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Water has been found on a distant super-Earth known as K2-18b

Alle McMahon with AP, September 12, 2019 6:45PM news.com.au

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Artist's impression of K2-18b super-Earth, the only super-Earth exoplanet known to host both water and temperatures that could support life. Picture: AFP/ESA/Hubble/M.Kornmesser media_cameraArtist's impression of K2-18b super-Earth, the only super-Earth exoplanet known to host both water and temperatures that could support life. Picture: AFP/ESA/Hubble/M.Kornmesser

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Scientists have discovered water on a distant super-Earth known as K2-18b, which has temperatures suitable for life.

It is the first time water vapour has been detected in the atmosphere of a super-Earth, which means a planet bigger than Earth but not as big as a gas giant.

K2-18b is 110 light years away in the constellation Leo. A light-year is a distance equal to how far light can travel in one year. One light-year is about 9.5 trillion kilometres, which is a very long way.

The exoplanet* is in its star’s Goldilocks zone — not too hot and not too cold but just the right distance from the star to possibly have life.

K2-18b orbits in the ‘habitable zone’ of the K2-18 star. Picture: Supplied media_cameraK2-18b orbits in the “Goldilocks” zone of the K2-18 star. Picture: supplied

It’s the only exoplanet known to have both water and temperatures needed for life, the team from University College London, UK reported in the journal Nature Astronomy this week.

Unfortunately, it’s unlikely to ever become a second home for humans, the study’s author, Dr Angelos Tsiaras, said.

“K2-18b is now the best candidate for habitability* that we know. It’s the only planet outside our solar system that we know has the correct temperatures, atmosphere and water,” the University of London (UCL) research associate said.

“At the same time, K2-18b is not a second Earth. This is a planet that is much bigger. It has a different atmospheric composition* and it’s orbiting a completely different star.

“The search for habitable planets is very exciting, but it’s here to always remind us that this is our only home. And it’s probably out of the question whether we’ll ever be able to travel to other planets,” he said.

Nonetheless, Tsiaras said K2-18b could help us know: “Is the Earth unique?”

A Canadian-led team announced similar findings this week.

In a paper just submitted to the Astronomical Journal for publication, these scientists suggest it might even be raining there.

“This represents the biggest step yet taken toward our ultimate goal of finding life on other planets, of proving that we are not alone,” the study’s lead astronomer, Bjorn Benneke of the University of Montreal, Canada, said in a statement.

Water found on exoplanet K2-18b

MEET K2-18b
This exoplanet is twice as big as Earth, with eight times the mass*.

It is a super-Earth, which is a name for a planet that has a mass greater than Earth but less than gas giants such as Uranus and Neptune. There are 1260 known super-Earths.

K2-18b takes 33 days to orbit its star, so one year there is one month here. At this distance from its star, temperatures range from minus 73C to 47C.

Water has been identified in the atmospheres of hot gas giants circling other stars but this is the first time water vapour has been detected in a type of exoplanet other than a gas giant.

K2-18b is thought to be rocky and no one knows whether water is flowing on the surface.

It was discovered in 2015 by NASA’s Kepler Space Telescope.

Its star is a red dwarf and is a lot smaller than our Sun, which is a yellow dwarf.

The exoplanet is twice the size of Earth and orbiting a small red dwarf star. Picture: The Sun media_cameraK2-18b is twice the size of Earth and was found by the Kepler Space Telescope. The New Horizon Probe, launched in 2006, is travelling at 57,936 kmh (36,000 mph) and would take 2.2 million light years to reach it. Picture: The Sun

The star, glowing red in the day sky, is believed to bombard the planet with radiation* harsh enough to quickly cause cancer in human visitors, although “life there may have evolved differently” in order to survive, noted the London team’s Ingo Waldmann.

Given K2-18b’s mass, it would have more gravity than Earth and it would be difficult to walk on the surface.

“Maybe not quite your vacation destination just yet,” Waldmann joked.

Both research teams studied information captured by the Hubble Space Telescope and other spacecraft.

media_cameraHubble Space Telescope. Picture: NASA

MORE TO KNOW
Scientists will learn more about K2-18b by using information collected in the future from NASA’s James Webb Space Telescope and the European Space Agency’s Ariel, which are both due to launch in the 2020s.

Future telescopes on Earth and in space could help us discover more super-Earths orbiting red dwarf stars.

Red dwarf stars are believed to be the most common planets and stars in our Milky Way galaxy.

Illustration of some of the watery exoplanets outside of the Solar System in comparison to Earth, located at the very end. Picture: The Sun media_cameraIllustration of some of the watery exoplanets outside of the Solar System in comparison to Earth, located at the very end. Picture: The Sun

GLOSSARY

  • exoplanet: planet outside our Solar System
  • habitability: whether anything can live there
  • composition: what it is made of
  • mass: how much of something there is, measured in kilograms
  • radiation: waves of energy coming from the star. Examples of radiation are X-rays, ultraviolet (UV) light or visible light

EXTRA READING

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QUICK QUIZ

  1. What is a light-year?
  2. What are the Canadian scientists suggesting about the weather on this planet?
  3. How long is a year on K2-18b? Why is that the length of its year?
  4. What would K2-18b’s gravity be like? Why?
  5. What is launching in the next few years that will help us know more about K2-18b?

LISTEN TO THIS STORY

CLASSROOM ACTIVITIES
1. Similarities and Differences

Draw a Venn Diagram (two large overlapping circles) to note down the similarities and differences between K2-18b and Earth.

In one circle write things unique to Earth (eg. life is known to exist here), in the other circle write things unique to K2-18b (eg. Red glow in the day sky). In the overlapping section write things that are similar to both (eg. have gravity)

Why are scientists not looking at this planet as a second home for humans? Write some reasons why it is not likely to be a viable option for humans to move there?

Time: allow 20 minutes to complete this activity
Curriculum Links: English, Science

2. Extension
Use the information that is known about K2-18b and your imagination to draw an artist’s impression of what you think a day on this planet might look like. Include a caption, that tells your audience what the conditions are like when you’ve created your picture (Is it morning or later in the day? Is it in a cold climate, or a warmer one? Would there be seasons like Earth?)

If you think there is life on K2-18b, what might it be like? How might life have evolved on the planet to suit the conditions?

Time: allow 20 minutes to complete this activity
Curriculum Links: English, Science, The Arts – Visual Arts

VCOP ACTIVITY
With a partner see if you can identify all the doing words/verbs in this text. Highlight them in yellow and then make a list of them all down your page. Now see if you and your partner can come up with a synonym for the chosen verb. Make sure it still makes sense in the context it was taken from.

Try to replace some of the original verbs with your synonyms and discuss if any are better and why.

HAVE YOUR SAY: Is it important to you that we looks for planets where there could be life? If so, why? If not, why not? What is more important to you?
No one-word answers. Use full sentences to explain your thinking. No comments will be published until approved by editors.

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