Astronomers using archival data from NASA’s Hubble Space Telescope found evidence of water vapor in
the thin atmosphere of Jupiter’s moon Ganymede.
Ganymede is the largest moon in our solar
system, larger than Mercury and Pluto, and three-quarters the size of Mars.
It’s an ice-covered world that may hold more water than all of Earth’s oceans combined,
but unlike Earth, Ganymede’s oceans are below its 100-mile-thick, icy crust.
Ultraviolet images taken in 1998 and 2010 using Hubble’s Space Telescope Imaging Spectrograph
revealed bands of charged particles at Ganymede similar to Earth’s polar auroral ovals,
the regions that give us our Northern and Southern lights, but the two observations revealed
differences in Ganymede’s auroral bands over time. The researchers thought these differences were
due to the presence of atomic oxygen, or single oxygen atoms, in Ganymede’s atmosphere.
Atomic oxygen affects one of the wavelengths of ultraviolet light the scientists were looking at.
In 2018, researchers used Hubble’s Cosmic Origins Spectrograph to measure
the amount of atomic oxygen in Ganymede’s atmosphere. They compared the 1998, 2010,
and 2018 data. To their surprise, the 2018 data revealed hardly any atomic oxygen in Ganymede’s
atmosphere. There had to be another explanation for the differences in the aurora images.
Ganymede’s surface temperature varies widely throughout the day, and around noon, near its
equator, it may get warm enough for surface ice to release water molecules. Instead of
melting and forming liquid water, the icy surface warms and changes from a solid directly to a gas,
a process called sublimation. Looking back at the original images, the team discovered the
differences they observed in Ganymede’s auroral bands are related to where water vapor would be
expected in the moon’s atmosphere.
Understanding the Jovian system and
unravelling its history, from its origin to the possible emergence of habitable environments,
will provide us with a better understanding of how gas giant planets and their satellites
form and evolve. Along with learning more about Jupiter and its mysterious moon Ganymede,
this exciting new discovery has brought us closer to understanding our own place in the universe.
[ MUSIC ]