orbits of Jupiter and Saturn separated from each other. In principle, two mechanisms are possible: (i) planetesimal driven migration or (ii) encounters of both Jupiter and Saturn with a third planet (presumably Uranus or Neptune). The first mechanism results in an exponential migration, but the characteristic τ cannot be faster than 5 My. Given the incompatibility of this value of τ with the current structure of the asteroidbelt, this process can be excluded. The second mechanism, dubbed ’jumping-Jupiter evolution’, results in a radial displacement of the orbits of Jupiter and Saturn on a time scale shorter than 0.1 My, but the migration of the planets cannot be well represented by an exponential law. We have simulated the evolution of the asteroidbelt during a jumping-Jupiter evolution and we have found that the final orbital structure of the belt matches well the observed one, provided that the original belt had an approximately uniform inclination distribution that extended up to ∼ 20 ◦
The main asteroidbelt is a dynamically living relic, with the shapes, sizes, and surfaces of most asteroids being altered by ongoing collisional fragmentation and cratering events ( Bottke et al. 2015 ). Space probes and ground-based observations have revealed a fascinating variety among asteroid shapes, where large asteroids are nearly spherical ( Park et al. 2019 ; Vernazza et al. 2020 ) and small asteroids are irregularly shaped ( Durech ˇ et al. 2010 ; Shepard et al. 2017 ; Fujiwara et al. 2006 ; Thomas et al. 2012 ). Most asteroids with diameters greater than ∼100 km have likely kept their internal structure intact since their time of formation because the dynamical lifetime of those asteroids is estimated to be comparable to the age of the Solar system ( Bottke et al. 2005 ). There are a few exceptions comprising es- sentially the largest remnants of giant families (e.g., (10) Hygiea,
510 – Asteroid Physical Characteristics: Surfaces II
510.01 – 3-µm Spectroscopy of Asteroid 16 Psyche
Asteroid 16 Psyche, an M-type asteroid, is thought to be one of the most massive exposed iron metal object in the asteroidbelt. The high radar albedos of Psyche suggest that this differentiated asteroid is dominantly composed of metal. Psyche was previously found to be featureless in the 3-µm spectral region. However, in our study we found that this asteroid exhibits a 3-µm absorption feature, possibly indicating the presence of hydrated silicates.
2. Understand the physics of activity on MBCs 3. Directly sample water in the asteroidbelt and test if MBCs are a viable source for Earth's water
4. Use the observed structure of an MBC as a tracer of planetary system formation and evolution.
There are millions of asteroids orbiting the Sun. The largest are around 1000 km in diameter; we have no firm lower size limit. Most of them orbit the Sun neatly between the orbits of Mars and Jupiter, forming what we refer to as the “asteroidbelt”. However a good number have highly elliptical orbits taking them between the inner and outer Solar System, crossing the paths of some planets, which raises the issue of collisions. Some cross the Earth’s orbit, and during our planet’s 4.5 billion- year history, we have been hit a number of times; one impact helped end the age of the dinosaurs. When we look at our world, the Moon, or other planets such as Mars and Venus, we see bodies that have changed and evolved over time, making it hard to deduce how things got started. What we need to look at is the basic building material from which the Solar System formed, and also stuff involved in various stages of its development. The Solar System, like the thousands or more of other star and planet systems we have found so far, formed from the collapse of a cloud of cosmic gas and dust. In the outer reaches of the Solar System, where it is dark and very cold, there remains a lot of the unused construction material. There is one spacecraft out there looking at some of it, but an easier route is to let that material come to us. On occasion a collision or some other sort of interaction puts a lump of it into an orbit that brings it into the inner Solar System. These lumps
mapping of the asteroidbelt. Nature 505, 629–634.
