In the search for habitable exoplanets that could host life like Earth, liquid water has played a key role in suggesting the possibility of life. While scientists have been searching for bodies of water similar to those on Earth, a study suggests that liquid water could exist on the surface of exoplanets for billions of years in other circumstances as well. Researchers from the Universities of Bern, Zurich and the National Center for Competence in Research (NCCR) Planets explain why the search for habitable exoplanets may require a different approach than the one currently employed.
According to Ravit Helled, professor of theoretical astrophysics at the University of Zurich and co-author of the study, “One of the reasons why water can be liquid on Earth is its atmosphere.” The natural greenhouse effect of the ocean will trap just the right amount of heat, creating favorable conditions for oceans, rivers and rain.
When the Earth formed, its atmosphere was mainly composed of hydrogen and helium, known as the primordial atmosphere. While Earth loses this atmosphere over time, some larger planets can retain it indefinitely.
“Such a large primordial atmosphere would also have caused a greenhouse effect—like the Earth’s atmosphere today. We therefore wondered whether these atmospheres helped create the necessary conditions for liquid water,” Helled said.
In their study, published in Nature Astronomy, the researchers modeled numerous planets and simulated their evolution over billions of years. They looked not only at the properties of the atmosphere, but also at the radiation intensity of the planet’s star and the internal heat it radiates outward.
“We found that in many cases, the original atmosphere is lost due to the intense radiation of the star, especially on planets close to the star. But in the presence of the atmosphere, conditions suitable for the existence of liquid water may arise,” said the study. said lead author Marit Mol Lous, a doctoral student.
The researchers stress that their findings suggest that these conditions can persist on planets for tens of billions of years. However, even if these planets had the right conditions, says another co-author, Christoph Mordasini, “it’s not clear how likely it is that life would arise in such an exotic potential habitat. “