Melita Wiles
S&E Editor
Recent observations of hail-like objects falling from Jupiter’s atmosphere may explain the low levels of ammonia detected on Uranus and Neptune. The planet Jupiter’s clouds consist of both water and ammonia. On Earth, during a thunderstorm, we may experience hail, which is when frozen water pellets fall from the clouds, like any other type of precipitation on this planet. There is a similar phenomenon on Jupiter, where hailstone-like pellets fall from the sky. But on Jupiter these pellets have a different name: mushballs. Mushballs are ammonia-rich hailstones, consisting of an ammonia and water slush. They grow from a small ice crystal, encased by ammonia-water, which then is encased by an additional crust of ice. This crust forms because these storms form many miles up in the atmosphere, where the temperature is close to the freezing point of water. As the mushballs fall through the atmosphere, they absorb more ammonia. Mixing ammonia and water can keep the liquid at close to -100 degrees Celsius, weighing in at nearly a kilogram.
This discovery has changed our understanding of larger planets’ atmospheres. Their atmospheres are made of gas and subject to higher pressure than here on Earth. From our observations, these mushballs could be the reason Uranus and Neptune are missing so much ammonia. Observations at infrared and radio wavelengths show that these planets lack ammonia in their atmospheres, which is surprising because they are rich in other components that are just as common as ammonia. These mushballs could be hidden deep in the planets’ atmospheres, where our human instruments cannot yet reach.
NASA’s Juno, a satellite mission currently observing and orbiting Jupiter could answer this question. The spacecraft can reach further up in the atmosphere than expected. This region of the atmosphere will be hard to explore on planets like Uranus and Neptune because the altitude at which the mushballs are created is even further up into the atmosphere compared to the area where mushballs are created in Jupiter’s atmosphere.
Other planets that are on the smaller side of the planetary scale, like Mars and Venus, are composed of mostly carbon dioxide, not containing ammonia, which explains why there is no mushball action on these planets. On Mars, their weather mostly consists of dust storms, yet this desert world is also prone to violent storms. Weather on Venus is extreme, where there are winds up to 60 times the planet’s rotational speed.
Be on the lookout for mushballs and contact the science editors of the Voice if you see some on Earth.
