At a mean diameter of ~650 m, the near-Earth asteroid (455213) 2001 OE84 (OE84 for short) has a rapid rotation period of 0.486542+-0.000002 hours, which is uncommon for asteroids larger than ~200 m. We revisited OE84 14 years after it was first, and last, observed by Pravec et al. (2002) in order to measure again its spin rate and to search for changes. We have confirmed the rapid rotation and, by fitting the photometric data from 2001 and 2016 using the lightcurve inversion technique, we determined a retrograde sense of rotation, with the spin axis close to the ecliptic south pole; an oblate shape model of a/b=1.32+-0.04 and b/c=1.8+-0.2; and no change in spin rate between 2001 and 2016. Using these parameters we constrained the body's internal strength, and found that current estimations of asteroid cohesion (up to ~80 Pa) are insufficient to maintain an intact rubble pile at the measured spin rate of OE84. Therefore, we argue that a monolithic asteroid, that can rotate at the rate of OE84 without shedding mass and without slowing down its spin rate, is the most plausible for OE84, and we give constraints on its age, since the time it was liberated from its parent body, between 2-10 million years.
The Earth contains between one and ten oceans of water, including water within the mantle, where one ocean is the mass of water on the Earth's surface today. With $n$-body simulations we consider how much water could have been delivered from the asteroid belt to the Earth after its formation. Asteroids are delivered from unstable regions near resonances with the giant planets. We compare the relative impact efficiencies from the $ν_6$ resonance, the 2:1 mean motion resonance with Jupiter and the outer asteroid belt. The $ν_6$ resonance provides the largest supply of asteroids to the Earth, wit…
The existence of Earth's Trojan asteroids is not well constrained and represents a major gap in our inventory of small bodies in near-Earth space. Their discovery would be of high scientific and human interest.
Fifteen orbital clusters (associations) were identified among ~20000 near Earth asteroids (NEAs). All associations were found with a high statistical reliability using a single linkage cluster analysis algorithm and three orbital similarity functions. The identified groups constitute a small fraction (4.74 %) of the entire sample. Nonetheless they may be hazardous to the Earth and its inhabitants. As it happens with meteoroid streams, every year the Earth comes very close to the orbits of each association. In two cases (2008TC3 and 2017FU102) the distance between the asteroid's and the Earth's…
A dynamical model for large near-Earth asteroids (NEAs) is developed here to understand the occurrence rate and nature of Cretaceous-Paleogene (K/Pg) scale impacts on the Earth. We find that 16--32 (2--4) impacts of diameter $D>5$ km ($D>10$ km) NEAs are expected on the Earth in 1 Gyr, with about a half of impactors being dark primitive asteroids (most of which start with semimajor axis $a>2.5$ au). These results explain why the Chicxulub crater, the third largest impact structure found on the Earth (diameter $\simeq180$ km), was produced by impact of a carbonaceous chondrite. They suggest, wh…
By means of a fully connected artificial neural network, we identified asteroids with the potential to impact Earth. The resulting instrument, named the Hazardous Object Identifier (HOI), was trained on the basis of an artificial set of known impactors which were generated by launching objects from Earth's surface and integrating them backward in time. HOI was able to identify 95.25% of the known impactors simulated that were present in the test set as potential impactors. In addition, HOI was able to identify 90.99% of the potentially hazardous objects identified by NASA, without being traine…
