We apply our novel Markov-chain Monte Carlo (MCMC)-based algorithm for asteroid mass estimation to asteroid (16) Psyche, the target of NASA's eponymous Psyche mission, based on close encounters with 10 different asteroids, and obtain a mass of $(1.117 \pm 0.039) \times 10^{-11} $ solar masses. We ensure that our method works as expected by applying it to asteroids (1) Ceres and (4) Vesta, and find that the results are in agreement with the very accurate mass estimates for these bodies obtained by the Dawn mission. We then combine our mass estimate for Psyche with the most recent volume estimate to compute the corresponding bulk density as $(3.88 \pm 0.25)$ g/cm$^3$. The estimated bulk density rules out the possibility of Psyche being an exposed, solid iron core of a protoplanet, but is fully consistent with the recent hypothesis that ferrovolcanism would have occurred on Psyche.
(16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Discovery-class Psyche mission. Despite gaining considerable interest in the scientific community, Psyche's composition and formation remain unconstrained. Originally, Psyche was considered to be almost entirely composed of metal due to its high radar albedo and spectral similarities to iron meteorites. More recent telescopic observations suggest the additional presence of low-Fe pyroxene and exogenic carbonaceous chondrites on the asteroid's surface. To better understand the abundances of these additional m…
Radar observations show that (16) Psyche is one of the largest and most massive asteroids of the M-class located in the main belt, with a diameter of approximately 230 km. This fact makes Psyche a unique object since observations indicated an iron-nickel composition. It is believed that this body may be what was left of a metal core of an early planet that would have been fragmented over millions of years due to violent collisions. In this work we study a variety of dynamical aspects related to the surface, as well as, the environment around this asteroid. We use computational tools to explore…
Detection of Rotational Spectral Variation on the M-type asteroid (16) Psyche
小行星（16）Psyche具有科学价值，因为它的质量约占小行星带总质量的1%，被认为是原行星的残余金属核心。雷达观测表明，表面存在大量金属，硅酸盐的百分比很小。先前的地面观测显示，这颗小行星的近红外光谱和雷达回波存在旋转变化。然而，到目前为止，还没有综合多波长数据的综合研究。在这里，我们提出了旋转分辨近红外光谱（0.7-2.5微米）的（16）Psyche获得的美国宇航局红外望远镜设施。这些数据与小行星每个旋转阶段的形状模型相结合。从近红外光谱中提取的光谱带参数显示辉石带中心在~ 0.92至0.94微米之间变化。谱带中心值被用来计算小行星的辉石化学成分，其平均值为Fs 30 En 65 Wo 5。还观察到条带深度的变化，值范围为1.0至1.5%。使用新的实验室光谱校准，我们估计平均斜方辉石含量为6+/-1%。普赛克的质量亏损区，表现出最高的雷达回波，也表现出最高的光谱斜率值和最小的频带深度。普绪客的光谱特征表明，它的母体并不具有分化身体所期望的典型结构，或者导致其当前状态的事件序列比以前认为的更复杂。
We develop a shape model of asteroid 16 Psyche using observations acquired in a wide range of wavelengths: Arecibo S-band delay-Doppler imaging, Atacama Large Millimeter Array (ALMA) plane-of-sky imaging, adaptive optics (AO) images from Keck and the Very Large Telescope (VLT), and a recent stellar occultation. Our shape model has dimensions 278 (-4/+8) km x 238 (-4/+6) km x 171 (-1/+5) km, an effective spherical diameter Deff = 222 -1/+4 km, and a spin axis (ecliptic lon, lat) of (36 deg, -8 deg) +/- 2 deg. We survey all the features previously reported to exist, tentatively identify several …
The asteroid (16) Psyche is the largest of the M-type asteroids, which have been hypothesized to be the cores of disrupted planetesimals and the parent bodies of the iron meteorites. While recent evidence has collected against a pure metal composition for Psyche, its spectrum and radar properties remain anomalous. We observed (16) Psyche in thermal emission with the Atacama Large (sub-)Millimeter Array (ALMA) at a resolution of 30 km over 2/3 of its rotation. The diurnal temperature variations are at the $\sim$10 K level over most of the surface and are best fit by a smooth surface with a ther…
Asteroid (16) Psyche is notable for the largest M-type asteroid and has the high radar albedo among the main-belt asteroids. The object is likely a mixture of metal and silicates because of its lower bulk density than metallic materials and observations inferring the existence of silicate materials on the surface. Here, we numerically investigate the interior layout when the structure of Psyche consists of a spherical iron core and two types of silicate-rich layers (compressed and uncompressed ones resulting from the compaction process. We develop an inverse problem algorithm to determine the …
The bulk density of an asteroid informs us about its interior structure and composition. To constrain the bulk density one needs an estimate for the mass of the asteroid. The mass is estimated by analyzing an asteroid's gravitational interaction with another object, such as another asteroid during a close encounter. An estimate for the mass has typically been obtained with linearized least-squares methods despite the fact that this family of methods is not able to properly describe non-Gaussian parameter distributions. In addition, the uncertainties reported for asteroid masses in the literatu…
