The Gravity-Locked Planet Is Eligible Habitable?

Away from Earth, in a star, there is a habitable planet that is locked by gravity on the star. Extreme heat and cold on two different "sides". Not just one, there are many similar planets in other stars. The question is, is there any life on the planet that is locked in gravity?

Finding life on another planet is not easy. It's like looking for a needle between the straw. All we know is the life we know on Earth. Therefore, we are looking for Earth-like features of life. The planet must be in the star habitable zone for water. That's the first and foremost criterion.

The search begins, especially in stars like the Sun. Apparently, Earth-sized planets similar to Earth are found in many red dwarf stars. This star is smaller and colder than the Sun. Therefore, the habitable zone where water can remain liquid on the surface of the planet is so very close to the star.

But there is another problem.

Planets that are very close to the star will produce a strong gravitational interaction between the star and the planet. In this condition the greater effect of star gravity causes the planet's rotation to slow down. As a result, the rotation of the planet will approach the period of planetary revolution orbiting the star. This condition is known as a tidal lock or is locked by gravity. The implication is that only one side of the planet will confront the star. Thus there is one side of the planet that is always day and the side that is not faced with the star will experience the eternal night. Air temperatures on both sides of the planet will be very different. Extreme heat and cold.

The question is, is it possible for life to evolve on a planet that is locked in gravity? With extreme temperatures, it is difficult for life to grow. But the discovery of rocky planets that locked gravity in a habitable area of the star would be a challenge in itself. Is there a chance for life to evolve?

Wind on the Planet Gravity Locked

On a planet that is locked in gravity, there is one area closest to the star that is right at the zenith. This area called the substellar point receives continuous light and starlight. As a result, this area is so unusually hot. Continuous heating of stars on one side can alter the weather on the planet, even controlling the weather and causing climate instability. This condition could trigger the planet to be habitable or just uninhabitable.

It was a hot area. In a cold area that never receives the light and heat of stars, the atmosphere becomes a denser gas, condensing into liquid and eventually becoming solid. It is estimated that this condition could trigger the occurrence of atmospheric circulation that triggers the planet to be habitable or it causes a deadly storm on the planet.

However, the presence of atmospheres in rocky planets is an important factor for us to know what chemical compounds exist in a planet. And whether it can support life as we know it.

On a planet that is locked in gravity, the atmosphere becomes an important component to distribute heat throughout the planet. The goal is to reduce the contrasting temperature difference on the day and night sides. Thus the planet is warm, including on the side of the night that had been frozen. For that, we must know whether there is a wind on the planet. Without the wind, no heat can be spread. Wind occurs because there is airflow from high pressure to low pressure. This is the way the atmosphere moves to spread heat to the surrounding area.

^{a large circulation showing the surface wind(atmospheric circulation),wikipedia}

Astronomers also try to do the modeling based on existing data and theories. The planet that is locked by gravity rotates very slowly. But that does not mean there is no atmospheric circulation.

In order for a planet that is locked in gravity to be considered habitable, then the planet must have an air conditioning system that is able to balance surface temperatures across dark and light areas. On one of the planet's weather models that are locked in gravity, the air-conditioning system must be replaced by strong winds moving eastward to distribute heat from the day area to the night area. It is estimated that on the day side, the temperature is more than 100º C and on the night side, the temperature is below freezing at -100ºC. The wind also moves across all latitudes. At high latitudes, there are ionized atmospheric interactions with the planet's magnetic field. As a result, winds at high latitudes can be muffled and there will be variations in wind speed as well as on strong wind circulation in the equator area.

In some cases, distributed heat can actually make the planet warm in dark areas and the planet could be potentially habitable.

^{Illustration of Proxima Centauri, the closest star to the Sun at 4.2 ly, is a red dwarf,pixabay}

Other modeling reveals that the planet surrounding the red dwarf at close range can escape from gravity locking. The key is in the atmosphere of the planet itself. If the planet has a thin atmosphere surrounding the red dwarf at a distance of 1/3 of the Sun-Earth distance, then there is still a chance that the planet will escape the gravitational lock. If the atmosphere is thicker and the distance is also closer to the star, then the planet can still escape from the locked condition of gravity by the star.

Weather

On a planet Earth, when rocks and minerals are exposed to air, there will be a chemical reaction with the gas inside. Rocks will erode and new layers will appear on the surface. This new layer then interacts again with air and more and more gas is changed. If the speed of this erosion process is aligned with the new gas released into the atmosphere, then the climate on the planet will be stable. The new gas can come from volcanic eruptions on the planet.

On a planet that is locked in gravity, the substellar area closest to the star will continue to receive heat and affect the weather and climate in the atmosphere. This happens because excessive heat flows can increase the weather changes in the most exposed areas of heat. Temperatures that are too high can also cause heavy rain that certainly affects the weather on the planet. Extremely heavy rain will increase the erosion of rocks on the planet. This means there will be an abundance of new rocks that continue to react with the atmosphere and spend the components there.

