A recent paper studied the flux of interstellar objects entering the Solar system from the nearest star system, Alpha Centauri, located about four light years away. The authors calculated a probability of one in a billion for an `Oumuamua-size object from Alpha Centauri to be within the orbit of the Earth around the Sun.

However, the important point to remember is delivered by Olbers’ paradox, namely the contradiction between the assumption of an infinite Universe filled with a uniform distribution of luminous stars and the night sky’s darkness. The paradox was formulated in terms of photons, but it applies to any type of particle or object ejected from star systems, such as Alpha Centauri.

The flux of interstellar objects arriving near Earth scales inversely with the square of the distance of the source star. But the number of stars scales with distance cubed for a nearly uniform local density of stars. This means that most interstellar objects arrive from the most distant source stars. The dominant sources for the Milky Way galaxy would be a few thousand light years away from the Sun, delineating the thickness of the Milky Way disk of stars. There are a billion stars within that volume, and their cumulative flux of interstellar objects is a billion times larger than that of Alpha-Centauri, even though the Alpha-Centauri system is a thousand times closer.

At distances larger than the thickness of the Milky Way disk, the number of contributing stars grows like the square of the distance, representing the two-dimensional surface area of the disk. So the flux of objects increases only logarithmically with distance. In summary, this new paper considers a part in a billion of the expected total flux of interstellar objects from all Milky Way stars. Indeed, two interstellar objects on the scale of 100 meters, `Oumuamua and Borisov, were spotted near Earth in recent years.

Could some of these interstellar messengers carry an important message to humanity, or should we ignore them since we are already familiar with rocks born within the Solar system?

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In recent years, witnesses in Congressional hearings testified under oath that the U.S. government hides information about materials retrieved in crash sites of extraterrestrial technological vehicles. If true, such a government finding would be equivalent to discovering a tennis ball from a neighbor in our backyard. The question would then be whether to inform our family members at the dinner table, who are unaware of any neighbors, about the finding or hide the information from them.