Signs of ground ice found on ancient protoplanet asteroid Vesta

Re: Ground Ice

Shurely the ice is a left over from a marathon Pan Galactic Gargle Blaster session at the ground breaking ceremony for the new Vogon-constructed hyperspatial express route?

Re: Water from comets or asteroids?

It probably came from the outer solar system.

When the sun and its accretion disk were first forming up, the radiation from the new central star created a radial heat gradient across the disk. Presumably the original material was fairly homogeneous and contained its share of primordial elements and simple compounds. Water was no doubt very common because hydrogen and oxygen are both plentiful elements.

So the disk was full of ices and minerals, but the sun quickly drove the icy, low melting point volatiles from the inner disk via heating, out to the "frost line" where it was cool enough for ice to remain ice. Then the rocky planets accreted from the remnants: silicate minerals and metals. After that, the water was delivered to the young Earth from the outer system by some undetermined means (whatever Jupiter didn't eat, anyway), and it was trapped there by high gravity and a thick atmosphere.

That's the most popular theory, anyway.

Re: Water from comets or asteroids?

If I'm not mistaken, most comets and asteroids are just the cooled-down clumps of residue from the original disc from which our Solar System sprang into being, not the result of planets crashing into each other.

The inner asteroid belt between Venus and Jupiter could have been a planet, but the material could not coalesce properly because of the gravitational influence between Jupiter and the inner planets.

As for the material in the Oort Cloud, there may be a planet lurking out there, but most of the material is likely just small clumps that never made planet-size either.

Re: Water from comets or asteroids?

Also: "asteroids may have brought water to Earth’s oceans. As asteroids crashed into Earth, the impact would have melted the icy deposits, leaving large pools of water"

How many asteroids would have needed to crash into Earth to provide the volume of all the Earth's oceans?

Re: Water from comets or asteroids?

"Did the water on Earth occur as a part of planet building (and also other planets)? Or did the water need to come from someplace else?"

Water would have been fairly evenly distributed amongst the stuff from which the Solar System formed and it also seems probable that the inner planets were at least partially formed by the time that Sol ignited because the solar pressure from Sol, after its ignition, would have prevented or disrupted their formation. Thus, it seems likely that Earth, and the other inner planets, would have already possessed as much water as anything else in the solar system when and as they formed.

Furthermore, if Earth acquired water from asteroid and cometary impacts then the vast majority of this would have arrived during the Late Heavy Bombardment, from about 4.1 to 3.8 billion years ago, but the earliest zircons found indicate that Earth already had surface water about 4.4 billion years ago. And whilst the asteroid and cometary impacts during the LHB would have delivered water to Earth, the high-energy nature of those impacts would have meant that a quite a bit of that water in those asteroids and comets would have been turned to free vapour by the impact and lost to space.

It seems then, that the asteroid and cometary impacts would have delivered some of Earth's water but didn't supply the majority of it.

Re: A bit late

Oppressing the OPA no doubt. Damn Earthers!

Re: A bit late

It appears it took them some time to interpret the data.

The linked article was first presented for publication in June 2016 and has just recently been included as a published article.

Re: What would stop the water evaporating when it hit the Earth

It would definitely evaporate during entry, but it would be trapped by gravity in the atmosphere. When the density got too high it would condense and fall as rain. Same net effect.