How are exoplanet habitable zones modeled? The Tale of Goldilocks and the Three Planets.

A planet orbiting in the "habitable zone" of its parent star has the potential to support liquid water on its surface, an essential ingredient for the emergence and maintenance of life. But what if the planet is in the habitable zone only part of the time? Can life flourish there?

Life on Earth is lucky that the zone around it suitable for it is stationary and motionless, providing it with a constant source of radiation. But this situation does not exist in every star system. Physicist Tobias Müller and astrophysicist Nader Haghighipour have written a computer program demonstrating how the position and shape of habitable zones can change rapidly in two- and three-star systems, which are thought to be extremely common in the universe.

The program, which they call the "HZ calculator", creates animations illustrating how the habitable zone distorts and evolves for a simulated star system.

On their website, the scientists created and posted a program (and made it available to other researchers) that was an animation of a model of a star system.

The three-star system KIC 4150611 has a peculiar orbit that creates a rapidly changing "habitable zone" (dark green). Black dots are stars.

The animation shows three stars with complex orbits - two of them (K1 and K2) are close to each other, completing one revolution around a common center of mass in less than two Earth days. The third star (A) rotates at a distance from them, spending about several months per revolution around the pair. Star A's orbit is not circular, so its distance to K1 and K2 varies. When three stars approach each other, they form a single habitable zone. But as they scatter, this zone splits into two separate zones. (In the video above, the dark green zone is the habitable zone, and the light green zones show places where scientists think there is potential for habitation, but this will also depend on other factors, including the nature of the planet's atmosphere).

The habitable zone of the triple star system is KID 5653126. The black dots are stars and the dark green area is the habitable zone.

Source: Tobias Müller / Nader Haghighipour / HZ Calculator

In another interesting scenario, in the star system KID 5653126, the orbit of the star pair is closely related to each other and creates a mostly stable habitable zone. A third star orbits the pair and wanders erratically through the habitable zone—a potentially catastrophic event for any planets that may be there.

Houses on Tatooine

The fictional planet Tatooine from the Star Wars universe is orbited by two suns. This place is a harsh desert, but presumably it died after life evolved on it. Scientists have proven that planets around systems with two stars exist in the Universe, and that they can even support life. But how do such orbits around binary stars affect the temperature on the planet?

The HZ calculator gives some insight into this issue. The real star system Kepler 453 has two stars, one of which is about five times larger than the other. This means that the smaller star is essentially orbiting the larger one (as opposed to two stars orbiting a point in space between them). At least one planet is found to orbit both stars, but the motion of the smaller star means the amount of radiation reaching the planet varies regularly.

The orbit of two stars in the Kepler 453 system causes a shift in the surrounding habitable zone. The white dot indicates a potential planet in the system that could be affected by changing radiation levels.

In the animation created by the HZ calculator, the planet's position in the habitable zone is an illustration of how much radiation the planet receives from its parent stars. Over the course of a year, the planet drifts from the middle of the habitable zone (dark green region) to the innermost edge of that zone (light green region), where temperatures may be too hot to support liquid water on the planet's surface.

Such a situation would lead to large seasonal variations in temperature on the planet's surface, says Elizabeth Tasker, associate professor of solar system science at the Japan Aerospace Agency (JAXA).

“If there are extreme seasons caused by an eccentric orbit, can we talk about the presence of life? Can life survive under such conditions? Of course, we don’t know this yet, but the prospects are not entirely bad.”

Tuster said exoplanet scientists have suggested that planets that drift along the inner edge of the habitable zone may experience extremely different seasons, but could still potentially retain liquid water during such fluctuations. Perhaps on the fictional planet Tatooine, Luke Skywalker's aunt and uncle suffer from an abundance of water during the cool seasons and live by collecting it during the harsher periods caused by the movements of the two suns.

It is also possible that life forms on the planet go into hibernation or suspended animation during severe hot or cold periods. If so, they may be difficult for Earth scientists to detect.

Such information may become relevant when scientists begin searching for signs of habitability of alien worlds. With thousands of planets to choose from, where will their eyes turn? The HZ calculator is one of the tools that researchers can use to reduce the list of planets for priority research.

Müller, a professor of mathematics and computer science at the University of Groningen in Germany, said the HZ calculator is useful for illustrating that habitable zones are not static, which can be difficult to understand without a visual aid.

No guarantees

This illustration shows the Earth's "habitable zone". Venus and Mars are outside the habitable zone, an area where only certain conditions can allow liquid water to exist on the surface.

