Oceans galore: new study suggests most habitable planets may lack dry land

April 20, 2017 by Dr Robert Massey
Continents on other habitable worlds may struggle to break above sea level, like much of Europe in this illustration, representing Earth with an estimated 80% ocean coverage. Credit: Antartis / Depositphotos.com

When it comes to exploring exoplanets, it may be wise to take a snorkel along. A new study, published in a paper in the journal Monthly Notices of the Royal Astronomical Society, has used a statistical model to predict that most habitable planets may be dominated by oceans spanning over 90% of their surface area.

The author of the study, Dr Fergus Simpson of the Institute of Cosmos Sciences at the University of Barcelona, has constructed a statistical model – based on Bayesian probability – to predict the division between land and water on habitable exoplanets.

For a planetary surface to boast extensive areas of both land and water, a delicate balance must be struck between the volume of water it retains over time, and how much space it has to store it in its oceanic basins. Both of these quantities may vary substantially across the full spectrum of water-bearing worlds, and why the Earth's values are so well balanced is an unresolved and long-standing conundrum.

Simpson's model predicts that most habitable planets are dominated by oceans spanning over 90% of their . This conclusion is reached because the Earth itself is very close to being a so-called 'waterworld' - a world where all land is immersed under a single .

"A scenario in which the Earth holds less water than most other habitable planets would be consistent with results from simulations, and could help explain why some planets have been found to be a bit less dense than we expected," explains Simpson.

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Animation showing how the Earth would appear as the amount of water in its oceans increases. Only a narrow window exists in which large areas of both land and water are present. Credit: F. Simpson

In the new work, Simpson finds that the Earth's finely balanced oceans may be a consequence of the anthropic principle – more often used in a cosmological context - which accounts for how our observations of the Universe are influenced by the requirement for the formation of sentient life.

"Based on the Earth's ocean coverage of 71%, we find substantial evidence supporting the hypothesis that anthropic selection effects are at work," comments Simpson.

To test the Simpson has taken feedback mechanisms into account, such as the deep water cycle, and erosion and deposition processes. He also proposes a statistical approximation to determine the diminishing habitable land area for with smaller oceans, as they become increasingly dominated by deserts.

Why did we evolve on this planet and not on one of the billions of other habitable worlds? In this study Simpson suggests the answer could be linked to a selection effect involving the balance between land and .

"Our understanding of the development of life may be far from complete, but it is not so dire that we must adhere to the conventional approximation that all have an equal chance of hosting intelligent life," Simpson concludes.

Explore further: A catalog of habitable zone exoplanets

More information: Fergus Simpson. Bayesian evidence for the prevalence of waterworlds, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stx516

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mauldred
3.7 / 5 (3) Apr 20, 2017
In our solar system alone, there is not only one but two different bodies with the right amount of liquid on their respective surfaces, featuring both emerged land and liquid-covered areas such as oceans and lakes: the Earth and Titan. If it can happen twice in just one solar system, it is probably not right to conclude from the results of a simulation that it must be something very rare and special.
syndicate_51
1 / 5 (4) Apr 20, 2017
In our solar system alone, there is not only one but two different bodies with the right amount of liquid on their respective surfaces, featuring both emerged land and liquid-covered areas such as oceans and lakes: the Earth and Titan. If it can happen twice in just one solar system, it is probably not right to conclude from the results of a simulation that it must be something very rare and special.


That's a big if you are working with.

Every time one of these articles comes up about life being everywhere all I say is use all the probabilities involved, not just the numbers that fit your narrative.

Alas true academic and scientific freedom about this subject doesn't exist in the world. Too much money at stake.
Osiris1
1 / 5 (4) Apr 20, 2017
Mauldred, make that three different bodies with incomplete oceanic coverage. So far as we know absollutely. We know Mars had a polar ocean that has since either departed or was frozen and subsequently covered by layer after layer of Mars dust accreting slowly over eons to 'dust-stone' or some kind of soft rock. As we discover more than the few candidate earths; and if a very significant number of these purport to be waterworlds, we may after we develop star travel decide to adjust the types of planetary shuttlecraft(s) that we carry on our exploration starships to include oceanic landing and takeoff capable submarines. Alien visitors to our world certainly have those capabilities. UFOs have been witnessed not only in our skies and landing on land, but also landing in water. Of the water landers, dual role capability of flight and submarine use (USO). Some say a our visitors have a base on the sea bed off Los Angeles, and this location is restricted on official maps.
Steelwolf
5 / 5 (2) Apr 20, 2017
Not only is there Earth, Mars and Titan, there is also Enceladus and Europa and Ganymede, all of which have water under ice which makes these possible places to look for more life forms.
Sigh
5 / 5 (1) Apr 20, 2017
Not only is there Earth, Mars and Titan, there is also Enceladus and Europa and Ganymede, all of which have water under ice which makes these possible places to look for more life forms.

Mauldred thought Titan was an example of an Earth-like balance of rock and ocean, but if it is water ice acting as rock, carbohydrates form the ocean, and the water covers the actual rock, that becomes debatable.

Another likely counterexample would be Pluto, where apparently an ocean completely covers the core. The ocean happens to be frozen on top, but that is a separate point.
TheGhostofOtto1923
5 / 5 (3) Apr 20, 2017
Monkey limbs evolved for living in trees which made them ideally suited for using technology. Opposing limbs with rigid bones are good for carrying, throwing, hammering, holding an object with one hand while working it with another. And we know that technology is essential to the emergence of sentience.

So how would cephalopods develop technology? How would tentacles which evolved to inhabit nooks and crannies be able to hammer metals and drive screws?

Without fire they could perhaps use the concentrated heat from volcanic lava for smelting. They could work in tandem to bore holes and carry heavy objects.

