Scientists predict Neptune’s chemical make-up


Voyager 2 took this picture of Neptune in 1989.

Scientists have helped solve the mystery of what lies beneath
the surface of Neptune – the most distant planet in our solar
system. A new study sheds light on the chemical make-up of
the planet, which lies around 4.5 billion kilometres from the

Frozen worlds

Extremely on planets like
Neptune – called ice giants – mean that chemicals on these
exist in a frozen state,
researchers say. Frozen mixtures of water, ammonia and methane
make up a thick layer between the planets’ atmosphere and core
– known as the mantle. However, the form in which these
chemicals are stored is poorly understood.

Using laboratory experiments to study these conditions is
difficult, as it is very hard to recreate the extreme pressures
and temperatures found on ice giants, researchers say. Instead,
scientists at Edinburgh ran large-scale computer simulations of
conditions in the mantle.

By looking at how the chemicals there react with each other at
very high pressures and low temperatures, they were able to
predict which compounds are formed in the mantle. “Computer
models are a great tool to study these extreme places, and we
are now building on this study to get an even more complete
picture of what goes on there,” says Dr Andreas Hermann.

Chemical compound

The team found that frozen mixtures of water and ammonia inside
Neptune – and other ice giants, including Uranus – likely form
a little-studied compound called ammonia hemihydrate. The
findings will influence how ice giants are studied in future
and could help astronomers classify newly discovered planets as
they look deeper into space.

The study, published in the journal Proceedings of the
National Academy of Sciences
, was supported by Engineering
and Physical Sciences Research Council. The work was carried
out in collaboration with scientists at Jilin University,

“This study helps us better predict what is inside icy planets
like Neptune. Our findings suggest that ammonia hemihydrate
could be an important component of the in ice giants, and will help improve our
understanding of these frozen worlds,” says Dr Hermann.

Explore further:

Probing methane’s secrets: From diamonds to Neptune

More information: Victor Naden Robinson et al.
Stabilization of ammonia-rich hydrate inside icy planets,
Proceedings of the National Academy of Sciences (2017).
DOI: 10.1073/pnas.1706244114

Journal reference:
Proceedings of the National Academy of Sciences

Provided by: University
of Edinburgh