On October 19, 2017, astronomers spotted the anomalous interstellar object `Oumuamua, as it arrived near Earth within a fifth of the Earth-Sun separation. At closest approach, it was moving at a speed of 54 miles per second relative to the Sun, traversing in one second the distance that a typical car crosses on the highway in one hour. At that speed, `Oumuamua was not bound by the Sun’s gravity and was heading out of the Solar system. It was the first large visitor to have been identified by astronomers from outside the Solar system. `Oumuamua had a diameter of order a hundred meters, the size of a football field. The brightness of sunlight reflected from its surface changed by a factor of ten as it was tumbling every 8 hours, suggesting a shape that is disk-like at the 91% confidence. Moreover, `Oumuamua exhibited non-gravitational acceleration away from the Sun without any visible signs of a cometary tail. The level of that acceleration, 0.1% of the gravitational acceleration induced by the Sun, required that the object lose about a tenth of its mass through standard cometary evaporation in order for it to obtain the observed push from the rocket effect. Such a high level of evaporation would have been easily observed in the form of a familiar cometary tail that reflects sunlight. However, no carbon-based molecules or dust particles were spotted around `Oumuamua following deep observations by the Spitzer space telescope. By now, `Oumuamua is 44 times farther than the Earth is from the Sun and 100 million times fainter than it was close to Earth. Its nature and origin remain mysterious. An artist’s impression of ‘Oumuamua, which means ‘messenger’ in Hawaiian. Last night, I gave a public lecture to an inspiring women’s organization near the Harvard College Observatory in Cambridge Massachusetts. While discussing `Oumuamua, I pointed out the analogy with a memorable dating experience. Just as in an intriguing encounter with someone who left the bar to the dark street before we could get enough information from them, we can search for past encounters with their family members in order to gain more information about their origins. One of the attendees asked: “Could we find elongated crater impacts from `Oumuamua’s family on the Moon?” This was late last night. As soon as I woke up this morning, I did the related calculation before my morning jog at sunrise. Given that one `Oumuamua-like object was detected within the orbit of the Earth around the Sun in seven years, the number of its family members per unit volume is about 0.1 per Earth-Sun-separation cubed. Adopting this abundance and the local speed of `Oumuamua, I calculated that there should have been a few impacts by `Oumuamua’s family members on the Moon during its 4.5 billion years history. Can we identify the craters they left behind? Given the high speed and large size of `Oumuamua, a related lunar crater could be up to 20 kilometers in diameter and possibly show evidence for the elongated shape of the impactor. Unfortunately, finding the few craters from `Oumuamua’s family on the Moon is like finding a needle in a haystack. Based on a recent census, there are at least a million lunar craters larger than a kilometer in diameter, 83 thousand above 5 kilometers and 7 thousand larger than 20 kilometers. This large number of scars on the face of the Moon is not surprising since the abundance of `Oumuamua-size rocks from the Solar system that are flying around the Earth is about of order a thousand times larger than those originating from interstellar space. Finding the graves of `Oumuamua’s family members on the Moon is therefore as challenging as finding the corpses of a few specific people among a few thousand unmarked graves in a mass grave. Should we instead search for relics of `Oumuamua’s family members on Earth? Since the surface area of the Earth is 13.4 times larger than that of the Moon, there were probably tens of related impacts on Earth but their craters were compromised by pre-impact ablation in the Earth’s atmosphere and post-impact geological activity over hundreds of millions of years. Given a thousand times more impactors from the Solar system, it is extremely difficult to trace `Oumuamua’s family members on Earth. A better way to proceed is to search for `Oumuamua’s family members as they pass near Earth without colliding, just as `Oumuamua did. Starting in 2025, the Rubin observatory in Chile will survey the southern sky every four days with a 3.2 giga-pixel camera. This survey will enable the discovery of many new family members of `Oumuamua without requiring them to crash on Earth or a Moon. After all, there are many more fish in the interstellar ocean than those captured by our fishing nets. The post The Graveyard of `Oumuamua’s Family on the Moon appeared first on Anomalien.com.