地球上最新的一颗小卫星将在明天离开我们之前运行最后一圈
地球上最新的一颗小卫星将在明天离开我们之前运行最后一圈
Last September, astronomers discovered 2020 SO, a small near-Earth object approaching our planet. In November, it was temporarily captured by Earth's gravity and spent a brief spell in close orbit, becoming what is known as a "mini-moon". But now its time with us has ended and on February 2, it will break free and return to its orbit around the Sun.
去年9月，天文学家发现了2020年，一个小型近地天体正在接近我们的星球。去年11月，它被地球引力暂时捕获，在近轨道上停留了一段时间，成为了所谓的“迷你月亮”。但现在它与我们在一起的时间已经结束，2月2日，它将挣脱束缚，返回绕太阳运行的轨道。
But first, mini-moon 2020 SO will make one final close approach to us at roughly 220,000 kilometers (140,000 miles) from Earth, just over halfway between Earth and the Moon.
但首先，迷你月球2020年将在距离地球约22万公里(14万英里)的地方最后一次接近我们，距离地球和月球的一半多一点。
Temporary satellites are fairly common. Small asteroids are captured for a brief time before going about their business away from Earth. But since the first detections of 2020 SO, researchers suspected that the new mini-moon was not in fact a natural object, but artificial.
临时卫星相当普遍。小小行星在离开地球之前会被捕获一小段时间。但自从2020年第一次探测到这颗卫星以来，研究人员怀疑这颗新的迷你月亮实际上不是一个自然物体，而是人造的。
Dr Alfredo Carpineti
It had a low relative velocity compared to Earth and sunlight significantly affected its orbit, a clear way to distinguish between natural and artificial small bodies in the proximity of Earth.
与地球相比，它的相对速度较低，阳光明显影响它的轨道，这是区分靠近地球的自然小天体和人造小天体的明确方法。
Light can be interpreted as a wave and as a particle. When we consider these particles, the photons, we are looking at massless particles that carry momentum, which means they can push things about. This is how solar sails work. In the case of 2020 SO, having a large surface area and a relatively light mass, led to the body showing an acceleration that could not be explained with gravity.
光既可以解释为波，也可以解释为粒子。当我们考虑这些粒子，光子时，我们看到的是无质量的带有动量的粒子，这意味着它们可以推动物体。这就是太阳帆的工作原理。在2020年的例子中，由于表面积大，质量相对较轻，导致物体呈现出重力无法解释的加速度。
"Solar radiation pressure is a non-gravitational force that is caused by light photons emitted by the Sun hitting a natural or artificial object," Davide Farnocchia, a navigation engineer at JPL who analyzed 2020 SO's trajectory for the Center for Near-Earth Object Studies (CNEOS), explained back in November. "The resulting acceleration on the object depends on the so-called area-to-mass ratio, which is greater for small and light, low-density objects."
“太阳辐射压力是一种非重力力，是由太阳发射的光子撞击自然或人造物体引起的，”喷气推进实验室的导航工程师戴维·法诺奇亚在11月解释说，他为近地天体研究中心分析了2020年的轨道。“物体产生的加速度取决于所谓的面积质量比，这对于小、轻、低密度的物体来说更大。”
This was an important piece of evidence suggesting 2020 SO was human-made, but another came from a detailed projection of its orbital parameters into the distant past. The object has gotten close to our planet several times, but in 1966 it was so close that it could have actually originated from Earth. In fact, it matched the launch of NASA's lunar lander.
这是一个重要的证据，表明2020年是人造的，但另一个证据来自对它的轨道参数对遥远过去的详细预测。该天体曾多次接近地球，但在1966年，它离地球如此之近，以至于它实际上可能起源于地球。事实上，它与美国国家航空航天局(NASA)发射的月球着陆器相匹配。
"One of the possible paths for 2020 SO brought the object very close to Earth and the Moon in late September 1966," said CNEOS Director Paul Chodas. "It was like a eureka moment when a quick check of launch dates for lunar missions showed a match with the Surveyor 2 mission."
CNEOS主任保罗·乔达斯说:“2020年的一条可能路径是在1966年9月下旬使这颗天体非常接近地球和月球。”“当对月球发射日期的快速检查显示与‘勘测者2号’的任务匹配时，这就像是一个顿悟的时刻。”
Observations in December, after its first close passage, revealed that it was made of stainless steel, confirming that it was indeed an old piece of the Surveyor 2 Centaur rocket's upper stage, launched on September 20, 1966.
在它第一次近距离飞行后，12月的观测显示它是由不锈钢制成的，证实它确实是1966年9月20日发射的“勘测者2号”半人马座火箭上一级的旧部件。
After tomorrow’s close passage, the piece of rocket will go back into deep space but it will continue to visit us over the next few decades despite staying millions of kilometers away from us.
在明天的近距离飞行后，这块火箭碎片将返回深空，但它将在未来几十年继续访问我们，尽管它距离我们数百万公里。
