When astronauts photograph Earth from space, they capture stunning views of blue oceans, white clouds, and green continents.
But according to a new study, our clear atmosphere may be unusual compared with many planets elsewhere in the universe.
Researchers from the University of Chicago suggest that many distant planets could be wrapped in thick layers of soot-filled haze, making them look more like giant smog factories than the beautiful worlds often imagined in science fiction.
The study, published in The Astrophysical Journal Letters, may help solve a mystery that has puzzled astronomers for years.
Scientists have discovered thousands of planets orbiting other stars, known as exoplanets. Among them is a common type called a “mini-Neptune.”
These planets are larger than Earth but smaller than Neptune and are surrounded by thick atmospheres. Interestingly, there is no equivalent type of planet in our own solar system.
Although astronomers have gathered increasing amounts of data on mini-Neptunes, many questions remain. One of the biggest mysteries emerged when NASA’s James Webb Space Telescope began studying their atmospheres in greater detail.
Instead of revealing clear chemical signatures, many of these planets appeared strangely featureless. Their atmospheres seemed unusually opaque, preventing scientists from seeing what was inside.
The answer may come from an unexpected source: combustion engines.
Lead author Jeehyun Yang, a University of Chicago postdoctoral researcher, previously studied combustion as a chemical engineer. While examining the exoplanet data, he noticed a pattern that looked familiar. The relationship between atmospheric temperature and opacity closely resembled patterns seen in gasoline engines, diesel engines, and jet engines.
When fuel burns at high temperatures, carbon-rich particles called soot can form. These particles are made up of complex molecules known as polycyclic aromatic hydrocarbons. On Earth, they are a major component of black smoke from engines and industrial emissions.
At first glance, the temperatures on these planets did not seem hot enough to produce soot. However, the researchers realized that conditions deep inside the planets’ thick atmospheres are very different. As pressure increases, temperatures also rise, creating the right environment for soot formation.
According to the team, the match between the predicted soot-producing conditions and the telescope observations was remarkably close.
The researchers believe soot may form deep within the atmosphere and then gradually rise upward, creating a thick haze that blocks light and makes the atmosphere appear opaque to telescopes.
These worlds are not considered suitable places for life. Many orbit extremely close to their stars and experience intense heat. Some may have oceans of molten rock, while others could be subjected to pressures so extreme that materials behave in unusual ways.
Even so, the discovery could provide valuable clues about how planets form.
Scientists think the amount of soot in a planet’s atmosphere may reveal information about the balance of carbon and oxygen present when the planet formed. These chemical fingerprints could help researchers better understand the history of distant planetary systems and improve future searches for potentially habitable worlds.
The study also highlights the value of bringing together ideas from different scientific fields. In this case, knowledge gained from studying engines on Earth may have helped explain what is happening in the atmospheres of planets hundreds of light-years away.
Source: University of Chicago.
