lord_jebus said:can anyone tell me how planets form and how we know that life can only exist in an environment where there is liquid water. is it possible that we only know how to observe or measure lifeforms we have previously encountered?
Planets form through a process known as accretion, where small particles of dust and gas collide and stick together, gradually growing in size. These particles eventually form larger bodies called planetesimals, which continue to collide and merge to form planets.
Liquid water is a key ingredient for life as we know it. It provides a medium for chemical reactions to occur, and also acts as a solvent, allowing essential molecules to dissolve and interact. Liquid water also helps to regulate the temperature of a planet, making it more hospitable for life to evolve.
The presence of liquid water on a planet depends on a variety of factors, including the distance from its star, the planet's atmosphere, and the composition of the planet's surface. Generally, a planet must be in the "habitable zone" of its star, where temperatures are suitable for liquid water to exist, and have a dense enough atmosphere to keep the water from evaporating.
The amount of time it takes for a planet to become habitable depends on many factors, such as the planet's size, distance from its star, and initial composition. It can take anywhere from a few million years to billions of years for a planet to form and become habitable. However, the development of complex life forms can take even longer, as it requires a stable environment and the right conditions for evolution to occur.
While liquid water is essential for life as we know it, there is a possibility that organisms could exist on planets with alternative solvents, such as liquid methane or ammonia. However, these types of planets are currently hypothetical and have not been discovered yet. It is also possible that life could exist in extreme environments on Earth, such as deep in the ocean or in hot springs, where liquid water may not be present.