One of the interesting scientific discoveries of the past decade has been that there are planets orbiting other stars (called exoplanets) and that many of these planets may have temperatures that would allow liquid water to exist on their surfaces. There has been a special interest in M dwarf exoplanets.
In theory, all stars could have a possible planet in a zone where the temperatures would be between zero and 100 degrees Celcius. However, that zone could be very small, and there are many factors required to make life possible, and many that would make life impossible. In an article in Science News dated June 24, 2017, (page 18) some of those factors were mentioned. They include stellar flares, gravitational locking, and especially the life expectancy of the star.
Stars age and the period during which their habitable zone could exist in a stable form is very short. M dwarf stars are held up as having long enough lifetimes for water to exist and biological processes to take place. Since they are the most common type of star in the Milky Way (70% of all the stars in our galaxy) scientists are studying them closely. We have reported before on one of them called TRAPPIST-1.
As more data comes in, it is becoming apparent that although M dwarf exoplanets remain as they are for very long times, they are still not stable enough to sustain life. Scientists hoping to find another “earth” orbiting another star are learning that M dwarfs are not good candidates even though they have some of the conditions necessary for life.
We commented in a previous post about extra-solar planets (planets orbiting other stars), and whether those planets could have life on them. The media seem to convey the idea that there are hundreds of “earths” all containing life-forms similar to us. They suggest that if there are many Earth-like planets with life on them, then that indicates that Earth and the life on it came about by chance processes. In February, NASA called a special news conference to announce that they had found a star they call TRAPPIST-1 which had seven Earth-sized planets orbiting it in the “Goldilocks Zone.” The Goldilocks Zone is the area where water could exist in the liquid state. Many media sources were quick to announce that NASA had found seven planets that were “Earth twins” and almost surely would be inhabited.
Let us emphasize again that finding life in space is not an issue of whether God exists. If scientists find life in space, it will have been created by God and will have a purpose in existing. This particular find, however, is just another example of how quickly and irresponsibly the media will jump to promote an agenda that will sell. As more data has become available, it is becoming increasingly obvious that this seven-planet system is not an ideal place for life. In fact, any life form that happened to be there would be destroyed by the properties of the system.
TRAPPIST-1, the star that serves as the “sun,” is a very cool dwarf star. That means it gives off a very limited spectrum of light. The critical wavelengths required for photosynthesis and chemosynthesis are simply not present. The masses of these planets range from .4 to 1.4 times the mass of Earth. That means the smaller planets will almost surely not have an atmosphere since they are smaller than Mars. The length of time for the planets to orbit their star varies from 1.5 days to 20 days. That makes a very short year. They are all less than 6 million miles from their parent star. That means all activity on the star would likely be lethal to life-forms on the planets. For a comparison, Mercury, the planet closest to our Sun is separated from it by 36.8 million miles. Earth is 93 million miles from the Sun.
Earth is very different from any other planet we have discovered inside or outside of our solar system. One key factor that makes our planet habitable is our Moon. The Moon serves several important roles, including holding Earth in a stable rotation. The Moon can be a stabilizer for Earth because of its relatively large size. Other planets have moons that are much smaller in comparison to the planets they orbit. Also, other planets in our solar system have multiple moons which make conditions less stable.
Many of the planets discovered outside of our solar system are huge and located incredibly close to their stars with highly eccentric orbits. A solar system in the constellation Serpens was found with a planet seventeen times as massive as Jupiter. Someone might respond with the observation that we can only see the big planets because those systems are so far away. That observation misses the point. These huge, Jupiter-sized and larger planets are located as close to their stars as we are to our Sun or closer. If there is a small planet in the vicinity, it would be twisted and wrenched about by the influences of the large planet. The problem with highly elliptical orbits and life is that there would be too much variation in the amount of energy that the planet receives from its star. Earth’s orbit is only slightly elliptical giving us stable temperatures. If we had only one planet in our solar system with a radically elliptical orbit, there would be a danger of it crashing into our planet. Circular orbits are important for stability. The instability produced by highly eccentric orbits of large planets would make the area sterile and void as far as life is concerned. Everything we see indicates that our solar system is a cosmic oddball.
There are many properties of our planet, Sun, solar system, and the galaxy in which we live that have to be exactly as they are for any kind of life, not just intelligent life, to exist. The galaxy has to be the right type of galaxy, we must be in the right position in the galaxy, and our Sun has to be the right type of star and at the right age in its life process. Our planet must have the right size, mass, tilt, magnetic field, distribution of land masses, chemical makeup, atmosphere, distance from the Sun, and much, much more.
An exoplanet is a planet orbiting a star other than our Sun. At the time that I am writing there are 3,565 known exoplanets, but by the time you read this, there could be over 4,000. In spite of what the media says, there have been no “Earth-twin,” “habitable,” or “Earth-like” planets found. These are cliches the media throws around which have very little scientific validity. When a scientist identifies a planet as being in a habitable zone, it simply means that water could exist on the planet in a liquid form. Scientists consider water, carbon, and oxygen essential for life. But there are many other variables that must be carefully chosen before an “Earth-like” planet could actually have life on it.
The exoplanets that have been discovered so far are an incredibly varied group. Most are too big, too hot, too gassy (like our gas giant Jupiter), or they have orbits that are too eccentric (ovals, not circles) to support life. Some planets are so hot that they rain glass. Others are so cold that no biological organism could exist on them. The stars around which these planets orbit are also an incredibly varied group with enormous ranges in size, activity, temperature, and radiation levels. In most cases, those stars are orbiting other stars making life nearly impossible.