"The two planets discovered this week orbiting a red dwarf near the Sun are good candidates for the search for life"

This is what Prof. Omri Vandel, an astrophysicist from the Rakah Institute of Physics at the Hebrew University, says in a conversation with the Hidan website. Prof. Wendel and Dr. Lev Tal-Or from Tel Aviv University who was a partner in the international group that discovered the planets yesterday submitted an article to the Astrophysical Journal

"The two planets discovered this week Those orbiting red dwarfs near the Sun are good candidates for the search for life." Says Prof. Omri Wendel, an astrophysicist from the Rakah Institute of Physics at the Hebrew University. Prof. Wendel and Dr. Lev Tal-Or from Tel Aviv University, who was a partner in the international group that discovered the planets, submitted yesterday An article for the Astrophysical Journal (initial submission made possible after the removal of the embargo on the original article in which the stars were revealed Halacht A.B.), in which they analyze the intensity of radiation absorbed by each of the planets and estimate the chance that water will exist on them in a liquid state for a long time, so that even the most primitive life can develop.

In an interview with the Hidan website, Prof. Wendel says that in the coming years, two giant observatories will start operating that will be able to distinguish the chemical signature of the atmospheres of those planets, NASA's James Webb Space Telescope, which should be launched in 2021, and the very large telescope of the European Space Agency in Che Yala, which will go into operation in 2026. This seal is outside the range of detection with the existing equipment, and also with the new means The chances of discovering it will increase due to the proximity of that system to us - about 12.5 light years.

As mentioned this week, an international group led by the CARMENES planet search survey, centered in Spain, revealed two planets orbiting a small and nearby star (Teegarden's Star, one of the 40 stars closest to the Sun, out of hundreds of billions of stars in our galaxy). Two Israelis were also members of the group, Prof. Aviv Ofir from the Weizmann Institute and Dr. Tal-Or.

The star Teegarden itself was only discovered in 2003, despite its proximity to the Sun, because it is relatively pale in visible light. It is a red dwarf that most of its little light is emitted in infrared radiation. Prof. Aviv, who was, as mentioned, a partner in the international research group, said that: "These details made us add the star to the list of targets of the Planet Search Survey CARMEN IS – A survey focusing on red dwarfs exactly. As part of CARMENES, a dedicated instrument was built capable of making precise measurements even for red dwarf stars, with the aim of discovering planets around them. The device actually measures the speed of the star with great precision and thus it is possible to see if there is another body (or more than one) that pulls the star back and forth, cyclically, and affects its speed - and thus infers the existence of the planets. The device, as well as the survey that uses it - both are the result of a German-Spanish collaboration in which I and another Israeli postdoctoral student, Dr. Lev Tal-Or (Talo University), are partners."

Gravitational lock

As mentioned, the article by Prof. Wendel and Dr. Tal-Or is a theoretical article that relies on the observational data. They attached a graph to the article that shows under what conditions areas with comfortable temperatures can exist on these planets: "The main important variable is the degree of efficiency of heat convection on the surface of the planet ." says Prof. Wendel. "The gravitational lock causes one side to face the sun and the other side to the planet There will be perpetual night, however, suitable conditions can exist in the intermediate region, provided that the heat conduction efficiency is low, and I dealt with this in a previous series of articles," explains Prof. Wendel. According to him, these planets orbit close to their sun and are therefore completely gravitationally locked, just as the moon is gravitationally locked in its orbit around Earth."

"Let's take the planet Mercury for example, it is indeed not completely gravitationally locked, but it moves in its path in which it completes three revolutions around its axis in every two revolutions of the sun (the day is longer than the year. AB). As a result, the movement of the sun in its name is very slow. Although by chance Mercury has no heat convection because it has no atmosphere, but these planets are similar in size to Earth and may have an atmosphere. Hundreds of studies have been published so far on the climate of Planets are gravitationally locked. It can be an interesting climate - a wide range of temperatures and areas where temperatures allow liquid water."

Different scenarios of heat conduction efficiency

The graph shows the distribution of temperatures in the two planets under different heat convection conditions. The intuitive assumption that because one area is hot and the other is cold there will be terrible winds blowing between them is not accurate. If there is a jet stream in the atmosphere and there is a slow circulation of the atmosphere, a situation of subtle heat transfer is possible. The question of how much the temperature will change depends on how massive the atmosphere is and how efficient the circulation is - those jet streams in the atmosphere that transport heat from one side to the other.

There are three red and three blue lines, each line corresponds to a different efficiency. The innermost lines - maximum efficiency, meaning an isothermal planet where the temperature is uniform. The more extreme lines where the heat conduction efficiency is fifty percent and twenty percent in the heat respectively and this causes a different distribution of the temperatures. The range that allows liquid water is wider the smaller the convection efficiency.

"The x-axis describes the amount of radiation a planet receives, the earth receives 1 unit per unit area, and the two planets receive one about as much as the earth, and the other about 0.37 of what the earth receives from its sun. The y-axis describes the compressibility of the atmosphere (More precisely, the degree of the heating effect of the atmosphere, mainly due to the greenhouse effect, related to the density and composition of the atmosphere) because we cannot yet observe In the atmosphere we can provide an estimate of what the chances would be in each scenario. As mentioned, the compression of the Earth is 1, and that of Mars is 50. The conclusion of the article is that a very large range of liquid water will be possible - from compressions of 0.3 0.3 compressibility of the Earth's atmosphere under conservative assumptions about convection over a wide range of atmospheric conditions at least One of the two planets, if not both, contains liquid water."

The turbulent history of the red dwarfs

In response to the question of what is the likelihood of life given liquid water, Prof. Wendel answered: "If there is liquid water, it is likely that there will be life of some kind, the most likely thing is single-celled creatures living in water, as was the case on Earth for three quarters of its existence. Because the age of Tigarten Twice that of the Sun - about 8 billion years, it is possible that much more developed life could have developed there. The question is when did life begin to develop there because red dwarfs have an obnoxious feature Their first billion years are very turbulent and they experience bursts of X-rays and strong solar winds that can cause damage to the atmospheres of those planets, so life may not have started right away It is 1.1-1.4 times the mass of the Earth, so the atmosphere they managed to collect is also more massive and less affected from these eruptions. If life there is much older, it may also be more developed than life on Earth."

And "there is also the Earth similarity index that weighs the combination of parameters that describe the Earth - the temperature, the mass, the atmosphere, the gravity on its surface. One of the two stars that were discovered receives a score of 0.94 in this index, meaning that it is the outer planet most similar to the Earth."

to the article by Vandel and Tal-Or

• More of the topic in Hayadan:
• Scientists have discovered evidence of two Earth-like planets orbiting a small sun only 12.5 light-years away.
• Planets for the most part - there is no life
• A system of seven Earth-like planets was discovered, three of them in the zone suitable for the existence of liquid water