If this substellar area gets cold, the weather change process will also slow. As a result, not many new rocks are available for chemical reactions and gas formation in the atmosphere. The volcanic process on the planet can release more matter in the atmosphere that can be absorbed by rocks. There is instability and can trigger excessive warming and cause the greenhouse effect. All this happens because the heat from the star is focused on just one area that is right in the face of the star.

The weathering process on one planet can produce a different story. On Earth, the greenhouse effect can be controlled. While on Venus, an excessive greenhouse effect takes place and makes the planet extraordinarily hot and unsuitable for life. Other extreme conditions that can happen are the changes of heat and cold that occur continuously throughout life. In extreme conditions like this certainly, life cannot develop. But, the evolution of life does not happen in an instant. It takes a long time for life to grow and thrive on Earth.

The longer lifespan of the red dwarf is obviously beneficial for the evolution of life. But the existence of a planet that is very close to the star so a challenge. In order to achieve weather stability, the substellar area that continuously receives heat must be at the ground level not in the ocean. And the gas absorbed must be a lot of gas in the atmosphere.

That's ideal. That obviously still needs observations to prove it all.

Gained from observation

To be able to know the detail conditions in exoplanet certainly not easy. We can not visit the planets. Even to find it even from the effects the planet has on the star. Likewise to know the existence of the wind on the planet that is very close to the star. Observations were made on a planet that is locked by gravity and easily observed in its atmosphere.

hot jupiter

The Jupiter-like planet has a large size and can provide a more significant effect than a small planet similar to Earth. The observations made on exoplanets are nothing but to determine the characteristics of the planet. On the star, by knowing the masses we can recognize the star. But not so with the planet. Examples in the Solar System, a mass that is almost similar to Venus and Earth does not make them similar, Similar but different.

When performing exoplanet observations, the information that can be obtained includes mass, radius, distance, composition, and temperature. From the primary transit when the planet passes in front of the star, the observer can know the size of the planet and the radiation of stars passing through the planet's atmosphere. In addition, the information of thermal radiation on the planet can be known from secondary transit as the planet disappears behind a star.

Observations show that a planet that is locked by gravity can have winds that flow from day to night or hot to cold. The wind has successfully detected the presence in the planet HD 1897333b which is locked in gravity on the star. This condition is evident from the rotation period that is in sync with the orbital period of the planet. Planet HD 1897333b is known to have a rotational speed of 3.4 km per second, with a rotation period of 1.7 days and its orbital period of 2.2 days.

^{planetary illustration HD 189733b,wikimedia}

The observations made with ESO's spectrograph showed the strong winds on the planet moving at a rate of 3 km per second. While in the upper layers of the atmosphere, the wind moves at a rate of 7 - 10 km per second. The existence of the wind is obviously very important for the distribution of heat to cold night areas, and can be seen from the temperature of the planet HD 1897333b stretching from 973 - 1212 K. This is an indication of the distribution of energy absorbed from the star through the atmosphere to the entire surface of the planet. Do not expect life on planet HD 1897333b. The planet is not a rocky planet and from its temperature, obviously, hot Jupiter planet like HD 1897333b will not be able to sustain life.

But the presence of wind on the planet that is locked by gravity gives a glimmer of hope that on rocky planets with similar cases, there is a wind that can deliver heat from the day to night and stabilize the temperature of the planet for the evolution of life. Especially in the red dwarf star who lived longer than the Sun. The planet can have a long time to evolve and so will life if it exists. Although to survive, there are other factors of the star that will also affect life.

Is it possible that planet is locked its gravity on a habitable star? Maybe. But whether life would be similar to Earth, it might not. Especially with the condition of the planet is divided into two with one side is always day and the other side is always night. Of course, the evolution of the planet will also be different from Earth. all that time and thank you!

BEST REGARDS @ aneuktulot

references and related reading :

https://www.space.com/13950-habitable-alien-planets-tidal-lock-life.html
https://newatlas.com/tidally-locked-exoplanets-potentially-habitable/39407/
https://www.astrobio.net/news-exclusive/tidal-locking-could-render-habitable-planets-inhospitable/
https://phys.org/news/2017-08-tidally-exoplanets-common-previously-thought.html
https://arxiv.org/abs/1708.02981
https://worldbuilding.stackexchange.com/questions/4850/how-would-winds-behave-on-a-tidally-locked-planet
https://www.quora.com/What-sort-of-a-weather-system-is-theorized-on-a-tidally-locked-planet
https://www.nasa.gov/feature/goddard/2018/hubble-finds-substellar-objects-in-the-orion-nebula
https://www.opengeography.org/ch-10-the-atmosphere.html
https://www.britannica.com/science/atmospheric-circulation
https://arxiv.org/abs/1601.00069
https://arxiv.org/abs/1610.03893
https://www.nasa.gov/feature/goddard/2017/nasa-finds-planets-of-red-dwarf-stars-may-face-oxygen-loss-in-habitable-zones
https://www.space.com/54-earth-history-composition-and-atmosphere.html
https://theextinctionprotocol.wordpress.com/2013/07/13/nasa-finds-deep-blue-planet-63-light-years-from-earth-that-may-be-a-living-hell/