Water worlds could support life: Analysis challenges idea that life requires 'Earth clone'

August 31, 2018, University of Chicago
This artist's concept depicts a planetary system. Credit: NASA/JPL-Caltech

The conditions for life surviving on planets entirely covered in water are more fluid than previously thought, opening up the possibility that water worlds could be habitable, according to a new paper from the University of Chicago and Pennsylvania State University.

The has largely assumed that covered in a would not support the cycling of minerals and gases that keeps the climate stable on Earth, and thus wouldn't be friendly to . But the study, published Aug. 30 in The Astrophysical Journal, found that ocean planets could stay in the "sweet spot" for habitability much longer than previously assumed. The authors based their findings on more than a thousand simulations.

"This really pushes back against the idea you need an Earth clone—that is, a planet with some land and a shallow ocean," said Edwin Kite, assistant professor of geophysical sciences at UChicago and lead author of the study.

As telescopes get better, scientists are finding more and more planets orbiting in other solar systems. Such discoveries are resulting in new research into how life could potentially survive on other planets, some of which are very different from Earth—some may be covered entirely in water hundreds of miles deep.

Because life needs an extended period to evolve, and because the light and heat on planets can change as their stars age, scientists usually look for planets that have both some water and some way to keep their climates stable over time. The primary method we know of is how Earth does it. Over long timescales, our planet cools itself by drawing down greenhouse gases into minerals and warms itself up by releasing them via volcanoes.

But this model doesn't work on a water world, with deep water covering the rock and suppressing volcanoes.

Kite, and Penn State coauthor Eric Ford, wanted to know if there was another way. They set up a simulation with thousands of randomly generated planets, and tracked the evolution of their climates over billions of years.

"The surprise was that many of them stay stable for more than a billion years, just by luck of the draw," Kite said. "Our best guess is that it's on the order of 10 percent of them."

These lucky planets sit in the right location around their stars. They happened to have the right amount of carbon present, and they don't have too many minerals and elements from the crust dissolved in the oceans that would pull carbon out of the atmosphere. They have enough from the start, and they cycle carbon between the atmosphere and ocean only, which in the right concentrations is sufficient to keep things stable.

"How much time a planet has is basically dependent on carbon dioxide and how it's partitioned between the , atmosphere and rocks in its early years," said Kite. "It does seem there is a way to keep a planet habitable long-term without the geochemical cycling we see on Earth."

The simulations assumed stars that are like our own, but the results are optimistic for , too, Kite said. Planets in red dwarf systems are thought to be promising candidates for fostering life because these stars get brighter much more slowly than our sun—giving life a much longer time period to get started. The same conditions modeled in this paper could be applied to planets around red dwarfs, they said: Theoretically, all you would need is the steady light of a star.

Explore further: Plate tectonics not needed to sustain life

More information: Astrophysical Journal (2018). DOI: 10.3847/1538-4357/aad6e0

Related Stories

Plate tectonics not needed to sustain life

July 30, 2018

There may be more habitable planets in the universe than we previously thought, according to Penn State geoscientists, who suggest that plate tectonics—long assumed to be a requirement for suitable conditions for life—are ...

Giant clue in the search for Earth 2.0

April 4, 2018

In a new study published today in the Astrophysical Journal, researchers from New York University Abu Dhabi and NASA's Jet Propulsion Laboratory (JPL) in Pasadena, CA, share new findings about how the presence of "giant" ...

Recommended for you

Video: Net successfully snares space debris

September 19, 2018

The RemoveDEBRIS satellite has successfully used its on-board net technology in orbit – the first demonstration in human history of active debris removal (ADR) technology.

Mercury studies reveal an intriguing target for BepiColombo

September 19, 2018

A month before the planned launch of the joint ESA-JAXA BepiColombo mission to Mercury, two new studies shed light on when the innermost planet formed and the puzzle of its chemical composition. The findings will be presented ...

31 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Old_C_Code
3 / 5 (2) Aug 31, 2018
They never said much in physics class about; a thrown stone that hits the water, falls at constant velocity losing it's acceleration after being submerged. So would life be weightless on jupiter if it did have a water/liquid surface?
PoppaJ
5 / 5 (6) Aug 31, 2018
I was not aware that there was a big push to believe that life required an earth clone. On the contrary. The general consensus based on my reading is that life is expected on many different types of planets and other bodies.
rrwillsj
1 / 5 (5) Sep 01, 2018
Ahh, the promise of 'simulations'

"He promised you this
and he promised you that...
When you woke up
in the morning?
He was gone,
with the wallet out of your purse.
And your car keys,
as you hear him drive away
merrily honking the horn!"