Descamps, P., Marchis, F., Berthier, J., Emery, J. P., Duchˆene, G., de Pater, I., Wong, M. H., Lim, L., Hammel, H. B., Vachier, F., Wiggins, P., Teng- Chuen-Yu, J.-P., Peyrot, A., Pollock, J., Assafin, M., Vieira-Martins, R., Camargo, J. I. B., Braga-Ribas, F., Macomber, B., Feb. 2011. Triplicity and physical characteristics of Asteroid (216) Kleopatra. Icarus 211, 1022–1033. Fujiwara, A., Kawaguchi, J., Yeomans, D. K., Abe, M., Mukai, T., Okada, T., Saito, J., Yano, H., Yoshikawa, M., Scheeres, D. J., Barnouin-Jha, O. S., Cheng, A. F., Demura, H., Gaskell, G. W., Hirata, N., Ikeda, H., Kominato, T., Miyamoto, H., Nakamura, R., Sasaki, S., Uesugi, K., 2006. The Rubble- Pile Asteroid Itokawa as Observed by Hayabusa. Science 312, 1330–1334. Fulvio, D., Brunetto, R., Vernazza, P., Strazzulla, G., Jan. 2012. Space weath-
The mutual orbit
Our orbit determination software uses the separation and position angle of the secondary with respect to the primary to solve for the orbital parameters in the two-body problem. The mutual orbital plane orientation is assumed constant, but heliocentric motions and light-time correc- tions are taken into account. Astrometric positions and their errors are specified at the mid-time of the exposure sequence. Starting from thousands of initial conditions, the software adjusts for seven parameters (six orbital elements plus the mass of the system) in the nonlinear ordi- nary least squares problem with a Levenberg-Marquardt technique. The covariance matrix and post-fit residuals are computed and inspected. Binary orbits have been computed with this al- gorithm for near-Earth asteroids (S15, S16), main-belt asteroids (S17, 18), Kuiper belt objects (S6), dwarf planets, and binary stars.
During our study we explored 2 different types of conductive yarn: a copper wire yarn (3 copper wires of 112 µm), further called in the article a copper yarn belt and a silver plated polymer core yarn, as a silver yarn belt respectively. The electronic circuit is simple and consists of two inverters and two capacitors combined to form an oscillating circuit. The resonance frequency of the oscillating circuit is proportional to the inductance of the belt. The electronic components are assembled on 0.3mm PCB of 8mm x 8mm using a conventional assembly technique that includes a solder paste dispensing, SMD placement, followed by solder reflowing process. The electronic is designed in such way that it requires only 3 connections to the breathing belt.
Received 6 April 2020 / Accepted 2 June 2020
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.
primary diameter ratio D s /D p = 0.015 ± 0.005, where a is the
semimajor axis of the system, D s and D p are the diameter of
the satellite and the primary respectively, and R P is the radius of
the primary. The comparison of the properties of the Euphrosyne binary system to other large asteroid systems are shown in Fig. 5 . Compared to the other systems, S/2019 (31) 1 has one of the smallest secondary-to-primary diameter ratios and is very close to the primary. Given the small size of the satellite, S/2019 (31) is expected to be tidally locked, that is, its spin period synchronizes to its orbital period on a million year timescale ( Rojo & Margot
2009), its orbit is stable on timescales of 100 Myr or longer, as we have verified by backward dynamical evolution using the Mercury integrator (Chambers 1999) starting from the current orbital elements of Gault. This implies that Gault is a native member of the main belt. Among the possible causes for the ac- tivity in these objects, impact, rotational breakup, and ice sub- limation (or even a combination of these) are usually invoked (see Jewitt et al. 2015 for a complete description of the possi- ble mechanisms involved). In principle, ice-sublimation-related activity on Gault seems unlikely owing to its character of inner beltasteroid. Likewise, the occurrence of two succesive impacts seems rather improbable.
, the color variation across the disk reflects a variation of albedo rather than a variation in topography. A map of the albedo variegation is shown in Fig. A.4 .
