suffer any events catastrophic enough to disrupt the body (which is very likely) by studying its topography, we might get insights into the early Solar system’s collisional history. When it comes to internal structure and composition, thoroughly assessing the volume and density uncertainties is necessary. In this work, we propose a method of uncertainty calculation of asteroid shape models based on light curve and adaptive optics (AO) images. We apply this method on four models of (7) Iris produced from independent Shaping Asteroids using Genetic Evolution and All-Data Asteroid Modelling inversion techniques and multiresolution photoclinometry by deformation. Obtained diameter uncertainties stem from both the observations from which the models were scaled and the models themselves. We show that despite the availability of high-resolution AO images, the volume and density of (7) Iris have substantial error bars that were underestimated in the previous studies.

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Shape models and dynamical properties of basaltic asteroids outside the dynamical Vesta family

10.5194/epsc2021-217 ◽

2021 ◽

Author(s):

Volodymyr Troianskyi ◽

Dagmara Oszkiewicz ◽

Anna Marciniak ◽

Pawel Kankiewicz ◽

Dora Fohring ◽

...

Keyword(s):

Numerical Modeling ◽

Parent Body ◽

Thermal Parameters ◽

Orbital Elements ◽

Main Belt ◽

Preliminary Results ◽

Shape Models ◽

Photometric Observations ◽

Current Location ◽

Dynamical Properties

<p>Through numerical modeling, Nesvorny et al. (2008) showed that asteroids can migrate due to Yarkovsky drift and resonances to outside of the boundaries of the Vesta family. In particular, they found that objects which end up in the scattered resonances region (so-called Cell I, defined by orbital elements 2.2 AU < a < 2.3 AU, 0.05 < e < 0.2, 0 < i deg < 10 deg) typically have retrograde rotations and thermal parameters that maximize Yarkovsky drift rates. These autors also showed, that asteroids migrating to the low inclination region (Cell II defined by 2.32 AU < a < 2.48 AU, 0.05 < e < 0.2, 2 deg < i < 6 deg) should be predominantly prograde rotators.</p> <p>We performe photometric observations and determine spins and shapes of V-type objects in Cell I and Cell II in order to characterize the dynamical properties of these asteroids more accurately. The results of dynamical modelling show that some asteroids may have migrated to their current location from the Vesta family within ~2 Gy. There are objects, however, whose origin in another parent body may also be plausible. This may support the hypothesis that the number of differentiated basaltic objects in the inner and middle Main Belt should be much higher than previously assumed. We will present preliminary results for the first ~10 asteroids in Cell I and Cell II.</p>

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Adaptive optics and lightcurve data of asteroids: twenty shape models and information content analysis

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731456 ◽

2017 ◽

Vol 607 ◽

pp. A117 ◽

Cited By ~ 13

Author(s):

M. Viikinkoski ◽

J. Hanuš ◽

M. Kaasalainen ◽

F. Marchis ◽

J. Ďurech

Keyword(s):

Content Analysis ◽

Information Content ◽

Adaptive Optics ◽

Shape Models

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Brief summary of Kleť photographic search programme for minor planets

International Astronomical Union Colloquium ◽

10.1017/s0252921100031419 ◽

1999 ◽

Vol 173 ◽

pp. 189-192

Author(s):

J. Tichá ◽

M. Tichý ◽

Z. Moravec

Keyword(s):

Ccd Camera ◽

Minor Planet ◽

Minor Planets ◽

Main Belt

AbstractA long-term photographic search programme for minor planets was begun at the Kleť Observatory at the end of seventies using a 0.63-m Maksutov telescope, but with insufficient respect for long-arc follow-up astrometry. More than two thousand provisional designations were given to new Kleť discoveries. Since 1993 targeted follow-up astrometry of Kleť candidates has been performed with a 0.57-m reflector equipped with a CCD camera, and reliable orbits for many previous Kleť discoveries have been determined. The photographic programme results in more than 350 numbered minor planets credited to Kleť, one of the world's most prolific discovery sites. Nearly 50 per cent of them were numbered as a consequence of CCD follow-up observations since 1994.This brief summary describes the results of this Kleť photographic minor planet survey between 1977 and 1996. The majority of the Kleť photographic discoveries are main belt asteroids, but two Amor type asteroids and one Trojan have been found.

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Adaptive optics (astronomy)

AccessScience ◽

10.1036/1097-8542.yb990105 ◽

2015 ◽

Keyword(s):

Adaptive Optics

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