Deuterium on Mars: The Abundance of HDO and the Value of D/H

Deuterium on Mars has been detected by the resolution of several Doppler-shifted lines of HDO near 3.7 micrometers in the planet's spectrum. The ratio of deuterium to hydrogen is (9 ± 4) × 10^-4; the abundance of H₂O was derived from lines near 1.1 micrometers. This ratio is enriched on Mars over the telluric value by a factor of 6 ± 3. The enrichment implies that hydrogen escaped more rapidly from Mars in the past than it does now, consistent with a dense and warm ancient atmosphere on the planet.