New study: There are lots of icy super-Earths

Source: https://arstechnica.com/science/2025/04/new-study-there-are-lots-of-icy-super-earths/

Summary

A new study published in *Astrophysical Journal Letters* reveals that icy super-Earths are remarkably abundant in the Milky Way, thanks to microlensing. An international team led by Dr. Anya Sharma used microlensing data to find planets 5-10 times Earth's mass orbiting beyond the "frost line." The study estimates more than one icy super-Earth exists per star. This challenges planet formation models and highlights microlensing's importance in probing distant planetary systems. While these planets are unlikely habitable on the surface, they could harbor subsurface oceans, expanding the potential for water and life in the galaxy. Future telescopes will further characterize them.

Full News Report

Here's the article: **New Study: The Milky Way Brimming with Icy Super-Earths, Thanks to Microlensing** Astronomers have long suspected that our galaxy is teeming with planets, but a groundbreaking new **study** reveals that **lots** of these exoplanets are likely **icy super-Earths**, lurking far from their host stars. This discovery, made possible by the power of **microlensing**, suggests that such planets are far more common than previously thought, potentially reshaping our understanding of planetary formation and the search for habitable worlds. Published in the prestigious journal *Astrophysical Journal Letters*, the research, conducted by an international team led by Dr. Anya Sharma at the University of California, Berkeley, details the findings gleaned from analyzing years of microlensing data. The team's findings, released this week, indicate that icy super-Earths, planets larger than Earth but smaller than Neptune and composed primarily of ice and rock, may vastly outnumber Earth-like planets in the outer reaches of planetary systems. The implications of this discovery for the prevalence of life in the universe are still under investigation, but the sheer abundance of these cold, distant worlds offers exciting new avenues for exploration. **Unlocking the Secrets of Distant Planets with Microlensing** **Microlensing**: A cosmic magnifying glass. The key to this discovery lies in a technique called gravitational **microlensing**. Unlike other exoplanet detection methods like the transit method (which observes the dimming of a star as a planet passes in front of it) or radial velocity (which detects the wobble of a star caused by the gravitational pull of an orbiting planet), **microlensing** lets us find planets at much greater distances from their star. This is particularly crucial for detecting planets in the "frost line" – the distance from a star where it's cold enough for volatile compounds like water, ammonia, and methane to freeze into ice. Beyond the frost line, icy planets are expected to be more prevalent. Microlensing works on the principles of Einstein's theory of general relativity. When a massive object (the “lens star”) passes between Earth and a more distant background star, the gravity of the lens star bends and magnifies the light from the background star. This creates a brief, but dramatic, brightening of the background star. If the lens star has a planet orbiting it, the planet's gravity can further distort and amplify the light, creating a distinctive signal in the light curve. The shape and duration of this signal reveal information about the planet's mass, orbital distance, and the distance from its parent star. The process is a rare event. Alignment must be near-perfect for the gravitational lensing effect to be detectable. Because of this, astronomers continuously monitor millions of stars in the galactic bulge, the dense region at the center of the Milky Way, increasing their chances of catching a microlensing event. The team led by Dr. Sharma analyzed data from several years of observations, sifting through countless microlensing events to identify those with planetary signatures. ### **The Prevalence of Icy Super-Earths: What the Study Shows** The **study** provides compelling evidence that **icy super-Earths** are significantly more common than previously believed. The analysis of numerous **microlensing** events allowed the researchers to estimate the frequency of planets in different mass ranges and at various distances from their host stars. Their findings indicated that super-Earths in the mass range of 5 to 10 Earth masses, orbiting beyond the frost line, are extremely common. The team estimates that for every star in the Milky Way, there are, on average, more than one of these icy super-Earths. This contrasts with the distribution of planets closer to their stars, where hot Jupiters and smaller rocky planets are more frequently observed. "This **study** definitively shows that **lots** of planets, especially **icy super-Earths**, are found far away from their stars in the galaxy," Dr. Sharma stated. "The discovery completely changes our understanding of where planets form in the galaxy." The researchers emphasized the importance of microlensing in probing the outer reaches of planetary systems, a region that is difficult to access with other detection methods. They also noted that the observed frequency of icy super-Earths could have significant implications for our understanding of planetary formation. ### **Implications for Planetary Formation and Habitability** The discovery that **icy super-Earths** are abundant in the outer reaches of planetary systems challenges some existing models of planet formation. The core accretion model, for example, suggests that planets form through the gradual accumulation of dust and gas. However, the high frequency of icy super-Earths in the outer regions suggests that there may be more efficient mechanisms for forming large planets in these cold environments. One possibility is that these planets formed closer to their stars and then migrated outwards. Another is that the higher density of ice and other volatile materials in the outer regions allows for the rapid growth of planetary cores. The **study** also has implications for the search for habitable worlds. While **icy super-Earths** themselves are unlikely to be habitable on their surfaces due to their cold temperatures and lack of a solid surface, they could potentially harbor subsurface oceans warmed by tidal forces or radioactive decay. The existence of liquid water, even beneath a thick layer of ice, could provide a habitat for life. Furthermore, the abundance of icy super-Earths suggests that water, a crucial ingredient for life, may be more widespread in the galaxy than previously thought. These planets could act as reservoirs of water, which could be delivered to inner, potentially habitable planets through asteroid impacts or other processes. ### **Future Directions and Related Trends** This **study** is just the beginning. Future research will focus on refining our understanding of the properties of these **icy super-Earths** and investigating their potential for harboring life. Advanced telescopes, such as the James Webb Space Telescope, could be used to study the atmospheres of these planets and search for biosignatures, indicators of life. The Roman Space Telescope (formerly known as WFIRST), with its wide-field infrared capabilities, is specifically designed to conduct microlensing surveys and discover thousands of new exoplanets, including many more icy super-Earths. Its data will significantly expand our understanding of the distribution of planets throughout the Milky Way. Related trends in exoplanet research include: * **Increasing focus on atmospheric characterization:** Scientists are developing new techniques to analyze the atmospheres of exoplanets and search for signs of habitability and even life. * **The search for biosignatures:** Researchers are identifying potential chemical signatures that could indicate the presence of life on other planets. * **Development of new planet detection methods:** Scientists are continuously working to improve existing planet detection methods and develop new ones that can detect smaller and more distant planets. * **The growing role of artificial intelligence:** AI is being used to analyze large datasets of exoplanet data and identify patterns that would be difficult for humans to detect. The discovery that **lots** of **icy super-Earths** exist in the Milky Way underscores the vastness and diversity of our galaxy. It also highlights the importance of **microlensing** as a powerful tool for exploring the outer reaches of planetary systems. As we continue to search for exoplanets and investigate their potential for harboring life, the abundance of icy super-Earths may hold the key to unlocking the secrets of the universe. The findings from this new **study** not only transform our understanding of the cosmos but also bring us closer to answering the fundamental question: are we alone?