YORP-induced fission events may form dynamically coherent pairs or even families of asteroids. The outcome of this process is well documented among members of the main asteroid belt, but not in the case of the near-Earth asteroid (NEA) population because their paths randomize very efficiently in a short time-scale. Mean-motion resonances (MMRs) may stabilize the orbits of small bodies by making them avoid close encounters with planets. In theory, YORP-induced fission of asteroids trapped in MMRs can preserve evidence of this process even in near-Earth space. Here, we show that two NEAs, 2017 S…
Astrometric and Photometric Investigations of 2009 WZ104 Near Earth Asteroid
2009年11月25日，美国亚利桑那州莱蒙山天文台的68厘米施密特卡特琳娜巡天望远镜发现了WZ 104小行星。新物体的观测结果得到了Schiaparelli天文台（意大利）60厘米反射镜和Alter Saltzberg天文台（奥地利维也纳）35厘米施密特-卡塞格伦望远镜的证实。这颗小行星被认为是潜在的危险近地小行星。最小轨道相交距离为0.0304 a.e.。自2009年底以来，普尔科沃天文台（俄罗斯）的MTM-500 M 50厘米弯月望远镜和ZA-320 M 32厘米镜面天体照相机继续对2009 WZ 104小行星进行观测。这些观测是在近地天体调查方案的框架内进行的。为调查确定了以下任务：获得天体测量和测光（BVRI波段）系列观测，根据观测数据改进小行星轨道，确定其分类类别和绝对星等，调查其旋转动力学，估计其物理参数。这颗小行星属于小行星群中的Aten。
Recently, phosphine was discovered in the atmosphere of Venus as a potential biosignature. This raises the question: if Venusian life exists, could it be related to terrestrial life? Based on the known rate of meteoroid impacts on Earth, we show that at least $\sim 6 \times 10^5$ asteroids have grazed Earth's atmosphere without being significantly heated and later impacted Venus, and a similar number have grazed Venus's atmosphere and later impacted the Earth, both within a period of $\sim 10^5$ years during which microbes could survive in space. Although the abundance of terrestrial life in t…
The observed near-Earth asteroid population contains very few objects with small perihelion distances, say, q<=0.2 au. NEAs that currently have orbits with larger q might be hiding a past evolution during which they have approached closer to the Sun. We present a probabilistic assessment of the minimum q that an asteroid has reached during its orbital history. At the same time, we offer an estimate of the dwell time, that is, the time q has been in a specific range. We have re-analyzed orbital integrations of test asteroids from the moment they enter the near-Earth region until they either col…
A co-orbital asteroid shares the orbit of a secondary body about its primary. Though more commonly encountered as an asteroid that shares a planet's orbit around the Sun, a co-orbital asteroid could similarly share the orbit of the Moon around the Earth. Though such asteroids would be close to Earth and so relatively bright, their rapid on-sky motion is such that they might escape detection by near-Earth asteroid surveys. The discovery of such lunar co-orbital asteroids (which we will refer to generically here as Lunar Trojans or LTs) would advance our understanding of inner Solar System orbit…
The DART spacecraft is planned to impact the secondary of the binary asteroid (65803) Didymos in 2022, to assess deflection strategies for planetary defense. The impact will create a crater and release asteroidal material, some of which will escape the Didymos system. Because the closest point of approach of Didymos to Earth's orbit is only 6 million km (about 16 times the Earth-Moon distance), some ejected material will make its way sooner or later to our planet, and the observation of these particles as meteors would increase the scientific payout of the DART mission. The DART project may al…
Due to their strong resonances with their host planet, Trojan asteroids can remain in stable orbits for billions of years. As a result, they are powerful probes for constraining the dynamical and chemical history of the solar system. Although we have detected thousands of Jupiter Trojans and dozens of Neptune Trojans, there are currently no known long-term stable Earth Trojans. Dynamical simulations show that the parameter space for stable Earth Trojans in substantial, so their apparent absence poses a mystery. This work uses a large ensemble of N-body simulations to explore how the Trojan pop…
