Ultraviolet and visible photometry of asteroid (21) Lutetia using the Hubble Space Telescope
H. A. Weaver, P. D. Feldman, W. J. Merline, M. J. Mutchler, M. F. A'Hearn, J. -L. Bertaux, L. M. Feaga, J. W. Parker, D. C. Slater, A. J. Steffl, C. R. Chapman,… 展开作者
H. A. Weaver, P. D. Feldman, W. J. Merline, M. J. Mutchler, M. F. A'Hearn, J. -L. Bertaux, L. M. Feaga, J. W. Parker, D. C. Slater, A. J. Steffl, C. R. Chapman, J. D. Drummond, S. A. Stern
The asteroid (21) Lutetia is the target of a planned close encounter by the Rosetta spacecraft in July 2010. To prepare for that flyby, Lutetia has been extensively observed by a variety of astronomical facilities. We used the Hubble Space Telescope (HST) to determine the albedo of Lutetia over a wide wavelength range, extending from ~150 nm to ~700 nm. Using data from a variety of HST filters and a ground-based visible light spectrum, we employed synthetic photometry techniques to derive absolute fluxes for Lutetia. New results from ground-based measurements of Lutetia's size and shape were used to convert the absolute fluxes into albedos. We present our best model for the spectral energy distribution of Lutetia over the wavelength range 120-800 nm. There appears to be a steep drop in the albedo (by a factor of ~2) for wavelengths shorter than ~300 nm. Nevertheless, the far ultraviolet albedo of Lutetia (~10%) is considerably larger than that of typical C-chondrite material (~4%). The geometric albedo at 550 nm is 16.5 +/- 1%. Lutetia's reflectivity is not consistent with a metal-dominated surface at infrared or radar wavelengths, and its albedo at all wavelengths (UV-visibile-IR-radar) is larger than observed for typical primitive, chondritic material. We derive a relatively high FUV albedo of ~10%, a result that will be tested by observations with the Alice spectrograph during the Rosetta flyby of Lutetia in July 2010.
A crucial topic in planetology research is establishing links between primitive meteorites and their parent asteroids. In this study we investigate the feasibility of a connection between asteroids similar to 21 Lutetia, encountered by the Rosetta mission in July 2010, and the CH3 carbonaceous chondrite Pecora Escarpment 91467 (PCA 91467). Several spectra of this meteorite were acquired in the ultraviolet to near-infrared (0.3 to 2.2 μm) and in the mid-infrared to thermal infrared (2.5 to 30.0 μm or 4000 to ~333 cm^-1), and they are compared here to spectra from the asteroid 21 Lutetia. There …
During the flyby in 2010, the OSIRIS camera on-board Rosetta acquired hundreds of high-resolution images of asteroid Lutetia's surface through a range of narrow-band filters. While Lutetia appears very bland in the visible wavelength range, Magrin et al. (2012) tentatively identified UV color variations in the Baetica cluster, a group of relatively young craters close to the north pole. As Lutetia remains a poorly understood asteroid, such color variations may provide clues to the nature of its surface. We take the color analysis one step further. First we orthorectify the images using a shape…
Inhomogeneities on the surface of 21 Lutetia, the asteroid target of the Rosetta mission
背景：2010年7月，欧空局的罗塞塔号航天器将飞越主带小行星21 Lutetia。到目前为止，已经对这颗小行星进行了几次观测，但它的表面组成和性质仍然是一个有争议的问题。很长一段时间以来，Lutetia被认为具有金属性质，因为它具有高的IRAS反射率。后来有人提出它的表面成分类似于原始的碳质球粒陨石，而进一步的观察则提出它可能与更进化的顽火辉石球粒陨石有遗传联系。目标：为了在解决Lutetia性质的难题方面做出重要贡献，我们于2008年11月在Telescopio Nazionale Galileo（TNG，La Palma，西班牙）对这颗小行星进行了可见光谱观测。方法：在不同旋转相位下获得13个可见光谱。研究结果：我们证实了Lazzarin等人（2009年）在Lutetia光谱中发现的约0.47-0.48微米处的窄光谱特征的存在。我们还发现了Lazzarin等人（2004年）在Lutetia光谱中发现的约0.6微米的光谱特征。更重要的是，我们的光谱在0.6和0.75微米之间表现出不同的光谱斜率，特别是，我们发现高达20%的Lutetia表面可以具有更平坦的光谱。结论：我们在不同的旋转阶段检测到光谱斜率的变化，这可以解释为可能是由于化学/矿物成分的差异，以及Lutetia表面结构的不均匀性（例如，在南半球的陨石坑或火山点的存在）。
One of the most accurate models currently used to represent the gravity field of irregular bodies is the polyhedral approach. In this model, the mass of the body is assumed to be homogeneous, which may not be true for a real object. The main goal of the present paper is to study the dynamical effects induced by three different internal structures (uniform, three- and four-layers) of asteroid (21) Lutetia, an object that recent results from space probe suggest being at least partially differentiated. The Mascon gravity approach used in the present work, consists of dividing each tetrahedron int…
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 +/…
Analytical modeling of the gravitational potential of irregularly shaped celestial bodies considering three distinct internal structures: application to (21) Lutetia
(21) Lutetia has been visited by Rosetta mission on July 2010 and observed with a phase angle ranging from 0.15 to 156.8 degrees. The Baetica region, located at the north pole has been extensively observed by OSIRIS cameras system. Baetica encompass a region called North Pole Crater Cluster (NPCC), shows a cluster of superposed craters which presents signs of variegation at the small phase angle images. For studying the location, we used 187 images distributed throughout 14 filter recorded by the NAC (Narrow Angle Camera) and WAC (Wide Angle Camera) taken during the fly-by. We photometrically …
