Extraterrestrials, if they existed, would probably inhabit rocky planets like ours, but new research proposes a completely new type of habitable world, which barely resembles Earth.
Earth it is the only functional model we have of a habitable world. It therefore makes sense for astrobiologists to hope to find evidence of extraterrestrials on Earth-like rocky exoplanets. In fact, they have the size of our planet, its chemical composition, temperature and its position in the solar system made her a friend of life, at least life as we know it.
But as a novelty research published in The Astrophysical Journal suggests that a whole new kind of planet, called Hicean worlds, could also be habitable. This type of planet does not exist in our solar system, but they are actually quite abundant in the galaxy. These are basically what you might expect if Earth and Neptune had a baby: Hicean planets are large and very warm, have atmospheres full of hydrogen, and are covered in a huge ocean all over the planet.
The new article theorizes that the Hicea planets are potentially habitable and that microbial life, or even more complex life forms, can exist within their oceans. In addition, researchers, led by Nikku Madhusudhan of the Cambridge Institute for Astronomy, proposed a set of biosignatures that astronomers should look for when studying these worlds, along with a list of promising nearby Hycean candidates (cosmologically speaking). .
Madhusudhan coined the term Hycean and is a portmalots of the words hydrogen and ocean, as he explained to me in an email. The astronomer came up with the idea student a potentially habitable mini-Neptune known as K2-18b. Intrigued by the conditions of this exoplanet, Madhusudhan and colleagues began more comprehensive research to explore the habitable potential of mini-Neptunes in general, or at least a specific subtype of mini-Neptunes.
G / O Media may receive a commission
Thousands of exoplanets have been detected since the 1990s; the vast majority of them are low-mass planets between one and four times the size of the Earth. For the new study, the researchers focused on the mini-Neptunes, which are (obviously) smaller than Neptune. but about 1.6 times the size of the Earth.
“These objects are smaller than ice giants, but too large to have predominantly rocky interiors like superterranes,” according to the study. “Past explorations of mini-Neptune interiors have found that in some cases the pressure and temperature under the [hydrogen]-I laugh [atmosphere] it would be too high to allow for habitability, “but” temperate mini-Neptunes with the right properties can allow habitable conditions in their interiors. “
The proposed new class of habitable exoplanet can be up to 2.6 times the size of Earth, with atmospheric temperatures of 392 degrees Fahrenheit (200 degrees Celsius). When asked what characteristics of the Hyceae worlds are susceptible to habitability, Madhusudhan said that the presence of liquid water, “Since the surface would be covered with ocean,” the presence of air pressure and Earth-like temperatures on the ocean surface i the hydrogen-rich atmosphere, which provides “both the required surface conditions and protection against harmful radiation.”
Hicean worlds can exist around an assortment of star types, Madhusudhan dit. He believes that a locked hycea exoplanet has the potential to be habitable, though one side never faces its host star (researchers refer to these exoplanets as dark Hycean worlds, which seems so science fiction). These exoplanets have the chemical properties needed to generate and maintain microbial life, Madhusudhan said Hicean planets should have “a lot of water, radiation and basic molecules in the atmosphere,” but “beyond that,” possible chemistry is an open question right now. “
The depth at which life could exist in the Pacific oceans depends on particular surface conditions, but researchers suspect that, in some cases, life could exist deeper than The ocean floor of the Earth. This life, if it existed, would probably be of a microbial nature, and Madhusudhan said it is an “open question” about whether a more complex life could evolve in this exotic environment. Possible barriers to habitability would be excessive ultraviolet radiation or a “lack of nutrients needed to form or sustain life,” he added.
One fortuitous thing about the Hycean worlds is that they exist within a more expansive habitable zone than we are used to. Also known as the Goldilocks area, it is the band within a stellar system within which liquid water may exist on the surface.
“A hiccup world can be very far from the star with little radiation and still be habitable,” Madhusudhan explained. “Similarly, the planet may be a little closer to the star than an Earth-like planet and still be habitable. This is due to the hthe hydrogen-rich atmospheric composition of the Hycean worlds and the fact that their surface temperatures can be significantly higher than those of Earth-like planets. ”
The new article will be of interest to astrobiologists. Hicean worlds are very common in the Milky Way, meaning that habitable exoplanets could be much more numerous than previously thought. The researchers also provided a list of biosignature traces that scientists should look for when observing these exoplanets, including oxygen, ozone, methane and nitrous oxide, as well as unusual gases, such as methyl chloride and dimethylsulfide, which are not indicative of life on Earth. but it could possibly signal of life in the Hycean worlds.
The team identified 11 candidate Hicean worlds orbiting nearby stars, all red dwarfs, that are considered promising targets for biosignature searches. The most promising is K2-18b, “for which we already have observations planned with the James Webb Space Telescope,” Madhusudhan said.
In fact, the James Webb Space Telescope (JWST), with its spectroscopic capabilities, will be a perfect tool for investigating K2-18b and other mini-Neptunes considered hiceans. The next-generation telescope is expected to be launched later this year, after many years of delay.
The most interesting thing about the hypothesis proposed in this article is that it can be tested. If spectroscopic explorations of the Hycean worlds produced zero trace of the proposed biosignatures, it is likely to be a sign that these exoplanets are inhospitable and dead worlds. But if these biosignatures appear in our observations, this would be a completely different story and a tempting result.