New research from NASA experts reveals something interesting about far-off exoplanets. These worlds, located way past our solar system, seem to be shrinking. This baffling trend has left astronomers and scientists scratching their heads.
The Diverse World of Exoplanets
The universe has all kinds of exoplanets, from huge gas ones like Jupiter to smaller, rocky ones like Earth, and even ‘super-puffs’, which are as light as cotton candy. But scientists have spotted a weird hole in this mix: there’s a clear lack of planets that are 1.5 to two times bigger than Earth.
The Mysterious Gap
NASA has found over 5,000 exoplanets and there’s an interesting trend. There’s a bunch of super-Earths, which are no more than 1.6 times bigger than our planet, and loads of sub-Neptunes, which are two to four times Earth’s width. But there aren’t many planets in between those sizes. This isn’t just by chance, says Jessie Christiansen, a scientist at Caltech and the head of research for the NASA Exoplanet Archive.
Uncovering the Cause: The Shrinking Process
The leading hypothesis for this phenomenon is that sub-Neptunes are gradually losing their atmospheres, thereby reducing in size until they resemble super-Earths. Christiansen’s recent research suggests that radiation emitted from the planets’ cores is pushing their atmospheres into space, thus contributing to their shrinkage.
Atmospheric Loss: Core-Powered Mass Loss vs. Photoevaporation
There are two main theories to explain atmospheric loss: core-powered mass loss and photoevaporation. Core-powered mass loss occurs when a planet’s core emits radiation, pushing the atmosphere away. On the other hand, photoevaporation theorizes that a planet’s atmosphere is dissipated by radiation from its host star. However, photoevaporation is thought to occur within the first 100 million years of a planet’s life, whereas core-powered mass loss could happen around the planet’s billionth year.
To differentiate between these hypotheses, Christiansen’s team examined data from NASA’s retired Kepler Space Telescope, focusing on star clusters over 100 million years old. Their findings suggested that core-powered mass loss is a more likely cause for the eventual loss of atmosphere in these planets.
The Ongoing Debate
Despite these findings, the mystery remains unsolved. Christiansen acknowledges that the understanding of exoplanets is still evolving and requires further research. A Harvard assessment posted online also suggests that both core-powered mass loss and photoevaporation might be operational in an ongoing mass-loss sequence.
Comparative Analysis: Earth vs. Exoplanets
The phenomenon of atmospheric escape is not unique to exoplanets. Earth, too, loses about 90 tons of air into space every day due to solar heating. However, this process is exceptionally slow, with estimates suggesting it would take Earth around 15 trillion years to be completely stripped of its atmosphere. In contrast, exoplanets, particularly those larger than Earth but smaller than Neptune, are actively pushing their atmospheres away through core-powered mass loss, a mechanism capable of shrinking a sub-Neptune to a super-Earth size.
Christiansen’s study, utilizing data from NASA’s Kepler 2 mission, analyzed sub-Neptunes orbiting stars in two-star clusters: the Praesepe or Beehive cluster and the Hyades cluster. In these clusters, almost all stars had sub-Neptunes with atmospheres, indicating that photoevaporation had not occurred. Conversely, in planets around stars more than 800 million years old in K2’s database, only 25% exhibited orbiting sub-Neptunes, supporting the core-powered mass loss theory.
Further Investigations into Exoplanet Atmospheres
Scientists are diving deeper into studying exoplanets, especially to understand how their atmospheres vanish. Their goal is to unravel the mystery behind the shrinking size of these distant worlds, its impact on their development, and their potential to harbor life. By examining the changes in these atmospheres, we learn more about distant star systems and gain insights into our own solar system’s function.
In conclusion, the diminishing sizes of exoplanets remain a subject of active research. The theories of core-powered mass loss and photoevaporation both provide compelling explanations, but further study is necessary to fully comprehend this complex process. Our knowledge about exoplanets is always growing, and it’s helping us discover more secrets about the enormous universe. To learn about exoplanets and what they’re like, check out NASA’s Exoplanet Exploration Program.