哈勃太空望远镜对近日点附近活跃的小行星324 P/La Sagra的观测显示，其质量持续减少，这与近地表冰的升华相一致。从轨道平面下方的有利位置测量的彗差的等像点与标称尺寸为$a \sim$ 100 $μ$ m的粒子的稳定发射最佳匹配。推断的质量损失率，$dM_d/dt \sim$ 0.2 kg s $^{-1}$，可以由在与太阳光热平衡的水冰升华提供，该升华来自小至930 m $^2$的区域，相当于大约0.2%的核表面。从距离324 P轨道平面仅0.6 \degr ~的有利位置进行的观测，为垂直于轨道平面的尘埃喷射速度设定了一个极限，即$V_{\perp} <$ 1 m s $^{-1}$。短期光度变化的近核区域，如果相关的旋转的基础核，排除周期PDMATHAMT 3.8小时，并建议旋转可能不会发挥核心作用，在驱动所观察到的质量损失。我们估计，在前一个轨道，324 P失去了约4 $\times$ 10 $^7$公斤的尘埃粒子，相当于6 $\times$ 10 $^{-5}$的质量550米的球形核假设密度$ρ$ = 1000公斤米$^{-3}$。如果继续下去，以这种速率的质量损失将把324 P的寿命限制在$\sim$ 1.6 $\times$ 10 $^4$轨道（大约10 $^5$年）。为了在1亿年到4亿年的时间尺度上生存下来，分别对应于动力学和碰撞稳定性，需要一个占空比$2\times 10^{-4} \le f_d \le 8\times 10^{-4}$。除非它在轨道上的时间被高估了许多数量级，否则324 P被揭示为大量休眠的含冰小行星中的一个短暂活跃的成员。
英文摘要：
Hubble Space Telescope observations of active asteroid 324P/La Sagra near perihelion show continued mass loss consistent with the sublimation of near-surface ice. Isophotes of the coma measured from a vantage point below the orbital plane are best matched by steady emission of particles having a nominal size $a \sim$ 100 $μ$m. The inferred rate of mass loss, $dM_d/dt \sim$0.2 kg s$^{-1}$, can be supplied by sublimation of water ice in thermal equilibrium with sunlight from an area as small as 930 m$^2$, corresponding to about 0.2\% of the nucleus surface. Observations taken from a vantage point only 0.6\degr~from the orbital plane of 324P set a limit to the velocity of ejection of dust in the direction perpendicular to the plane, $V_{\perp} <$ 1 m s$^{-1}$. Short-term photometric variations of the near-nucleus region, if related to rotation of the underlying nucleus, rule out periods $\le$ 3.8 hr and suggest that rotation probably does not play a central role in driving the observed mass loss. We estimate that, in the previous orbit, 324P lost about 4$\times$10$^7$ kg in dust particles, corresponding to 6$\times$10$^{-5}$ of the mass of a 550 m spherical nucleus of assumed density $ρ$ = 1000 kg m$^{-3}$. If continued, mass loss at this rate would limit the lifetime of 324P to $\sim$1.6$\times$10$^4$ orbits (about 10$^5$ yr). To survive for the 100 Myr to 400 Myr timescales corresponding, respectively, to dynamical and collisional stability requires a duty cycle $2\times 10^{-4} \le f_d \le 8\times 10^{-4}$. Unless its time in orbit is over-estimated by many orders of magnitude, 324P is revealed as a briefly-active member of a vast population of otherwise dormant ice-containing asteroids.
