Where are rivers and oceans in the solar system?

(ORDO NEWS) — Some moons of Jupiter and Saturn are so rich in water that it forms whole seas there. On the surface of Titan, in turn, liquid hydrocarbons flow in channels, and the largest reservoir of liquid exceeds the Caspian Sea in area. Gazeta.Ru talks about extraterrestrial oceans in which, hypothetically, life can exist, and in some you can even swim.

In 2021, Russian scientists discovered huge reserves of water on Mars, the area of ​​\u200b\u200bwhich is comparable to Lake Ladoga, but they exist in the form of ice.

In general, the search for liquid water on Mars is one of the key tasks for the researchers of this planet, since it is water that is usually associated with the suitability of the planet for life. Now scientists have come to the conclusion that only small salty, quickly drying up streams can flow on the surface of Mars, and lakes should be looked for under the surface.

Meanwhile, in the solar system there are bodies on which geysers hit and there are entire seas, and they are located further from the Sun than Mars – behind the asteroid belt. The existence of some of these seas is known for sure, and scientists even have approximate data on the conditions in them.

Different ways to keep warm

At first glance, this seems strange: if even on Mars it is too cold for rivers, then why are unearthly seas even further from the Sun? The fact is that sunlight is not the only possible source of heat for a planet or satellite. If a large number of radioactive isotopes are present in the core of a celestial body, then they will provide an intense heat flow from the center to the surface. This also happens on Earth, where a 47 terawatt flux passes through its surface, and 70 percent of the core heat loss is restored due to the radioactive decay of uranium, thorium and potassium-40.

In addition to radiogenic heating, tidal forces can be a source of heat. Gravity decreases in proportion to the square of the distance from the body, and therefore affects the near and far sides of the satellites with different strengths, causing them to stretch under the action of tidal forces.

If the satellite does not rotate in a circular, but in an elliptical orbit in a tidal lock, then as it moves along it, the tidal forces are constantly changing, which causes deformation of the body. During deformation, friction occurs, which produces heat.

Finally, seas can be made up of more than just water. Methane and ethane remain liquid down to -182 degrees, ammonia – up to -77. On hot worlds, on the contrary, an ocean of sulfuric acid can survive at temperatures above 300 degrees, but astronomers are not yet aware of examples of such planets.

Where can you swim

The most famous extraterrestrial ocean is on Jupiter’s moon Europa. Europa is almost the size of the Moon, but one and a half times lighter than it. The surface of this moon is made of ice, and the ocean of liquid water is under it. This happens precisely because both radiogenic and tidal heating act on the body from the inside, and in the case of Europa, the second is much greater than the first.

It is worth noting that the tidal heating of Europa is possible only thanks to Io and Ganymede, other moons of Jupiter. Europa is in orbital resonance with them, that is, it makes one revolution for two revolutions of Io and one for Ganymede. Without this, the expenditure of energy on tidal forces would gradually round the orbit, and the deformations of Europa would stop.

The internal ocean of Europe can reach a depth of 100 kilometers and is two to three times the volume of the World Ocean of the Earth.

If the layer of ice is compared with the earth’s crust, then the water under it will be an analogue of the earth’s magma. This ice crust floats on the water, periodically forming cracks and faults that are clearly visible from orbit, and for 12 thousand years the ice makes a complete revolution around the bowels of Europa. Under the ocean is a mantle of rocks, and in the very center is a metal core.

Scientists argue about the thickness of Europa’s ice crust: according to different models, it can be from 30 kilometers to several thousand meters. However, to study water, it is not at all necessary to drill the surface – with the help of the Hubble telescope, astronomers found out that geysers hundreds of kilometers high are beating from Europe. True, it is still unclear whether they hit directly from the ocean or from isolated polynyas. This can be clarified in more detail using the NASA Europa Clipper, which is expected to launch in 2024.

Where are rivers and oceans in the solar system 2

Large geysers also hit from Enceladus, a satellite of another giant planet Saturn. They also reach hundreds of kilometers in height, and they are clearly visible in the pictures of the Cassini spacecraft.