An example of a system for finding the habitable zone depending on the type of stars.

In astronomy, habitable zone, habitable zone, life zone (habitable zone, HZ) is a conditional region in space, determined from the calculation that the conditions on the surface of those in it will be close to the conditions on and will ensure the existence of water in the liquid phase. Accordingly, such planets (or theirs) will be favorable for the emergence of life similar to that on Earth. The probability of life arising is greatest in the habitable zone in the vicinity ( circumstellar habitable zone, CHZ ), located in the habitable zone ( galactic habitable zone, GHZ), although research on the latter is still in its infancy.

It should be noted that the location of a planet in the habitable zone and its favorableness for life are not necessarily related: the first characteristic describes the conditions in the planetary system as a whole, and the second - directly on the surface of the celestial body.

In English-language literature, the habitable zone is also called Goldilocks zone (Goldilocks Zone). This title is a reference to an English fairy tale Goldilocks and the Three Bears, known in Russian as “Three Bears”. In the fairy tale, Goldilocks tries to use several sets of three similar objects, in each of which one of the objects turns out to be too large (hard, hot, etc.), the other is too small (soft, cold...), and the third, intermediate between them , the item turns out to be “just right.” Likewise, to be in the habitable zone, a planet must be neither too far from the star nor too close to it, but at the “right” distance.

Habitable zone of a star

The boundaries of the habitable zone are established based on the requirement for the presence of liquid water on the planets located in it, since it is a necessary solvent in many biochemical reactions.

Beyond the outer edge of the habitable zone, the planet does not receive enough solar radiation to compensate for radiative losses, and its temperature will drop below the freezing point of water. A planet located closer to the star than the inner boundary of the habitable zone will be excessively heated by its radiation, causing water to evaporate.

The distance from the star where this phenomenon is possible is calculated from the size and luminosity of the star. The center of the habitable zone for a particular star is described by the equation:

Habitable zone in the solar system

There are different estimates of where the habitable zone extends:

Galactic habitable zone

Considerations that the location of a planetary system within a galaxy should influence the possibility of the development of life led to the concept of the so-called. "galactic habitable zone" ( GHZ, galactic habitable zone ). The concept was developed in 1995 Guillermo Gonzalez, despite its challenge.

The galactic habitable zone is, according to currently available ideas, a ring-shaped region located in the plane of the galactic disk. The habitable zone is estimated to be located in a region 7 to 9 kpc from the galactic center, expanding with time and containing stars 4 to 8 billion years old. Of these stars, 75% are older than the Sun.

In 2008, a group of scientists published extensive computer simulations suggesting that, at least in galaxies like the Milky Way, stars like the Sun could migrate over long distances. This contradicts the concept that some areas of the galaxy are more suitable for the formation of life than others.

Search for planets in the habitable zone

Planets in habitable zones are extremely interesting to scientists who are searching for both extraterrestrial life and future homes for humanity.

The Drake equation, which attempts to determine the likelihood of extraterrestrial intelligent life, includes a variable ( n e) as the number of habitable planets in star systems with planets. Finding Goldilocks helps clarify the values ​​for this variable. Extremely low values ​​may support the unique Earth hypothesis, which states that a series of extremely unlikely events led to the origin of life on . High values ​​can reinforce the Copernican principle of mediocrity in position: a large number of Goldilocks planets means that the Earth is not unique.

The search for Earth-sized planets in the habitable zones of stars is a key part of the mission, which uses (launched March 7, 2009, UTC) to survey and collect characteristics of planets in the habitable zones. As of April 2011, 1,235 possible planets had been discovered, of which 54 were located in habitable zones.

The first confirmed exoplanet in the habitable zone, Kepler-22 b, was discovered in 2011. As of February 3, 2012, four reliably confirmed planets are known to be in the habitable zones of their stars.

With a discussion about the translation of the astrophysical term “habitable zone,” we are opening a new section, “The Translator’s False Friend,” in which the correctness and adequacy of the translation will be discussed. Send examples of terms that, in your opinion, are incorrectly translated into Russian, explaining why the translation you propose is better and more accurate than others.

The introduction of new scientific terms is a responsible matter. You use a ringing word without thinking, and then people will suffer for centuries. Ideally, for each new scientific concept, it would be desirable to come up with a new word that did not previously have a stable meaning. But this rarely happens. A good example is the “quark” used by physicists. Related concepts are usually called cognate words, which is quite convenient (geology, geography, geomagnetic). But scientists often act contrary to these traditions, giving names according to the principle of “what came to mind.” An example from astronomy is “planetary nebulae”, which have nothing to do with planets, which every time has to be explained to non-specialists.

