Stars are objects that emit light and heat. Within a certain distance around the stars, water may exist in the form of liquid water, so every star has its own habitable zone.
Since the discovery of the first exoplanet in 1995, as of October last year, scientists have identified 4118 exoplanets. In these exoplanets, there are a large number of planets in the habitable zone, which are likely to have life.
But although exoplanets may contain liquid water, oxygen and other substances that can give birth to life, scientists are still very cautious, because habitable zone planets and habitable planets are two different concepts.
Habitable planet vs habitable planet
There are different kinds of planets in the habitable zone. As shown in the figure below, among the 4118 exoplanets discovered, they can be divided into two categories: in the habitable zone and not in the habitable zone.
Not in the livable zone accounted for the majority, 3496.
The remaining 622 planets are divided into three categories, of which only 129 are completely located in the habitable zone, 301 have only part of their orbits in the habitable zone, and the remaining 192 have most of their orbits in the habitable zone.
But of the 192 planets that seem promising, 24 are rocky. We all know that living things can’t live on rocky planets or gaseous planets like Jupiter.
Out of the livable zone
Is it disappointing to see that there are so many habitable planets here, but most of them have been eliminated for various reasons. Is it so difficult to breed life out of the system?
Don’t worry. Let’s keep talking.
In fact, planets in the habitable zone may not necessarily be habitable planets, and habitable planets do not necessarily exist in the habitable zone.
Take our solar system as an example. The earth and Mars are both located in the habitable zone of the solar system. Let’s see what a vibrant planet the earth is, with thousands of life species.
Look at Mars. So far, no human probe has found any sign of life on Mars.
If you look at Europa and Titan, although they are hundreds of millions of kilometers away and have a surface temperature of at least minus 100 degrees Celsius, they may be more livable than Mars and the moon.
Why do you say that?
Because they’re all supposed to be liquid. Scientists predict that there may be a very rich liquid ocean under Europa, and there may be a large number of liquid alkane oceans or lakes on the surface of Titan.
Since the liquid ocean may exist, it means that the temperature is relatively appropriate, so it is very promising to breed life, but this life form may be completely different from what we know.
However, to judge whether a planet is livable or not, we need to have multiple conditions at the same time, not just in the livable zone.
It’s also related to the mass of the planet. If the mass is too small, it’s very difficult for the planet to have an atmosphere. If there is no atmosphere, there will be no air, let alone life.
If the mass is too large, it will turn into a gaseous planet. The gaseous planet not only has no solid ground, but also has a high pressure, so there will be no life in this environment.
So even if we meet the conditions we speculate, life may not appear. Xiaobian believes that instead of spending a lot of time and energy to find the so-called habitable zone planets, it is better to directly look for traces of extrasolar life.
What do you think of that? Welcome to comment area.
(pictures of the article are from the Internet)