In terms of structure, Enceladus resembles Europe: it also consists of an ice crust, a layer of liquid water and a stone core, however, the radius of this satellite is only 250 kilometers. But the thickness of the ice of Enceladus in the region of the south pole is only two kilometers, and hot springs beat at the bottom of the ocean more than 30 kilometers deep. In addition, according to a 2021 study, the global currents of this ocean should carry heat from the depths to the surface, and from the poles to the equator.

Where are rivers and oceans in the solar system 3

It is the confirmed hydrothermal activity that makes Enceladus so interesting for exobiologists. In the jets of its geysers, scientists found significant amounts of hydrogen and methane, which should have been formed in hot springs.

Such hydrothermal reactions are similar to those that took place in the ancient oceans of the Earth and which became a source of energy for the first organisms.

Large organic molecules, in particular fragments of benzene, were also found in the geysers. However, the Cassini equipment is not designed to search for life and cannot provide astrobiologists with information sufficient for confident conclusions.

Enceladus’s low gravity, which is 80 times weaker than Earth’s, will potentially make it easier for research vehicles to dive into its ocean, since the pressure at its bottom is equivalent to pressure at a depth of 500 meters in Earth’s seas. True, while scientists are only discussing the concept of such missions.

Where you can’t swim

Quite different seas are found on Titan, another moon of Saturn. Titanium is 5,000 kilometers across and has a dense, opaque atmosphere of nitrogen, whose surface pressure is 1.5 atmospheres. Unlike Europa and Enceladus, Titan’s liquid pools are right on the surface but are made up of ethane, methane, and propane. Since this satellite is very cold (approximately -180 °), there can be no liquid water on its surface despite the appropriate atmospheric pressure.

The surface of Titan is not visible from orbit in the optical range, but the coastlines recognizable to the inhabitants of the Earth are visible on radar images.

Where are rivers and oceans in the solar system 4

The Kraken Sea, the largest reservoir of liquid on this satellite, reaches a length of 1000 kilometers and is larger than the Caspian Sea in area.

In addition to the seas, Titan also has channels with flowing liquid hydrocarbons hundreds of kilometers long. NASA scientists believe that, as in terrestrial rivers, rapids, “whirlpools” and “waterfalls” can form there. However, swimming in the seas and channels of Titan will not work, at least without a special suit. In liquid ethane, a person has negative buoyancy, and a temperature of about -170 ° will lead to instant death.

In 2005, the Huygens probe landed on Titan and saw a rounded “pebble” on the ground, resembling wet sand. The surface looked like it had been exposed to liquid for a long time, but the liquid itself was not visible. Probably, in the landing area, at the equator, reservoirs can exist only after rare methane rains.

In 2027, NASA plans to launch the Dragonfly, an eight-rotor multicopter powered by a radioisotope energy source, to Titan. However, there are other ideas for exploring this satellite – using autonomous boats or even “aircraft carriers” carrying a swarm of small drones.

Potentially liquid oceans may also exist inside Ganymede, Neptune’s moon Triton, as well as Pluto and Charon, but information about them cannot be compared with data on Europa, Enceladus and Titan in terms of completeness and reliability.

Is there life there?

The main source of energy for life on Earth is the Sun. Plants, bacteria, and archaea convert light into chemical bond energy through photosynthesis, which is then consumed by other organisms. Since, in the case of Europa and Titan, water is under a thick crust of ice, photosynthesis cannot take place in it.

However, in addition to photosynthesis, there is another source of energy – chemosynthesis. Some chemosynthetic bacteria live in the ocean at great depths, where light does not penetrate, but where hydrogen sulfide is released from the earth’s crust. Large populations of living things can be maintained by chemosynthetic bacteria and archaea in white and black smokers, methane clathrates, and isolated underground water caves.

According to deep-sea drilling data, a rich microbial life exists at depths of about 1600 meters below the seabed, where a variety of thermophilic archaebacteria live at temperatures above 60 degrees. Moreover, it was chemosynthesis that most likely was the first source of energy for terrestrial life, and organisms learned photosynthesis in the process of evolution.

As for life in the ethane-methane seas of Titan, scientists have no data on this. Astrobiologists are discussing the possibility of the existence of an alternative biochemistry, where liquid hydrocarbons would play the role of a solvent instead of water, but there are no confirmations of such hypotheses at the moment.

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