New Research Suggests Earth-Like Planets Can Hold Onto Water Even Around Highly Variable Stars

Astronomers have long worried that stars with unstable behavior might make life nearly impossible on nearby planets. A new scientific study, however, adds an intriguing twist to that assumption. According to recent research accepted for publication in The Astronomical Journal, Earth-like planets orbiting variable stars may still be capable of retaining water—even when their host stars regularly fluctuate in brightness and activity.

This finding offers fresh insight into how astronomers should think about exoplanet habitability, especially around stars that behave very differently from our relatively calm Sun.

Understanding the Core Question Behind the Study

The central focus of the study is simple but important: How does stellar variability affect a planet’s climate and its ability to keep water? Stellar variability refers to changes in a star’s brightness over time, often caused by sunspots, flares, magnetic activity, or rotational changes. These variations can alter how much energy a planet receives, which could, in theory, affect surface temperatures and long-term water retention.

To explore this, researchers analyzed nine known exoplanets, each orbiting a different star located within its star’s habitable zone—the region where liquid water could exist on a planet’s surface.

The Nine Exoplanets Studied

The planets examined in this research are spread across a wide range of distances from Earth and include:

• TOI-1227 b (328 light-years away)
• HD 142415 b (116 light-years)
• HD 147513 b (42 light-years)
• HD 221287 b (182 light-years)
• BD-08 2823 c (135 light-years)
• KELT-6 c (785 light-years)
• HD 238914 b (1,694 light-years)
• HD 147379 b (35 light-years)
• HD 63765 b (106 light-years)

Each of these planets orbits a star known to show elevated levels of variability, making them ideal test cases for understanding how stellar behavior might influence planetary conditions.

What the Scientists Were Measuring

One of the key concepts in this study is equilibrium temperature. This is the temperature a planet would have if it simply absorbed energy from its star and re-radiated it back into space, without accounting for atmospheric effects like greenhouse warming.

The researchers wanted to know whether fluctuations in a star’s brightness would significantly change this equilibrium temperature and, in turn, threaten a planet’s ability to keep water—especially for planets located near the inner edge of the habitable zone, where conditions are already warmer.

The Main Findings May Surprise You

After analyzing the data, the researchers reached two important conclusions:

First, stellar variability had very little effect on the equilibrium temperature of the exoplanets studied. Even though the stars showed noticeable changes in brightness, those fluctuations did not meaningfully alter the long-term energy balance of the planets.

Second, and perhaps more importantly, planets orbiting near the inner edge of the habitable zone were still able to retain water, regardless of how variable their host stars were.

This challenges the idea that variable stars automatically doom nearby planets to dry, inhospitable conditions.

A Diverse Group of Stars

Another strength of the study is the diversity of stars included. The researchers examined stars ranging from 0.17 to 1.25 times the mass of the Sun, covering several stellar types:

• M-type stars (small and cool)
• K-type stars
• G-type stars (like our Sun)
• F-type stars (larger and hotter)

This range allows scientists to compare how different kinds of stars influence planetary climates and helps broaden the search for potentially habitable worlds.

Why M-Type Stars Are So Important

Much of the excitement—and concern—around this research centers on M-type stars, also known as red dwarfs. These stars are:

• The most common stars in the Milky Way
• Known to have extremely long lifetimes, sometimes lasting trillions of years
• Frequently highly variable, with strong flares and magnetic activity

Because of their abundance and longevity, M-type stars are prime targets in the hunt for habitable exoplanets. However, their violent outbursts have raised serious questions about whether nearby planets could hold onto atmospheres or surface water.

Famous Examples: Proxima Centauri and TRAPPIST-1

Two well-known M-type star systems illustrate this concern perfectly.

Proxima Centauri, just 4.24 light-years away, hosts a rocky planet within its habitable zone. Unfortunately, the star is extremely active, producing intense ultraviolet radiation and powerful flares that may strip away planetary atmospheres.

TRAPPIST-1, about 39.5 light-years away, is even more intriguing. It hosts seven rocky planets, with at least one potentially located in the habitable zone. Despite the star’s high variability, some researchers believe one or more of these planets could still support liquid water under the right conditions.

The new study supports the idea that stellar variability alone may not be enough to rule out habitability, especially when other planetary factors are favorable.

Important Limitations to Keep in Mind

While the findings are encouraging, the researchers are careful not to overstate their conclusions. The stars in this study show moderate variability, not the most extreme behavior seen among red dwarfs. Extremely active stars may still pose serious risks to planetary atmospheres and surface water.

Additionally, the study assumes that planetary orbital periods are much longer than the timescales of stellar variability, which may not always be true in real systems.

Why This Research Matters for Exoplanet Science

This work represents a small but meaningful step toward understanding how planetary climates respond to dynamic stars. As astronomers discover more exoplanets and gather longer-term data on stellar behavior, models of habitability will become more accurate and less biased against variable stars.

The results suggest that scientists should not automatically dismiss planets around active stars when searching for life. Instead, water retention and climate stability depend on a combination of factors, not stellar variability alone.

Looking Ahead

Future missions and continued observations will help refine these conclusions. As researchers discover more planets around variable stars—and learn more about their atmospheres—our understanding of where life might exist in the universe will continue to evolve.

For now, this study offers a hopeful message: even under a flickering, restless star, a planet may still manage to hold onto one of life’s most essential ingredients—water.

Research paper:
https://arxiv.org/abs/2511.19646