No less careful consideration should be given to the translation of English terms into your native language. This has always been a problem: for example, star clusters ( star cluster) at the beginning of the twentieth century were called star heaps. I’m not even talking about the transliteration of the names of scientists: for example, the astronomer H. N. Russell is presented in Russian-language literature in six versions - Russell, Russell, Russell, Russell, Ressel and Russell. For modern search engines, these are different people.

In recent years, the problem of terminology has worsened for several reasons: illiterate journalists and unprofessional authors publish their translations on the Internet, without bothering to familiarize themselves with the existing Russian terminology, but simply transliterating English words. Thus, the word “transit” began to appear more and more often, meaning the passage of a planet against the background of a star’s disk. For professional astronomers, the terms “transit,” “occultation,” and “eclipse” have their own specific meanings that are not reflected in the word “transit.”

Unfortunately, most online publications lack scientific editing, and even paper publishers rarely allow themselves this “luxury.” It would seem that there is Wikipedia, in which, through joint efforts, the terminology should be clarified. Sometimes this is actually successful, but professionals still prefer to invest in one common platform called Wikipedia, leaving the content of Wikipedia (Russian-language) to the conscience of amateur enthusiasts.

When a new and, especially, unsuccessful term begins to come into use, there is time to consider the problem and democratically come to a common opinion. Therefore, as a start, I propose to discuss the translation of the English term “ circumstellar habitable zone", or, in short, " habitable zone”, which has recently become very popular among researchers of exoplanetary systems.

We are talking about the range of distances from the star, within which the temperature on the surface of the planet ranges from 0 to 100 ° C. At normal atmospheric pressure, this opens up the possibility of the existence of liquid water, and therefore life in its current understanding. In domestic publications on this topic, there are currently three competing translations of the term “ habitable zone” - life zone, habitable zone And habitable zone. Let's try to figure it out.

The complete unsuitability of the term is immediately obvious habitable zone, indicating the presence of living beings in this zone and even hinting at the presence of a person there. “Dictionary of the Russian Language” by S. I. Ozhegov (1987) gives the definition: inhabited- inhabited by people, having a population; an example is an inhabited island.

Indeed, “deserted island” does not mean that it is sterile; there are simply no people there.

A broader meaning is given by the “Explanatory Dictionary of the Russian Language” by S. I. Ozhegov and N. Yu. Shvedova (1992): inhabited- inhabited by people, having a population; generally one where there are living beings. Examples - habitable earth, island inhabited by seagulls. Anyway, inhabited means populated, A " habitable zone"- a populated area in which SOMEONE LIVES. In reality, we are talking about the presence of CONDITIONS FOR LIFE, and not at all about the presence of creatures in it. It is obvious that authors who use the term habitable zone are the least sensitive to the meanings of their native language.

What is it habitable zone? Word habitability in Russian there is. But what is it?

1. Ushakov's explanatory dictionary: habitability - the degree of population (about an area).
2. Naval historical reference book (A. Loparev, D. Loparev): ship habitability is a complex of factors characterizing the living conditions of people on the ship. Elements of habitability: dimensions of cabins, utility rooms, passages; composition, dimensions and location of cabin equipment; indicators of ship motion, vibration, noise, ease of maintenance of ship equipment, instruments, systems, etc.
3. Glossary of terms of the Ministry of Emergency Situations (2010): Habitability is a set of factors characterizing human living conditions.
4. River Dictionary by A. A. Lapin (2012): vessel habitability - duration of voyage without replenishment. Typically applied to tourist vessels; calculated in days.

As we see, the common denominator of these slightly different interpretations is the person whose presence is assumed.

Direct translation habitable according to the dictionary it gives the following options - habitable, suitable for habitation. We have already dealt with habitability, but suitability for habitation, for life, accurately reflects the meaning of the term habitable zone. In general, in English - -able speaks of possibility, not availability. The most adequate translation would be the long expression “zone suitable for life” or the somewhat pretentious “livable zone”. The simpler and shorter “life zone”, in my opinion, accurately conveys the meaning of the English expression. Convenience of pronunciation also plays an important role. Compare: life zone or habitable zone. I am for the life zone. What about you?

Comments

,
doc. physics and mathematics sciences, head Department of Physics and Evolution of Stars, Institute of Astronomy RAS

In my practice, I use the “habitable zone” option, although I undoubtedly admit that Vladimir Surdin is right in the sense that this term does not provide an adequate understanding of its essence. But the “livable” zone is no better in this regard, if not worse!

