It has rain, water, clouds: so, maybe life too!

Wet, cold and bare: how one scientist unflatteringly described K2-18b yesterday.

What a wonderful find — but does it have any point? Astronomers are thrilled by yesterday’s announcement about a habitable planet. The bad news: it would take two million years to get there.

The extreme gravity would make walking impossible, and the sunlight is so fierce that, for a human, developing cancer would be inevitable.

Yet planet K2-18b, which lies 110 light-years away in the constellation Leo, is the first world ever to be discovered which could realistically support alien life.

Scientists have detected water vapour for the first time in the atmosphere of a planet beyond our solar system, where the temperature is in a survivable range.

“Finding water in a potentially habitable world other than Earth is incredibly exciting,” said Angelos Tsiaras of University College London, where a team of astronomers made the discovery by analysing data from the Hubble Space Telescope. “This planet satisfies more requirements for habitability than any other we know about now.”

The exoplanet orbits a red dwarf star. It is in what is known as the super-Earth category, with a mass eight times that of our home planet and twice its diameter.

Life could, in theory, have evolved on K2-18b, given the existence of water and tolerable temperatures for biological molecules.

The planet is closer to its star than Earth is to the Sun, orbiting once every 33 days. But the star is smaller and cooler than the Sun, giving it surface temperature similar to Earth.

But any organisms there would not look like terrestrial life because they would have to tolerate the planet’s stronger gravity, and the likelihood of higher levels of radiation from its parent star than Earth receives from our Sun.

The search for exoplanets around stars beyond the solar system began just 25 years ago. Since then, about 4,000 have been detected: a minute fraction of the 100 billion planets that our galaxy is thought to contain.

The technology is only just reaching the point at which scientists can deduce something about characteristics of distant planets beyond their mere existence.

But it will soon be hugely improved by scientific advances, including Hubble’s successor, the James Webb space telescope due to go operational in 2021, and the European Space Agency’s Ariel mission, a specialised planet-hunting observatory, scheduled for launch in 2028.

Long shot

This is all very interesting but of absolutely no relevance to us at all, according to one argument. Using current rocket technology, it would take two million years to get to K2-18b. It is pointless to dream about space colonies there. The most this discovery does is to keep lots of astronomers happy and fuel a few more sci-fi novels.

“Entirely missing the point,” goes the opposing view. Can’t you see that if you find just one place where life could exist, then there will be others? Since the universe is so great and its size so vast — with hundreds of billions of stars in the Milky Way alone — then, unless the Earth is astonishingly special, the universe should be teeming with life. The only question is where are they all?.

You Decide

  1. Do you think there is alien life in the universe?
  2. Should publicly-funded science always be useful?


  1. Using this article and the Expert Link to our Briefing on Exoplanets, draw an infographic of fascinating facts about the universe.
  2. You have been instantly teleported to K2-18b — wearing just the clothes you’re standing in. It is awfully damp and chilly. The gravity is huge. You have 30 minutes to write a letter home. Write it now!

Some People Say...

“To my mathematical brain, the numbers alone make thinking about aliens perfectly rational.”

Stephen Hawking, (1942-2018), Professor of Mathematics

What do you think?

Q & A

What do we know?
K2-18b (also known as EPIC 201912552 b) is an exoplanet orbiting the red dwarf star K2-18, located about 111 light-years away from Earth. The planet, initially discovered through the Kepler Space Observatory, was later determined to be about eight times the mass of Earth, with a 33-day orbit within the star’s habitable zone.
What do we not know?
What it is like to be there. The planet could be tidally locked, always showing one face to the red dwarf, just as Earth’s moon always shows us its near side. If that’s the case, then K2-18 b would have a ‘day side’ and a ‘night side’, with a strip of permanent twilight separating the two. It could be completely flooded, for instance, or a world with lakes and oceans, but lots of exposed land, study team members said. If most of the exoplanet is solid rock and ice, a visitor to the planet’s surface would feel 37% heavier than they felt on Earth.

Word Watch

The distance that light travels in a vacuum in one year.
Hubble Space Telescope
A space telescope that was launched into low Earth orbit in 1990, and remains in operation. It was not the first space telescope, but it is one of the largest and most versatile.
A planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917, but was not recognised as such. The first confirmation of detection occurred in 1992.
Red dwarf star
The most common type of star in the Milky Way, it is the smallest with the coolest surface temperature.
James Webb
The James Webb Space Telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.


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