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Why do we have seasons on Earth? The axial inclination of the planet, of course. But the tilt does more than just push us from spring to summer, to autumn, to winter. It is also an important stabilizing force for our atmosphere – without which life on Earth would almost certainly be impossible. It is therefore logical to think that inclination could play an important role in the promotion of life of other worlds . This brings us to new discoveries, published in The Astronomical Journal which suggest that a pair of potentially livable exoplanets has stable inclinations, which reinforces the chances that they will be more like Earth than we imagined.
Planets are Kepler-186f and Kepler-62f, 550 and 990 light-years from Earth, respectively. The first, whose discovery was announced in 2014, was in fact the first Earth-size exoplanet found in the habitable zone of its star; the latter has a mass 2.8 times that of the Earth (making a super-Earth). "We already knew that these two exoplanets are probably rocky, and they reside in the habitable region, where liquid water could exist on the surface of the planets," says author of the Gongjie study. Li, assistant professor at Georgia Tech. We seek to further constrain the habitability of these planets, to better understand the probability of life of these two planets.
The axis of spins essentially determines how heat and radiation emanating from a star are distributed when it reaches this planet. Some axes will allow this distribution to be relatively soft, while others could cause more extreme environments. In addition, the tilt of one planet sometimes oscillates back and forth, and larger oscillations on the axis could cause greater variations in the propagation of this starry radiation, affecting the circulation of the atmosphere and the climate of the planet. detail how spins and climate axis variations actually influence the existence of life in general – robust life forms could also exist in extreme environments – but a stable environment could be a good way to start, "says Li. It is thought that the axial tilt is one of the reasons why Mars, although being in the habitable zone of our solar system, has lost a thick atmosphere and is passed from a warm and aquatic world to a cold and dry desert landscape over the four billion years. The axial tilt of the red planet has varied enormously from zero to 60 degrees, and this instability signifies an inability to maintain a good grip on its atmosphere. On the other hand, the Earth's axis oscillates between 22.1 and 24.5 degrees, roughly every 10,000 years, which is why the blue planet has been so good at life for so long. Li's co-author, Yutong Shan of the Harvard-Smithsonian Astrophysics Center, points out that "the axial angle of the Earth would have been also more unstable if it had not such a moon which, at least in this case, has a stabilizing effect. "
Kepler-62f and Kepler-186f were of particular interest as they exist farther away from their host stars than the Earth or Mars. "It is also important," says Shan, "that the dynamics of spin axes is the richest in multi-planetary systems because the variability of the spin axis results from gravitational interactions between planets. Both 62f and 186f are in systems with five planets, and we understand very well the properties of the other planets because they all transit by their star. "
After doing some calculations, the pair did simulations based on the numbers they had, and found that the axes of rotation of the two planets are fairly stable, although both of them do not. Although they have to cope with a few neighboring exoplanets in their respective star systems, they do not face gravitational effects that would destabilize their axes. "This is good news for the kind of forms of life whose emergence and survival rely on the long-term stability of their domestic planets, "says Shan.
Li thinks that this type of dynamic analysis can be easily applied to other exoplanetary species "I think it's exciting to take away," says Eric Agol, an astronomer from the University of Washington who first discovered Kepler. -62f, "is that this type of study dynamic can be connected to real systems. We now have possible perspectives of characterizing planetary systems [multi-] like this one. Many times this is a theoretical work problem – with so many parameters to take into account, it is not always clear which targets are the most promising [for habitability] and which ones do not have any . "
Lisa Kaltenegger, director of the Carl Sagan Institute in Cornell and part of the Kepler-62f discovery team (and 62nd), think the results are part of a lively discussion on the role of the axial inclination on the habitability of exoplanets, but it insists the worlds … should be able to develop for any axis inclination. probably evolved differently if the Earth had a different axis, but no one knows if the differences would have been substantial or if we would simply live in different parts of our own world. "
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