A number of the combicbook fantasists will gullibulllee accept this simulation as definitive proof of their fairytale dreams.

After strident denunciations of many other simulations and the speculative conclusions drawn!

Notice the line in this article "Our best guess is that it's on the order of 10 percent of them."

Which if correct? Has reduced the probability of "Lining Worlds" by another nine-tenths.

Still flogging the red dwarfs for possible LWs? Anyone yet find a red dwarf that isn't spitting out violent outbursts of x-rays on a regular basis?

The high-order probability is, any rocky planet in a stable sweet spot orbit will be a dried-up, airless skull rolling about it's primary.
humy
2 / 5 (2) Sep 01, 2018
I don't doubt that life, of some sort, could thrive on some of these 'ocean planets' (planets completely covered in oceans).
But, somehow, I don't think it would be likely to be as interesting as life that evolved on land.
I am fairly certain that if we are interested in intelligent life with technology in particular, because life on an ocean planet is very unlikely to evolve to such intelligent life with technology due to a lack of solid materials available for basic tool-making (I assume there cannot be a "stone-age" as a precursor to it), ocean planets may be of little interest to those of us searching for life because of this. But I guess it just depends on what interests you and what you are looking for.
Old_C_Code
3.7 / 5 (3) Sep 01, 2018
humy: advanced life could evolve in oceans, an opposable thumb is key.
Surveillance_Egg_Unit
4 / 5 (4) Sep 01, 2018
humy: advanced life could evolve in oceans, an opposable thumb is key.


It would also be very useful to have a good pair of gills to breathe underwater. If humans ever arrive at such a water world, a surgical procedure may be necessary; or a way to grow gills found, in order to provide a human foetus with natural gills. On the sides of the neck, not far from the windpipe.
IIRC the human embryo, after its cells have grown sufficiently to have a heart in its chest, is endowed with gills - somewhat similar to fish gills.
I have always been curious about that phase in human development.
Parsec
3.7 / 5 (3) Sep 02, 2018
One of the problems of course with red dwarfs is the extreme flaring and explosive solar activity we see around them, especially in their earlier years. This leads to the conclusion that the average time between sterilization events in a earth-like clone is around a few million years for most systems.

Water is one of the best radiation shields there is however, and a few hundred meters of water should prevent global sterilization from occurring, especially if the surface is ice covered like Europa is today. Then we only need some way to provide energy, and it shouldn't really matter what the actual surface temp is, as long as significant amounts are liquid, i.e. energy input.
humy
3 / 5 (2) Sep 02, 2018
humy: advanced life could evolve in oceans, an opposable thumb is key.

What would the opposable thumb evolve to do in the ocean where there isn't much solid material to make into tools? What would the first tools be made of?
Ojorf
1.7 / 5 (3) Sep 02, 2018
Even before our opposable thumb, grasping hands evolved in tree climbing species, never in the ocean. It's hard to see how a hand similar to ours could evolve on a water world, it would have to be something that does not swim for a living leaving some hands free, like an octopus.

Even presuming an intelligent octopus, it would be very hard to develop almost any technology without fire.
Surveillance_Egg_Unit
3.7 / 5 (3) Sep 02, 2018
It would be presumptuous to claim that any planet could be exclusively a water planet with no land whatsoever. It just is not possible, unless the water has no wave activity and there are no winds to drive possible currents. On Earth there are very high mountains under the surface of the oceans, as well as underwater volcanic activities that are island builders. And, depending on the type of material at the ocean bottom, water is often found seeping down into the upper mantle where it eventually fills cavernous places.
Ojorf
2 / 5 (4) Sep 02, 2018
SEU this article is about water worlds, not dry planets like the earth. The earth only has 0.05% water/mass, water worlds have much more.
Even a small body like Enceladus might have an ocean more than 30km deep and on larger worlds the oceans are speculated to be so deep that even at high temperatures a mantle of ice forms at depth due to the extreme pressure.
humy
5 / 5 (1) Sep 02, 2018
It would be presumptuous to claim that any planet could be exclusively a water planet with no land whatsoever. It just is not possible,
Surveillance_Egg_Unit

Why no?
Jupiter has no land area and is covered in oceans; just not water oceans. And some of the moons in our solar system are covered in water oceans covered in thick layers of ice so it isn't a huge stretch that a water-ocean planet could exist not covered in ice.
unless the water has no wave activity and there are no winds to drive possible currents.