(α max = 8.7 ◦ ). This was verified by testing the Hapke param-
eters of other asteroid types, resulting in similar shape models. The best point-spread function (PSF) to use for the convolution of the synthetic images was determined by testing a range of Gaussian PSF on the ADAM model. The PSF resulting in the low- est χ 2 had a full width at half maximum (FWHM) of 2.1 pixels
Results for Ryugu have been obtained assuming minimum and maximum particle sizes of 0.02 m and 140 m, respectively, and these results are robust with respect to the cutoff at small particle sizes D min . Only shifting the cutoff D min to values larger than 0.30 m has a noticeable effect on the macroporosity. The upper cutoff size D max was chosen to correspond to the Otohime boulder, which is the largest boulder observed on Ryugu's surface. However, boulders larger than Otohime could potentially reside in Ryugu's interior, which would decrease the obtained macroporosity through a filling of void spaces. Reasonable upper limits on monolith sizes are 200 m, as derived from observations of fast rotators in the asteroid population (Pravec & Harris, 2000 ) and the catastrophic disruption threshold (Benz & Asphaug, 1999 ; Jutzi et al., 2010 ). Assum- ing D max = 200 m reduces ϕ Macro to 15%.
over the year, but the number of cold cloud points is so small in JAS (Fig. 1b) that NAT-like points are almost negligible during this season. This percentage and spatial distribution are consistent with results from Chepfer et al. (2007).
Moreover, both the NAT-like spatial distribution (Fig. 4) and the values of color ratio (Fig. 3b) are in extremely good agreement with the tropical tropopause NAT belt suggested by Voigt et al. 2008 (Fig. 4 and 7) - i.e. the particle size measured in situ and the NAT-like geographical distribution predicted by global chemistry model.
R E S U M E
APPROCHE METALLOGENIQUE DU "GREENSTONE BELT" DE BOGOI N (R . C .A . ) . SA MINERALISATION EN OR.
La min éral i s at i on aur ifère primai re du secteur de Bogoi n se pré sente sous forme d ' un stockwerk quartz'eux de d i rect i on N-S enc ai s sé dan s des roches vertes . Ces dern i ères app art iennent à une sér i e méta morph i que ( l imite fac i ès sch i stes verts-amph i bol i te ) pl i ssée en un syn c l i nori um de d i �ection N-S qu i dess i ne un "doi gt de gant " dans un vaste mas s i f gran i to-gnei s s i que . La fo l i ation pri nci pale (SP) est p l an axi al de cette structure . L ' ensemb l e est réputé archéen . Le sync l i n al s l en noi e vers l e Sud sous une couverture gréso-quartzi t i que protérozoïque supérieur .
The asteroid (144898) 2004 VD17 is a Near Earth Object (NEO) belong- ing to the Apollo group, discovered by the LINEAR asteroid survey on the 7th of November, 2004. Its orbital parameters are summarized in Table 1. It will encounter the Earth several times during the next 100 years: in 2032, 2041, 2067 and 2102. Between February and May 2006, the available astrom- etry did not exclude the possibility of an impact with the Earth at the last encounter of the sequence, the one taking place in early May 2102. This impact was rated 2 on the Torino Scale (TS, Binzel 2000) and in excess of
For asteroids smaller than ~10 km, which are expected to be rub- ble piles with no internal differentiation (8), there is a more limited history of gravity field measurements and interpretations. The NEAR (Near Earth Asteroid Rendezvous) mission measured the gravity field of the ~10-km asteroid (433) Eros up to degree and order 10 (9, 10). A direct comparison of Eros’ measured gravity field with the constant-density field computed from its shape was found to be statistically relevant up to degree and order 6 and showed al- most no heterogeneity within the body, although there were some indications of a possible surface layer of less dense material (11). Furthermore, comparison of its bulk density with its meteorite ana- log indicated a porosity of 10 to 30% for the asteroid (12). From these observations, Eros was classified as a “shattered monolith,” a body whose interior was likely fractured, which had never been fully disassembled or accreted from multiple other bodies. The Hayabusa mission to the ~320-m-diameter asteroid (25143) Itokawa found a very different situation. Although the mission was unable to mea- sure the asteroid’s higher-order gravity field coefficients, the overall bulk density of Itokawa, together with its S-type classification, indi- cated a porosity of 41% (13), which, combined with the visual appearance, demonstrated that this body was a rubble pile. There have been tentative constraints placed on Itokawa’s mass distribu- tion consistent with its “head” having a higher density than its over- all “body”; however, these have not been directly tested (14, 15) and may be explained by other interpretations (16).