A planet just 124 light-years from Earth may be teeming with life as you read these words.
Astronomers have done an in-depth analysis of the properties of a medium-weight exoplanet (between Earth and Neptune) and found that it may contain life. The discovery expands the range of planets that astronomers can include on their lists of searches for extraterrestrial life.
The planet in question is called K2-18b. Perhaps you are familiar with it – this is because last year, astronomers discovered water vapor in its atmosphere. However, at the time, the potential for livability was unclear.
It orbits the red dwarf star K2-18, in the middle of the habitable zone – not hot enough for liquid water to evaporate from the surface, and not cold enough to freeze completely. But habitability requires more than just being at the right distance; Mars is a great example of this.
Astronomers also tend to believe that rockiness – a planet like Earth, Venus, Mars, and Mercury – is a prerequisite for habitability. 2.6 times larger and 8.6 times heavier than Earth, K2-18b looks more like a mini-Neptune than a rocky planet.
“Water vapor has been detected in the atmosphere of a number of exoplanets, but even if the planet is in the habitable zone, that does not necessarily mean habitable conditions on the surface,” said astronomer Nikku Madhusudhan of the University of Cambridge.
“In order to establish the prospects for habitability, it is important to obtain a common understanding of the internal and atmospheric conditions on the planet – in particular, whether liquid water can exist under the atmosphere.”
And here's the thing. Even a mini-Neptune in the habitable zone could potentially support life, new analysis suggests.
Astronomers have found that the atmosphere is rich in hydrogen: 0.02 to 14.8% water (in Earth's atmosphere, 0 to 5% water). Small amounts of methane and ammonia have also been identified that can be produced by both biological and non-biological processes. Researchers believe that this cannot be ruled out at this stage.
This information was then applied to a wide variety of planetary models to find out which best fit the data. And they found that the maximum amount of hydrogen that could explain the observed properties of the planet was about 6 percent of its mass, although there was much less hydrogen in most solutions.
The minimum amount of hydrogen was about one millionth of the planet's mass – similar to the proportions found on Earth. And some of the scenarios assumed a liquid ocean.
This is not conclusive evidence that K2-18b is definitely habitable. This means that we must not limit our search for habitable worlds to rocky habitable planets.
“Future observations, such as with the James Webb Space Telescope, may improve our results,” the researchers write in their paper.
“We argue that planets like K2-18b may indeed have the potential to approach habitable conditions, and the search for biosignatures need not be limited to rocky planets.”
The study was published in the Astrophysical Journal Letters.
Sources: Photo: Amanda Smith
