可能会危害地球的小行星之轨道

2021年8月29日

Orbits of Potentially Hazardous Asteroids
Image Credit: NASA, JPL-Caltech

Explanation: Are asteroids dangerous? Some are, but the likelihood of a dangerous asteroid striking the Earth during any given year is low. Because some past mass extinction events have been linked to asteroid impacts, however, humanity has made it a priority to find and catalog those asteroids that may one day affect life on Earth. Pictured here are the orbits of the over 1,000 known Potentially Hazardous Asteroids (PHAs). These documented tumbling boulders of rock and ice are over 140 meters across and will pass within 7.5 million kilometers of Earth — about 20 times the distance to the Moon. Although none of them will strike the Earth in the next 100 years — not all PHAs have been discovered, and past 100 years, many orbits become hard to predict. Were an asteroid of this size to impact the Earth, it could raise dangerous tsunamis, for example. To investigate Earth-saving strategies, NASA’s Double Asteroid Redirection Test (DART) is planned for launch later this year. Of course rocks and ice bits of much smaller size strike the Earth every day, usually pose no danger, and sometimes creating memorable fireball and meteor displays.

Tomorrow’s picture: ice sky fire

可能会危害地球的小行星之轨道
影像提供: NASA, JPL-Caltech

说明: 小行星会造成危害吗？有些会，但一颗危险小行星在特定年会撞击地球的可能性则很低。在过往，小行星撞击曾导致生物大灭绝事件，所以，人类把寻找和编录未来可能会危害地球生命的小行星之工作列为优先。上图呈现了超过1,000颗可能有危害性小行星 (PHAs)的轨道。这些已登录、在太空翻滚的巨石或冰块，大小超过140公尺，而通过地球时的间距小于7百50万公里，大约是月球距离的20倍。虽然这些小行星在未来百年之中，都不会冲撞地球，但并非所有危害性小行星都已找到，而且一百年后有些小行星的轨道难以预测。如果上述这种寛140公尺的小行星之一冲撞地球，危害之一是会引起危险的海啸。为探索救护地球的策略，美国航太总署规画在今年底进行双小行星改向测试（DART）任务。事实上，每天都有许多的细小的石块和冰块撞击地球，通常它们不会带来危害，偶而会形成火流星或流星雨。

明日的图片: ice sky fire