Editor’s note: This story is also published at Science for the Future.
Astronomers have found that red dwarf stars emit far more ultraviolet (UV) radiation during flares than previously believed, posing significant risks to nearby planets’ potential to support life.
A groundbreaking study from the University of Hawaiʻi’s Institute for Astronomy (IfA), published in the Monthly Notices of the Royal Astronomical Society, reveals that these intense UV flares could erode planetary atmospheres, making them less habitable. However, the same radiation could also drive the chemical reactions needed to form the building blocks of life.
“Our findings show that many more stars may generate enough UV radiation through flares to impact planet habitability,” said Vera Berger, the lead author who conducted the study as part of the Research Experiences for Undergraduates program at IfA.
A Dual-Edged Sword
UV radiation from stellar flares has a complex role. While it can strip away a planet’s atmosphere, it can also contribute to the formation of RNA building blocks essential for life. The study analyzed data from 300,000 stars using the GALEX space telescope and discovered that far-UV emissions from these flares are, on average, three times more energetic than previously assumed and can be up to twelve times stronger.
Most studies have assumed a 9000 K blackbody spectrum for stellar flares, which produces more near-UV flux than far-UV flux. However, Berger’s team found the opposite, with excess far-UV reaching ratios roughly three to twelve times higher than expected. This discrepancy has major implications for understanding the true impact of stellar flares on exoplanets.
“A change of three is the same as the difference in UV in the summer from Anchorage, Alaska, to Honolulu,” explained Benjamin J. Shappee, an associate astronomer at IfA who mentored Berger. Such differences highlight the potential for far-UV radiation to significantly alter planetary conditions.
Implications for Habitability
This discovery challenges existing models of stellar flares and their impact on exoplanets. Higher levels of far-UV radiation could erode planetary atmospheres, reducing their ability to support life. This radiation can break down molecules like ozone, which protect planets from harmful UV radiation. The loss of ozone could leave a planet’s surface exposed to damaging radiation, making it less hospitable for life.
On the other hand, these intense flares might also foster prebiotic chemistry, creating RNA building blocks. High levels of UV radiation can drive chemical reactions that form complex organic molecules, essential for the development of life. This dual role of UV radiation from stellar flares makes the study of red dwarf stars particularly intriguing for astronomers searching for habitable exoplanets.
“This study has changed the picture of the environments around stars less massive than our Sun,” said Jason Hinkle, a PhD candidate at IfA and co-author of the study. Stars that were once considered benign may actually pose significant challenges for planetary habitability.
Looking Forward
The exact cause of the stronger far-UV emissions remains unclear, prompting calls for more data from space telescopes. Future missions like the planned Ultraviolet Transient Astronomy Satellite (ULTRASAT) may provide further insights into these emissions and their effects on exoplanetary atmospheres.
ULTRASAT aims to observe over 100,000 flaring and variable stars in the near-UV range. It will help scientists understand the frequency and intensity of UV flares, shedding light on their potential to impact planetary atmospheres. The Monitoring Activity from Nearby Stars with UV Imaging and Spectroscopy (MANTIS) mission will complement these observations by providing detailed UV spectra of cool stars, helping to differentiate between line and continuum emission during flares.
“Combining modern computer power with gigabytes of decades-old observations allowed us to search for flares on thousands of nearby stars,” noted Michael Tucker, a PhD graduate of IfA and now a postdoctoral fellow at Ohio State University. This approach underscores the importance of revisiting and reanalyzing archival data with new tools and perspectives.
Understanding these dynamics is crucial for accurate assessments of exoplanet habitability and the search for life beyond our solar system. The findings highlight the complex interplay between stellar activity and planetary environments, suggesting that planets around red dwarf stars face significant challenges in maintaining atmospheres conducive to life.
As of now, astronomers have identified over 5,000 exoplanets, encompassing a wide variety of types, including gas giants, rocky planets, and ice worlds. Many of these exoplanets orbit red dwarf stars, making the study’s findings particularly relevant. The potential impacts of UV radiation are critical for assessing the habitability of these diverse worlds, emphasizing the need for ongoing research.
For more details, read the full study in the Monthly Notices of the Royal Astronomical Society here.
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