“It would be tantalizing to find microfossils of extraterrestrial forms of life on the moon. Even more exciting would be to find traces of technological equipment that crashed on the lunar surface a billion years ago, amounting to a letter from an alien civilization saying, “We exist,” writes Harvard University’s chief astronomer Avi Loeb, asking can the moon provide clues for extraterrestrial life?
A new paper Loeb wrote with Manasvi Lingam answers this question with a resounding “yes”, suggesting to consider the moon’s surface for interstellar objects collected over time and potentially deliver building blocks of life from the habitable environments around other stars.
“The absence of a lunar atmosphere,” writes Loeb in “The Moon as a Fishing Net for Extraterrestrial Life”, “guarantees that these messengers would reach the lunar surface without burning up. In addition, the geological inactivity of the moon implies that the record deposited on its surface will be preserved and not mixed with the deep lunar interior. Serving as a natural mailbox, the lunar surface collected all impacting objects during the past few billions of years. Most of this “mail” comes from within the solar system.”
But the solar system also intercepts objects from interstellar space, ranging from dust particles to free-floating planets and stars. A detection of the first interstellar object, ‘Oumuamua, with a size on the order of 100 meters was reported in 2017. This year, ‘Oumuamua’s cousin was tentatively discovered in the form of a meter-size meteor from outside the solar system that burned up in Earth’s atmosphere in 2014. And most recently, yet another interstellar visitor may have been identified.
With the detection of the first interstellar object in 2017 it is now possible for the first time, to calibrate the flux of interstellar objects to calculate the amount of interstellar material that has collected on the moon’s surface over its history. On Earth, the oldest microfossils, with unambiguous evidence for cells that lived about 3.4 billion years ago, were discovered in the Strelley Pool Formation in Western Australia, perhaps foreshadowing similar discoveries on the lunar surface.
Earth may prove to be an analog to what is hidden on the moon. On August 19, The Galaxy reported that rare iron-60 was discovered in Antarctica. Outer space objects ranging from dust to meteors regularly fall to Earth, but they are generally made of the same materials as our planet, since everything in the solar system, including the sun itself, assembled from the same building blocks billions of years ago. Because iron-60 is not among those common materials, it must have arrived from somewhere beyond the solar system.
Another new paper with Loeb’s undergraduate student, Amir Siraj, showed that a two-meter telescope on a satellite in orbit around the moon can observe interstellar impactors as they crash and later extract these biomarkers by analyzing lunar surface samples.
“Identifying biomarkers from debris of material that originated in the habitable zone around other stars,” observes Loeb, “would inform us about the nature of extraterrestrial life. The fundamental question is whether distant life resembles the biochemical structures we find on Earth. Similarities might imply that there exists a unique chemical path for life everywhere or that life was transferred between systems.”
Either way, Loeb concludes, a lunar study shortcuts the need to send spacecraft on extremely long missions to visit other star systems.