scholarly journals VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis

2021 ◽  
Vol 654 ◽  
pp. A56
Author(s):  
P. Vernazza ◽  
M. Ferrais ◽  
L. Jorda ◽  
J. Hanuš ◽  
B. Carry ◽  
...  
Keyword(s):  
Rotation Period ◽  
High Angular Resolution ◽  
Main Belt ◽  
Volume Estimate ◽  
Multiple Systems ◽  
3D Shape ◽  
Asteroid Exploration ◽  
Reconstruction Methods ◽  
C Complex ◽  
Compositional Diversity

Context. Until recently, the 3D shape, and therefore density (when combining the volume estimate with available mass estimates), and surface topography of the vast majority of the largest (D  ≥ 100 km) main-belt asteroids have remained poorly constrained. The improved capabilities of the SPHERE/ZIMPOL instrument have opened new doors into ground-based asteroid exploration. Aims. To constrain the formation and evolution of a representative sample of large asteroids, we conducted a high-angular-resolution imaging survey of 42 large main-belt asteroids with VLT/SPHERE/ZIMPOL. Our asteroid sample comprises 39 bodies with D  ≥ 100 km and in particular most D  ≥ 200 km main-belt asteroids (20/23). Furthermore, it nicely reflects the compositional diversity present in the main belt as the sampled bodies belong to the following taxonomic classes: A, B, C, Ch/Cgh, E/M/X, K, P/T, S, and V. Methods. The SPHERE/ZIMPOL images were first used to reconstruct the 3D shape of all targets with both the ADAM and MPCD reconstruction methods. We subsequently performed a detailed shape analysis and constrained the density of each target using available mass estimates including our own mass estimates in the case of multiple systems. Results. The analysis of the reconstructed shapes allowed us to identify two families of objects as a function of their diameters, namely “spherical” and “elongated” bodies. A difference in rotation period appears to be the main origin of this bimodality. In addition, all but one object (216 Kleopatra) are located along the Maclaurin sequence with large volatile-rich bodies being the closest to the latter. Our results further reveal that the primaries of most multiple systems possess a rotation period of shorter than 6 h and an elongated shape (c∕a ≤ 0.65). Densities in our sample range from ~1.3 g cm−3 (87 Sylvia) to ~4.3 g cm−3 (22 Kalliope). Furthermore, the density distribution appears to be strongly bimodal with volatile-poor (ρ ≥ 2.7 g cm−3) and volatile-rich (ρ ≤ 2.2 g cm−3) bodies. Finally, our survey along with previous observations provides evidence in support of the possibility that some C-complex bodies could be intrinsically related to IDP-like P- and D-type asteroids, representing different layers of a same body (C: core; P/D: outer shell). We therefore propose that P/ D-types and some C-types may have the same origin in the primordial trans-Neptunian disk.

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

2018 ◽  
Vol 618 ◽  
pp. A154 ◽  
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.

scholarly journals Asteroid (16) Psyche’s primordial shape: A possible Jacobi ellipsoid

2020 ◽  
Vol 638 ◽  
pp. L15 ◽  
Author(s):  
M. Ferrais ◽  
P. Vernazza ◽  
L. Jorda ◽  
N. Rambaux ◽  
J. Hanuš ◽  
...  
Keyword(s):  
Bulk Composition ◽  
Three Dimensional ◽  
Rotation Period ◽  
Data Sets ◽  
Similar Data ◽  
Small Deviations ◽  
3D Shape ◽  
Large Program ◽  
Solar System Object ◽  
Equilibrium Figures

Context. Asteroid (16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Psyche mission. It is also the only asteroid of this size (D >  200 km) known to be metal rich. Although various hypotheses have been proposed to explain the rather unique physical properties of this asteroid, a perfect understanding of its formation and bulk composition is still missing. Aims. We aim to refine the shape and bulk density of (16) Psyche and to perform a thorough analysis of its shape to better constrain possible formation scenarios and the structure of its interior. Methods. We obtained disk-resolved VLT/SPHERE/ZIMPOL images acquired within our ESO large program (ID 199.C-0074), which complement similar data obtained in 2018. Both data sets offer a complete coverage of Psyche’s surface. These images were used to reconstruct the three-dimensional (3D) shape of Psyche with two independent shape modeling algorithms (MPCD and ADAM). A shape analysis was subsequently performed, including a comparison with equilibrium figures and the identification of mass deficit regions. Results. Our 3D shape along with existing mass estimates imply a density of 4.20  ±  0.60 g cm−3, which is so far the highest for a solar system object following the four telluric planets. Furthermore, the shape of Psyche presents small deviations from an ellipsoid, that is, prominently three large depressions along its equator. The flatness and density of Psyche are compatible with a formation at hydrostatic equilibrium as a Jacobi ellipsoid with a shorter rotation period of ∼3h. Later impacts may have slowed down Psyche’s rotation, which is currently ∼4.2 h, while also creating the imaged depressions. Conclusions. Our results open the possibility that Psyche acquired its primordial shape either after a giant impact while its interior was already frozen or while its interior was still molten owing to the decay of the short-lived radionuclide 26Al.

