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"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, submitted an article to the Astrophysical Journal yesterday

Iconography showing the habitable zone around the planet Teegarden in two conservative and optimistic scenarios, compared to our solar system and other planets discovered in their star's habitable zone. The scale is normalized to the size of our solar system. In practice the planets Teegarden b and Teegarden c are much closer to their sun. Illustration: C. Harman
Iconography showing the habitable zone around the planet Teegarden in two conservative and optimistic scenarios, compared to our solar system and other planets discovered in their star's habitable zone. The X axis does not represent the distance from the sun (the star) but the amount of radiation the planet receives from the mother star. In practice the planets Teegarden b and Teegarden c are much closer to their sun. Illustration: C. Harman

"The two planets discovered this week Those orbiting red dwarfs near the Sun are good candidates for the search for life." Says Prof. Omri Vandel, an astrophysicist from the Rakeh 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 an article to the Astrophysical Journal yesterday (initial submission made possible after the embargo was lifted on the original article in which the AB planets were revealed), And in it they analyze the intensity of the 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 site, 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 come into operation in 2026. This seal is outside the range of detection with the existing equipment, and even with the new means the chances of detecting it will increase thanks 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 based on the observational data. They attached a graph to the article that shows the conditions under which regions 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." Prof. Wendel says. "The gravitational locking means that one side will face the sun and the other side of the planet will have perpetual night, however, in the intermediate region, suitable conditions can exist, 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 the Earth."

"Let's take the planet Mercury for example, it is not completely gravitationally locked, but it moves in its path where it completes three rotations 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 his name is very slow. Although in the case of Mercury there is no heat convection because there is no atmosphere, but these planets are similar in size to Earth and may have an atmosphere. Hundreds of studies on the climate of gravitationally locked planets have been published so far. It can be an interesting climate - a wide range of temperatures and areas where the 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 chance of life on the planets discovered around the planet Tigarden, according to different scenarios of the ability to transport heat in their atmospheres. Illustration: Omri Vandel and Lev Tal-Or
The chance of life on the planets discovered around the planet Tigarden, according to different scenarios of the ability to transport heat in their atmospheres. Illustration: Omri Vandel and Lev Tal-Or

"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 approximately as much as the Earth, and the other approximately 0.37 of what the Earth receives from its Sun. The Y-axis describes the compressibility of the atmosphere (more precisely, the rate of the heating effect of the atmosphere, mainly due to the greenhouse effect, which is related to the density and composition of the atmosphere). Since we cannot yet directly observe the atmosphere we can provide an estimate of what the odds would be in each scenario. As mentioned 1 this is the compression of the earth. The density of Venus is 50, and that of Mars is 0.3. The conclusion of the article is that a very large range of atmosphere will still allow liquid water - from compressions of 0.3 to 15 times the compression of the Earth's atmosphere under conservative assumptions about convection. In 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 being single-celled creatures living in water, as was the case on Earth for three quarters of its existence. Since the age of Tigarten is twice that of the Sun - about 8 billion years, it is possible that a much more developed life could have developed there. The question is when did life begin to develop there because red dwarfs have the obnoxious feature that their first billion years are very turbulent and they experience bursts of X-radiation and strong solar winds that can cause damage to the atmosphere of those planets, so life may not have started right away. On the other hand, the masses of the planets are slightly greater than the mass of the Earth, with the most probable mass range being 1.1-1.4 times the mass of the Earth. And so the atmosphere they were able to collect is also more massive and is less affected by 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 which weighs the combination of the 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 Earth."

to the article by Vandel and Tal-Or

11 תגובות

  1. Anonymous. There is a situation where you are completely disrupting what astrophysicists do say about life outside the universe

  2. I am not a fan of the theory of astro-physicists that says that life of one kind or another must be found in outer space!!! Because of the large mass of the planets in space. I am of the opinion that this position is based on a principle (the aspiration for thought)!!! I would like to say that we are an exceptional case!!!

  3. However, studies and computer simulations of the climate on locked planets surrounding red dwarfs show that liquid water may exist there under certain conditions, the main one being the existence of a thick enough atmosphere. The same goes for the effect of the radiation from the red dwarf. A recent review was published in our article https://arxiv.org/abs/1510.03484

  4. Gal, in the scientific article (the link at the end of the article) there is a reference to the points you raised. The magnetic field is related to the rotation of the planet around an axis, so it is likely that these planets have no magnetic field or it is very weak, as in the case of Mercury.

  5. Rafi, the prevailing opinion among astrobiologists today is that life (at least basic) is indeed common to this extent, more or less, but intelligent life is apparently much rarer. Otherwise we would have already discovered them, or they would have discovered us, for example through radio transmissions. The "Great Barrier Theory" is only one of dozens of explanations for the fact that this has not yet happened, known as the "Ferrami Paradox".

  6. If the two stars chose to revolve around a red dwarf, why did they choose the name "blue-white"? How do you realize the potential for sprouting a new life? Or is it only in Israel

  7. A magnetic field is not mentioned, because there is (yet) no way to detect a magnetic field from such distances. There are so many things that can go wrong with these stars, orbiting very close red dwarfs. These are very unstable stars, which sometimes produce terrible solar flares, much worse than the flares of our sun, and simply roast the planets that surround them.

    In my uneducated estimation, the hope that there might be water (and life) on these types of planets is going to dry up soon, like these charred planets.

  8. Why is there no mention in the article of a magnetic field whose role is to protect the atmosphere, and biological creatures
    In case there are ??, can a magnetic field be formed on a gravitationally locked planet?
    Radiation sources reach the planets in this system from the mother star, (and not only in the first billion years I think?), and from a galactic source.
    The radiation intensities can affect those planets.
    Why is there no reference in the article to this topic?

  9. It would be amusing to know that life in the universe is as common as the planets that can support such life. If we discover life already on the first planet we manage to test in the future, this will probably verify the "Great Barrier Theory": life is common, but when it reaches the level of self-consciousness, it disappears.

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