Are we alone in space – or is there life beyond Earth? In searching for an answer to this question, astrophysicists have so far focused mainly on exoplanets covered with oceans. Water is an essential requirement for life as we know it. A research team from the University of California has now published a study in the Astrophysical Journal, the results of which significantly widen the circle of potentially habitable planets.
The team led by physicist and astronomer Ana Lobo analyzed the conditions for life on exoplanets attached to their star in rotation. This means that the rotation of the planet is not independent of the orbital period around the central body, but is coupled to it. The time it takes for the planet to rotate on its axis is equal to the time it takes to revolve around its star. Moreover, the direction of rotation of the two celestial bodies is the same.
A spin-locked planet therefore always looks the same side to its star – as is the case with the moon, which always shows us the same side. However, unlike the moon, a planet’s bound rotation means there is permanent day on one side and night on the other. The temperatures are therefore: on the day side it is very hot, on the other side it remains in icy darkness. If the planet has an atmosphere, this temperature difference would cause violent storms; however, this would also lead to a certain temperature compensation.
These extreme conditions seem anything but hospitable to life, and until now rotation-bound planets have not been considered candidates for extraterrestrial life. But in the narrow twilight zone along the equally permanent boundary between day and night (called the terminator in astronomy) between the two hemispheres of such a planet, there could be areas where life is possible. It wouldn’t be too hot or too cold in these terminator zones, which surround the planet, and therefore liquid water could exist.
“With our study, we now want to focus attention on planets with limited water resources, which don’t have vast oceans, but which may have lakes or other smaller amounts of liquid water — and these climates could even be promising,” says Lobo. in a statement from the university.
Terrestrial exoplanets orbiting their central star in a fixed rotation should not be rare. Their parent stars – so-called M dwarfs, i.e. long-lived dwarf stars of the spectral class M and unequally known as “red dwarfs” – are very common, making up about 70 percent of all stars. However, none of them can be seen with the naked eye in our night sky because they are too faint. This even applies to the well-known star closest to the sun, Proxima Centauri: this red dwarf is also not visible from Earth with the naked eye. The mass of these stars is also quite small; it ranges from about 0.1 to 0.8 solar masses.
Red dwarfs regularly have planets. But because they were considered too cool, they weren’t considered stars around which life-friendly planets could orbit for long periods of time. This has changed in recent years; Astrobiologists now believe there are quite valuable targets in these common galaxies. However, the habitable zone – that is, the area in which liquid water could theoretically be found – around such red dwarfs is much closer to the central star than to our sun.
Rocky planets located in this habitable zone therefore orbit their star much faster – in weeks or even days rather than months or years – and in a much closer orbit. This results in the majority of them being locked in rotation by their star’s tidal forces. If the results of the study are correct, the circle of possible candidates for extraterrestrial life will suddenly widen due to the large number of such planets.
Lobo and her team calculated the model simulations of the climate on rotational exoplanets in the habitable zone with software that is also used for Earth’s climate. On the one hand, water worlds were modeled and on the other, planets dominated by the mainland. The result is surprising: Under such conditions, ocean worlds do not offer the best chances of a life-friendly terminator zone, as assumed.
“If a planet was originally almost completely covered with water, the water on the permanent day side would most likely completely evaporate, packing the entire planet into a dense water vapor envelope,” Lobo explained. This would lead to a self-reinforcing greenhouse effect, which in turn would affect the terminator zone, which would also warm up too much. However, in the ocean itself, conditions may still be favorable for life.
However, long-term stable and habitable twilight zone climates can develop on a land planet. “Our global climate model shows that such a planet can have sweltering temperatures on the sun side and freezing temperatures on the night side,” notes Lobo. “But the terminator zone could have a temperate climate because there is little atmospheric energy transport.”
Lakes or other bodies of water with liquid water would therefore be possible there. The water could have come from glaciers melting on the night side near the terminator zone. According to the simulations, land-dominated planets also exhibit more stable conditions in the twilight zone, as they are less likely to lose water vapor to space or freeze water on the night side.
The authors emphasize that this is the first study to show that planets with locked rotations can still be habitable. This may be an exaggeration; there have been previous studies that came to this conclusion with different approaches.
Studying climates increases the chances of finding and correctly identifying a habitable planet in the near future, Lobo says. To find potentially habitable zones, for example using the James Webb telescope, astrobiologists would have to take into account that corresponding biosignatures – such as complicated organic compounds – are found only in certain parts of the atmosphere, namely above the Earth. twilight zone.
But what would life be like on such a planet? In addition to the strong temperature contrasts, the high-energy bursts of radiation from the parent star – red dwarfs are more active than our sun – can make life more difficult. These so-called flares can literally roast the exoplanets orbiting close to Earth, destroying their atmospheres and any magnetic field. However, new findings show that such flares rarely occur on the equatorial plane of the red dwarfs and thus miss the planets.
Nevertheless, life forms on such exoplanets, if they exist, should be quite heavy. Life is still conceivable – there are also extremophile organisms on Earth, which thrive in extremely inhospitable conditions. These include bacteria that have thermostable proteins and can survive temperatures of up to 80 degrees Celsius.
The chance that more complex organisms or even intelligent creatures can develop under these conditions is probably smaller than on Earth. However, such a development would be aided by the fact that red dwarfs live significantly longer than our sun and therefore have a lot of time available to them. But if a civilization similar to humanity were to emerge on such a planet, it would probably differ from that on Earth in a number of important ways.
Perhaps the most profound difference is the concept of time. Ever since the first living cells, all life on earth has been shaped by the alternation between day and night, which is a result of the rotation of the earth itself. If this natural clock of the day-night cycle were to disappear, it is difficult to imagine that a similar conception of time would arise – in any case, there would be nothing comparable to the circadian rhythm of terrestrial living things.
However, this only applies to the full extent of spin-bound exoplanets whose axis of rotation is perpendicular to the ecliptic. In fact, only small fluctuations in brightness would be felt on them, caused by the variable distance from the parent star due to the elliptical orbit. However, on exoplanets with a tilted spin axis, such as Earth’s, there would be fluctuations in the amount of light arriving at a given location on the day side – analogous to our seasons of the year, which are also a result of the tilted Earth’s axis. Towards the poles, there would even be areas where the sun would rise and set over the course of an orbit.
Finally, the question of what level of knowledge a civilization would have on such an exoplanet is also interesting. So it hardly seems possible that she couldn’t explore the surface of her own planet without enormous difficulties, since huge areas would probably be too hostile for life – imagine an eternally dark icy desert covering almost half of the planet.
And even looking into space would be extremely difficult on a planet whose habitable zone has its parent star permanently just above the horizon, bathing the sky in a permanent reddish-yellow light. The starry sky would only be visible on the dark side of the planet, at most in the dark edges of the terminator zone, where the host star’s stellar disk is only partially above the horizon. Of course, other planets of the system could also be visible, which then appear larger than the solar system planets on Earth (but not as large as the Moon) because of the closer distances.
Nevertheless, should such a civilization get any idea of the nature of the stars, its astronomers may very well be racking their brains over whether there is life on Terra, the blue third planet of the Sol system – or that the hostile constant alternation of light and dark makes this impossible.
Source: Blick
I am Ross William, a passionate and experienced news writer with more than four years of experience in the writing industry. I have been working as an author for 24 Instant News Reporters covering the Trending section. With a keen eye for detail, I am able to find stories that capture people’s interest and help them stay informed.