We present ultraviolet photometry (NUV band, 180--280 nm) of 405 asteroids observed serendipitously by the Galaxy Evolution Explorer (GALEX) from 2003--2012. All asteroids in this sample were detected by GALEX at least twice. Unambiguous visible-color-based taxonomic labels (C type versus S type) exist for 315 of these asteroids; of these, thermal-infrared-based diameters are available for 245. We derive NUV-V color using two independent models to predict the visual magnitude V at each NUV-detection epoch. Both V models produce NUV-V distributions in which the S types are redder than C types w…
The need for more accurate asteroid models is perhaps secondary to the need to measure their quality. The uncertainties of models' parameters propagate to quantities like volume or density -- the most important and informative properties of asteroids -- affecting conclusions about their physical nature. Our knowledge on shapes and spins of small solar system bodies comes mostly from visual, disk-integrated photometry. In this work we present a method for asteroid model uncertainty assessment based on visual photometry (lightcurves and sparse-in-time absolute measurements) allowing the determin…
Aims. The aim of our study is to obtain the near-ultraviolet to visible (NUV-VIS, 0.35 - 0.95 micron) reflectance spectra of primitive asteroids with a focus on members of the Themis and Polana-Eulalia complex families. This characterization allows us to discuss the origin of two recent sample return mission target asteroids, (162173) Ryugu and (101955) Bennu. Methods. We obtain low-resolution visible spectra of target asteroids down to 0.35 micron using the telescopes located at the Roque de los Muchachos Observatory and revisit spectroscopic data that have already been published. We study th…
In an effort to better understand the role dark material plays in the reflectance spectrum of carbonaceous asteroids, we performed laboratory studies focusing on quantifying how the addition of relevant dark material (graphite, magnetite and troilite) can alter the ultraviolet-visible and near-infrared spectrum of a neutral silicate mineral. We find that addition of graphite, magnetite and troilite all darken the reflectance spectrum of our forsterite samples and cause the spectral slope to decrease (become blue). These spectral changes can be caused by both nm- and micron-sized grains. In the…
We have used the XSHOOTER echelle spectrograph on the European Southern Obseratory (ESO) Very Large Telescope (VLT) to obtain UVB-VIS-NIR (ultraviolet-blue (UVB), visible (VIS) and near-infrared (NIR)) reflectance spectra of two members of the Eureka family of L5 Mars Trojans, in order to test a genetic relationship to Eureka. In addition to obtaining spectra, we also carried out VRI photometry of one of the VLT targets using the 2-m telescope at the Bulgarian National Astronomical Observatory - Rozhen and the two-channel focal reducer. We found that these asteroids belong to the olivine-domin…
Aims. We aim to assess the suitability in the near-ultraviolet (NUV) region of the solar analogues selected by the team responsible for the asteroid reflectance included in Gaia Data Release 3 (DR3) and to suggest a correction (in the form of multiplicative factors) to be applied to the Gaia DR3 asteroid reflectance spectra to account for the differences with respect to the solar analogue Hyades 64. Results. We find that the solar analogues selected for Gaia DR3 to compute the reflectance spectra of the asteroids of this data release have a systematically redder spectral slope at wavelengths s…
The recently launched Lucy mission aims to understand the dynamical history of the Solar System by examining the Jupiter Trojans, a population of primitive asteroids co-orbital with Jupiter. Using the G280 grism on the Hubble Space Telescope's Wide Field Camera 3 we obtained near ultraviolet spectra of four of the five Lucy mission targets -- (617) Patroclus-Menoetius, (11351) Leucus, (3548) Eurybates, and (21900) Orus -- to search for novel spectral features. We observe a local reflectance minimum at 0.4 $μ$m accompanied by an increase in reflectance from 0.35-0.3 $μ$m in the spectra of Patro…
We present an analysis of the blank sky spectra observed with the Faint Object Spectrograph on board the Hubble Space Telescope. We study the diffuse sky emission from ultraviolet to optical wavelengths, which is composed of the zodiacal light (ZL), diffuse Galactic light (DGL), and residual emission. The observations were performed toward 54 fields distributed widely over the sky, with the spectral coverage from 0.2 to 0.7 um. In order to avoid contaminating light from the earthshine, we use the data collected only in orbital nighttime. The observed intensity is decomposed into the ZL, DGL, a…