scholarly journals NGTS clusters survey – I. Rotation in the young benchmark open cluster Blanco 1

2020 ◽  
Vol 492 (1) ◽  
pp. 1008-1024 ◽  
Author(s):  
Edward Gillen ◽  
Joshua T Briegal ◽  
Simon T Hodgkin ◽  
Daniel Foreman-Mackey ◽  
Floor Van Leeuwen ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Open Cluster ◽  
Rotation Period ◽  
High Mass ◽  
Single Star ◽  
Multiple Systems ◽  
Rotation Periods ◽  
M Stars ◽  
Photometric Monitoring ◽  
Rotation Sequence

ABSTRACT We determine rotation periods for 127 stars in the ∼115-Myr-old Blanco 1 open cluster using ∼200 d of photometric monitoring with the Next Generation Transit Survey. These stars span F5–M3 spectral types (1.2 M⊙ ≳ M ≳ 0.3 M⊙) and increase the number of known rotation periods in Blanco 1 by a factor of four. We determine rotation periods using three methods: Gaussian process (GP) regression, generalized autocorrelation function (G-ACF), and Lomb–Scargle (LS) periodogram, and find that the GP and G-ACF methods are more applicable to evolving spot modulation patterns. Between mid-F and mid-K spectral types, single stars follow a well-defined rotation sequence from ∼2 to 10 d, whereas stars in photometric multiple systems typically rotate faster. This may suggest that the presence of a moderate-to-high mass ratio companion inhibits angular momentum loss mechanisms during the early pre-main sequence, and this signature has not been erased at ∼100 Myr. The majority of mid-F to mid-K stars display evolving modulation patterns, whereas most M stars show stable modulation signals. This morphological change coincides with the shift from a well-defined rotation sequence (mid-F to mid-K stars) to a broad rotation period distribution (late-K and M stars). Finally, we compare our rotation results for Blanco 1 to the similarly aged Pleiades: the single-star populations in both clusters possess consistent rotation period distributions, which suggests that the angular momentum evolution of stars follows a well-defined pathway that is, at least for mid-F to mid-K stars, strongly imprinted by ∼100 Myr.

scholarly journals An Efficient and Lightweight Illumination Model for Planetary Bodies Including Direct and Diffuse Radiation

2020 ◽  
Vol 6 (9) ◽  
pp. 84
Author(s):  
Marco Scharringhausen ◽  
Lars Witte
Keyword(s):  
Small Body ◽  
Diffuse Radiation ◽  
Radiation Wavelength ◽  
Main Belt ◽  
Multiple Systems ◽  
Direct Radiation ◽  
Illumination Model ◽  
Digital Terrain ◽  
Simulated Images ◽  
Tracing Method

We present a numerical illumination model to calculate direct as well as diffuse or Hapke scattered radiation scenarios on arbitrary planetary surfaces. This includes small body surfaces such as main belt asteroids as well as e.g., the lunar surface. The model is based on the ray tracing method. This method is not restricted to spherical or ellipsoidal shapes but digital terrain data of arbitrary spatial resolution can be fed into the model. Solar radiation is the source of direct radiation, wavelength-dependent effects (e.g. albedo) can be accounted for. Mutual illumination of individual bodies in implemented (e.g. in binary or multiple systems) as well as self-illumination (e.g. crater floors by crater walls) by diffuse or Hapke radiation. The model is validated by statistical methods. A χ2 test is utilized to compare simulated images with DAWN images acquired during the survey phase at small body 4 Vesta and to successfully prove its validity.

scholarly journals The close circumstellar environment of Betelgeuse

2018 ◽  
Vol 609 ◽  
pp. A67 ◽  
Author(s):  
Pierre Kervella ◽  
Leen Decin ◽  
Anita M. S. Richards ◽  
Graham M. Harper ◽  
Iain McDonald ◽  
...  
Keyword(s):  
Mass Loss ◽  
Hot Spot ◽  
Rotation Period ◽  
Line Emission ◽  
Rotation Velocity ◽  
Polar Axis ◽  
Position Angle ◽  
Convection Cell ◽  
High Angular Resolution ◽  
Angular Rotation

