Humans like to call Earth the "Blue Planet" and have always been proud of its vast oceans. But in fact, we may not be the only body in our solar system with liquid water, especially in some places far from the sun, there are some "frozen stars".

For example, we will introduce the Io today, scientists believe that it is the solar system's "super reservoir", the amount of water on Earth is not even a fraction of it.

So, is Io really such a vast ocean? Are the seas there exactly the same as on Earth?

The amazing "Io"

As we all know, Jupiter, as the "big brother" in the solar system, not only has a prominent body, but also has a much larger number of "little brothers" than other planets.

Yes, as of the end of 2019, 79 moons have been discovered around it, and Io, while not the closest, is the largest.

In the ranking of the size of the moons in the solar system, Io easily won the crown, and the diameter of this guy is even larger than Mercury. Although its mass is only half that of Mercury, it would have had no problem joining the family of planets in the solar system if it had not been captured by Jupiter years ago.

Of course, the magic of Io is not only the size, because this guy is also the only one in the solar system found in the human "magnetosphere" of the satellite.

This means that Io may have a core like Earth's and then emit a magnetic field from the inside out, and if this field is strong enough, then life on Io may also be less likely to be attacked by cosmic radiation.

With its large size and magnetosphere, Io's existence is even more intriguing, and humans have sent a number of probes to visit Io, such as Pioneer 10 and the Voyager brothers, which have already flown into interstellar space.

They have returned less information, but still prove that Io is larger than Titan.

Of course, the greatest contribution was made by Galileo, which, after entering Jupiter's orbit, made several flybys of Io, the closest being only 264 km from its surface. In addition, it also found that Io has a special feature, that is, it has a vast "underground ocean".

So, how big is the ocean on Io?

"Io's oceans are different

When we introduced Io above, we mentioned that it is very large, but only half the mass of Mercury. In this case, Io should be very light, but why is it said to be the "super reservoir" of the solar system?

First of all, looking at the composition of Io, it has an average density of 1.936 g/cm3, a density that suggests that it has about the same amount of rock and water on it. Of course, the water here is not all liquid water, but basically exists in the form of solid ice, and these ice bodies account for more than 46% of its total mass.

Secondly, from the internal structure of Io, in addition to a core with a radius of about 700 meters, the rest is a shell of ice bodies or silicate ground cover.

Previously the Hubble Telescope observed and analyzed the auroral spectrum of Io and found that this guy has a minimum of 400 km of ocean. Later, more scientists said that this 400 km deep ocean may only be the "first layer of ocean" that we see, under which there are two layers of ocean, they are like a lasagna, separated by ice.

Heidi Hamel, executive vice president of the Association of Universities for Exploratory Astronomy, said, "Hubble Space Telescope observations have already demonstrated that there is a saltwater ocean beneath the surface of Io, and there will be even more exciting discoveries once Jupiter's Ice Satellite Explorer enters its orbit in the future. "

In this case, Io's oceans should be able to exceed 1000 km in depth and the volume of water could reach 15 billion cubic kilometers. If this is true, then the amount of water on Earth is not even a fraction of it.

Of course, as to what this uniqueness of Io's oceans will turn them into, scientists believe that the volume, composition, and temperature of each layer of the ocean may vary. If you take the elevator to the core of Io, you will be able to see "all kinds" of oceans along the way.

In addition, since the average temperature of Io's surface is about minus 174 degrees Celsius, there may be some differences between its surface ice and what we think of as "ice".

Simply put, the ice on it may be harder and also thicker, so that these ice layers are like the rocks of the Earth's crust.

But although there is currently the largest ocean found in the solar system, but does not mean that there is life on Io, because the presence of flowing water is only a criterion for a habitable environment, if other places do not meet the standard, then it is very difficult to give birth to life.

It is worth mentioning that, in fact, in addition to Io, there are many places in the solar system where there are also seas, so let's take a look!

Go see the sea in the solar system

First of all, let's talk about Io's brother, Io, a satellite codenamed Europa, which is arguably one of the satellites that have attracted the most attention from humans in recent years, and even imagined and filmed the science fiction movie "Io Report" based on its existing situation.

As Io, which also has a surface full of cold ice, its ocean is also particularly deep. Of course its surface is also thick ice, and the bottom of the ocean is presumed to be at least 100 to 200 km deep, which is really "unfathomable" compared to the deepest part of the Earth's oceans, the Marianas Trench.

Of course the reason Io's oceans are of more interest is that its interior is very active, and just like Earth, Io's ocean floor is also home to a number of volcanoes. The eruptions of these volcanoes not only keep the water liquid, but also bring a large number of elements, which may give birth to "initial life".

For example, when scientists previously explored the Antarctic subglacial lake, they found a number of single-celled organisms in it. In the depths of the ice where sunlight cannot pass through, these creatures are supposed to feed on the material brought by the submarine volcanoes.

If the conditions in Io's oceans are the same as those in Antarctic subglacial lakes, then we do have a chance of encountering "extraterrestrial life" when we visit Io to see the ocean.

The second is Titan, which had a size battle with Io. As the largest of Saturn's moons, Titan's oceans do not differ much from Earth's oceans on the surface. But because Titan's gravity is limited and its oceans are basically composed of methane and ethane, it's hard to float when you jump into the water.

Not so with Titan, the brightest moon in our solar system, which has not only oceans but also spectacular "geysers". When the U.S. Cassini visited here previously, it found significant cracks on Titan, and geysers have been coming out of these cracks.

In general, moons or planets that are farther away from the Sun are extremely limited in the amount of heat they can absorb, in which case they become "frozen stars". However, according to the human requirements for liquid water, the cold and little internal activity of the object, obviously does not meet our "sea-viewing" needs.

In order to find out whether there are oceans in the interior of these frozen stars, more exploration programs will be launched in the future, such as the previous "Orbiter Exploration Program" specifically for Io.

Io orbiter exploration program

The only target of Io's orbiter exploration program is Io, and this exploration needs to accomplish five objectives.

The first is to observe the state of Io's oceans, deep interior, and other geological features; the second is to investigate the basic composition of its atmosphere; the third is to monitor the effects of the solar wind on it; the fourth is to observe Io and Io in resonant orbits; and finally, to study Io's interactions with other moons in the Jupiter system.

In short, with Io's vast ocean base, human exploration of it will certainly become more frequent in the future. However, although there is a lot of water, the sea is also very deep, but still salt water, so at this stage want to use should be impossible. However, humans will still treat it as a precious "backup resource".