Since the beginning of mankind, humanity has always wondered if they exist alone in the universe. Once humans gained enough resources and advanced in technology, that they could start searching for the life on other planets, they started searching for ancient or current life on different planets.
Before we could answer this complex question, we needed to get the idea of What is needed to sustain life on other planets. NASA’s exoplanet program was launched to find unmistakable signs of current life on a planet beyond Earth. Although we haven’t found signs of life on other planets yet but we have painted a picture of what is needed to support life.
Galactic Habitable Zones
Habitable zones are places where the probability of human life existing or thriving is higher. Galactic Habitable zones are places in galaxies where there is a high probability of a solar system supporting life. Since stars are not uniformly distributed in a galaxy, the location of a star within it is also important.
As approaching the center of a spiral galaxy , the density of stars increases, resulting in shorter distances between stars and a greater number of neighbors per star. A solar system close to the densely packed stars in a galaxy will make it a region of high activity i.e. interaction between stars, turbulence, high radiation flux, frequent supernovae. It significantly reduces the chances of any life surviving.
Suitable Star Type
Our Sun is categorized as a G-type yellow-dwarf main sequence star. “Main Sequence” is just like the adulthood stage of stars. It is the longest and most stable stage in star’s life.
Big stars or “Giants” are usually unstable and have small life on a cosmic time scale. The lifetime of a star is roughly inversely proportional to its mass cubed. This isn’t a perfect relation , but it isn’t too far off. So a star ten times more massive than our sun would live for just 1/1000th as long (10 million years). That’s far too short for life to develop and thrive on any of its planets.
Too small stars have habitable zone so close that planets will become tidally locked(the same side always facing the star). One side is extremely hot and other side is extremely cold. Whether life could develop and thrive on a tidally locked planet is still the subject of debate but it doesn’t make it an ideal place to look for life
Smaller stars are frequently observed to be quite violent, with some displaying massive flare activity and their habitable zones receive abundance of UV and X-rays. This supports the conclusion that small stars are not the best place to search for habitable planets in the first place.
A list of 1235 extrasolar planetary candidates was published in February 2011 by the Kepler Space Observatory mission team of which only 54 were in habitable zone. Based on these findings, The Kepler team predicted that the Milky Way would have “at least 50 billion planets,” of which the ones in habitable area would be “at least 500 million”.
Type of Planet
Planets that are about one order of magnitude in mass of Earth, mostly made up of silicate rocks and have not accreted the gaseous outer layers of hydrogen and helium found on gas giants, have the highest probability of supporting life. The probability of life arising in the cloud tops of giant planets has not been definitively ruled out, though it is considered impossible considering that they have no surface and immense gravity. Meanwhile, natural satellites of giant planets continue to be viable candidates for hosting life.
A team from the University of Montreal studied 355 stars that contained 909 planets and what they found out was, In most cases, planets were roughly the same size and evenly spread out. After nine years of collecting data from deep space, NASA’s Kepler Telescope has discovered over 2,600 planets outside of our solar system, many of which may be suitable for life.
Earth’s moon is part of the earth. It stabilizes our rotation and bring tides. The Earth might have rolled over its axis regularly causing the Earth’s water to be redistributed entirely. Astronomers believe this occurred on Mars because it never had a big enough move to stabilize it .
These tides made by the moon might have caused dramatic fluctuations in salinity around coastlines which could have driven the evolution of early DNA-like biomolecules. It looks like the moon is important after all. Important to the geology of Earth, and important to the evolution of life itself. It seems that the moon is Important after all. Important to the Earth’s geology and important to life’s growth itself.
Earth is the only planet with tectonic plates with fissures that allow superheated gases to escape and thicken the atmosphere which traps heat and creates a whole system of rains. This system of tectonic plates created a cycle of thickening our atmosphere at the start which led to a stable environment.
These processes that create an atmosphere for a planet are mostly volcanic processes from a molten core. In the first, the few million years of a planet’s existence volcano’s produce massive amounts of gas. It’s what happened on Mars and on Earth. But Mars is smaller than Earth and its core cooled down and volcanic outgassing stopped. The greenhouse effect that helped warm the planet lessened. Its light gravity allowed the atmosphere an easier escape to space.
Atmosphere and Ozone
The atmosphere is a gaseous mixture that envelops a Planet. It’s also known as air. Nitrogen, oxygen, and carbon dioxide are among the gases that are contained in the atmosphere. The atmosphere, along with water vapors, is essential for life to exist. Earth would be a cold and desolate place if it didn’t exist.
These gases maintain a temperature that is suitable for life. During the day, the gases block some of the Star’s scorching rays and trap heat so it doesn’t radiate into space for night. The Sun UV and Infrared rays are absorbed by the gases in atmosphere especially Ozone which resides in stratosphere. Cosmic rays, gamma rays, and x-rays are all absorbed by dense layers of molecular gases, stopping these energetic particles from striking living things and causing mutations and other genetic damage. During a solar flares, when the sun’s damaging output is significantly increased, the atmosphere is able to block the harmful effects thus saving life on the planet.
According to NASA, Every day, more than 100 tones of space debris reaches Earth, mainly in the form of dust and small particles, . However, as they come into contact with the molecules that make up Earth’s atmosphere, the friction destroys them. Even the meteor are destroyed by out planet’s atmosphere before they could reach the surface saving humans from the disastrous impacts.
Movement of water( Water cycle) is a vital process for life to start on any planet. Water makes up most of the any living organism on earth. Atmosphere is responsible for the continuation of this cycle which supplies water to driest regions on planet. Without an atmosphere, remain frozen in pockets below the surface of the planet or water would simply boil away into space.
A planet’s magnetic field is caused by a dynamo effect. The motion of convection currents of a mixture of molten iron and nickel generates electric currents. The rotation of a planet on its axis causes these electric currents to form a magnetic field which extends around the planet.
Life could not survive without the magnetosphere. Planet’s magnetic field acts as a shield for planet against charged particles from the Star. It also saves planet’s atmosphere from solar winds and storms. Without a planet’s magnetic field, The solar winds and the charged particles from thee star would strip the atmosphere away from the planet. When Mars molten core cooled down it also lost its magnetic field and its atmosphere was exposed to the full brunt of the solar wind which has steadily eroded its atmosphere.