Oceans On Huge Exoplanets Can Be Bottomless
Experiments have shown that the oceans on large exoplanets outside the Solar system should not have a clear bottom, because, at high temperatures and pressure, water begins to "dissolve" in silicate rocks. The results were published in the scientific journal Proceedings of the National Academy of Sciences.
"Initially, astronomers thought that on such planets there is a clear border between the ocean floor and the water column. Our experiments have shown that it is, in fact, blurred at high pressures and temperatures," commented Carol Nisr, one of its authors, a geologist from the University of Arizona (USA).
Over the past few years, astronomers have discovered more than a thousand exoplanets and several thousand possible candidates for this role. Most of them are so-called hot Jupiters. However, scientists are increasingly finding smaller planets that are comparable in size to Earth. The growing number of potential earth counterparts makes us wonder how many of them can support life.
Many such planets are among the so-called super-earths, which in mass, size and density are located approximately in the middle between the Earth and the gas and giants. Therefore, astronomers believe that these planets are not exactly similar to Earth. Most likely, they are oceanic planets, most of the mass of which is water.
Nisr and her colleagues decided to find out whether these oceans and the planets themselves will differ significantly in their properties from how the hydrosphere is arranged on The earth's surface. In particular, geologists have tried to understand whether the great depth of the oceans, significant gravity and other distinctive properties of super-earths will affect the characteristics and evolution of their water envelope.
To answer this question, geologists in a series of experiments tried to reproduce the conditions that are typical for a depth of several tens or hundreds of kilometers from the surface of the ocean. To do this, scientists placed small amounts of water and typical rocks from the bottom of the earth's oceans in special diamond anvils, compressed them to several tens or hundreds of thousands of atmospheres and heated them.
It turned out that at sufficiently high pressure and temperature, water begins to "dissolve" inside silicate rocks. This results in a new form of matter that is physically and chemically stable. It differs in properties from both water and "normal" rocks.
Thanks to this, scientists have made an unexpected conclusion: the oceans on such planets do not have a clear bottom. Its place is taken by a very blurry layer of a similar matter, which is more like water in its upper layers and gradually turns into a stony structure as it moves deeper into the bowels of the super-earth.
All this, the researchers explain, does not allow us to use the Earth and its oceans to illustrate what large ocean worlds look like and how the interactions of their waters and rocks can affect the likelihood of life developing. Moreover, now it will be very difficult for planetary scientists to understand how much pure water is in the oceans of super-earths.
Something similar, according to Nisr and her colleagues, can occur in the bowels of Uranus and Neptune, if there is a significant amount of water. This should also strongly influence their structure, including the formation of the magnetic fields of these giant planets, some of whose properties astronomers can not yet explain.