Are there any habitable exoplanets out there? Recently researchers announced that they found water vapor in the atmosphere of a planet called K2-18b. The planet is larger than Earth. When researchers talk about traces of water on another planet we think about if the planet is habitable or not? What does habitable planet means? Does it mean that it must have life?
The habitable zone is the area around a star where planets can have liquid water on their surface. We compare these planets to Earth in size, the distance between that planet and its star, and how does it compare the Earth and to the Sun. So far, we know only one planet that is habitable and that planet is Earth.
There are two planets on the edge of the habitual zone in our solar system. The most famous one is Mars. Scientists believe that Mars might have hosed life in the past. It’s also possible that it has microbes today. We know that Mars used to have a thick atmosphere in the past just like Earth has today. Billions of years ago Mars had running water, maybe even oceans. What happened? According to the most popular theory, the sun’s energy simply eroded the atmosphere from Mars because the planet did not have a magnetic field to protect it. As the atmosphere of the Red Planet thinned, the planet lost the ability to contain running water. Usually, water means life. Maybe there are some microbes deeply buried under the sand of Mars or in frozen ice caps. Maybe, there is nothing left. It’s hard to say until a spacecraft spots something that we can examine.
Another planet that could have been a habitable world is Venus. Now, unshielded spacecraft can’t land on the planet and even if it could, it would only last for a few minutes since Venus is a planet with extremely high temperatures. The entire planet is in clouds which are not easy to escape. Today, Venus is a hellish place with volcanos, lavas, hot spots and it does not look hospitable or habitable at all. Still, as with Mars, there might be some microbes in the cooler areas of Venus. We need way more probes to determine if there is any truth to this.
What’s left? Planet Earth! The only planet with life. What is important to remember is that we are looking for life as we know it. We might have stumbled on life in space but haven’t recognized it as life. Other planets we compare with what we know, which is life on Earth.
Habitable for us assumes a rocky planet. The main reason behind this is because life as we know it evolved on one rocky planet such as Earth. It’s very difficult for us to imagine life in different surroundings which does not include a rocky planet without atmosphere and water.
Another assumption that might limit us when we look into space is if habitable conditions can remain long enough for a planet to host life for an extensive period of time. It’s unclear for scientists to determine when life started on Earth because it might have had a few unsuccessful and false starts. We can see confirmed records of life from approximately 3.5 billion years ago on a planet which is 4.5 billion years old.
We are lucky to have a neighborhood as we have it with a stable star. Other stars emit dangerous radiation that could ruin life easily. Our planet went through a lot of changes but life managed to survive all those changes.
We need better telescope technology to determine which planets are most likely habitable. As of now with the technology we have, scientists believe that we might have 55 possible habitable worlds out there in the universe.