Assumptions about exo-oceans

Mar 04, 2011
Earth-like planets that orbit around Sun-like stars might be likely to harbor liquid oceans. Credit: ESO/L. Calçada

Some estimates indicate that 25% of Sun-like stars have Earth-like planets. A new study now shows that these planets are almost certain to have oceans if they are located in the right temperature zone around their host stars.

Not only may up to 25% of Sun-like stars have Earth-like – but if they are in the right temperature zone, apparently they are almost certain to have oceans. Current thinking is that ’s oceans formed from the accreted material that built the planet, rather than being delivered by comets at a later time. From this understanding, we can start to model the likelihood of a similar outcome occurring on rocky exoplanets around other stars.

Assuming terrestrial-like planets are indeed common – with a silicate mantle surrounding a metallic core – then we can expect that may be exuded onto their surface during the final stages of magma cooling, or otherwise out-gassed as steam which then cools to fall back to the surface as rain. From there, if the planet is big enough to gravitationally retain a thick atmosphere and is in the temperature zone where water can remain fluid, then you’ve got yourself an exo-ocean.

We can assume that the dust cloud that became the Solar System had lots of water in it, given how much persists in the left-over ingredients of comets, asteroids and the like. When the Sun ignited some of this water may have been photo-dissociated, or otherwise blown out of the inner Solar System. However, cool rocky materials seem to have a strong propensity to hold water, and in this manner, could have kept water available for .

Meteorites from differentiated objects (i.e. planets or smaller bodies that have differentiated such that, while in a molten state, their heavy elements have sunk to a core displacing lighter elements upwards) have around 3% water content – while some undifferentiated objects (like carbonaceous asteroids) may have more than 20% water content.

Mush these materials together in a planet formation scenario and materials compressed at the centre become hot, causing outgassing of volatiles like carbon dioxide and water. In the early stages of planet formation much of this outgassing may have been lost to space – but as the object approaches planet size, its gravity can hold the outgassed material in place as an atmosphere. And despite the outgassing, hot magma can still retain water content – only exuding it in the final stages of cooling and solidification to form a planet’s crust.

Mathematical modelling suggests that if planets accrete from materials with 1 to 3% water content, liquid water probably exudes onto their surface in the final stages of planet formation – having progressively moved upwards as the planet’s crust solidified from the bottom up.

Otherwise, and even starting with a water content as low as 0.01%, Earth-like planets would still generate an outgassed steam atmosphere that would later rain down as fluid water upon cooling.

If this ocean formation model is correct, it can be expected that rocky exoplanets from 0.5 to 5 Earth masses, which form from a roughly equivalent set of ingredients, would be likely to form oceans within 100 millions years of primary accretion.

This model fits well with the finding of zircon crystals in Western Australia – which are dated at 4.4 billion years and are suggestive that liquid water was present that long ago – although this preceded the Late Heavy Bombardment (4.1 to 3.8 billion years ago) which may have sent all that water back into a steam atmosphere again.

Currently it’s not thought that ices from the outer Solar System – that might have been transported to Earth as comets – could have contributed more than around 10% of Earth’s current water content – as measurements to date suggest that ices in the outer have significantly higher levels of deuterium (i.e. heavy water) than we see on Earth.

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User comments : 16

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droid001
5 / 5 (6) Mar 04, 2011
Must be lot of fish around.
Royale
5 / 5 (5) Mar 04, 2011
don't you mean exo-fish? heh. I want me an exo-fish. Even if he has to live in liquid methane..
panorama
5 / 5 (6) Mar 04, 2011
don't you mean exo-fish? heh. I want me an exo-fish. Even if he has to live in liquid methane..

And I thought having a salt water aquarium was high maintenance...
Modernmystic
1.9 / 5 (7) Mar 04, 2011
"Some estimates indicate that 25% of Sun-like stars have Earth-like planets"

WTL did they pull that figure out of...a hole that sees very little sunlight?
kaasinees
4.5 / 5 (4) Mar 04, 2011
Its a guestimate, chill.
Like the title says, ASSUMPTIONS.

They are forgetting planet distance versus star brightness...
Red dwarf stars with close planet relation could harbor liquid oceans.
GSwift7
4.4 / 5 (7) Mar 04, 2011
"Some estimates indicate that 25%,,,

WTL did they pull that figure out of...


Mercury, Venus, Earth and Mars. The four rocky planets we know anything about. One of them has oceans. That's 25%. I wouldn't be surprised if that's how the assumption works here.

