Goldilock Stars: meet the best qualities for looking for life
I personally believe that not having the proof that there are other forms of life as that in our planet in the vastness of the Universe is not even a reason to neglect it. In fact, it is its infinity and wonderfulness what makes, at least to me, obvious the fact that we are definitely not alone in the Universe.
As it is well known, life can adopt several forms in the large chain from microorganisms to intelligent beings, and the capacity of a planet to hold it depends on a fundamental basis: liquid water. Hand by hand with this fact, is that of the planet’s atmosphere, which must unify certain conditions in order to conserve the planet’s ecosystems and protect it against the radiation coming mainly from the star it orbits.
Should we look for stas similar to our Sun?
Earth is about 4 billion years of age, and Sun its in the halfway of its lifetime, which is about 10 billion years. Our star enters into the category of G-stars, which are short-lived, bigger and more luminous than the most abundant type of stars in our galaxy, the so called red dwarfs, which are M-type stars that distinguish because of their small size, long lifetime and lower luminosity, therefore not visible to the naked eye from Earth. However it is interesting the fact that not all M-class stars are red dwarfs, since supergiants Antares and Betelguese, among others, do also belong to this category and are actually visible to the naked eye: Antares seen next to Jupiter and Betelguese seen in Orion’s constellation.
Something that is always referred to when we talk about planets with the possibility of holding life is the so-called habitable zone. This is a zone around the star which is warm enough to hold life if the planets’ atmospheres within it unify the proper conditions. This zone must be at some distance to the star such that its radiation ejection does not dry the planets’ atmospheres. In the case of M-class red dwarf stars, their habitable zone is so narrow and close to it that any planet within would experience X-ray and UV radiation about x1000 times that which Earth receives from Sun. Red dwarf habitable-zone planets would end up with their atmospheres stripped away and therefore not developing into more hospitable worlds.
Contrary to these M-sized stars, G-type stars as our Sun live for much less years. Also a star limit how much time a planet’s atmosphere can remain stable. Considering the Sun, in some billion years the Earth will orbit its inner habitable zone region. Recall that this motion is due to the Newton’s law of universal gravity which states that two bodies will be attracted with a force proportional to the product of both masses and inversely proportional to the squared distance between them. Furthermore, the habitable zone will move outwards ate the same time the Sun grows warmer and brighter until becoming a red giant, one of the latest phases of stellar evolution, ranging from dwarfs (brown, red, etc.), to giants (super and hyper).
K-type stars: Goldilock Stars
These stars are a mid-size and have a lifetime with respect to between M-type red dwarfs and G-type giant stars. Also these stars are warm enough such that the habitable zone around them provides the best qualities for developing hospitable planets and therefore makes them the right place to look for life. Furthermore, the longer lifetime these stars have means a slower migration of the habitable zone, which is the space-shifting outwards of the zone due to the star size increase.
There are apprximately three K-type stars more than G-type stars in our galaxy, the Milky Way. Also, these stars have less intensely magnetic fields that power strong X-ray and UV emissions and energetic outbusts. In fact the X-ray emissions gotten by their surrounding planets would be about 1/100th times of those received in the habitable-zone of class M stars.
An example of a promising system is Kepler-422, which is a goldilock star that hosts a goldilock planet, Kepler-442b, a rocky planet whose mass is about twice that of Earth. The system’s name Kepler is due to the Kepler satellite whose mission is to examine similar Earth-sized exoplanets.
Professors Edward Guinan and Scott Engle from Villanova Univesity in Pennsilvanya were working in a program called the “GoldiloKs” Project over the last 30 years with undergraduate students and they have determined relationships among stellar age, rotation rate, X-ray and far-ultraviolet emissions and flare activity in a sampling of mostly cool G and K stars.
Thank you for reading!
|NASA. Goldilock Stars Are Best Places to Look for Life. https://www.nasa.gov/feature/goddard/2020/goldilocks-stars-are-best-places-to-look-for-life|