Planet killer: Life on Earth-like planets could be wiped out by supernovae from distant stars

Life on Earth-like planets could be obliterated if distant stars explode, according to new research. Astronomers, utilizing data from NASA’s Chandra X-ray Observatory and other telescopes, have discovered a new threat to life on planets similar to our own.

The study reveals a phase during which intense X-rays emitted by exploded stars can impact planets over 100 light-years away. According to scientists, this discovery carries implications for the examination of exoplanets and their habitability.

NASA explains, “This newly found threat originates from a supernova’s blast wave striking dense gas surrounding the exploded star. When this impact occurs, it can produce a large dose of X-rays that reaches an Earth-like planet months to years after the explosion and may persist for decades. Such intense exposure may trigger an extinction event on the planet.”

Radiation can impact the health of faraway planets

The study, which reports this threat, is based on X-ray observations of 31 supernovae and their aftermath—primarily from NASA’s Chandra X-ray Observatory, Swift and NuSTAR missions, and ESA’s XMM-Newton. The findings indicate that planets can be subjected to lethal doses of radiation from sources as far as 160 light-years away.

Four of the supernovae in the study (SN 1979C, SN 1987A, SN 2010jl, and SN 1994I) are featured in composite images containing Chandra data in the supplemental image.

Prior to this discovery, NASA states that most research on the effects of supernova explosions had centered on the danger from two periods: the intense radiation produced by a supernova in the days and months following the explosion, and the energetic particles that arrive hundreds to thousands of years later.

The space agency asserts, “If a torrent of X-rays sweeps over a nearby planet, the radiation could severely alter the planet’s atmospheric chemistry. For an Earth-like planet, this process could wipe out a significant portion of ozone, which ultimately protects life from the dangerous ultraviolet radiation of its host star. It could also lead to the demise of a wide range of organisms, particularly marine ones at the foundation of the food chain, resulting in an extinction event.”

Illustration of an Earth-like planet before and after radiation exposure.
Illustration of an Earth-like planet before and after radiation exposure. (Credits: NASA/CXC/M. Weiss)

Could this happen to Earth?

After years of lethal X-ray exposure from the supernova’s interaction, and the impact of ultraviolet radiation from an Earth-like planet’s host star, a large amount of nitrogen dioxide may be produced, causing a brown haze in the atmosphere, as illustrated. A “de-greening” of land masses could also occur due to damage to plants.

Although Earth and the Solar System are currently in a safe location concerning potential supernova explosions, many other planets in the Milky Way are not. These high-energy events would effectively reduce the areas within the Milky Way galaxy, known as the Galactic Habitable Zone, where conditions are favorable for life as we know it.

Given the sparse X-ray observations of supernovae, particularly of the variety that strongly interact with their surroundings, the authors advocate for follow-up observations of interacting supernovae for months and years after the explosion.

The paper describing these results was published in the April 20, 2023 issue of The Astrophysical Journal. Other authors of the paper include Ian Brunton, Connor O’Mahoney, and Brian Fields (University of Illinois at Urbana-Champaign), Adrian Melott (University of Kansas), and Brian Thomas (Washburn University in Kansas).

What is the Chandra X-Ray Observatory?

NASA’s Chandra X-ray Observatory is a space-based observatory launched on July 23, 1999. It is part of NASA’s Great Observatories program, which also includes the Hubble Space Telescope, the Compton Gamma Ray Observatory, and the Spitzer Space Telescope. Chandra is designed to detect and observe X-ray emissions from extremely hot regions of the universe, such as exploded stars, clusters of galaxies, and matter around black holes.

The Chandra Observatory has significantly contributed to our understanding of the universe by providing high-resolution X-ray images and spectra, enabling scientists to study phenomena that would otherwise be invisible or difficult to observe. Some of its key discoveries include insights into dark matter, black holes, supernovae, and the large-scale structure of the universe.

Chandra is named after the Indian-American astrophysicist Subrahmanyan Chandrasekhar, who made significant contributions to the field of astrophysics, including the study of stellar evolution, white dwarfs, and black holes. His work on the maximum mass of a stable white dwarf, known as the Chandrasekhar limit, earned him the Nobel Prize in Physics in 1983.

South West News Service writer Dean Murray contributed to this report.

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