A group of astronomers admitted that in the Universe there is another type of exoplanet – the “eyeball”, which is always located on one side of the mother star due to the synchronization of rotation around its own axis and the star. Scientists have only mathematically calculated the possible existence of such planets, however, this type has already been described in sufficient detail. Hi-Tech talks about the interesting hypothetical type of exoplanets in the form of an eyeball and what other types of planets exist.

“Eyeball”? What is it like?

Usually planets revolve around the mother star and around its axis. Different planets, even in the solar system, have different time periods of rotation around their axis – for example, a day on Mercury lasts about 50 days, on Earth – 24 hours, on Mars – like ours, and on Jupiter – only 9 hours.

Moreover, there is a phenomenon of tidal blocking, when the orbital body rotates at the same speed with which it moves in its orbit. This causes an effect in which the planet is always in relation to the star with only one side and the other in the opposite direction. The most striking example of this phenomenon is the Moon, in which we always see only one side.

The day side of such exoplanets is very different from the night side, scientists say. Depending on how close the planet is to its star, one side of it can be dry and very hot, since all the water evaporates from the strong influence of the star, and on the other half there may be a giant ice cap.

Synchronous rotation of a planet around a star

Between these quite different sides is an ice ring with a neutral temperature. Hypothetically, these zones on such exoplanets can be inhabited – in eternal twilight, with water from melting glaciers, which allows creating a fertile region where vegetation can exist.

According to the hypothesis of the astronomer Sean Raymond, the day side may not be dry and rocky, but liquid or even icy, because the exoplanets “eyeballs” can be at different distances from their stars.

“Red-hot eyeballs and such ice-cold exoplanets are still extreme cases. But any planet that is tidally tied to its star will probably be very different on the day and night sides. Differences can come from, among other things, clouds grouped in certain areas – for example, from melting ice on only one side”. – Sean Raymond, astronomer.

But even in eternal darkness, the ice will still melt, but already from the pressure of a many-kilometer layer of ice. This will cause ice to glide toward land, as happens with the glaciers of the Earth. The thick ice cap of the exoplanet will constantly move to the day side and will probably evaporate there. It may even look like rivers that flow from the night side to the day side, and there they simply evaporate.

In addition, there is a danger to conditional life on such a planet. In the event that the exoplanet moves away from the star, which creates very hot conditions on the planet, possible life may face the danger of freezing all the water. If for some reason the ocean, located on the day side of the exoplanet, freezes once, then the probability of its reverse transformation into a liquid form is practically zero, scientists say. The fact is that liquid water, being dark, absorbs almost all the sunlight that enters it. In this case, solid ice reflects light, so the amount of energy that the exoplanet absorbs will fall even more – like its temperature.

Planet red-hot eyeball

Why have scientists still not found such an exoplanet?

There is still not enough technical capacity. The search for exoplanets was mainly carried out by the TESS, Hubble and Kepler telescopes, while the Hubble has been in orbit for 30 years and half of its technology has not been working.

Kepler is NASA’s space observatory, launched in 2009 to search for exoplanets. Until the mission was completed in October 2018, the device was in a heliocentric orbit, one astronomical unit from the surface of the Earth. Over the nine years of operation, the telescope discovered 2.6 thousand exoplanets, the existence of which was confirmed, 61 supernova, and also provided data on 530.5 thousand stars.

In 2021, the JWST telescope (James Webb – High Tech), which is now considered the most innovative in this field, will be launched into orbit. The diameter of the mirrors of the Webb telescope is 6.5 m, while this part of the Hubble telescope does not exceed 2.4 m. In addition, the telescope will study the sky not only from ultraviolet to near infrared, but also at longer waves – this allow him to see the galaxies of the early universe. Perhaps it is JWST that will be able to find exoplanets in the form of eyeballs.

In addition, since 2018, NASA has been developing another space telescope – WFIRST, which is scheduled to launch in the late 2020s. The cost of the project is more than $ 3.5 billion. WFIRST is being developed to perform two tasks – it will search for previously unknown exoplanets using gravitational microlensing, and will also observe space in an attempt to understand the nature of dark energy.

What else are exoplanets?

Now it is precisely known that 4 160 exoplanets exist in 3 090 planetary systems, in 676 of which there are more than one planet. In addition, astronomers have several thousand candidates for exoplanets, but to obtain this status they need to re-register using ground-based telescopes.

The total number of exoplanets in the Milky Way alone is estimated at 100 billion, of which up to 20 billion are considered land-like.

Estimated sizes of various planet types

There are two main types of exoplanets by analogy with the solar system – stone and gas giants. Each of these types is divided into dozens of subspecies, some of them are not in the territory of the solar system, for example, super-earth – this is the most common type of exoplanets in the Universe.