Discovery of water on a super-hot gas giant exoplanet – what it means

The James Webb Space Telescope has detected traces of water vapor in the atmosphere of a super-hot gas giant exoplanet. The planet orbits its star in about 23 hours per Earth day, and is ten times larger than Jupiter, the largest planet in our solar system. It is much closer to its star than the nearest planet to our sun, Mercury.

The exoplanet, named WASP-18b, is a gas giant and orbits its star at a distance of 1.9 million miles — whereas Mercury is 39.4 million miles away. This planet is 400 light years away from Earth. But what exactly is an exoplanet, and what does it mean to find traces of water vapor on a planet? Here’s what you need to know.

Simply put, planets outside our solar system are called exoplanets. The planets in our solar system revolve around our star, which we call the Sun. Exoplanets are very difficult to see directly with telescopes because they are often obscured by the glare of the stars they orbit.

One way scientists look for exoplanets is to look for 'pushing’ stars – which is actually a visual effect where a line around its center doesn’t go around its star, causing the star to wobble from a distance. However, this method, although popular, can only detect large planets. Another way is to launch spacecraft like Kepler.

Kepler uses the transit method, where when a planet passes in front of its star, it is called a

Transits and slightly blocks the star’s light. Astronomers can observe how the star’s brightness changes as it travels and, in turn, determine the planet’s size. By examining the time between transits, one can also find out how far the planet is from the star. WASP-18b was discovered by transit method.

WASP-18b was first discovered in 2009 and is a gas giant exoplanet orbiting an F-type star – a main-sequence star that converts hydrogen into helium. This star emits a white-blue light and is 6,000 to 7,000 Kelvin.

Scientists have detected water vapor in the atmosphere and created a temperature map of the planet, NASA said. The same side of WASP-18b, called dayside, always faces its star, just as the near side of the Moon always faces Earth. This means that WASP-18b is tidally locked, meaning that there is a significant difference in temperature on the planet’s surface.

Because of Webb’s measurements, scientists can now map these differences in detail, and because of its proximity, most water molecules are expected to break away.

This is stated in the report issued by NASA: „The spectrum of the planet’s atmosphere, despite extreme temperatures of nearly 5,000 degrees Fahrenheit (2,700 degrees Celsius), clearly shows several small but precisely measured water features that speak to Webb’s extraordinary sensitivity to detect remaining water.” By detecting vapors, scientists can trace a planet’s atmosphere, providing a clearer picture of how exoplanets form instead.