[Paper Review] Searching the Moon for Extrasolar Material and the Building Blocks of Extraterrestrial Life

Manasvi Lingam, Abraham Loeb|arXiv (Cornell University)|Jul 11, 2019

Origins and Evolution of Life4 references4 citations

TL;DR

This paper proposes that the Moon's airless, geologically inactive surface preserves extrasolar material from interstellar objects, estimating ~30 ppm extrasolar material and ~0.3 ppm organic carbon. By analyzing lunar samples using isotope ratios and molecular diagnostics, researchers could detect biomolecular building blocks and potential biosignatures, offering a novel pathway to astrobiological insights beyond Earth-based observations.

ABSTRACT

Due to its absence of an atmosphere and relative geological inertness, the Moon's surface records past impacts of objects from the Solar system and beyond. We examine the prospects for discovering extrasolar material near the lunar surface and predict that its abundance is $\mathcal{O}(10)$ parts-per-million (ppm). The abundances of extrasolar organic carbon and biomolecular building blocks (e.g., amino acids) are estimated to be on the order of $0.1$ ppm and $< 0.1$ parts-per-billion (ppb), respectively. We describe strategies for identifying extrasolar material and potentially detecting extrasolar biomolecular building blocks as well as molecular biosignatures of extinct extraterrestrial life. Thus, viewed collectively, we argue that \emph{in situ} lunar exploration can provide vital new clues for astrobiology.

Motivation & Objective

• To assess the feasibility of detecting extrasolar material on the Moon due to its lack of atmosphere and geological inactivity.
• To estimate the flux and abundance of extrasolar impactors on the lunar surface, particularly focusing on organic compounds and biomolecular building blocks.
• To propose detection strategies for identifying extrasolar debris, including isotope ratios, elemental abundances, and molecular biosignatures.
• To evaluate the scientific value of finding such material for understanding planetary system diversity, exo-Oort cloud formation, and the potential for extraterrestrial life.

Proposed method

• Modeling the mass flux of extrasolar impactors using a power-law distribution with a power-law index of -1.14, derived from empirical data and spacecraft measurements.
• Estimating the number flux of extrasolar impactors on the Moon as ~4.4×10⁻²² m⁻²s⁻¹ per kg, based on Earth's atmospheric flux and lunar surface area.
• Using isotope ratios (especially oxygen) and elemental abundances as key diagnostics to distinguish extrasolar material from terrestrial or solar system origin.
• Proposing laboratory techniques to detect organic compounds such as amino acids, carboxylic acids, and nucleobases via isotopic heterogeneities and enantiomeric excesses.
• Outlining methods to search for molecular biosignatures, including chiral preference and structural isomer selection, as indicators of extinct extraterrestrial life.
• Applying these detection strategies to Apollo return samples and future lunar in situ missions to identify and analyze extrasolar debris.

Experimental results

Research questions

• RQ1 What is the expected flux of extrasolar impactors on the lunar surface, and how does it compare to Earth's atmospheric flux?
• RQ2 What are the predicted abundances of extrasolar organic carbon and biomolecular building blocks (e.g., amino acids) in lunar regolith?
• RQ3 Can isotope ratios and elemental abundances in lunar samples be used to distinguish extrasolar material from indigenous solar system material?
• RQ4 What molecular biosignatures could indicate the presence of extinct extraterrestrial life in lunar samples?
• RQ5 How might the detection of extrasolar organics or biosignatures advance our understanding of planetary system formation and habitability?

Key findings

• The abundance of extrasolar material in the lunar surface is estimated at ~30 ppm, with ~3 ppm from impacts occurring >4 billion years ago.
• The abundance of extrasolar organic carbon is estimated at ~0.3 ppm, with maximal abundances of ~300 ppt for carboxylic acids, ~30 ppt for amino acids, and ~3 ppt for nucleobases.
• The flux of extrasolar impactors on the Moon is ~4.4×10⁻²² m⁻²s⁻¹ per kg, consistent with in situ measurements from Ulysses and Galileo.
• Detection of extrasolar material is feasible through isotope ratios (especially oxygen), elemental abundances, and molecular diagnostics such as enantiomeric excesses.
• The discovery of such material could constrain planetary formation models, assess exo-Oort cloud evolution, and reveal chemical diversity in extrasolar systems.
• Detection of molecular biosignatures, such as isotopic heterogeneities or chiral preferences, could provide evidence for extinct extraterrestrial life, with profound implications for astrobiology.