Theory 019/Earth & Space /Planetary science
Mercury's Volatiles Came in One Size
Volatiles are assumed to arrive from many sources. One size class may have survived the trip.
The volatile inventory of Mercury was delivered by a narrow size range of impactors rather than by a broad spectrum, so the abundance pattern should show a cutoff at the size that survived solar heating.
01The evidence
Mercury has more volatiles than models of formation in a hot inner disk predict, and the excess is attributed to late delivery.
02The tension
Delivery models integrate over a size distribution and over time, producing a mixture that cannot be distinguished from other mixtures. The resulting predictions are broad and hard to test.
03The mechanism
Small impactors are heated throughout during atmospheric passage and lose volatiles; large ones deliver more but are rarer and may not have hit Mercury in the relevant window.
That leaves an intermediate size that delivers efficiently, and the volatile pattern should reflect that class rather than a broad mixture.
04What this is not
Mixture models sum over sizes. This predicts a dominant size class, which gives a sharper compositional prediction.
05Predictions
- P1Volatile ratios should match a narrow impactor class.
- P2There should be a cutoff at the survival size.
- P3The pattern should differ from a broad mixture.
06Refutation
Volatile ratios matching a broad mixture would leave the single-class account unnecessary.
07What it changes
It would sharpen the interpretation of Mercury surface chemistry.