Astronomers may have detected water vapor in the atmosphere of Ganymede


Two Hubble Space Telescope observations in 1998 revealed oxygen in the moon's atmosphere.Image : NASA / ESA / L. Roth
Two Hubble Space Telescope observations in 1998 revealed oxygen in the moon's atmosphere.Image : NASA / ESA / L. Roth

Observations made 20 years apart by the Hubble Space Telescope suggest that water vapor is present in the atmosphere of Ganymede, Jupiter's icy moon. The findings make the icy moon an even more intriguing target in the search for extraterrestrial life.


The apparent detection of water vapor came after researchers compared two observations of Ganymede in 1998 with another round of observations made in 2018. An analysis determined that sublimated water in the atmosphere was the most likely culprit for a discrepancy found in the 1998 data. The team that made the 2018 observations has published their results in Nature Astronomy.


In 1998, Hubble's Space Telescope Imaging Spectrograph ( STIS ) took two ultraviolet images of Ganymede, which revealed bands in the moon's atmosphere similar to Earth's auroras, which would mean that the moon had a permanent magnetic field. There were slight differences in the ultraviolet observations taken by Hubble at the time, which were attributed to the presence of atomic oxygen in the atmosphere.


Those observations were followed in 2018 by ultraviolet observations of Ganymede using Hubble's Cosmic Origins Spectrograph, which sought to measure the amount of atomic oxygen in the atmosphere and compare it with earlier data, both from 1998 and 2010. But the new team of researchers found almost no atomic oxygen in Ganymede's atmosphere, indicating that earlier ultraviolet images showed something else.


The team found the answer in how Ganymede's aurora was distributed in the two 1998 images. Over the course of one day on Ganymede, its surface temperature rises and falls. When it's around noon on the moon, the surface could get hot enough to release water molecules.


Lorenz Roth, the lead author of the study and planetary astronomer at the KTH Royal Institute of Technology in Sweden, wrote in a recent blog post “ Behind the Paper ” for Nature, that “the difference in the images is exactly there, where you would expect it to be. find the water in the atmosphere. And water vapor has a similar effect to atomic oxygen on the spectral signal ... ”In other words, what appeared to be a discrepancy in atomic oxygen could be water vapor that appears in one image but not the other. , due to the areas of the atmosphere, they were targeting.


In a statement from the European Space Agency, Roth added that the upcoming Jupiter ICy moons Explorer (Jupiter icy moons explorer. JUICE) mission could incorporate the recent finding into its investigations of Ganymede and the other moons. Jupiter, Europa, and Callisto frosts. In fact, Europa is believed to have columns of water shooting out of an underground ocean, and a spacecraft may have flown through one of these columns in 1997. Ganymede's water vapor makes these worlds even more interesting. for astrobiologists.

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