Jupiter's Icy Moon Europa Has Water Vapour, But In One Hemisphere, NASA Hubble Finds Proof

NASA's Hubble Space Telescope has observed the presence of persistent water vapour in the trailing hemisphere of Jupiter's icy moon, Europa

A photograph of Jupiter's icy moon Europa taken in June 1997 by NASA's Galileo spacecraft | Photo NASA

New Delhi: Jupiter's icy moon Europa has the presence of persistent water vapour, NASA's Hubble Space Telescope has found. However, surprisingly, the evidence of this was found only in one hemisphere.

Europa has an icy surface, underneath which a vast ocean flows. The ocean may provide conditions favourable to support life. This observation is of utmost importance because astronomers now better understand the atmosphere of icy moons. 

Also, future missions can be sent to the Jovian system, which is half-a-billion miles away from the Sun, to explore whether an environment located so far away from the Sun is suitable to support life.

The results of the study were recently published in the Geophysical Research Letters journal.

Previous Observations Of Water Vapour On Europa

Hubble had photographed plumes erupting through the ice on Europa on 2013. These observations of water vapour are analogous to geysers on Earth, according to NASA. However, the plumes were observed to extend higher than 60 miles. The pressure exerted by the transient blobs of water vapour in Europa's atmosphere is just one-billionth the surface pressure of Earth's atmosphere.

How Is The New Discovery Different?

Hubble observations made from 1999 to 2015 have shown water vapour on Europa, but the new results reveal that water vapour is spread over a larger area than before. This is indicative of the fact that water vapour has been persistent in Europa for a long time. The portion of Europa, which is always opposite its direction of motion along its orbit is the moon's trailing hemisphere, and it is in this hemisphere that water vapour has been observed. Scientists do not understand yet the reason behind this asymmetry between the leading and trailing hemispheres.

Recently, Lorenz Roth of the KTH Royal Institute of Technical, Space and Plasma Physics, Sweden, had used a technique which led to the discovery of water vapour in Ganymede, another moon of Jupiter. When the technique was used to analyse Hubble archival images and spectra, the new discovery in Europa's atmosphere was made.

Roth said there is an increased understanding of the atmospheres of icy moons due to the observations of water vapour on Ganymede and on the trailing hemisphere of Europa, according to a statement by NASA. However, he added, a stable water abundance on Europa is more intriguing because Europa has a lower surface temperature than Ganymede. The lower surface temperature is likely to condense the water vapour.

The temperature on Europa does on exceed -260°F. The surface of Europa is 60 degrees Fahrenheit cooler than Ganymede because the former reflects more sunlight than the latter. Another reason why the new observations are surprising is that the water ice directly transforms from solid to vapour without converting into a liquid phase, despite the low temperatures. This phenomenon is known as sublimation, and has been observed on Europa as well as Ganymede.

How Was The Study Conducted?

Roth selected ultraviolet observations of Europa from the archival Hubble datasets, for the years, 1999, 2012, 2014, and 2015, while the moon was at different orbital positions. Hubble's Space Telescope Imaging Spectrograph (STIS) was used to make these observations. Oxygen is one of the constituents of water, and using the ultraviolet SITS observations, Roth determined the abundance of oxygen in Europa's atmosphere. He inferred the presence of water vapour by interpreting the emission strengths at different wavelengths.

Why Is The Discovery Important?

The discovery is important because this will help future probes conduct more extensive research of Europa. NASA's Europa Clipper and European Space Agency's Jupiter Icy Moons Explorer mission are some examples of such probes. Astronomers can also get clues about Jupiter-like planets around other stars in the Milky Way Galaxy with proper understanding of the formation and evolution of Jupiter and its moons.