Astronomers using data from NASA’s Chandra X-ray Observatory and other telescopes have identified a new threat to life on planets like Earth: a phase during which intense X-rays from exploded stars can affect planets over 100 light-years away. This result, as outlined in our latest press release, has implications for the study of exoplanets and their habitability.
This newly found threat comes from a supernova’s blast wave striking dense gas surrounding the exploded star, as depicted in the upper right of our artist’s impression. When this impact occurs it can produce a large dose of X-rays that reaches an Earth-like planet (shown in the lower left, illuminated by its host star out of view to the right) months to years after the explosion and may last for decades. Such intense exposure may trigger an extinction event on the planet.
A new study reporting this threat is based on X-ray observations of 31 supernovae and their aftermath — mostly from NASA’s Chandra X-ray Observatory, Swift and NuSTAR missions, and ESA’s XMM-Newton — show that planets can be subjected to lethal doses of radiation located as much as about 160 light-years away. Four of the supernovae in the study (SN 1979C, SN 1987A, SN 2010jl, and SN 1994I) are shown in composite images containing Chandra data in the supplemental image.
Prior to this, most research on the effects of supernova explosions had focused on the danger from two periods: the intense radiation produced by a supernova in the days and months after the explosion, and the energetic particles that arrive hundreds to thousands of years afterward.
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, especially marine ones at the foundation of the food chain, leading to an extinction event.
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 shown in the illustration. A “de-greening” of land masses could also occur because of damage to plants.
A separate artist’s impression (panel #1) depicts the same Earth-like planet as having been abundant with life at the time of the nearby supernova, years before most of the X-ray’s impacts are felt (panel #2).
Among the four supernovae in the set of images, SN 2010jl has produced the most X-rays. The authors estimate it to have delivered a lethal dose of X-rays for Earth-like planets less than about 100 light-years away.
There is strong evidence — including the detection in different locations around the globe of a radioactive type of iron — that supernovae occurred close to Earth between about 2 million and 8 million years ago. Researchers estimate these supernovae were between about 65 and 500 light-years away from Earth.
Although the Earth and the Solar System are currently in a safe space in terms of potential supernova explosions, many other planets in the Milky Way are not. These high-energy events would effectively shrink the areas within the Milky Way galaxy, known as the Galactic Habitable Zone, where conditions would be conducive for life as we know it.
Because the X-ray observations of supernovae are sparse, particularly of the variety that strongly interact with their surroundings, the authors urge follow-up observations of interacting supernovae for months and years after the explosion.
The paper describing this result appears in the April 20, 2023 issue of The Astrophysical Journal, and is available here. The other authors of the paper are 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).
NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
This release features a suite of images, including artist’s illustrations that tell the story of intense X-rays from exploded stars triggering extinction events on nearby planets.
In one illustration, labeled ‘View When Supernova Occurs’, a large Earth-like planet occupies the left half of the image. A brilliant, gleaming supernova appears in the distance at our upper right. Light from the planet’s host star, out of view to the right, illuminates the blue oceans and largely green landmasses on one side of the Earth-like planet. White clouds dot the planet’s thin atmosphere, but the colors beneath remain crisp and clear.
In a subsequent illustration, labeled ‘View Decades After Supernova Occurs’, the supernova at our upper right is now a smaller speck of light, encircled by a blast wave. The blast wave, which contains a lethal dose of X-rays, has a cottony white outer ring, and fiery orange inner ring. Both are streaked with fine lines emanating from the gleaming speck at the core. A fine blue haze surrounds the supernova and blast wave. On our left, the large Earth-like planet is no longer bright blue and green. The landmasses are now rendered in muted shades of brown and grey. Yellowed clouds dot the thin, hazy atmosphere, dulling the colors beneath, including the blues of the now murky oceans. These changes were caused by X-rays wiping out most of the planet’s ozone layer. This caused an increase in ultraviolet radiation reaching the planet’s surface and triggered an extinction event.
This illustration is the featured image in today’s release, and is presented with and without annotation.