What has "wave action" or "wind" or "currents" got to do with it?
Jupiter has no land area and is covered in oceans and has "wave action" and "wind" and "currents" and it exists just fine. If that can exist (like it does) then why not a water-ocean planet with "wave action" and "wind" and "currents"?
Old_C_Code
3.7 / 5 (3) Sep 02, 2018
humy: there's plenty of solid material in the ocean, plenty of intact rock formations there.
granville583762
4 / 5 (4) Sep 02, 2018
Without land there will be no trout, or salmon, or turtles, or crocodiles and alligators or water snakes, or beavers, or any type of fish that requires land, as no coral reefs a whole plethora of fish that require islands would not exist and with no floating flotsam for the fish congregate, fish need land – a lonely watery world
Cusco
5 / 5 (2) Sep 02, 2018
advanced life could evolve in oceans, an opposable thumb is key


I don't see why tentacles, claws, or mandibles or any other manipulatory appendages wouldn't work. You just need to be able to hold something solid while you work on it.
humy
3 / 5 (1) Sep 02, 2018
Cusco

I agree. But I still think it unlikely that an ocean life form would become technologically advanced.
In an ocean planet, what kind of solid materials suitable to make a tool out of would be in the ocean that an intelligent animal's tentacles/claws could hang on to and form complex useful tools? How would its version of an 'industrial revolution' get started and then result in, say, the building and launch of the first weather satellite etc? I assume there would have to be some mining of the deep ocean floor to get at the necessary raw materials to manufacture it and then it would have to be manufactured without furnaces etc; I would imagine this would be very difficult!

I would imagine it would also be hard to do basic science research all underwater esp in physics and chemistry and esp electronics (because electronics and water don't tend to mix well). Perhaps they could first invent some floating platforms and conduct their science experiments on top of them?
Old_C_Code
3.7 / 5 (3) Sep 02, 2018
Glove boxes in fume hoods sealing off water. But geez, chemistry would be tough, yes.
rrwillsj
3 / 5 (2) Sep 02, 2018
We have, one, singular planet known to have intelligent, oceanic lifeforms. The whales, dolphins, porpoise and pennipeds.

All mammal, none with opposable thumbs. Or any tool-crafting digits. Okay, maybe otters? All evolved (de-evolved?) from ancestral land animals.

Until Homo Savagerous showed up? They had reasonably cushy lives aside from naturally evolved predators.

The only other noticeably brainy creature is the octopus. Tentacles are a poor substitute for hands. But their greatest handicap is short lifespan.

The female octopus generally lives only a year or so. Just long enough to reproduce. The males can live a few years longer but by the last year or two show definite signs of dementia.

Form does not just follows function. Form is selected by function. Cephalopoda have existed several hundred million years without developing tool use.

- cont'd-
rrwillsj
3 / 5 (2) Sep 02, 2018
- - cont'd -

Between then and today's ocean mammals have been endless varieties of ocean-going amphibians, reptiles, dinosaurs, and avians.

None have left detected signs of tool use. (you have no idea how much it pains me to make that concession in phrasing!)

It is my still unproven conjecture that the ice-capped moons such as Enceladus have sterile oceans. Until we come along and contaminate them with our bungling enthusiasm.

I will concede a faint hope for life on Titan. However, I would expect we would detect traces of by-products by now.

And even if native life is discovered any where in our Solar System? At best I expect it to be simple, Archean-type slimes and molds.

Frankly and ernestly I hold out little hope of detecting interstellar Living Ocean Worlds. If in four hundred million years, all the different varieties of intelligent marine life failed to advance past "The Whale Dream"? I doubt if we will, in our existence, ever find it across the stars.
Surveillance_Egg_Unit
3.7 / 5 (3) Sep 03, 2018
SEU this article is about water worlds, not dry planets like the earth. The earth only has 0.05% water/mass, water worlds have much more.
Even a small body like Enceladus might have an ocean more than 30km deep and on larger worlds the oceans are speculated to be so deep that even at high temperatures a mantle of ice forms at depth due to the extreme pressure.
says Ojorf

Then your "water worlds" must not have tectonic plates, volcanic actions, subduction of plates, or any other movement on, within, or below the top of its mantle. There is also extreme pressures at the bottom of the Marianas Trench, but there is also the possibility of some form of movement of the upper mantle in spite of compression, due to shifting of the Earth's crust. If there is no movement of the crust and upper mantle even on a water world, then the enormous pressure may crack the surface at the bottom that would allow some of the contents of the hot molten core to flow out.
Ojorf
2.3 / 5 (6) Sep 03, 2018
SEU, why do you not at at least get a modicum of knowledge about the subject under discussion before you comment?
Before commenting on water worlds or genetics or evolution or whatever, at least google it and see what it is about, before you give free range to your overwhelming urge to write something.
This is a clear trend in your comment history.
Why do you feel you have to comment on something you know nothing about?
granville583762
3.7 / 5 (3) Sep 03, 2018
Remember beaching whales - no land no sea life as we know it

