Water found for first time on 'potentially habitable' planet



NASA points out that K2-18b is one of hundreds of previously discovered super-Earth exoplanets; it was identified by the Kepler Space Telescope back in 2015 and later observed by the Hubble Space Telescope.

Astronomer Jonti Horner of the University of Southern Queensland told ABC News that the discovery was the first step towards finding smaller Earth-like planets capable of supporting life. The lead researcher, Prof Giovanna Tinetti of University College London (UCL) depicted the disclosure as "mind-blowing".

Nonetheless, Tsiaras said K2-18b could help determine, "is the Earth unique?"

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.

Without a real surface, so to speak, landing on the planet would also be almost impossible to land on, especially because the gas is so thick and has such an incredibly high pressure that any Earth-created spacecraft sent there would be destroyed. The range is so large because of various unknown factors, including the temperature of the star and the distance between the star and the planet and the planet's atmosphere and pressure, which is why it's unclear if water exists on the surface.

They believe that other molecules including nitrogen and methane may be present but, with current observations, they remain undetectable. K2-18 b's parent star is quiescent by red dwarf standards, Waldmann said, but the star may still bathe the planet in higher quantities of damaging ultraviolet radiation than we're used to.

That's because this 33-day orbit is right smack-bang in the middle of the star's habitable zone - not too hot that liquid water would evaporate from the surface, and not so cold that it would totally freeze.

Data from the planet have been available for several years, but the UCL team developed specialist software to re-examine the wavelengths of light, looking for signs of water.

Meanwhile, Benneke and his team come down hard on the conclusion that K2-18b has clouds made of water-lots of them. Some super-Earths have turned out to be more like sub-Neptunes, with big gaseous envelopes, but this planet's average density is similar to the density of the Moon or Mars.

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In contrast, the proportion of water vapor in the planet's atmosphere varies between 0.2 percent over the rods and around four percent at the tropics.

This artist's concept shows two super-Earth exoplanets, K2-18 b and c, orbiting the red dwarf star K2-18.

Even when they did, many Earth-like planets are too far out of their celebrities to possess liquid water so near that any H2O has vanished.

Only K2-18b revealed the molecular signature of water, which is a vital ingredient for life on Earth. Additionally, it could have a hydrogen-rich atmosphere with just water all over.

The planet's temperatures fall within bounds for the existence of liquid water and this means there is a chance there may be carbon-based life.

"We're going to need more observations", she said. This puts K2-18 b near the upper limit of what we call a super-Earth - which typically refers to planets between about one and 10 Earth masses.

"Over 4,000 exoplanets have been detected but we don't know much about their composition and nature", said Tinetti.

The next generation of space telescopes, including the NASA/ESA/CSA James Webb Space Telescope and ESA's ARIEL mission, will be able to characterize atmospheres in more detail as they will carry more advanced instruments.

Prof David Charbonneau, also from Harvard University, said the fact that K2-18b's atmosphere was detected was proof in itself that it could not support life.

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