Asteroid Florence——近距离通过地球的最大小行星

  • 一个大型的近地小行星,将于2017年9月1日近距离通过地球

小行星弗罗伦斯(Florence),是一个大型的近地小行星,将于2017年9月1日,预计在距离我们约为700万公里(18倍的地月距离)的地方,安全通过。

来自NASA斯皮策空间望远镜以及近地天体广角红外线探测望远镜的测量结果,预计小行星弗罗伦斯的大小约为4.4公里。

自NASA探测和跟踪近地小行星以来,尽管有很多小行星,有以几倍的地月距离通过地球,比小行星弗罗伦斯距离我们还要近,但这些小行星都相对比较小,小行星弗罗伦斯是近距离通过地球的最大的小行星,下一次这么近距离通过预计要到2500年了。

Credits: NASA/JPL-Caltech

这颗小行星于1981年3月由位于澳大利亚的赛丁泉天文台(Siding Spring Observatory)发现,以弗罗伦斯(Florence Nightingale)的名字命名,用于纪念现代护理的创始人弗罗伦斯·南丁格尔(1820-1910)。

在8月下旬和9月上旬,小行星弗罗伦斯的星等为9级,天文爱好者们可试着通过小型望远镜进行捕捉。另外这么相对较近的距离,也为科学家们提供了观测和研究的机会。

  • 新发现了第三个三合小行星系统

Credits: NASA/JPL-Caltech

小行星弗罗伦斯(Florence),是一个大型的近地小行星,于2017年9月1日,在距离我们约为700万公里(18倍的地月距离)的地方安全通过。

动图详见:https://cneos.jpl.nasa.gov/images/news/florence.p5us.1Hz.s382.sep01.gif
Credits: 
NASA/JPL

在8月29日至9月1日期间,通过NASA的Goldstone深空通信网络,获得的小行星弗罗伦斯的雷达图像,显示它有两颗小卫星。

小行星弗罗伦斯是发现的第三个三合小行星系统(triple asteroid),有必要提的是,迄今为之我们已知近地天体的数量超过了16400颗,所以三合小行星系统比较罕见。

Goldstone深空通信网络确认了小行星弗罗伦斯的大小约为4.5千米(2.8英里),但这两个卫星的尺寸大小还不能确定,大小估计在100米至300米之间(300英尺至1000英尺)。这两个卫星的轨道周期也未能精准确定,靠近弗罗伦斯的轨道周期约为8小时,外层卫星的轨道周期约为22小时至27小时。

  • Radar Reveals Two Moons Orbiting Asteroid Florence

Radar images of asteroid 3122 Florence obtained at the 70-meter antenna at NASA’s Goldstone Deep Space Communications Complex between August 29 and September 1 have revealed that the asteroid has two small moons, and also confirmed that main asteroid Florence is about 4.5 km (2.8 miles) in size. Florence is only the third triple asteroid known in the near-Earth population out of more than 16,400 that have been discovered to date. All three near-Earth asteroid triples have been discovered with radar observations and Florence is the first seen since two moons were discovered around asteroid 1994 CC in June 2009.

The sizes of the two moons are not yet well known, but they are probably between 100 – 300 meters (300-1000 feet) across. The times required for each moon to revolve around Florence are also not yet known precisely but appear to be roughly 8 hours for the inner moon and 22 to 27 hours for the outer moon. The inner moon of the Florence system has the shortest orbital period of any of the moons of the 60 near-Earth asteroids known to have moons. In the Goldstone radar images, which have a resolution of 75 meters, the moons are only a few pixels in extent and do not reveal any detail.

Animated sequence of radar images of asteroid Florence obtained on Sep. 1, 2017 using the 70-m antenna at the Goldstone Deep Space Communications complex. The resolution of these images is about 75 meters. The images show two moons orbiting the much larger central body, which is about 4.5 km in diameter. The inner moon briefly disappears as it moves behind the central body and is hidden from the radar. (NASA/JPL).
Animated sequence of radar images of asteroid Florence obtained on Sep. 1, 2017 using the 70-m antenna at the Goldstone Deep Space Communications complex. The resolution of these images is about 75 meters. The images show two moons orbiting the much larger central body, which is about 4.5 km in diameter. The inner moon briefly disappears as it moves behind the central body and is hidden from the radar. (NASA/JPL).

The radar images also provide our first close-up view of Florence itself. Although the asteroid is fairly round, it has a ridge along its equator, at least one large crater, two large flat regions, and numerous other small-scale topographic features. The images also confirm that Florence rotates once every 2.4 hours, a result that was determined previously from optical measurements of the asteroid’s brightness variations.

The animated sequence to the left is built from a series of radar images of Florence. The sequence lasts several hours and shows more than two full rotations of the large, primary body. The moons can be clearly seen as they orbit the main body. Radar images are different from pictures taken with a digital camera but are similar to ultrasound images. The geometry in radar images is analogous to seeing an object from above its north pole with the illumination coming from the top. Projection effects can make the positions of Florence and its moons appear to overlap even though they are not touching.

Florence reached its closest approach to Earth early on September 1 and is now slowly receding from our planet. Additional radar observations are scheduled at NASA’s Goldstone Solar System Radar in California and at the National Science Foundation’s Arecibo Observatory in Puerto Rico through September 8. These observations should show more surface detail on Florence and provide more precise estimates of the orbital periods of the two moons. Those results are valuable to scientists because they can be used to estimate the total mass and density of the asteroid.

Ref:

  1. http://www.nasachina.cn/news/%e4%b8%80%e4%b8%aa%e5%a4%a7%e5%9e%8b%e7%9a%84%e8%bf%91%e5%9c%b0%e5%b0%8f%e8%a1%8c%e6%98%9f%ef%bc%8c%e5%b0%86%e4%ba%8e2017%e5%b9%b49%e6%9c%881%e6%97%a5%e8%bf%91%e8%b7%9d%e7%a6%bb%e9%80%9a%e8%bf%87.html
  2. www.nasachina.cn/information/新发现了第三个三合小行星系统.html
  3. https://cneos.jpl.nasa.gov/news/news199.html
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