12/27/2021 – Ephemeris – Where did Earth’s water come from?

This is Ephemeris for Monday, December 27th. Today the Sun will be up for 8 hours and 49 minutes, setting at 5:08, and it will rise tomorrow at 8:19. The Moon, 1 day past last quarter, will rise at 2:02 tomorrow morning.

The element hydrogen has two stable forms: Ordinary hydrogen with a single proton as its nucleus, and deuterium with a proton and a neutron as its nucleus. Both can combine with oxygen to form water. Deuterium and oxygen make heavy water. Water of any kind would not have survived Earth’s formation. Astronomers have long thought that collisions of asteroids and comet brought water to the Earth. Comets, however, have an overabundance of deuterium. Asteroids are close, also dust particles exposed to the solar wind have an under abundance of deuterium. Apparently, about a 50-50 mixture of dust and asteroids appear the right combination to fill the Earth’s with the right ratio of normal and heavy water.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). They may be different for your location.

Addendum

The three isotopes of hydrogen: protium, or ordinary hydrogen; deuterium; and tritium. Protium and deuterium are stable, while tritium is unstable and decays into helium 3 and an electron. Tritium has a half-life of 12.32 years.

Heavy water D₂O vs. normal water H₂O. Heavy water is about 11% heavier than water. A heavy water ice cube would sink in a glass of water.