Far out cosmology:Tidally locked planets explained-2 (Introduction)

by David Turell , Sunday, August 28, 2016, 15:35 (2795 days ago) @ David Turell
edited by David Turell, Sunday, August 28, 2016, 15:46

The star close to us with a planet is discussed: - http://nautil.us/blog/our-nearest-star-has-a-planet-and-these-are-the-ways-it-could-be-... - "The discovery of Proxima b, announced today, has motivated a handful of in-depth studies. I was involved with two that address the question of whether Proxima b could really be habitable. I'm not about to buy any real estate there, but, as far as I can tell, there are reasons to be optimistic. - 
"The biggest difference between Proxima b and Earth are their stars: They have drastically different histories, and futures. Our sun is a bright, lazy yellow star that will, in about 5 billion years, become a hostile red giant, subsuming Earth's orbit. Proxima Centauri, on the other hand, is a fidgety red dwarf only about 10 percent as massive as the sun and 1/700th as bright; it'll be friendly to Proxima b for another 4 trillion years. Though Earth and Proxima b receive a similar amount of energy, in the form of starlight, growing up in Proxima's neighborhood is much more of a challenge—like the difference between a gang-ridden inner city and an affluent suburban cul-de-sac. Proxima b's orbit is only 5 percent as wide as Earth's, and its year is only 11 days long. - *** - "When rocky planets get cooked like this, potentially life-bearing “Earths” can turn into dry, inhospitable Venuses. Did this happen to Proxima b? We modeled this process in one of our studies. We found that, before reaching the habitable zone, Proxima b could have lost up to 1 “Earth ocean” of water (the amount of water on Earth's surface) to evaporation. But it may also have an additional source of water trapped in the mantle; Earth, for example, has roughly between 0.3 and 10 Earth oceans underneath the surface. If our oceans were suddenly zapped into space, water would be replenished to some degree by outgassing from volcanoes. - *** - "Earth, as you may have noticed, spins fast—365 times for every orbit of the sun. Proxima b, by contrast, is so close to its star that tides limit the planet's spin to two possibilities. Proxima b could be rotating synchronously, always showing the same face to the star, as the moon does to Earth; or Proxima b could be locked in a spin-orbit resonance, spinning exactly three times for every two orbits, like Mercury. The planet is definitely in one of these states but we don't know which. - *** - "So the punch line is that Proxima b can retain liquid water on its surface for a wide range of conditions—but only if it held on to some water while its star went through its youthful tantrums. Another potential obstacle to habitability is the amount of energetic radiation Proxima b receives compared to Earth: 250 times more X-rays and 30 times more extreme ultraviolet light. What this means for the planet's atmosphere is unclear, but it's probably not a deal-breaker for life. - 
"This is the planet we have been waiting for." - Comment: Long theoretical article using our knowledge of our solar system and how planets evolved and assumed their positions, then applied to this planet. It will provide lots of material for study, which is why the author is so excited. Many explanations and diagrams to be read if interested.