Astronomers find water vapour in the atmosphere of a potentially habitable world 100 light years away. Signs of life?


The news: Astronomers have found water vapor and helium in the surrounding atmosphere of an alien planet 100 light-years away.  These findings heat up our search for extra-terrestrial life outside the solar system.

Some vocabulary:

Planets outside the solar system that orbit around a host star are called exoplanets.

Super-Earths are exoplanets with a mass greater than that of Earth’s but not greater than Neptune’s.

One light-year is the distance light travels in a year i.e. approximately 10 trillion km.

Photo Credit: Alex Boersma

What do we know about exoplanet K2-18b?

It was discovered in 2015 by NASA’s Kepler spacecraft. This Super-Earth is twice the size but more than 8 times the mass of Planet Earth. It’s about 100 light-years from our solar system. That’s very far!  It takes the sun’s rays 100 years to reach the planet!

This exoplanet is unique because it orbits a sweet spot around its dim star known as the habitable zone where temperatures are just right for liquid water to exist on a planet’s surface.

That means this planet checks some of the important criteria in an astronomer’s laundry list of what’s necessary to support life.

The context: Since the first discovery of exoplanets more than 20 years ago, astronomers have recorded more than 4,000 exoplanets of all types and sizes. Though researchers have found the water vapor molecule around some of these exoplanets before, none of them have been suitable places for life to exist. They have been large balls of gas, similar in size to Jupiter or Neptune, lacking any type of surface for life as we know to exist.

How did they discover it? The team used data from NASA’s Hubble Space Telescope from 2016-2017. They observed how starlight changed as the planet passed in front of it. When the starlight passes through gas molecules, it gets minutely distorted. The type of distortion shows the molecules that are present. Researchers have also run rough models on a limited data set that indicate that the exoplanet might enjoy similar temperatures to that of Earth.

The significance: Thus K2-18b is the only planet right now outside the solar system that has the correct temperature to support water, it has an atmosphere, and it has water in it.  The planet can possibly host life! But this data now raises more important questions.

What don’t we know? Still, there’s quite a lot we don’t know about this planet such as the other chemicals and molecules in the atmosphere and the composition of its surface. The atmosphere that surrounds the exoplanet can tell us a lot about what might be hiding on the surface of the alien world.

Some astronomers doubt there can be life. They believe the size and mass of the exoplanet suggest that the surface isn’t rocky. They believe it could have a rocky ice core and a thick gaseous atmosphere like Neptune.

The exoplanet lies too far away to send a spacecraft but there are many powerful telescopes set to launch in the years ahead that will help answer these questions. Especially, NASA’s upcoming James Webb Space Telescope which launches in 2021.

Next Steps:  So while today’s findings are big, the search is still on for the top prize of all: a rocky exoplanet with water in its atmosphere with habitable temperatures!

Note: Two separate research teams have announced the discovery of water vapour on the exoplanet K2-18b

  1. A study has been published  in Nature Astronomy by a group of researchers from University College London
  2. A Study has been submitted by Björn Benneke, a professor of astronomy at the University of Montreal and the lead author to the Astronomical Journal. It has yet to be reviewed.
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