The dynamically hazardous asteroid 2025 TV$_{10}$. A new co-orbital asteroid of Venus
São Paulo State University (UNESP)（圣保罗州立大学）；Laboratório Interinstitucional de e-Astronomia（跨机构电子天文学实验室）；LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（LIRA，巴黎天文台，巴黎文理研究大学，索邦大学，巴黎西岱大学，CY塞尔吉巴黎大学，法国国家科学研究中心）
Time-series photometry of Earth flyby asteroid 2012 DA14
上下文2012 DA 14是一颗近地小行星，大小为几十米。它于2013年2月15日接近地球，为精确测量这颗小行星提供了机会。目标。2012 DA 14的太阳相位角在其最接近时变化很大，但在接下来的夜晚几乎保持不变。我们在这两个夜晚进行了时间序列测光观测，以确定旋转特性和相位效应。方法.观测是使用日本琦玉大学的0.55米望远镜进行的。R波段图像连续获得超过2小时的时间在最近的方法和约5小时的第二天晚上。结果从第二个夜晚的光变曲线数据表明旋转周期为11.0 + 1.8/-0.6小时和1.59 +/-0.02马格的峰-峰振幅。最近的方法之前和之后的亮度变化被分成两个分量，来自旋转和相位效应。我们发现，这颗小行星的相位曲线斜率明显比其他L-型小行星要浅。结论.我们认为2012 DA 14的表面粗糙，缺乏细风化层颗粒和/或高反射率表面。
This paper presents a robust linear method for impact probability estimation of near-Earth asteroids with the Earth. This method is a significantly modified and improved method, which uses a special curvilinear coordinate system associated with the nominal orbit of an asteroid. One of the coordinates of this system is the mean anomaly in the osculating orbit of an asteroid. A normal distribution of errors of coordinates and velocities of this system is assumed. Because of the usage of the curvilinear coordinate system, the fact that the confidence region is curved and stretched mainly along th…
Metal-rich near-Earth asteroids (NEAs) represent a small fraction of the NEA population that is mostly dominated by S- and C-type asteroids. Because of this, their identification and study provide us with a unique opportunity to learn more about the formation and evolution of this particular type of bodies, as well as their relationship with meteorites found on Earth. We present near-infrared (NIR) spectroscopic data of NEAs 6178 (1986 DA) and 2016 ED85. We found that the spectral characteristics of these objects are consistent with those of metal-rich asteroids, showing red slopes, convex sha…
Asteroid pairs are genetically related asteroids that recently separated ($<$few million years), but still reside on similar heliocentric orbits. A few hundred of these systems have been identified, primarily in the asteroid main-belt. Here we studied a newly discovered pair of near-Earth objects (NEOs): 2019 PR2 and 2019 QR6. Based on broad-band photometry, we found these asteroids to be spectrally similar to D-types, a type rare amongst NEOs. We recovered astrometric observations for both asteroids from the Catalina Sky Survey from 2005, which significantly improved their fitted orbits. With…
Spin Parameters and Shape Models of Near-Earth Asteroids (4660) Nereus, (21088) Chelyabinsk, (66146) 1998 TU3, and (297418) 2000 SP43
Instituto Universitario de Ciencias y Tecnologías Espaciales de Asturias (ICTEA), University of Oviedo（阿斯图里亚斯太空科学与技术大学研究所，奥维耶多大学）；Departamento de Matemáticas, Facultad de Ciencias, Universidad de Oviedo（奥维耶多大学理学院数学系）；Departamento de Informática, Facultad de Ciencias, Universidad de Oviedo（奥维耶多大学理学院计算机系）；Instituto de Astrofísica de Canarias (IAC)（加那利群岛天体物理研究所）；Departamento de Astrofísica, Universidad de La Laguna（拉帕尔马大学天体物理学系）；Light Bridges S. L., Observatorio Astronómico del Teide（光桥有限公司，泰德天文台）；Observatorio Isaac Aznar-MPC Z95（艾萨克·阿兹纳尔小行星中心观测站 Z95）；Departamento de Explotación y Prospección de Minas, Universidad de Oviedo（奥维耶多大学矿产开发与勘探系）
Though pairs of dynamically associated asteroids in the Main Belt have been identified and studied for over a decade, very few pair systems have been identified in the near-Earth asteroid population. We present data and analysis that supports the existence of two genetically related pairs in near-Earth space. The members of the individual systems, 2015 EE7 -- 2015 FP124 and 2017 SN16 -- 2018 RY7, are found to be of the same spectral taxonomic class, and both pairs are interpreted to have volatile-poor compositions. In conjunction with dynamical arguments, this suggests that these two systems f…