We observed Betelgeuse using ALMA’s extended configuration in band 7 (f ≈ 340 GHz, λ ≈ 0.88 mm), resulting in a very high angular resolution of 18 mas. Using a solid body rotation model of the 28SiO(ν= 2, J = 8−7) line emission, we show that the supergiant is rotating with a projected equatorial velocity of νeqsini = 5.47 ± 0.25 km s-1 at the equivalent continuum angular radius Rstar = 29.50 ± 0.14 mas. This corresponds to an angular rotation velocity of ω sini = (5.6 ± 1.3) × 10-9 rad s-1. The position angle of its north pole is PA = 48.0 ± 3.5°. The rotation period of Betelgeuse is estimated to P/ sini = 36 ± 8 years. The combination of our velocity measurement with previous observations in the ultraviolet shows that the chromosphere is co-rotating with the star up to a radius of ≈ 10 au (45 mas or 1.5 × the ALMA continuum radius). The coincidence of the position angle of the polar axis of Betelgeuse with that of the major ALMA continuum hot spot, a molecular plume, and a partial dust shell (from previous observations) suggests that focused mass loss is currently taking place in the polar region of the star. We propose that this hot spot corresponds to the location of a particularly strong “rogue” convection cell, which emits a focused molecular plume that subsequently condenses into dust at a few stellar radii. Rogue convection cells therefore appear to be an important factor shaping the anisotropic mass loss of red supergiants.

Small body exploration in China

2020 ◽  
Author(s):  
Jiangchuan Huang ◽  
Xiaojing Zhang ◽  
Tong Wang ◽  
Zhuoxi Huo ◽  
Xian Shi ◽  
...  
Keyword(s):  
Solar System ◽  
Design Research ◽  
Small Body ◽  
Measurement Data ◽  
Main Belt ◽  
Small Bodies ◽  
Asteroid Exploration ◽  
Full Picture ◽  
Exploration Mission ◽  
And Migration

<p align="left"><span>The past twenty years have seen an evolution in the definition and categorization of small bodies in the Solar System. While new types of bodies are being discovered at an increasing pace, objects familiar to us have been rediscovered with traits previously unknown, resulting in “hybrid” bodies like “Main-belt comets” or “active asteroids” [1]. New knowledges of small bodies are essential to further our understanding of the solar system as they directly shed light on planetary formation and evolution scenarios, the distribution and migration of water, and the emergence of life. To get a full picture of these small bodies, it is necessary to carry out detailed and comprehensive investigations, especially with dedicated space missions. As demonstrated by the success of a number of such missions recently completed and ongoing, a growing consensus is emerging that future missions should: 1) cover a diversity of targets, especially those never visited before; 2) characterize the structure and composition of the target body with highest possible resolution. The first Chinese small body mission is designed to take on both challenges by performing sample return from a quasi-satellite of the Earth—2016 HO3 and visiting for the first time a “main-belt comet”--133P/Elst-Pizarro.</span></p> <p align="left"><a name="_GoBack"></a><span>In April 2019, CNSA released an open call of onboard opportunity for an asteroid exploration mission [2]<span lang="zh-CN">，</span>which encourages international cooperation. This asteroid exploration mission is characterized by multi-task, multi-target and multi-mode (e. g. joint exploration by multiple devices, landing and sampling etc.). On the basis of feasibility demonstration, design research and key techniques research, various work of the mission is currently in progress, such as the scientific research of small celestial particles, that is, combining remote sensing and surface in-situ measurement data and features of different scales (sub-millimeter to decimeter) to obtain clues of composition and evolution of small bodies. </span></p> <p align="left"> </p> <p align="left"><span>[1] Hsieh, Henry H., David C. Jewitt, and Yanga R. Fernández. The Astronomical Journal 127(5):2997. (2004).</span></p> <p align="left"><span>[2] http://www.cnsa.gov.cn/n6758823/n6758839/c6805886/part/6780392.pdf </span></p>

scholarly journals How many satellites have been discovered in the Solar System after Galileo?

