Chirality Comes From Magnetite

01The evidence

• Amino acids in Bennu samples formed through multiple pathways in the early solar system, and their carbon and nitrogen isotopes record those pathways rather than a single synthetic route.PNAS, Bennu amino acids
• Chiral discrimination of amino acids in meteorite extracts has now been demonstrated with single-molecule nanogap conductance, which gives the field a way to measure handedness at the level of individual samples.Nature Communications, 2026
• Magnetite has been proposed since at least 2014 as a template for the synthesis of chiral organics in carbonaceous chondrites, on the grounds that its surfaces can bias adsorption and reaction geometry.NASA NTRS, 2014

02The tension

Enantiomeric excess is measured in meteorites, but its magnitude varies and its sign is not consistently explained. Aqueous alteration accounts for some variation. Circularly polarised light is the popular alternative, but it requires a source and predicts a wavelength-dependent sign that has not been confirmed.

03The theory

Magnetite is ubiquitous in carbonaceous chondrites and forms with well-defined crystal faces. Those faces present a chiral arrangement of adsorption sites. When organic molecules adsorb and react on them, one handedness is favoured, and the bias is amplified by repeated adsorption and desorption cycles during aqueous alteration.

There is a second, stronger mechanism available. Electron transport through chiral molecules is spin-selective, a well-established effect in molecular electronics. If magnetite mediates electron transfer during synthesis, the spin polarisation of the electrons passing through the adsorbed intermediate can favour one enantiomer over the other.

The prediction is therefore mineralogical. Enantiomeric excess should correlate with magnetite content and grain size within and between samples, and different magnetite morphologies should give different signs. Aqueous alteration should matter only insofar as it produces or dissolves magnetite.

This is testable with existing sample material, including the Bennu and Ryugu collections, and it makes a laboratory prediction that can be checked directly: synthesise amino acids on characterised magnetite surfaces and measure the excess.

04What this is not

05Predictions

• P1Within a single meteorite, enantiomeric excess should correlate with magnetite abundance and grain size.
• P2Different magnetite morphologies should produce opposite signs of excess in controlled synthesis.
• P3Laboratory synthesis on characterised magnetite should reproduce the sign observed in the meteorite it was modelled on.

06What would refute it

No correlation between excess and magnetite across a well-characterised sample set would return the problem to external sources.

07What it would change

It would make the origin of biological handedness a mineralogy question, answerable with samples already in hand.