Scientists Think They've Narrowed Down The Star Systems Most Likely to Host Life

We will need to be more selective when choosing the targets for our search for indications of life because the number of verified exoplanets in the Milky Way is increasing.

The possibilities have been reduced by a group of astronomers led by Anna Shapiro of the Max Planck Institute for Solar System Studies in Germany.

A recent research suggests that Earth-like exoplanets with relatively little metal content that orbit Sun-like stars are more likely to be shielded from damaging UV radiation that poses a risk of genetic damage to life.

Since that stars with a lower metal composition radiate more ultraviolet radiation, this may appear counterintuitive. Yet, the team's research demonstrates that an oxygen-rich planet has a stronger ozone layer than one with a metal-rich host, providing a world orbiting a metal-poor star with more protection.

Our results suggest that the ideal places to look for sophisticated life on land are planets inhabited by stars with low metallicity, the authors wrote in their study.

Not every star is made equally. They might be little, chilly, and gloomy or big, blazing, and scorching. Even while they share certain fundamental components, their chemical make-up might differ greatly.

This is due to the absence of heavy elements at the beginning of the universe's history. There was essentially only hydrogen and helium; from these components, the earliest stars were formed, their centers being enormous motors that crashed smaller, lighter atoms together.

These stars' violent deaths produced even heavier elements, which were then ejected and seeded into space where they were absorbed by newborn stars formed from clouds of interstellar dust and gas.

The star's radiation emission is altered by these components. Higher metallicity, or stars with more elements heavier than hydrogen and helium, produce less ultraviolet radiation than stars formed of lighter materials. And because humans have spent our whole lives on Earth, we are aware that UV radiation may damage DNA in many ways in sensitive land-dwelling species.

Shapiro and her coworkers looked at how UV irradiation would affect whether or not an alien world might support life by using Earth as a model.

It's possible that an extraterrestrial civilisation observing the Solar System from a considerable distance might find Earth to be uninhabitable. According to the researchers, UV-C and UV-B radiation levels are "far over the maximum tolerated range for terrestrial life" at our present distance from the Sun.

Yet most of it is blocked by our atmosphere, which has layers of oxygen (O2) in the upper atmosphere, which absorbs most UV-C, and ozone (O3) in the center, which absorbs UV-B.

Ozone is produced and destroyed by ultraviolet light. O2 molecules can be fragmented at wavelengths below 240 nanometers, at which point floating O atoms may meet and bond with O2 molecules to create O3. Yet longer wavelengths cause the O3 to dissociate by photodissociation. Then, the produced O atoms might unite again to form O2.

The metallicity and temperature of a star, along with other parameters, all affect the UV radiation of that star. Shapiro and her colleagues created computer models of planets similar to Earth orbiting stars similar to the Sun, adjusting the settings to determine how UV radiation would affect the orbiting exoplanet.

They discovered that, contrary to what may be expected, metallicity has a greater impact on the habitability of the exoplanet than temperature. The likelihood of habitable planets was higher for stars with lower metallicities and higher UV radiation.

That's because less UV light reached the exoplanet's surface as a result of how the UV radiation interacted with the oxygen in the atmosphere, which improved the shield.

The associated stellar radiative spectrum in oxygenated planetary atmospheres allows less O3 formation, which enhances UV penetration, making the conditions on planets orbiting these stars less hospitable for the biosphere on land. This is paradoxical because higher metallicity stars, which have emerged later in the history of the Universe, emit less UV radiation.

"Therefore, we discover that the UV radiation exposure on the surfaces of planets around metal-rich stars is greater than that on planets orbiting metal-poor stars. The greatest places to look for complicated life on earth are planets in the habitable zones of stars with low metallicities.

It's not sufficient to completely rule out stars with greater metallicities just yet. Yet the classification and study of exoplanet atmospheres using tools like the James Webb Space Telescope will assist researchers in determining whether their discoveries are on the correct track, putting us a small bit closer to discovering evidence of life on an extraterrestrial planet.

The research has been published in Nature Communications.