In a major first, scientists have detected water vapor and possibly even liquid water clouds that rain in the atmosphere of a strange exoplanet
In a major first, scientists have detected water vapor and possibly even liquid water clouds that rain in the atmosphere of a strange exoplanet that lies in the habitable zone of its host star.
"This is the only planet right now that we know outside the solar system that has the correct temperature to support water, it has an atmosphere, and it has water in it, making this planet the best candidate for habitability that we know right now" said lead author Angelos Tsiaras, an astronomer at University College London
The new study focuses on K2-18 b, an exoplanet discovered in 2015 and orbits a red dwarf star close enough to receive about the same amount of radiation from its star as Earth does from our sun.
Planet K2-18 b sits some 110 light years away in the constellation Leo, and it orbits a rather small red dwarf star that's roughly one-third the mass of our own Sun. Red dwarfs are infamous for being active stars that emit powerful flares, but the researchers point out that this particular star appears to be surprisingly docile.
This bodes well for the water-bearing planet, as its 33-day orbit brings it about twice as close to its star as Mercury is to the Sun. "Given that the star is much cooler than the Sun, in the end, the planet is receiving similar radiation to the Earth," said Tsiaras. "And based on calculations, the temperature of the planet is also similar to the temperature of the Earth."
Today’s technology is too feeble to take photos of the surfaces of such distant worlds, and they are too far away to send probes to. But space-based telescopes can glean some information about the atmospheres on alien planets.
The UCL team turned to Nasa’s veteran Hubble space telescope, which observed K2-18b in the two years after its discovery. In particular, they analysed measurements of starlight from the red dwarf as the planet wandered across its face on eight separate occasions.The data revealed that as K2-18b crossed in front of its star, wavelengths of light that are absorbed by water suddenly dropped off, and then rose again as the planet moved on. The effect is seen as a smoking gun for water vapour in the planet’s atmosphere.
Don't go booking a ticket to K2-18b just yet.
The newly discovered exoplanet, described as being the closest thing to a new Earth found so far, is unlikely to welcome refugees from our wrecked homeworld.
"If you're standing on the planet, you'll probably be crushed," according to astrobiologist Kathy Campbell
At twice the width and eight times the mass of Earth, the gravity on K2-18b would make us all weigh twice as much and our bodies are just not equipped to deal with that.
There's also a good chance it doesn't have a surface to stand on.
The team plans to expand this research even further by studying K2-18 b with NASA's James Webb Space Telescope, which is set to launch in 2021 but until then, we have to make do with the planet we already have.
https://www.nature.com/articles/s41550-019-0878-9
https://arxiv.org/abs/1909.04642
Phedias Hadjicharalambous
Cyprus Astronomy Organisation