Whales come into the shallow waters away from predators to have and bring up their of spring, without land there will be no whales, the same with penguins - no land no penguins, this watery world is getting lonelier by the second
The crabs, whales, sharks and plethora of Marianas Trench seabed life rely on whales and other creature that reproduce on land to provide their bodies as food for the 7mile sea bed club to survive, no land and no Marianas Trench seabed life
granville583762
3.7 / 5 (3) Sep 03, 2018
Can anyone see where this going – no land means no fish

In fact the crabs are related to land crabs so there is a possibility the Marianas Trench crabs might never have evolved without land crabs, the fish that inhabit coral reefs only exist because of the existence of coral reefs, no land no coral reef, if someone does not quickly interject there's not going to be an life left in the sea and therein lies another fact - there are thousands of miles of uninhabited seas, because fish need land, no land means no fish which means no food chain for predatory fish
Fish cannot live of water alone they need food, usually other fish where these other fish need land for their food and protection from predatory fish.
Old_C_Code
4 / 5 (2) Sep 03, 2018
gran says: "no land means no fish", wrong, there would be rock formations and mountain ranges submerged. And not all fish need land.
granville583762
3.5 / 5 (4) Sep 03, 2018
No land mean no land, except on the sea bed
gran says: "no land means no fish", wrong, there would be rock formations and mountain ranges submerged. And not all fish need land.

That is land, that cheating!
humy
5 / 5 (1) Sep 03, 2018
Whales come into the shallow waters away from predators to have and bring up their of spring,
granville583762

This is simply not true for all whales and only partly because many aren't usually bothered that much from predators but also because sometimes deep ocean is the best place to avoid predators anyway. For example, there is the blue whale that in some places breeds in deep oceans.

https://seethewil...ory-map/

If you look at the above map, it clearly shows at least two breeding grounds (in red) that are in deep ocean. And in some cases their feeding grounds (in green) is also in deep ocean. Thus all the oceans could be deep and they wouldn't go extinct, no problem. How they could evolve without land is another matter.
without land there will be no whales
Yes, but only because whales evolved from land animals, NOT because they all must breed in shallow water.

humy
5 / 5 (2) Sep 03, 2018
No land mean no land, except on the sea bed
gran says: "no land means no fish", wrong, there would be rock formations and mountain ranges submerged. And not all fish need land.

That is land, that cheating!
granville583762

Look up the word "land" then come back to us.
Let me help you with that;
https://en.oxford...ion/land
"the part of the earth's surface that is not covered by water"
Old_C_Code
5 / 5 (2) Sep 03, 2018
P.S. There were fish in the sea before there was vegetation on that barren land 400 million years ago.
granville583762
3.7 / 5 (3) Sep 03, 2018
Turtles are ancient creatures, have seen extinctions come and go, they still come up on the beach under a full moon to lay their eggs as all the first sea creatures came up on land to lay their eggs or have we all forgotten it is only mammals that do not lay eggs
humy
3 / 5 (2) Sep 03, 2018
Turtles are ancient creatures, have seen extinctions come and go, they still come up on the beach under a full moon to lay their eggs as all the first sea creatures came up on land to lay their eggs or have we all forgotten it is only mammals that do not lay eggs
granville583762

So now you are arguing that sea animals cannot evolve to lay eggs in the oceans; Wow you are stupid!
All one has to to is point to just one of the many examples of a sea animal that lay eggs in the oceans.
Squid.
granville583762
3.7 / 5 (3) Sep 03, 2018
"Gonatus onyx is one of the most abundant species of squid in the Pacific and Atlantic Oceans and is an important food source for many predators. They spend most of their lives in shallow waters but dive to great depths to lay eggs. It's a shallow-living squid for most of its life, but then it dives down to 2,500 meters, lays 2,000 to 3,000 egg",
It then it collects them and carries them around for months, it's not laying eggs and leaving them as salmon do. This is the precursor to evolving an egg that develops and is born as in mammals.
sea horse's hatch eggs in pouches but then sea horse like coral reefs this why turtle bury their eggs as even Gonatus onyx lives all it life in shallow water so it needs land, there's no escaping the beaches, coral, rocky out crops, volcanic islands which are the reason there is so much diversity in the sea.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.