It may seem a bit early for the July Journal of Astronomical Telescopes Instruments and Systems (vol. 11 issue 3)- it’s ‘in progress’. But considering the next (October) issue is already being served on the site, I’m going to go ahead and blog this July paper:
Lis, D. C. Cordiner, M. Biver, N. et al. Isotopic composition of cometary water and the origin of Earth’s oceans 031605 .11.3.031605
Earth’s water: from whence came it? The inner Solar System is poor in deuterium (2H), while the outer Solar System is (relatively) deuterium rich. But the inner Solar System is also hot (relatively, and certainly during the young, formative periods). Earth, while forming, should have baked off its water, leaving it dry. A common assumption, then, is that comets brought water back, from the outer Solar System.
Common, but an assumption nonetheless. How many problems are there with this model? Earth’s water is deuterium poor, indicating an inner Solar System origin. Comets have inclined, very elliptical orbits. Hitting Earth- actually hitting, not having paths cross- with such an orbit is unlikely and rare. And even if intersection occurs (leading to impact), the impact energy of such steep crossings vaporizes the volatiles. Water should bake off, escaping back to space.
Lis et al. consider, to the extent possible in early-2025, water from comets and water-rich asteroids. You know, water-rich asteroids, eh? The objects with less-inclined, more circular orbits? The ones more likely to encounter Earth (geometrically), then have their volatiles retained (energetically)? And the ones we’ve visited with more missions, generating more data?