There are probably lots of oceans, even if it's only .000025% that's still lots. However, the likelyhood that those oceans are places where you would want to take a swim is a bit more uncertain. We may find that our own salty sea with a nearly neutral pH is rare. We could find that soupy mud filled with sulfur is more likely (think yellowstone).

On the other hand, think about how exciting it would be if it turns out that temperate oceans are common? How long do you think it will take us to organize an expedition if we discover one with telescopes? If it takes more than a human lifetime to reach the nearest one, would you want to be on the ship?
Skultch
4.8 / 5 (5) Mar 04, 2011
If it takes more than a human lifetime to reach the nearest one, would you want to be on the ship?


Since I plan on living for 200+ years, HELL YES!! :)

I'll have porn, right? I'm not going if there's no porn. VR porn is preferable. I don't really care about real life female mates. I'll seduce one of the other crew members. I'm pretty confident about that one. ........ Ok, FINE! My wife can come. ;)
GSwift7
4.4 / 5 (8) Mar 04, 2011
If it takes more than a human lifetime to reach the nearest one, would you want to be on the ship?

Since I plan on living for 200+ years, HELL YES!! :)


I don't think I would want to go.

Yeah, a sexual partner would be a must since it would be your children who actually reach the destination. However, a wife? Wouldn't a pet be a better idea?

lol. Imagine a zero G cat; you know how they always land on their feet? Would placing a cat in zero G be like a voilation of cosmic laws and just make the universe explode or something?
Modernmystic
1 / 5 (3) Mar 04, 2011
I'd just honestly like to know where they got the figure...really. This IS supposed to be a science site isn't it?

Would it be "cool" if temperate oceans on Earth like planets were that common? I sure as heck think it would be.

The facts are that the metalicity of most "Sun like" stars is much lower than ours. A great many of them are binaries. A percentage are inhospitably variable. The list goes on...let's just say I'm dubious.

J-n
5 / 5 (8) Mar 04, 2011
I took a look at Universe Today (who contributed the article to Physorg) and it did have a separate link describing the statement that "25% of sun like stars may have earth like planets"

From the first paragraph of that article:
"A five-year survey of nearby solar-mass stars has provided astronomers with an estimate of how many stars of this type could have Earth-size planets. Andrew Howard and Geoffrey Marcy from the University of California Berkeley studied 166 G and K stars within 80 light-years of Earth, determining the number, mass and orbital distance of any of the stars planets. Since Earth-sized worlds have not yet been found, they extrapolated the number of that size of planets, based on the fraction of stars that host Neptune to super-Earth sized planets."

i hope that helps!! :)
ShotmanMaslo
not rated yet Mar 04, 2011
Earth-size planets.


So it is Earth-size planets, not Earth-like planets. That figure may be quite realistic, then, altough still optimistic, IMHO.
Modernmystic
2.7 / 5 (3) Mar 04, 2011
i hope that helps!! :)


Indeed it does thank you sir, I guess I could/should have looked myself.

My suspicions are correct though...it's an EXTREMELY specious estimate based on the available data. I thought they might have data not released yet to the public.
Skultch
3 / 5 (2) Mar 04, 2011
Yeah, a sexual partner would be a must since it would be your children who actually reach the destination. However, a wife?


I'd actually rather have a wife on the trip than a gf or two. Too much drama risk for that long of a voyage. On the other hand, 80 years of the same punani sounds like it would get old. Holodeck! That's the answer! That's not cheating, right? :)
fuviss_co_uk
4 / 5 (3) Mar 04, 2011
I am sure, that in time, when we will be flying to stars, our lifespans will be a lot longer than in 2010, medicine and technology will be so advanced, that we can't even imagine that now...
Even in next 10 years changes will be so enormous, that when some guy from 2030 could travel in time, and tell us what will be feasible in 2020 or 2030 we will be amazed by all his stories. Looking at rapid progress in nanotechnology and biotechnology, I will not be suprised if our lifespans in 2030, will reach 150 or more, and that's quite near future, hard to imagine what we will se in 2040 or 2050
Birger
2.5 / 5 (2) Mar 04, 2011
If the Earth-like planets have a bit too much water, the volcanoes cannot reach the surface. Earth's continents were built by amassing volcanic island arcs. Chemical weathering of the continents regulates the carbon dioxide in the atmosphere, and therefore temperature. The nearly anoxic proterozoic ocean had more oxygen close to coasts, and so on. A world without any land might produce bacteria, but don't expect multiple-cell life.
Terrible_Bohr
5 / 5 (2) Mar 04, 2011
^ Everyone is reporting these posts, right? I know they've been spamming this site for a while, but it's just especially annoying to me to day.

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