Discovery, Follow-up, and Calibration of Near-Earth Objects

AST 0709500TholenDr.托伦将利用该奖项开展与近地天体有关的三项任务。第一项任务是继续努力寻找太阳延伸度小于90度的新近地天体，某些类型轨道上的物体可能在太阳延伸度小于90度的地方度过大部分时间，如果不是全部时间的话。第二项任务是对近地天体进行后续天体测量，重点是视星等在20至24等范围内的天体，目前在这一范围内几乎没有后续能力。第三项任务涉及获取绝对星等在17至19等范围内的近地天体的校准光度测定，以便更好地确定绝对星等18等以上天体的真实数量。 地球以一群小行星碎片的形式围绕太阳运行，这些碎片的大小从大约10公里到微小的尘埃颗粒不等。这些碎片的大小-频率分布是这样的，只有少数物体存在于分布的大端，而数十亿的尘埃颗粒遍布太阳系内部。这些物体与地球碰撞的速率与它们的数量成正比。虽然与尘埃粒子的碰撞基本上是连续的，可见的表现形式被称为流星，但与较大物体的碰撞相对较少。每隔几百年就会有一个50米的物体撞击地球，最近的例子是1908年的通古斯事件。更大的物体与地球相撞的影响可能是毁灭性的，6500万年前恐龙的灭绝归因于10公里物体的撞击。为了清点潜在危险的小行星，几个小组正在对地球轨道以外的太阳系进行勘测，但很少关注地球轨道内部的太阳系区域。先前在太阳小伸长范围内的观测工作可能导致了迄今为止最重要的近地天体发现，即（99942）阿波菲斯，这是一个300米的天体，将于2029年4月13日在6个地球半径范围内通过。在以发现之日为中心的20年时间里，该天体95%的时间都处于太阳延伸小于90度的状态。还有多少类似的物体？本书旨在回答这个重要问题。对专业调查发现的较亮近地天体进行天体测量跟踪是一项涉及全世界数百名业余天文学家的活动，不分性别、种族或地理界限。这次调查在这方面也不会有什么不同。该项目将直接涉及一名博士后研究员和/或一名研究生，从而提供天体测量学、测光学和天体力学等学科的教育和培训。由于小行星撞击和恐龙灭绝之间存在明显的联系，近地小行星的主题几乎和恐龙的主题一样受年轻学生的欢迎。它提供了一个机会，教育公众关于太阳系的结构，超越了传统上在小学记忆的八大行星。虽然在不久的将来发现一个与地球相撞的巨大物体的可能性很小，但这种发现的更广泛影响将是巨大的，包括灾难准备，影响预测和威胁缓解等主题。近年来，这个主题变得如此受欢迎，以至于催生了两部主要的戏剧电影、一部电视迷你剧和许多纪录片。*

AST 0709500TholenDr. Tholen will use this award to address three tasks related to near-Earth objects (NEOs). The first task is a continuation of efforts to find new NEOs at solar elongations of less than 90 deg, where objects in certain types of orbits can spend the majority, if not the entirety, of their time. The secondtask is for follow-up astrometry of NEOs, concentrating on objects in the 20 to 24 apparent magnitude range, where little follow-up capability currently exists. The third task involves the acquisition of calibrated photometry of NEOs in the 17 to 19 absolute magnitude range to do abetter job of determining the true number of objects brighter than absolute magnitude 18. The Earth orbits the Sun in a swarm of asteroidal debris ranging in size from roughly 10 km down to tiny dust particles. The size-frequency distribution of this debris is such that only a few objects exist at the large end of the distribution, while billions of dust particles pervade the inner Solar System. The rate of collision between these objects and the Earth is proportional to their number. While collisions with dust particles are essentially continuous, the visible manifestation being known as meteors, collisions with larger objects are correspondingly rarer. A 50 m object hits the Earth every few hundred years, the most recent example being the Tunguska event of 1908. The effects of even larger objects colliding with the Earth are potentially devastating, the demise of the dinosaurs 65 million years ago being attributed to the impact of a 10 km object. To inventory potentially hazardous asteroids, several groups are surveying the Solar System beyond the orbit of the Earth, but little attention has been given to the region of the Solar System interior to the Earth's orbit. Previous survey work at small solar elongations has resulted in perhaps the most significant NEO discovery to date, that of (99942) Apophis, a 300 m object that will pass within 6 Earth radii on 2029 April 13. During a 20-year span centered on the date of discovery, this object spends 95 percent of its time at solar elongations of less than 90 deg. How many other similar objects are there? This program is designed to answer that important question. Astrometric follow-up of the brighter NEOs found by the professional surveys is an activity that involves hundreds of amateur astronomers throughout the world, with no gender, ethnic, or geographic boundaries. This survey will be no different in this regard. The project will directly involve a postdoctoral fellow and/or a graduate student, thus providing both education and training in the subjects of astrometry, photometry, and celestial mechanics. Because of the apparent connection between asteroid impacts and the extinction of the dinosaurs, the subject of near-Earth asteroids has become nearly as popular with younger students as has the subject of dinosaurs. It provides the opportunity to educate the public about the structure of the Solar System beyond the eight major planets traditionally memorized in grade school. And although the probability of finding an object of significant size on a collision course with Earth in the near future is quite small, the broader impact of such a discovery would be enormous, including the topics of disaster preparation, impact prediction, and threat mitigation. So popular has the subject become in recent years that it has spawned two major theatrical motion pictures, a television mini-series, and numerous documentaries.***