Ammonia-Bearing Compounds Detected on Europa for First Time
A new analysis of archival data from the Near Infrared Mapping Spectrometer (NIMS) aboard NASA’s Galileo spacecraft has revealed the first evidence of ammonia-containing compounds on Jupiter’s icy moon Europa, offering new clues about its subsurface ocean and recent geological activity.
In this composite image, red pixels mark locations on Europa’s surface where ammonia-containing compounds have been detected; purple indicates that there is no such detection. Image credit: NASA/JPL-Caltech.
“The detection of ammonia (NH3) or ammonia-containing components (ammonia hydrate, salts or minerals) on icy planetary bodies in the Solar System are of significant interest in understanding their geology, potential habitability and astrobiological relevance,” said study author Dr. Al Emran, a researcher at NASA’s Jet Propulsion Laboratory.
“On Jupiter’s moon Europa, the presence of ammonia or ammonia species is particularly important for constraining ocean chemistry, assessing habitability, and reconstructing the moon’s early atmosphere.”
“Ammonia acts as an antifreeze; its abundant presence can lower the freezing point of liquid water by up to 100 K and allow subsurface ocean retention for icy bodies.”
“Although it is unclear whether Europa’s subsurface ocean is directly connected to its surface, the detection of ammonia compounds may suggest such a connection, because these materials are unstable to space radiation.”
In his new article published in the Journal of Planetary SciencesDr. Emran reports the detection of a characteristic ammonia absorption feature at 2.20 microns in the near-infrared spectra of the surface of Europa.
The signal was identified in observations from Galileo’s NIMS instrument, which studied Europa during flybys in the 1990s.
Ammonia hydrate and ammonium chloride are the most plausible materials responsible for the detected feature.
Ammonia is unstable under intense space radiation, a property that makes its presence on the surface of Europa significant.
According to the paper, the survival of the ammonia-containing materials suggests that they were transported from Europa’s subsurface ocean or shallow basement to the surface in the Moon’s recent geologic past, perhaps through effusive cryovolcanism or a similar mechanism.
The analysis also highlights broader implications for Europe’s internal structure.
The presence of ammonia compounds is consistent with a thinner ice shell and a chemically reduced, high pH subsurface ocean.
Ammonia acts as an antifreeze agent, able to lower the freezing point of water ice and help maintain liquid oceans beneath icy crusts.
“Hidden in the data were faint signals of ammonia near fractures on the frozen surface of the moon, through which liquid water containing dissolved ammonia compounds would be expected to rise,” Dr Emran said.
“The compounds may have reached the surface through geologically recent cryovolcanism.”
“This is because ammonia significantly lowers the freezing point of water, acting as a kind of antifreeze.”
While ammonia-containing species have been identified on other icy bodies in the outer solar system, including Pluto, Charon, several Uranian moons, and Saturn’s moon Enceladus, previous attempts to confirm their presence on Europa had produced inconclusive or contradictory results.
“The detection of ammonia-containing components in this study provides the first evidence for the existence of nitrogen-containing species on Europa, an observation of considerable astrobiological importance due to the fundamental role of nitrogen in the molecular basis of life,” said Dr Emran.
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A.Emran. 2026. Detection of a NH3 Absorption band at 2.2 μm on Europa. Planet. Sci. J. 6, 255; doi: 10.3847/PSJ/ae1291
