使用済みロケット、月の裏側に衝突か　時速９３００キロ

【ＡＦＰ＝時事】月面のクレーターがまた一つ増えたようだ。（写真は月）
　科学者の軌道計算によると、長年にわたって宇宙を漂っていた使用済みロケットが４日、月に衝突した。ただし、直接観測できておらず、画像確認にも時間がかかる可能性がある。
　この衝突を最初に予測した天文学者のビル・グレイ氏は、月の裏側で米東部時間４日午前７時２５分（日本時間午後９時２５分）に衝突したはずだとＡＦＰに語った。
　約４トンのロケットは時速９３００キロで月に衝突し、「直径１０～２０メートル」のクレーターができたはずだという。
　「超常現象によって消滅していない限り、けさ、月にぶつかったはずだ」とグレイ氏は主張した。
　深宇宙に存在する宇宙ごみを記録して追跡する公的機関はないため、このロケットの素性は議論の的となっている。
　使用済みロケットが宇宙に放棄されるのは珍しいことではなく、米アポロ計画で地震計の試験として意図的に月面へ衝突させた例などもある。ただし、月面への意図しない衝突が予測されたのは今回が初めてとされる。【翻訳編集ＡＦＰＢＢＮｅｗｓ】

〔ＡＦＰ＝時事〕（2022/03/07-10:08）

Add one more crater to the long list of pockmarks on the lunar surface.
According to orbital calculations, a rocket hurtling through space for years crashed into the Moon on Friday, but the strike wasn't directly observed, and there might be a wait for photographic evidence.
The impact would have taken place at 7:25 am Eastern Time (1225 GMT), on the far side of the Moon, said the astronomer Bill Gray, who was the first to predict the collision.
Racing through the cosmos at around 5,800 mph (9,300 kph), the roughly four ton object should make a crater 10 or 20 meters across, Gray told AFP.
Its speed, trajectory, and time of impact were calculated using Earth-based telescope observations.
We had lots (and lots) of tracking data for the object, and there is nothing acting on it except the forces of gravity and sunlight, he said, with the latter pushing the cylinder gently away from the Sun.
Unless the object was removed by an occult hand, it hit the Moon this morning.
The identification of the rocket has been a subject of debate, since there is no official entity responsible for listing and tracking junk in deep space.
Gray, an independent contractor who has created orbital calculation software used by NASA, hunts for and monitors human-made debris, so that scientists do not confuse it for asteroids and study it unnecessarily.
He initially thought what he was seeing was a SpaceX rocket, but later changed his mind and said it was a third-stage booster of Chang'e 5-T1, launched in 2014 as part of the Chinese space agency's lunar exploration program.
Beijing denied responsibility, saying the booster in question had safely entered the Earth's atmosphere and was completely incinerated.
But according to Gray, the statement by China's foreign ministry conflated two missions with similar names, and was actually talking about a rocket launched much later.
Whatever the case, only NASA's Lunar Reconnaissance Orbiter and India's Chandrayaan-2, both of which orbit the Moon, will be able to image the crater.
The US space agency said in late January it wanted to survey the crater, but said that finding it would be a challenge that might take weeks to months.
According to Gray, both probes are able to observe any region on the Moon once a month.
It's not unusual for rocket stages to be abandoned to the cosmos after serving their purpose of launching spacecraft.
But this would mark the first time an unintentional collision with the Moon has been projected.
Spacecraft have been intentionally crashed into the Moon before for scientific purposes, such as during the Apollo missions to test seismometers.