Enabling tomorrow's planetary defence and space resource economy: Autonomous fleet-based asteroid rendezvous missions
University of Liverpool（利物浦大学）；NASA（美国国家航空航天局）；Colorado Center for Astrodynamics, University of Colorado（科罗拉多大学轨道动力学中心）；Institute of Space and Astronautical Science (ISAS), JAXA（宇宙科学研究所 (ISAS)，日本宇宙航空研究开发机构）
Knowledge of the interior density distribution of an asteroid can reveal its composition and constrain its evolutionary history. However, most asteroid observational techniques are not sensitive to interior properties. We investigate the interior constraints accessible through monitoring variations in angular velocity during a close encounter. We derive the equations of motion for a rigid asteroid's orientation and angular velocity to arbitrary order and use them to generate synthetic angular velocity data for a representative asteroid on a close Earth encounter. We develop a toolkit AIME (Ast…
Outer main belt asteroid (223) Rosa is a possible flyby target of opportunity for ESA's (European Space Agency) JUpiter ICy moons Explorer (JUICE) mission when passing the asteroid belt on the way to Jupiter. The very low albedo and the featureless red spectra indicate a P-type asteroid in the Tholen taxonomy, though the yet known bulk density did not match very well this classification. Aim of this work was to derive new estimates for the mass and for the bulk density for (223) Rosa. The mass of Rosa was derived by analyzing the gravitational deflection of small `test' asteroids which had a c…
A rotating frequency analysis in a previous paper, showed that two samples of C and S-type asteroids belonging to the Main Belt, but not to any families, present two different values for the transition diameter to a Maxwellian distribution of the rotation frequency, respectively 48 and 33 km. In this paper, after a more detailed statistical analysis, aiming to verify that the result is physically relevant, we found a better estimate for the transition diameter, respectively $D_C = 44 \pm 2$ km and $D_S = 30 \pm 1$ km. The ratio between these estimated transition diameters, $D_C/D_S = 1.5 \pm 0…
Exploration of asteroid (101955) Bennu by the OSIRIS-REx mission has provided an in-depth look at this rubble-pile near-Earth asteroid. In particular, the measured gravity field and the detailed shape model of Bennu indicate significant heterogeneities in its interior structure, compatible with a lower density at its center. Here we combine gravity inversion methods with a statistical rubble-pile model to determine the density and size-frequency distribution (SFD) index of the rubble that constitutes Bennu. The best-fitting models indicate that the SFD of the interior is consistent with that o…
Asteroid (3200) Phaethon, a B-type asteroid, has been active during its perihelion passages. This asteroid is considered to be a source of the Geminid meteor stream. It is reported that this asteroid is spinning at a rotation period of $3.60 \ hr$ and has a top shape (an oblate body with an equatorial ridge) with a mean equatorial diameter of $6.25 \ km$. Here, we report that Phaethon's rotation state may be close to or above its critical rotation period when the bulk density is $0.5 \ - \ 1.5 \ {g/cm^3}$ (a typical bulk density of a B-type asteroid). We found that in this condition, the struc…
The triaxial ellipsoid dimensions, rotational pole, and bulk density of ESA Rosetta target asteroid (21) Lutetia
我们寻求小行星（21）Lutetia的最佳尺寸估计，其自旋轴的方向，和它的体积密度，假设它的形状是很好地描述了一个光滑的无特征的三轴椭球体，并评估偏离这一假设。方法.我们从307张用凯克II和VLT的自适应光学（AO）获得的小行星视星盘的图像中获得这些量，并将这些与最近的质量测定相结合，以估计体积密度。我们的最佳三轴椭球的Lutetia直径，仅基于我们的AO图像，是a x b x c = 132 x 101 x 93 km，不确定性为4 x 3 x 13 km，包括估计的系统学，旋转极点在5度内。ECJ 2000 [长，纬度] = [45，-7]或EQJ 2000 [RA，DEC] = [44，+9]。AO模型拟合本身具有1 x 1 x 8 km的内部精度，但很明显，无论是从有限的视角导出的模型还是在配套文件中给出的半径矢量模型，Lutetia都与理想化的椭球体有显着的偏差。特别是，长轴可能会被高估约10公里，单独从AO图像。因此，我们将半径矢量和椭球模型的最佳方面结合到一个混合椭球模型中，作为我们的最终结果，124 +/- 5 x 101 +/- 4 x 93 +/- 13 km，可用于估计体积，大小和投影面积。所采用的极位在5度以内。[长，纬度] = [52，-6]或[RA DEC] = [52，+12]。使用两个单独确定的质量和我们的混合模型的体积，我们估计密度为3.5 +/…
Context. CM-like asteroids (Ch and Cgh classes) are a major population within the broader C-complex, encompassing about 10% of the mass of the main asteroid belt. Their internal structure has been predicted to be homogeneous, based on their compositional similarity as inferred from spectroscopy (Vernazza et al., 2016, AJ 152, 154) and numerical modeling of their early thermal evolution (Bland & Travis, 2017, Sci. Adv. 3, e1602514). Aims. Here we aim to test this hypothesis by deriving the density of the CM-like asteroid (41) Daphne from detailed modeling of its shape and the orbit of its small…
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%. 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 mas…
We use the known surface boulder-size distribution of the C-type rubble pile asteroid Ryugu (NEA 162173) to determine its macroporosity, assuming it is a homogeneous granular aggregate. We show that the volume-frequency distribution of its boulders, cobbles and pebbles, is well represented by a lognormal function with $σ= 2.4 \pm 0.1$ and $μ= 0.2 \pm 0.05$. Application of linear-mixture packing theory yields a value for the macroporosity of $ϕ= 0.14 \pm 0.04$. Given its low bulk density of 1.19 gm cm$^{-3}$, this implies an average density for Ryugu's rocks of $1.38 \pm 0.07$ gm cm$^{-3}$ thro…
