Planets tilted on their axis, like Earth, are more capable of evolving complex life. This finding will help scientists refine the search for more advanced life on exoplanets. This NASA-funded research was presented today at the Goldschmidt Geochemistry virtual conference.

Since the first discovery of exoplanets (planets orbiting distant stars) in 1992, scientists have been looking for worlds that might support life. It is believed that to sustain even basic life, exoplanets need to be at just the right distance from their stars to allow liquid water to exist; the so-called Goldilocks zone. However, for more advanced life, other factors are also important, particularly atmospheric oxygen. 

Oxygen plays a critical role in respiration, the chemical process which drives the metabolisms of most complex living things. Some basic life forms produce oxygen in small quantities, but for more complex life forms, such as plants and animals, oxygen is critical. Early Earth had little oxygen even though basic life forms existed.

The scientists produced a supercomputer model of the conditions required for life on Earth to be able to produce oxygen. The model allowed them to input different parameters, to show how changing conditions on a planet might change the amount of oxygen produced by photosynthetic life.

Lead researcher Stephanie Olson (Purdue University) said "The model allows us to change things such as day length, the amount of atmosphere, or the distribution of land to see how marine environments and the oxygen-producing life in the oceans respond."

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

"The most interesting result came when we modeled 'orbital obliquity' - in other words how the planet tilts as it circles around its star," explained Megan Barnett, a University of Chicago graduate student involved with the study. She continued "Greater tilting increased photosynthetic oxygen production in the ocean in our model, in part by increasing the efficiency with which biological ingredients are recycled. The effect was similar to doubling the amount of nutrients that sustain life."

Earth's sphere tilts on its axis at an angle of 23.5 degrees. This gives us our seasons, with parts of the Earth receiving more direct sunlight in summer than in winter. However, not all planets in our Solar System are tilted like the Earth: Uranus is tilted at 98 degrees, whereas Mercury is not tilted at all. "For comparison, the Leaning Tower of Pisa tilts at around 4 degrees, so planetary tilts can be quite substantial," said Barnett.

Dr. Olson continued "There are several factors to consider in looking for life on another planet. The planet needs to be at the right distance from its star to allow liquid water and have the chemical ingredients for the origin of life. But not all oceans will be great hosts for life as we know it, and an even smaller subset will have suitable habitats for life to progress towards animal-grade complexity. Small tilts or extreme seasonality on planets with Uranus-like tilts may limit the proliferation of life, but a modest tilt of a planet on its axis may increase the likelihood that it develops oxygenated atmospheres that could serve as beacons of 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 evolve complex life. This helps us narrow the search for complex, perhaps even intelligent life in the Universe."

Timothy Lyons, Distinguished 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 oceans are milestones in the history of life on Earth. Studies of Earth teach us that oxygen may be one of our most important biosignatures in the search for life on distant exoplanets. By building from the lessons learned from Earth via numerical simulations, Olson and colleagues have explored a critical range of planetary possibilities wider than those observed over Earth history. Importantly, this work reveals how key factors, including a planet's seasonality, could increase or decrease the possibility of finding oxygen derived from life outside our solar system. These results are certain to help guide our searches for that life."

In March of 2020, thousands of scientists around the world united to answer a pressing and complex question: what genetic factors influence why some COVID-19 patients develop severely, a life-threatening disease requiring hospitalization, while others escape with mild symptoms or none at all?

A comprehensive summary of their findings, reveals 13 loci, or locations in the human genome, are strongly associated with infection or severe COVID-19. The researchers also identified causal factors such as smoking and high body mass index. These results come from one of the largest genome-wide association studies ever performed, and it includes nearly 50,000 COVID-19 patients and two million uninfected controls.

The findings could help provide targets for future therapies and illustrate the power of genetic studies in learning more about infectious diseases.

This global effort, called the COVID-19 Host Genomics Initiative, was founded in March 2020 by Andrea Ganna, group leader at the Institute for Molecular Medicine Finland (FIMM), University of Helsinki, and Mark Daly, director of FIMM and institute member at the Broad Institute of MIT and Harvard. The initiative has grown to be one of the most extensive collaborations in human genetics and currently includes more than 3,300 authors and 61 studies from 25 countries.

Ben Neale, co-director of the Program in Medical and Population Genetics at the Broad and co-senior author of the study, said that while vaccines confer protection against infection, there is still substantial room for improvement in COVID-19 treatment, which can be by genetic analysis. He added that improving treatment approaches could help shift the pandemic -- which has necessitated the large shutdowns in much of the world -- to an endemic disease that is more localized and present at low but consistent levels in the population, much like the flu.

"The better we get at treating COVID-19, the better equipped the medical community could be to manage the disease," he said. "If we had a mechanism of treating infection and getting someone out of the hospital, that would radically alter our public health response."

Harnessing diversity

To do their analysis, the consortium pooled clinical and genetic data from the nearly 50,000 patients in their study who tested positive for the virus, and 2 million controls across numerous biobanks, clinical studies, and direct-to-consumer genetic companies such as 23andMe. Because of the large amount of data pouring in from around the world, the scientists were able to produce statistically robust analyses far more quickly, and from a greater diversity of populations, than any one group could have on its own.

Of the 13 loci identified so far by the team, two had higher frequencies among patients of East Asian or South Asian ancestry than in those of European ancestry, underscoring the importance of diversity in genetic datasets.

"We've been much more successful than past efforts in sampling genetic diversity because we've made a concerted effort to reach out to populations around the world," said Daly. "I think we still have a long way to go, but we're making very good progress."

The team highlighted one of these two loci in particular, near the FOXP4 gene, which is linked to lung cancer. The FOXP4 variant associated with severe COVID-19 increases the gene's expression, suggesting that inhibiting the gene could be a potential therapeutic strategy. Other loci associated with severe COVID-19 included DPP9, a gene also involved in lung cancer and pulmonary fibrosis, and TYK2, which is implicated in some autoimmune diseases.

Mari Niemi, also at FIMM and lead analyst for the study, says the consortium prioritized communication as the scientists analyzed data, immediately releasing results on their website after they had been checked for accuracy. The team hopes their results might point the way to useful targets for repurposed drugs.

The researchers will continue to study more data as they come in and update their results. They will begin to study what differentiates "long-haulers", or patients whose COVID-19 symptoms persist for months, from others, and continue to identify additional loci associated with infection and severe disease.

"We'd like to aim to get a good handful of very concrete therapeutic hypotheses in the next year," Daly said. "Realistically, we will most likely be addressing COVID-19 as a serious health concern for a long time. Any therapeutic that emerges this year, for example from repurposing an existing drug based on clear genetic insights, would have a great impact."

A new space for genetics

Ganna emphasized that the scientists were able to find robust genetic signals because of their collaborative efforts, a cohesive spirit of data-sharing and transparency, and the urgency that comes with knowing the entire world faces the same threat at the same time. He added that geneticists, who regularly work with large datasets, have known the benefits of open collaboration for a long time. "This only illustrates just how much better science is -- how much faster it goes and how much more we discover -- when we work together," Ganna said.

Daly, for his part, is excited by how clear and interpretable their results have been for geneticists. He says the insights from this work have been unique and potentially paradigm-shifting for the field of human genetics, which has been dominated by studies of common chronic diseases, rare genetic diseases, and cancer.

"These discoveries have been really informative and that has made us realize that there's a lot of untapped potential in using genetics to understand and potentially develop therapeutics for infectious disease," Daly said. "I hope this sets an example for how we might bring population genetics approaches to a new set of problems that are especially important in developing parts of the world."