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back to article Watery asteroid discovered 150 light-years off hints at habitable worlds

A European trio of researchers has discovered a "circumstellar disk" – a corpse, in other words – of a minor planet that was about 26 per cent water. The discovery of the rocky remains, found orbiting a white dwarf star 150 light years over the rainbow, gives credence to the theory that our own Earth's watery condition was …

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getting unsoaked in the dark?

sounds like the pub was open late

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150 millon light years away?

Are you sure? Because detecting a white dwarf and an asteroidal body comparable to Ceres at the equivalent distance of a galaxy on the far side of the Virgo Cluster is no mean feat! What incredible instrument did they use to pull that off?

Or did you mean 150 light years and got a bit overenthusiastic about the distance?

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Ceres is 26% water? Hmmm...

So how does the total amount of water in Ceres compare to that in Earth? Earth's diameter is roughly 8.5x that of Ceres, so its volume should be a bit over 600x larger. Therefore, Earth has about 47x more water than Ceres. If these back of the envelope calculations are correct, that means Earth would have had to have been hit by one hell of a lot of stuff - the equivalent of 47 Ceres, to supply it with the amount of water it has if it received its water via impact.

Surely it would be simpler to postulate that water was already present during Earth's formation (if nothing else in the form of hydrogen and oxygen, some of which combined as H2O) and the water, being lighter than the elements making up the crust, mantle and core, ended up on the surface (below the even lighter atmospheric gasses)

Perhaps bodies that form in water-rich or hydrogen/oxygen rich areas end up with lots of water like this unfortunately planet, and Ceres, and others that form in less water-rich areas are comparatively dry, so much so that there are actually parts of the surface not covered by water! Perhaps our having only 2% water makes us unusual or even rare among other Earth-like planets, and we may be far more likely to encounter planets covered in vast deep oceans with no dry land at all than to encounter our mixed environment of oceans and dry land.

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Re: Ceres is 26% water? Hmmm...

Earth might have had a LOT of water during the early stage of its formation - however the impact that lead to the formation of the moon would have resulted in the vast majority of the surface water being lost.

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Boffin

Re: Ceres is 26% water? Hmmm...

I got out the fag packet:

Wikipedia says Venus's atmosphere has a mass of 5×1016 kg and is 20ppm water, giving 1016kg of water.

It then handly gives volume of water on Earth as 109 km3, which at standard density is 1021kg. I'm not sure variations in density are going to account for 5 orders of magnitude (I can't be arsed to figure it out) so Earth probably has more water.

That could be down to atmospheric loss, but the upper atmospheres are pretty similar on both. OTOH if water arrived from comets in the outer solar system, then you would expect Earth to catch more of them and end up with more water.

But, as I say, back of the fag packet.

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Re: Ceres is 26% water? Hmmm...

It could have been a bit of both, maybe?

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Re: Ceres is 26% water? Hmmm...

I think you misread, it was not Ceres that was 26% water, which is more massive than the "circumstellar disk" but has roughly the same amount of water. Or something.

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Re: Ceres is 26% water? Hmmm...

Perhaps people have thought of this. Perhaps there are people on this particular rock other than you that have the ability to form simple hypothesis and then afterwards check to see if it holds water or not.

I am pretty far from being an astronomer or an astrophysicist, but as far as I can speculate and a brief reading on the subject the theory is this (keep in mind that my knowledge of this is extremely limited, if in doubt seek an adult or an expert (which normally would be both)):

In the beginning you have a disc of gas. The atoms and molecules bumped into each other and slowed down causing the disc to contract and heat up. Then the center had enough pressure and heat to ignite, i.e. hydrogen starting to fusion. The result was a pressure of particles pushing outwards. The light materials like hydrogen would evaporate due to the heat and stay as gas and be pushed outwards beyond what is called the condensation perimeter where it would be cold enough to condense and it would allow them to stay together and form planets thus reducing the surface area per mass enough that the solar winds would not affect them so much anymore. Further in you were left with the heavier elements and molecules that managed to stay together in the heat and continue to form planets. Therefor you have rock planets in the inner solar system, gas planets at the outskirts and more rocky planets and objects further out again since you have less gas there in the first place and it was dumped large amounts of gas right outside the condensation border, but not any further than that.