2010 ◽  
Vol 6 (S269) ◽  
pp. 250-253
Author(s):  
Zhanna Pozhalova ◽  
Dmitrij Lupishko
Keyword(s):  
Solar System ◽  
Kuiper Belt ◽  
Main Belt ◽  
Trojan Asteroids ◽  
Kuiper Belt Objects ◽  
Multiple Systems ◽  
Natural Satellites ◽  
Near Earth Asteroids

AbstractBy the beginning of 2010 the total number of natural satellites and multiple systems in the Solar System was equal to 350, including: 168 satellites of large planets, 119 multiple asteroids (including main-belt and near-Earth asteroids, Mars-crossers and Jupiter Trojan asteroids) and 63 multiple transneptunian and Kuiper-belt objects. Meanwhile, we cannot count precisely how many moons in total have been discovered to date due to the deficiency of accepted definitions.

scholarly journals Space weathering of asteroids: similarities and discrepancies between Main Belt asteroids and NEOs

2006 ◽  
Vol 2 (S236) ◽  
pp. 239-242 ◽  
Author(s):  
S. Marchi ◽  
P. Paolicchi ◽  
M. Lazzarin ◽  
S. Magrin
Keyword(s):  
Ion Flux ◽  
Space Weathering ◽  
The Sun ◽  
Spectral Slope ◽  
Main Belt ◽  
Complex Objects ◽  
General Behavior ◽  
The Poor ◽  
C Complex ◽  
Near Earth Objects

AbstractA sample of 35 C–complex objects is present among near–Earth objects. In spite of the poor statistics, some striking differences compared to Main Belt asteroids can be established: for instance the percentage of near–Earth objects (NEOs) showing hydration features is very small. Moreover the spectral slope of C–complex NEOs seems to be anti–correlated with the exposure to the ion flux coming from the Sun, in contrast with the general behavior of C–complex Main Belt asteroids (and of most asteroids, in general). We discuss some possible implications and suggest some preliminary partial explanations.

scholarly journals Questioning the spatial origin of complex organic molecules in young protostars with the CALYPSO survey

2020 ◽  
Vol 635 ◽  
pp. A198 ◽  
Author(s):  
A. Belloche ◽  
A. J. Maury ◽  
S. Maret ◽  
S. Anderl ◽  
A. Bacmann ◽  
...  
Keyword(s):  
Organic Molecules ◽  
A Priori ◽  
Accurate Determination ◽  
High Angular Resolution ◽  
Evolutionary Status ◽  
Multiple Systems ◽  
Chemical Differentiation ◽  
Low Mass ◽  
Accretion Shock ◽  
Complex Organic

Context. Complex organic molecules (COMs) have been detected in a few Class 0 protostars but their origin is not well understood. While the usual picture of a hot corino explains their presence as resulting from the heating of the inner envelope by the nascent protostar, shocks in the outflow, disk wind, the presence of a flared disk, or the interaction region between envelope and disk at the centrifugal barrier have also been claimed to enhance the abundance of COMs. Aims. Going beyond studies of individual objects, we want to investigate the origin of COMs in young protostars on a statistical basis. Methods. We use the CALYPSO survey performed with the Plateau de Bure Interferometer of the Institut de Radioastronomie Millimétrique to search for COMs at high angular resolution in a sample of 26 solar-type protostars, including 22 Class 0 and four Class I objects. We derive the column densities of the detected molecules under the local thermodynamic equilibrium approximation and search for correlations between their abundances and with various source properties. Results. Methanol is detected in 12 sources and tentatively in one source, which represents half of the sample. Eight sources (30%) have detections of at least three COMs. We find a strong chemical differentiation in multiple systems with five systems having one component with at least three COMs detected but the other component devoid of COM emission. All sources with a luminosity higher than 4 L⊙ have at least one detected COM whereas no COM emission is detected in sources with internal luminosity lower than 2 L⊙, likely because of a lack of sensitivity. Internal luminosity is found to be the source parameter impacting the COM chemical composition of the sources the most, while there is no obvious correlation between the detection of COM emission and that of a disk-like structure. A canonical hot-corino origin may explain the COM emission in four sources, an accretion-shock origin in two or possibly three sources, and an outflow origin in three sources. The CALYPSO sources with COM detections can be classified into three groups on the basis of the abundances of oxygen-bearing molecules, cyanides, and CHO-bearing molecules. These chemical groups correlate neither with the COM origin scenarios, nor with the evolutionary status of the sources if we take the ratio of envelope mass to internal luminosity as an evolutionary tracer. We find strong correlations between molecules that are a priori not related chemically (for instance methanol and methyl cyanide), implying that the existence of a correlation does not imply a chemical link. Conclusions. The CALYPSO survey has revealed a chemical differentiation in multiple systems that is markedly different from the case of the prototypical binary IRAS 16293-2422. This raises the question of whether all low-mass protostars go through a phase showing COM emission. A larger sample of young protostars and a more accurate determination of their internal luminosity will be necessary to make further progress. Searching for correlations between the COM emission and the jet/outflow properties of the sources may also be promising.

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