Earth features an "overturning" circulation that is driven by differences in the temperatures and salt content of waters.
With the explosion of exoplanet discoveries in recent years, we are learning more and more about what the universe can produce - inevitably sparking a Saganesque mix of science and sheer imagination, as researchers try to apply what they know about the Earth's workings to discern what's possible elsewhere.
The latest result of this line of inquiry has now determined that an Earth-like or terrestrial exoplanet - the crown jewel of the exoplanet search - might nonetheless have a very different ocean circulation and, therefore, a very different type of climate than what we're used to.
"We're saying, it's important to know the potential diversity of oceans that we might see on exoplanets," said Manoj Joshi, a researcher with the Center for Ocean and Atmospheric Sciences at the University of East Anglia in Britain, who conducted the work with two university colleagues. The new study was published Monday in the Proceedings of the National Academy of Sciences.
Exoplanet research is proceeding both through actual observations - those big discoveries we keep hearing about - but also simulations, as researchers use climate and other models to try to figure out how these planets would actually work. To this end, the new research used a 3-D ocean circulation model to home in on the circulation of their seas in particular.
Earth features an "overturning" circulation that is driven by differences in the temperatures and salt content of waters. In the North Atlantic, for instance, warm salty water flows northward at the ocean's surface, but naturally cools as it travels farther (even as it also warms these northern latitudes). As the water gets colder, it becomes more dense. And that added density, combined with the already higher density of salt water, causes the water to sink and then flow back southward below the surface. Something similar happens in the Southern Ocean.
The new study, though, found that if a planet with oceans has enough salt in them - a content roughly that of the very salty Dead Sea, or seven times that of the Earth's oceans - something very different could happen. There can be a situation in which there is enough evaporation of ocean water at lower latitudes to increase its remaining salinity (and thus, density) to the point where sinking occurs closer to the equator, rather than the poles (as on Earth). In this situation, the oceans' circulation becomes the reverse of our own, and that warm sinking water travels poleward and resurfaces at the polar regions, warming them considerably.
"When an ocean becomes salty enough, evaporation in the subtropics - it's only fresh water that's evaporating - leaves salty water behind, for a very, very saline ocean," Joshi said. "This could actually make the water become so dense and salty that you get a circulation being driven by salt gradients."
That could have key implications for the habitability of exoplanets themselves, the study suggests, saying that such ocean circulations, by changing temperatures, could potentially enlargen the "width of the habitable zone" around a given star - although Joshi added that the researchers "haven't quantified the effect" on habitability.
Granted, there are many other parameters that affect how oceans behave - for instance, the number and location of continents - that this rather idealized study did not consider. If there is some impediment to their flow, such as a landmass - or conversely, if there is some opening that allows flow to occur - then that's clearly a crucial factor in determining the nature of an ocean's circulation.
Joshi said Earth originally owes its oceans to bombardment with comets and what he calls "outgassing from magma," implying that other planets could surely have very different volumes of water to begin with. But then on top of that, salinity, or the water's salt content, depends on processes, such as geological weathering, and can also vary.
"If the planet's early geological history is different, weathering of rocks, volcanism, each of these things could set the volume of the oceans and the salinity of the oceans to different values. There's no reason to expect it would be like Earth," Joshi said.
Back on Earth, meanwhile, ocean circulation is getting to be a very big topic, in that a changing climate also seems able to alter it - and in fact, there is evidence of multiple ocean reorganizations, associated with ice-age cycles, in the planet's past history.
This has raised concerns that if surface waters freshen enough in polar regions where sinking or deep-water formation normally occurs, that could block this process by reducing water density - with huge climatic repercussions. On our planet, climate change could mean less heat transport, by the oceans, northward, leading to cooling in regions that were once warmed by these circulations. On another planet, well, who knows.
"We need to remember that the oceans may be very different, and if they are, you can get very different types of circulations happening," Joshi said.
© 2016 The Washington Post
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
The latest result of this line of inquiry has now determined that an Earth-like or terrestrial exoplanet - the crown jewel of the exoplanet search - might nonetheless have a very different ocean circulation and, therefore, a very different type of climate than what we're used to.
"We're saying, it's important to know the potential diversity of oceans that we might see on exoplanets," said Manoj Joshi, a researcher with the Center for Ocean and Atmospheric Sciences at the University of East Anglia in Britain, who conducted the work with two university colleagues. The new study was published Monday in the Proceedings of the National Academy of Sciences.
Exoplanet research is proceeding both through actual observations - those big discoveries we keep hearing about - but also simulations, as researchers use climate and other models to try to figure out how these planets would actually work. To this end, the new research used a 3-D ocean circulation model to home in on the circulation of their seas in particular.
Earth features an "overturning" circulation that is driven by differences in the temperatures and salt content of waters. In the North Atlantic, for instance, warm salty water flows northward at the ocean's surface, but naturally cools as it travels farther (even as it also warms these northern latitudes). As the water gets colder, it becomes more dense. And that added density, combined with the already higher density of salt water, causes the water to sink and then flow back southward below the surface. Something similar happens in the Southern Ocean.
The new study, though, found that if a planet with oceans has enough salt in them - a content roughly that of the very salty Dead Sea, or seven times that of the Earth's oceans - something very different could happen. There can be a situation in which there is enough evaporation of ocean water at lower latitudes to increase its remaining salinity (and thus, density) to the point where sinking occurs closer to the equator, rather than the poles (as on Earth). In this situation, the oceans' circulation becomes the reverse of our own, and that warm sinking water travels poleward and resurfaces at the polar regions, warming them considerably.
"When an ocean becomes salty enough, evaporation in the subtropics - it's only fresh water that's evaporating - leaves salty water behind, for a very, very saline ocean," Joshi said. "This could actually make the water become so dense and salty that you get a circulation being driven by salt gradients."
That could have key implications for the habitability of exoplanets themselves, the study suggests, saying that such ocean circulations, by changing temperatures, could potentially enlargen the "width of the habitable zone" around a given star - although Joshi added that the researchers "haven't quantified the effect" on habitability.
Granted, there are many other parameters that affect how oceans behave - for instance, the number and location of continents - that this rather idealized study did not consider. If there is some impediment to their flow, such as a landmass - or conversely, if there is some opening that allows flow to occur - then that's clearly a crucial factor in determining the nature of an ocean's circulation.
Joshi said Earth originally owes its oceans to bombardment with comets and what he calls "outgassing from magma," implying that other planets could surely have very different volumes of water to begin with. But then on top of that, salinity, or the water's salt content, depends on processes, such as geological weathering, and can also vary.
"If the planet's early geological history is different, weathering of rocks, volcanism, each of these things could set the volume of the oceans and the salinity of the oceans to different values. There's no reason to expect it would be like Earth," Joshi said.
Back on Earth, meanwhile, ocean circulation is getting to be a very big topic, in that a changing climate also seems able to alter it - and in fact, there is evidence of multiple ocean reorganizations, associated with ice-age cycles, in the planet's past history.
This has raised concerns that if surface waters freshen enough in polar regions where sinking or deep-water formation normally occurs, that could block this process by reducing water density - with huge climatic repercussions. On our planet, climate change could mean less heat transport, by the oceans, northward, leading to cooling in regions that were once warmed by these circulations. On another planet, well, who knows.
"We need to remember that the oceans may be very different, and if they are, you can get very different types of circulations happening," Joshi said.
© 2016 The Washington Post
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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