After all, what is habitable zone? This is some fairly conventionally defined interval of distances within which the existence of liquid water is possible. Not life, but only water! It must be remembered that the possibility of the existence of water does not mean that water exists, and the presence of water does not guarantee vitality.

In other words, in this case (as in many others) we are trying to describe a very complex concept in two words. It will not be possible to do this adequately, so it is quite acceptable to use an established translation. Moreover, it is still almost always necessary to explain what it means.

In astronomy this happens all the time, and there are countless examples. From the recent times one can, for example, recall “near-Earth asteroids”, which may not be near-Earth in the literal sense of the word. We also use another, slightly more precise term - near-Earth asteroids - but it is also not ideal from the point of view of conveying meaning. There have been attempts to introduce the correct term “asteroids capable of approaching the Earth” - but try to apply it in practice! A third of the lecture or report will be spent on speaking it out.

In general, I adhere to a rather conformist position in this regard. When I say “planetary nebula,” I don’t worry about the fact that it has nothing to do with planets. The main thing is that both I and my interlocutor understand what is meant.

In astronomy there are two thirds of such controversial terms. Who can guess the meaning of the words “right ascension”? Who will guess that “metallicity” is often referred to as oxygen content? What about novae and supernovae?

,
translator of M. S. Gorbachev, now head of the press service of the Gorbachev Foundation

In this matter, Vladimir Surdin is certainly right. The fact is that the English language in this case clearly separates the possibility and its implementation: habitable- a place to live, inhabited- the place where they live. In most cases the suffix is able and the Russian suffix - removable- are quite equivalent ( renewable- renewable), and in the case where there is a negation in the definition, they are completely equivalent (since the possibility cannot be realized: impenetrable - impenetrable, unsinkable- unsinkable, etc.)

But in the case of the word “uninhabited,” there was some “glitch” in the Russian language (which is quite normal in natural languages), and it does not mean “a place where one cannot live,” but “a place where one does not live.” In English- uninhabited. That's why habitable it is advisable to translate it so that the meaning of the English suffix is able was preserved and there was no possibility of misinterpretation. So “zone suitable for life” or “zone of possible life” is correct in meaning and correct in Russian. And the word “habitability” is artificial and unnecessary (although some artificial words may be necessary, see the “inventive” experience of Karamzin and his contemporaries).

, science journalist

There is still no clearly fixed translation of the term for habitable zone. Yes, actually, not in English either. They also use the “Goldilocks zone” ( Goldilocks Zone), which allows us to abstract from descriptiveness, but it will be clearly incomprehensible to our reader (our analogue is the fairy tale about Masha and the three bears). We use a lot of things; “life zone” and “habitable zone” are the most common and, in my opinion, never “erroneous”. A term is a term; it does not have to be supported by a verbal construction that is ideal from all points of view. There are much worse cases that are already firmly established; let's say, the same “planetary nebula”... Well, what to do - you have to live with it, don’t organize “holiwars” every time...

We had a similar discussion in the journal Science in Focus. In the end, they chose the “habitable zone” with the possibility of sometimes remembering the “life zone.” I was neutral. So be it, although I am not at all against the “life zone” with an appropriate explanation. No worse. The remaining options - “inhabited zone”, “habitat zone” - were decided to be excluded. “A zone where the existence of liquid water in open bodies of water is possible” is, of course, extremely cumbersome, only possible as an explanation once, and even then in the case where the reader is assumed to be completely ignorant...

The option proposed by Pavel Palazhchenko (“zone of possible life”) is also cumbersome and does not explain everything, not to mention widespread (the term should be, if possible, ALREADY widespread, so as not to end up in the margins with the old options when it finally finally will be fixed).

In addition to being cumbersome and not being as widespread as possible, the “zone of possible life” is also bad because it only creates the illusion of correctness. After all, firstly, we are talking only about water, and secondly, about life in the forms known to us (theoretically, life can arise on a different basis...).

Out of interest, I looked up what term we used earlier in the Trinity Variant. There is complete confusion here. Alexey Paevsky wrote about the “habitable zone” and the “habitable zone” (less often). Boris Stern - about the “habitat zone”. Sergey Popov - “Earth-like planets in habitable zones”. And only I used to write about the “life zone” (but now in the magazine I change it to the “habitable zone”).

I also forgot to say that instead of “life zone” you can write “life belt”, that is, the first word in this term can also be argued for a long time and with taste.