Goldilocks ’tilting’ planets like Earth are more capable of evolving into complex life

Planets tilted on their axis, like Earth, are more capable of evolving into complex life. This discovery will help scientists refine the search for more advanced life on exoplanets. This NASA-funded research is presented at the Goldschmidt Geochemistry Conference.

Since the first discovery of exoplanets (planets orbiting distant stars) in 1992, scientists have been looking for worlds that could house life. It is believed that to maintain even basic life, exoplanets must be the correct distance from their stars to allow liquid water to exist; the so-called “Goldilocks zone”. However, for a more advanced life, other factors are also important, in particular atmospheric oxygen.

Oxygen plays an essential role in respiration, the chemical process that governs the metabolism of the most complex living things. Some basic life forms produce oxygen in small amounts, but for more complex life forms, such as plants and animals, oxygen is essential. The early Earth had little oxygen even though basic life forms existed.

Scientists have produced a sophisticated model of the conditions required for life on Earth to produce oxygen. The model allowed them to enter different parameters, to show how changing conditions on a planet could change the amount of oxygen produced by photosynthetic life.

Principal investigator Stephanie Olson (Purdue University) said, “The model allows us to modify things like day length, amount of atmosphere or land distribution to see how marine environments and life produce. oxygen in the oceans react.

The researchers found that increased day length, increased surface pressure, and the emergence of continents all influence ocean circulation patterns and associated nutrient transport in ways that increase the production of oxygen. They believe that these relationships may have contributed to the oxygenation of the Earth by promoting the transfer of oxygen to the atmosphere as the Earth’s rotation slowed, its continents expanded, and surface pressure increased over time. over time.

“The most interesting result came when we modeled ‘orbital obliquity’ – in other words how the planet tilts as it revolves around its star,” said Megan Barnett, a graduate student at the ‘University of Chicago involved in the study. She continued, “A greater tilt increased photosynthetic oxygen production in the ocean in our model, in part by increasing the efficiency with which organic ingredients are recycled. The effect was similar to doubling the amount of nutrients that support life.

The earth’s sphere tilts on its axis at an angle of 23.5 degrees. This gives us our seasons, with some parts of the Earth receiving more direct sunlight in summer than in winter. However, not all of the planets in our solar system are tilted like the Earth: Uranus is tilted at 98 degrees, while Mercury is not tilted at all. “For comparison, the Leaning Tower of Pisa tilts about 4 degrees, so planetary tilts can be quite large,” Barnett said.

Dr Olson continued, “There are several factors to consider when looking for life on another planet. The planet must be at the correct distance from its star to allow liquid water and have the chemical ingredients necessary for the origin of life. But not all oceans will be excellent hosts for life as we know it, and an even smaller subset will have suitable habitats for life to progress to animal-grade complexity. Small tilts or extreme seasonality on planets with Uranus-like tilts can limit the proliferation of life, but a modest tilt of a planet on its axis can increase the likelihood that it will develop oxygenated atmospheres that could serve as a beacons to microbial life and fuel the metabolisms of large organisms. The bottom line is that worlds that are modestly tilted on their axes may be more likely to develop complex lives. This helps us to refine the search for complex, perhaps even intelligent life in the Universe. “

Timothy Lyons, Emeritus Professor of Biogeochemistry in the Department of Earth and Planetary Sciences at the University of California, Riverside commented:

“The first biological production of oxygen on Earth and its first appreciable accumulation in the atmosphere and the oceans are milestones in the history of life on Earth. Studies on Earth tell us that oxygen may be one of our most important biosignatures in the search for life on distant exoplanets. Drawing on lessons learned from Earth via numerical simulations, Olson and his colleagues explored a critical range of planetary possibilities larger than those observed in Earth’s history. Importantly, this work reveals how key factors, including a planet’s seasonality, could increase or decrease the possibility of finding life-derived oxygen outside our solar system. These findings are certain to help guide our research for this lifetime.