We present Hubble Space Telescope observations of active asteroid P/2020 O1 taken to examine its development for a year after perihelion. We find that the mass loss peaks <~1 kg/s in 2020 August and then declines to nearly zero over four months. Long-duration mass loss (~180 days) is consistent with a sublimation origin, indicating that this object is likely an ice-bearing main-belt comet. Equilibrium sublimation of water ice from an area as small as 1580 m^2 can supply the observed mass loss. Time-series photometry shows tentative evidence for extremely rapid rotation (double-peaked period < …
Large and publicly available astronomical archives open up new possibilities to search and study Solar System objects. However, advanced techniques are required to deal with the large amounts of data. These unbiased surveys can be used to constrain the size distribution of minor bodies, which represents a piece of the puzzle for the formation models of the Solar System. We aim to identify asteroids in archival images from the ESA Hubble Space Telescope (HST) Science data archive using data mining. We developed a citizen science project on the Zooniverse platform, Hubble Asteroid Hunter (www.as…
Space Science Institute（空间科学研究所）；International Computer High School of Constanţa（康斯坦察国际计算机高中）；International Computer High School of Bucharest（布加勒斯特国际计算机高中）
We present an application of Deep Learning for the image recognition of asteroid trails in single-exposure photos taken by the Hubble Space Telescope. Using algorithms based on multi-layered deep Convolutional Neural Networks, we report accuracies of above 80% on the validation set. Our project was motivated by the Hubble Asteroid Hunter project on Zooniverse, which focused on identifying these objects in order to localize and better characterize them. We aim to demonstrate that Machine Learning techniques can be very useful in trying to solve problems that are closely related to Astronomy and…
Intermittent dust mass loss from activated asteroid P/2013 P5 (PANSTARRS)
我们目前的观测和激活小行星P/2013 P5（PANSTARRS）的尘埃环境的模型。该物体在观测期间显示出复杂的形态，存在多个尾巴。我们将自己的观测结果与之前发布的哈勃太空望远镜（HST）图像结合起来，所有这些观测都是通过连接到La Palma上的10.4 m Gran Telescopio Canarias（GTC）上的仪器进行的，以建立一个旨在拟合所有观测结果的模型。总的来说，这些数据涵盖了整整3个月的观测期，这可以用间歇性的尘埃损失来解释。最合理的假设是，一颗小行星旋转，旋转轴垂直于轨道平面，从赤道区域释放质量，这与旋转分裂相一致。假设粒子的喷射速度（v $\sim$ 0.02-0.05 m s $^{-1}$）对应于逃逸速度，则对于体积密度3000至1000 kg m $^{-3}$，物体直径被约束为$\sim$ 30-130 m。
We present a dynamical analysis of the fragmented active asteroid 331P/Gibbs. Using archival images taken by the Hubble Space Telescope from 2015 to 2018, we measured the astrometry of the primary and the three brightest (presumably the largest) components. Conventional orbit determination revealed a high-degree of orbital similarity between the components. We then applied a fragmentation model to fit the astrometry, obtaining key parameters including the fragmentation epochs and separation velocities. Our best-fit models show that Fragment B separated from the primary body at a speed of $\sim…
Some active asteroids have been proposed to be the result of impact events. Because active asteroids are generally discovered serendipitously only after their tail formation, the process of the impact ejecta evolving into a tail has never been directly observed. NASA's Double Asteroid Redirection Test (DART) mission, apart from having successfully changed the orbital period of Dimorphos, demonstrated the activation process of an asteroid from an impact under precisely known impact conditions. Here we report the observations of the DART impact ejecta with the Hubble Space Telescope (HST) from i…
Active asteroids show (typically transient) cometary activity, driven by a range of processes. A sub-set, sometimes called main-belt comets, may be driven by sublimation and so could be useful for tracing the present-day distribution of asteroid ice. Object P/2018 P3 has a Tisserand parameter 3.096 but a high eccentricity 0.415, placing it within the dynamical boundary between asteroids and comets. We aim to determine the cause of activity (sublimation or something else) and assess the dynamical stability of P3, in order to better constrain the intrinsic ice content in the main belt. We obtain…
We describe active asteroid 331P/Gibbs (2012 F5) using archival Hubble Space Telescope data taken between 2015 and 2018. 331P is an outer main-belt active asteroid with a long-lived debris trail that formed in 2011. Embedded in the debris trail we identify 19 fragments with radii between 0.04 and 0.11 km (albedo 0.05 assumed) containing about 1 percent of the mass of the primary nucleus. The largest shows a photometric range (1.5 magnitudes), a V-shaped minimum and a two-peaked lightcurve period near 9 hours, consistent with a symmetric contact binary (Drahus and Waniak 2016). Less convincing …
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 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…
Space-based telescopes offer unparalleled opportunities for characterising exoplanets, Solar System bodies and stellar objects. However, observatories in low Earth orbits (e.g. Hubble, CHEOPS, Twinkle and an ever increasing number of cubesats) cannot always be continuously pointed at a target due to Earth obscuration. For exoplanet observations consisting of transit, or eclipse, spectroscopy this causes gaps in the light curve, which reduces the information content and can diminish the science return of the observation. Terminus, a time-domain simulator, has been developed to model the occurre…
