Hubble finds evidence of water vapor at Jupiter's moon Ganymede

Date:
July 26, 2021
Source:
Space Telescope Science Institute (STScI)
Summary:
Astronomers have uncovered evidence of water vapor in the atmosphere
of Jupiter's moon Ganymede. This water vapor forms when ice from
the moon's surface sublimates -- that is, turns from solid to
gas. Astronomers re- examined Hubble observations from the last
two decades to find this evidence of water vapor.



FULL STORY ========================================================================== [Illustration of the | Credit: (c) ianm35 / stock.adobe.com] Illustration
of the planet Jupiter and moon Ganymede (stock image).

Credit: (c) ianm35 / stock.adobe.com [Illustration of the | Credit:
(c) ianm35 / stock.adobe.com] Illustration of the planet Jupiter and
moon Ganymede (stock image).

Credit: (c) ianm35 / stock.adobe.com Close For the first time, astronomers
have uncovered evidence of water vapor in the atmosphere of Jupiter's
moon Ganymede. This water vapor forms when ice from the moon's surface sublimates -- that is, turns from solid to gas.


========================================================================== Scientists used new and archival datasets from NASA's Hubble Space
Telescope to make the discovery, published in the journal Nature
Astronomy.

Previous research has offered circumstantial evidence that Ganymede,
the largest moon in the solar system, contains more water than all of
Earth's oceans. However, temperatures there are so cold that water on
the surface is frozen solid. Ganymede's ocean would reside roughly 100
miles below the crust; therefore, the water vapor would not represent
the evaporation of this ocean.

Astronomers re-examined Hubble observations from the last two decades
to find this evidence of water vapor.

In 1998, Hubble's Space Telescope Imaging Spectrograph (STIS) took the
first ultraviolet (UV) images of Ganymede, which revealed in two images colorful ribbons of electrified gas called auroral bands, and provided
further evidence that Ganymede has a weak magnetic field.

The similarities in these UV observations were explained by the presence
of molecular oxygen (O2). But some observed features did not match
the expected emissions from a pure O2 atmosphere. At the same time,
scientists concluded this discrepancy was likely related to higher concentrations of atomic oxygen (O).



==========================================================================
As part of a large observing program to support NASA's Juno mission in
2018, Lorenz Roth of the KTH Royal Institute of Technology in Stockholm,
Sweden led the team that set out to measure the amount of atomic oxygen
with Hubble. The team's analysis combined the data from two instruments: Hubble's Cosmic Origins Spectrograph (COS) in 2018 and archival images
from the Space Telescope Imaging Spectrograph (STIS) from 1998 to 2010.

To their surprise, and contrary to the original interpretations of the
data from 1998, they discovered there was hardly any atomic oxygen in Ganymede's atmosphere. This means there must be another explanation for
the apparent differences in these UV aurora images.

Roth and his team then took a closer look at the relative distribution
of the aurora in the UV images. Ganymede's surface temperature varies
strongly throughout the day, and around noon near the equator it may
become sufficiently warm that the ice surface releases (or sublimates)
some small amounts of water molecules. In fact, the perceived differences
in the UV images are directly correlated with where water would be
expected in the moon's atmosphere.

"So far only the molecular oxygen had been observed," explained
Roth. "This is produced when charged particles erode the ice surface. The
water vapor that we measured now originates from ice sublimation caused by
the thermal escape of water vapor from warm icy regions." This finding
adds anticipation to ESA (European Space Agency)'s upcoming mission,
JUICE, which stands for JUpiter ICy moons Explorer. JUICE is the first large-class mission in ESA's Cosmic Vision 2015-2025 program. Planned
for launch in 2022 and arrival at Jupiter in 2029, it will spend at
least three years making detailed observations of Jupiter and three of
its largest moons, with particular emphasis on Ganymede as a planetary
body and potential habitat.



========================================================================== Ganymede was identified for detailed investigation because it provides
a natural laboratory for analysis of the nature, evolution and potential habitability of icy worlds in general, the role it plays within the system
of Galilean satellites, and its unique magnetic and plasma interactions
with Jupiter and its environment.

"Our results can provide the JUICE instrument teams with valuable
information that may be used to refine their observation plans to optimize
the use of the spacecraft," added Roth.

Right now, NASA's Juno mission is taking a close look at Ganymede and
recently released new imagery of the icy moon. Juno has been studying
Jupiter and its environment, also known as the Jovian system, since 2016.

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. In addition, new insights will hopefully be
found on the habitability of Jupiter- like exoplanetary systems.

The Hubble Space Telescope is a project of international cooperation
between NASA and ESA (European Space Agency). NASA's Goddard Space
Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts
Hubble science operations.

STScI is operated for NASA by the Association of Universities for Research
in Astronomy in Washington, D.C.

========================================================================== Story Source: Materials provided by
Space_Telescope_Science_Institute_(STScI). Note: Content may be edited
for style and length.


========================================================================== Related Multimedia:
* Hubble's_views_of_Jupiter's_moon_Ganymede ========================================================================== Journal Reference:
1. Lorenz Roth, Nickolay Ivchenko, G. Randall Gladstone, Joachim
Saur, Denis
Grodent, Bertrand Bonfond, Philippa M. Molyneux, Kurt
D. Retherford. A sublimated water atmosphere on Ganymede detected
from Hubble Space Telescope observations. Nature Astronomy, 2021;
DOI: 10.1038/s41550-021- 01426-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210726132125.htm

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