The thermal inertia of an asteroid's surface can provide insight into regolith properties, such as the presence of a layer of fine dust, the density and thermal conductivity of a rocky surface, and, together with other observational data, mineralogy. Knowledge of the surface characteristics of asteroids is important for planetary defense initiatives and the extraction of resources ("asteroid mining"). A simple means of estimating asteroid thermal inertia has been proposed by Harris & Drube, which is suitable for application to large sets of thermal-infrared observational data, such as those ob…
An increasing number of Near Earth Asteroids (NEAs) in the range of a few hundred meters to a few kilometres in size have relatively high spin rates, from less than 4 h, down to $\sim$2.2 h, depending on spectral type. For some of these bodies, local acceleration near the equator may be directed outwards so that lift off of near-equatorial material is possible. In particular, this may be the case for asteroid Didymos, the primary of the (65803) Didymos binary system, which is the target of the DART (NASA) and Hera (ESA) space missions. The study of the dynamics of particles in such an environm…
We report observations of the Jupiter Trojan asteroid (3548) Eurybates and its satellite Queta with the Hubble Space Telescope and use these observations to perform an orbital fit to the system. Queta orbits Eurybates with a semimajor axis of $2350\pm11$ km at a period of $82.46\pm0.06$ days and an eccentricity of $0.125\pm0.009$. From this orbit we derive a mass of Eurybates of $1.51\pm0.03 \times 10^{17}$ kg, corresponding to an estimated density of $1.1\pm0.3$ g cm$^{-3}$, broadly consistent with densities measured for other Trojans, C-type asteroids in the outer main asteroid belt, and sma…
Digital tracking enables telescopes to detect asteroids several times fainter than conventional techniques. We describe our optimized methodology to acquire, process, and interpret digital tracking observations, and we apply it to probe the apparent magnitude distribution of main belt asteroids fainter than any previously detected from the ground. All-night integrations with the Dark Energy Camera (DECam) yield 95\% completeness at $R$ magnitude 25.0, and useful sensitivity to $R=25.6$ mag when we use an analytical detection model to correct flux overestimation bias. In a single DECam field ob…
Context. The recent estimates of the 3D shape of the M/Xe-type triple asteroid system (216) Kleopatra indicated a density of 5 g.cm$^{-3}$. Such a high density implies a high metal content and a low porosity which is not easy to reconcile with its peculiar dumbbell shape. Aims. Given the unprecedented angular resolution of the VLT/SPHERE/ZIMPOL camera, we aim to constrain the mass and the shape of Kleopatra with high accuracy, hence its density. Methods. We combined our new VLT/SPHERE observations of Kleopatra recorded in 2017 and 2018 with archival data, as well as lightcurve, occultation, an…
The $\sim$4 km diameter main belt asteroid 6478 Gault has ejected dust intermittently since at least 2013. The character of the emission, including its episodic nature and the low speed of the ejected particles ($V \sim $ 0.15 m s$^{-1}$), is most consistent with mass loss from a body rotating near rotational breakup. Owing to dust contamination of the nucleus signal, this conclusion has not yet been confirmed. To test this idea, we have obtained new images of Gault in August 2020, in the absence of dust. Our photometry shows a lightcurve having a very small amplitude (maximum $\sim 0.05$ mag)…
The NASA Double Asteroid Redirection Test (DART) mission performed a kinetic impact on asteroid Dimorphos, the satellite of the binary asteroid (65803) Didymos, at 23:14 UTC on September 26, 2022 as a planetary defense test. DART was the first hypervelocity impact experiment on an asteroid at size and velocity scales relevant to planetary defense, intended to validate kinetic impact as a means of asteroid deflection. Here we report the first determination of the momentum transferred to an asteroid by kinetic impact. Based on the change in the binary orbit period, we find an instantaneous reduc…
Asteroids and other small bodies in the solar system tend to have irregular shapes, owing to their low gravity. This irregularity does not only apply to the topology, but also to the underlying geology, potentially containing regions of different densities and materials. The topology can be derived from optical observations, while the mass density distribution of an object is only observable, to some extent, in its gravitational field. In a companion paper, we presented geodesyNets, a neural network approach to infer the mass density distribution of an object from measurements of its gravitati…
