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，天文學家發現了2020年，一個小型近地天體正在接近我們的星球。去年11月，它被地球引力暫時捕獲，在近軌道上停留了一段時間，成為了所謂的“迷你月亮”。但現在它與我們在一起的時間已經結束，2月2日，它將掙脫束縛，返回繞太陽執行的軌道。
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年將在距離地球約22萬公里(14萬英里)的地方最後一次接近我們，距離地球和月球的一半多一點。
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.
臨時衛星相當普遍。小小行星在離開地球之前會被捕獲一小段時間。但自從2020年第一次探測到這顆衛星以來，研究人員懷疑這顆新的迷你月亮實際上不是一個自然物體，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.
與地球相比，它的相對速度較低，陽光明顯影響它的軌道，這是區分靠近地球的自然小天體和人造小天體的明確方法。
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.
光既可以解釋為波，也可以解釋為粒子。當我們考慮這些粒子，光子時，我們看到的是無質量的帶有動量的粒子，這意味著它們可以推動物體。這就是太陽帆的工作原理。在2020年的例子中，由於表面積大，質量相對較輕，導致物體呈現出重力無法解釋的加速度。
"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."
“太陽輻射壓力是一種非重力力，是由太陽發射的光子撞擊自然或人造物體引起的，”噴氣推進實驗室的導航工程師戴維·法諾奇亞在11月解釋說，他為近地天體研究中心分析了2020年的軌道。“物體產生的加速度取決於所謂的面積質量比，這對於小、輕、低密度的物體來說更大。”
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.
這是一個重要的證據，表明2020年是人造的，但另一個證據來自對它的軌道引數對遙遠過去的詳細預測。該天體曾多次接近地球，但在1966年，它離地球如此之近，以至於它實際上可能起源於地球。事實上，它與美國國家航空航天局(NASA)發射的月球著陸器相匹配。
"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主任保羅·喬達斯說:“2020年的一條可能路徑是在1966年9月下旬使這顆天體非常接近地球和月球。”“當對月球發射日期的快速檢查顯示與‘勘測者2號’的任務匹配時，這就像是一個頓悟的時刻。”
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.
在它第一次近距離飛行後，12月的觀測顯示它是由不鏽鋼製成的，證實它確實是1966年9月20日發射的“勘測者2號”半人馬座火箭上一級的舊部件。
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.
在明天的近距離飛行後，這塊火箭碎片將返回深空，但它將在未來幾十年繼續訪問我們，儘管它距離我們數百萬公里。