Maybe tech use would cause tentacles to evolve bones and joints. But its hard to imagine how electricity could come into common use underwater. Perhaps early cephalopods would begin to build rafts to escape predators much as beavers build dams, and floating villages would cause them to become air-breathers as well as tech users in ways that would be familiar to us.
Mark Thomas
not rated yet Apr 20, 2017
"two different bodies with the right amount of liquid on their respective surfaces, . . . Earth and Titan."

As written, the "right amount of liquid," does not make sense. What liquid? What makes it right? The liquid covering 71% of the Earth is mostly salt water, while the few percent of Titan with surface liquid is primarily methane (with some ethane) near the polar regions at cryogenic temperatures (roughly -290 F).

https://en.wikipe...n_(moon)

Mark Thomas
not rated yet Apr 20, 2017
The study cited above is trying to shed some light on the important question of just how rare it is to have a land/water surface balance like Earth. The answer has huge implications for life out there and may play a role in answering the Fermi Paradox. My personal guess is that this is one of a large set of factors limiting the number of technological civilizations like us. It is not hard to imagine that many habitable zone worlds have too much liquid water while others have too little.
SRDUB2
not rated yet Apr 20, 2017
Without fire they could perhaps use the concentrated heat from volcanic lava for smelting. They could work in tandem to bore holes and carry heavy objects.


Once they reach a bronze era level of energy usage from various geological processes and material sciences, could they focus on biological research? genetic engineering and using a completely biological base for their technology? Breading coral analogs to create structures, breading some kind electric eel analog with a programmable root network for electricity and then a different bread of coral analog for 'wire' insulation? So on and so forth.
TheGhostofOtto1923
not rated yet Apr 20, 2017
could they focus on biological research?
Uh how would they make microscopes?

They would need to make machines. Out of metal. Just like us.
mauldred
not rated yet Apr 21, 2017
"As written, the "right amount of liquid," does not make sense. What liquid? What makes it right? The liquid covering 71% of the Earth is mostly salt water, while the few percent of Titan with surface liquid is primarily methane (with some ethane) near the polar regions at cryogenic temperatures (roughly -290 F).


The model is simulating worlds in the temperature range for liquid water to exist. Change the range of temperatures to the temperature of Titan's surface, change water with methane or ethane, logically the model should show equally that the liquid methane/ethane covers entirely the surface in most cases. However this is not the case on Titan. This was not the case on Mars 3 Gy ago. So there seems to be a bias towards liquid/solid ratios that are just right for emerged lands to exist on small telluric worlds.
humy
not rated yet Apr 21, 2017
In our solar system alone, there is not only one but two different bodies with the right amount of liquid on their respective surfaces, featuring both emerged land and liquid-covered areas such as oceans and lakes: the Earth and Titan. If it can happen twice in just one solar system, it is probably not right to conclude from the results of a simulation that it must be something very rare and special.

mauldred

Firstly, Titan isn't a planet but a freezing cold moon around a gas giant.
Secondly, Titan has no liquid water.
Thus we cannot draw any conclusions from Titan and Earth about the likely coverage of water over typical Earth-like planets and, in this context, we are only interested in Earth-like planets with liquid water in the inhabitable zone. Why would we be interested in how much ocean coverage there is on planetary bodies that are too hostile for life?
mauldred
not rated yet Apr 21, 2017
Of course 3 planetary bodies, one of them being an icy moon with a different liquid on its surface, is not enough to conclude. If our solar system is really very special, then the model can still be generally right. But if we believe in the principle of mediocrity, the existence of emerged lands on 3 worlds in just our solar system should point towards an error in the model, not to some statistically improbable feature in our very local neighborhood.
mauldred
not rated yet Apr 21, 2017
Don't get me wrong: I don't believe in UFOs or that NASA is lying to us or any of this kind of b*llsh*t. I am a rational person and when I see some paper saying 'our model shows that something is very unlikely to happen in the universe' and we can see this so-called unlikely thing happening in our close vicinity not just once but several times, it makes me think that the model is wrong, not that we are in a special place around which the universe revolves.
SRDUB2
not rated yet Apr 21, 2017
could they focus on biological research?
Uh how would they make microscopes?

They would need to make machines. Out of metal. Just like us.


I mean there's that mollusk the Limpet that have teeth made of fibers that have a tensile strength 6.5 Gpa. That's pretty damn impressive feat of material engineering for just natural selection. Give a species a couple hundred thousand years of manipulating an analog species simply through cross breading, why couldn't they create some kind of combustion chamber? Mine some coal, separate some water using the electric worms, create snail tooth chamber, and bam you have a furnace.

TheGhostofOtto1923
1 / 5 (1) Apr 21, 2017
why couldn't they create some kind of combustion chamber?
Ever hear the theory of dragons making methane in their gut for flying and fire belching?

I suppose that, given enough time, they could evolve rocket engines in their butts and fly up to meet us. But i doubt it.

Youve got to ask yourself the question, "why do i continue to misspell the word breeding?" I had another one in mind but that one jumped into my head.
Mark Thomas
not rated yet 19 hours ago
"So there seems to be a bias towards liquid/solid ratios that are just right for emerged lands to exist on small telluric worlds."

I sincerely hope you are right and all these habitable worlds we are discovering aren't simply water worlds. But that is far, far too much to conclude with the paltry evidence at hand. You are arguing based on a sample size of two and I am suggesting because of the vast differences between Earth and Titan, it is a sample size of one.

BTW, only a few percent of Titan has liquid on the surface. Even if it were water, it would nearly be a desert world.

"However radar observations have shown that lakes cover only a few per cent of the surface and are concentrated near the poles, making Titan much drier than Earth."

https://www.newsc...oonscap.

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