So we are left with little gas, most importantly hydrogen at the inner solar system. Oxygen is not so rare since it easily form with heavier elements. Then we have the contraction and forming of rock planets which is violent and reach extreme temperatures. Without any atmosphere, extreme high temperature and a steady solar wind you would lose the rest of your hydrogen very quick. The Earth would probably not form a solid surface in a long long time and let alone any surface cool enough to hold any water. We are now here a few billion years later and still most of the planet is molten rock. Only a thin slice of about 60 km is frozen solid.

So the theory is that we have had to have a rather large import of hydrogen after the formation of the planet itself. And I am guessing that since the oxygen here already was tightly bound to other elements and free hydrogen would be lost to space again if it didn't find anything to cling to, you would be much better off if it came as water in the first place. And there was a "hell of a lot" of stuff in orbit out there in the beginning. The formation took a long long time and we are not yet done with clearing the system of debris.

As for the rare among "Earth-like planets". Er...what do you mean by that? We do know that of the four rock planets in this system only ours have any water to speak of. But you are trying to define them out of your probability calculation, but leaving rock planets with more water in? Yes, that would make Earth unusual dry. Kind of like when I stack of cards by removing all two, three and fours and replacing them with kings and asses. That would make any cards less than six rare.

My point is this: Yes, surely it is simpler to postulate that water was already present during Earth's formation. That is the bleedin' point. If it is simpler to postulate and the collective of scientists that have spent the decades on this dismiss the theory, then you should maybe consider that they have actually thought it through. And if you are curious as to why, pick up a book or visit the Internet.

Bah, now I sound harsh and mean again, but I made a pun I think, so...happy.

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Alien

Re: Ceres is 26% water? Hmmm...

Wrong kind of water. Ceres County Council have a hosepipe ban anyway.

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Pint

I like that idea

I think its widely accepted that the Earth/Moon system is the remnant of a collision. But the idea that it was a very wet collision just seems right somehow. Friday beers all round.

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Yag
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"potential for habitable planets"

is this right? or should it be "potential for formerly habitable planets"?

A white dwarf don't strike me as a good candidate for finding habitable planets... Did I missed something?

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Re: "potential for habitable planets"

No, you're not missing anything. They're dead, Jim.

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*** Exclusive - New Death Star weapon discovered ***

Well, it looks like the Death star no longer needs to blow a planet to bits, it just nudges it towards the nearest white dwarf, then runs in the opposite direction...

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Thumb Up

Excellent work. 150 LY is a bit far, but *very* promising for other locations

Possibly somewhat nearer to Earth?

BTW one notion for Terraforming Mars is to crash asteroids/comets into it.

Thumbs up for good observations.

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Coat

Krypton...

Mine's the red cape over by the door.

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Anonymous Coward

Wet impact

Many are looking out for rogue asteroids hitting the earth. Even plans on painting them to help nudge them off trajectory.

But what about a big wet asteroid hitting us? A big one could raise the sea level enough to make lower lying areas uninhabitable. It would also effect the gulf stream and possibly cool down the bits of the UK still sticking out the water.

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Re: Wet impact

Are you serious? Hard to tell on the Internet.

In case you are not, after all numbers in science, and specially astronomy, can be hard to get a feeling of:

To increase the sea level with one and a half centimeter we can say that we need to cover the surface with one centimeter of water since one third is land. So how much water is that? Well since a centimeter is so small compared to the radius of the Earth it is simply the surface times a centimeter. The surface of a sphere is:

Ae = 4*pi*re^2

The volume of the water, Vw is then:

Ae*h

We assume a spherical roid hitting us so we figure out how big a sphere we need for that amount of volume, it radius rr would have to be

Vw = 4 * pi * rr^3 / 3

So we end up with:

rr = (3 * re^2 * h) ^(1/3) = 10km

So a roid twenty kilometers across, that is a hell of a big roid, and I think it would cause slightly more problems than one and a half centimeter increased sealevel.

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Anonymous Coward

Re: Wet impact

I was mostly joking about the sea levels. It would have to be of a size that could take out the moon and would give one massive tsunami round the planet. Anything of that size (solid or even pure water) would be an extinction level event.

At least Bruce Willis wouldn't have to go up and drill. Just send him up with payload of paper towels. (Or one sheet of Plenty)

Sounds like it could be an interesting What-If question of XKCD.

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