A reanalysis of data collected twenty years ago has revealed traces of ammonia on Jupiter’s moon Europa—a substance that can act as a natural antifreeze. This discovery points to possible cryovolcanic activity and suggests that Europa’s subsurface ocean may be more resistant to freezing than previously thought.

The Role and Origin of Ammonia

Ammonia (NH3) is a compound that quickly breaks down under solar radiation. Without a dense atmosphere, its molecules are especially vulnerable. Ammonia has previously been found on the surfaces of Pluto, its moons, and Uranus’s satellites, indicating a steady supply from internal sources, since the solid crusts of these bodies cannot produce it chemically.

New Discovery on Europa

Planetary scientist Ali Emran from NASA’s Jet Propulsion Laboratory has detected traces of ammonia on Europa—a moon with a diameter of 3,120 kilometers orbiting Jupiter at a distance of 0.67 million kilometers. Europa’s surface area is comparable to that of Africa. The research findings were published on the Cornell University preprint server.

Attempts to detect ammonia on Europa have spanned decades. In the 1980s, signs of its presence were observed near the moon, but more modern instruments failed to confirm these results for a long time.

Ali Emran conducted a new analysis of data from the Near-Infrared Mapping Spectrometer (NIMS) aboard the Galileo spacecraft, which orbited Jupiter from 1995 to 2003. This instrument enabled the detection of ammonia absorption bands on Jupiter’s moons.

The Significance of the Discovery

The scientist concluded that ammonia on Europa may be present as part of hydrates or chlorides. Since Jupiter is closer to the Sun than Uranus or Pluto, the presence of ammonia on Europa suggests it is being supplied from beneath the surface, likely from the subsurface ocean. Despite extremely low surface temperatures (down to minus 220 °C at the poles), the existence of a subsurface ocean on Europa had already been hypothesized.

The traces of ammonia indicate that Europa’s hidden ocean could be deeper and larger than previously estimated, with a thinner ice shell above it. When mixed with water, ammonia lowers the freezing point to minus 100 °C, making the ocean less likely to freeze. Earlier estimates suggested this ocean could contain twice the volume of all Earth’s oceans combined.

Geological Scenarios and Cryovolcanism

For a long time, planetary scientists debated two possible geological models for Europa. In the first, the ice above the ocean is very thick, preventing cryovolcanoes from reaching the surface. In the second, the ice shell is thinner, allowing cryovolcanic activity to occasionally break through. The new study supports the latter scenario as more likely.

Biological Significance

The detected compound contains the first known traces of nitrogen on Europa. Nitrogen is essential for Earth-like life, as it is a component of DNA. Ammonia had previously been found on the surface of Enceladus, Saturn’s moon, where it was also linked to the potential habitability of its subsurface ocean.

Why Ammonia Is Rarely Detected

The reasons why ammonia is not observed in all studies remain unclear. Its appearance may be linked to cryovolcanic eruptions, during which liquid water from the subsurface ocean rises to the surface. If such eruptions are rare, ammonia has time to break down under ultraviolet radiation, making it harder to detect.

Cryovolcanism is typical for icy moons of giant planets and dwarf planets like Ceres and Pluto. If the intervals between eruptions on Europa are long, ammonia is destroyed, which explains the difficulty in detecting it.