The real reason behind the colour differences of Neptune & Uranus –
Online features editor Catherine Stone discusses the recent findings which explain the differences between Neptune and Uranus despite their close proximity
Neptune and Uranus, the ‘ice giant’ planets of our solar system, composed of hot, dense fluid of water, methane and ammonia around a proportionally small rock core, have long been fairly obscure. New research studying clouds and hazes of the ice giant atmospheres using the Hubble and Gemini North space telescopes has shed light on their colour differences with dark spot formation as an ‘unexpected bonus’. The project additionally used information from the Voyager 2 spacecraft launched in 1977, the last mission to visit the ice giants between 1986 and 1989.
A new study from the University of Oxford led by planetary physicist Professor Patrick Irwin has used models that synthesise observations of reflected sunlight across the range of wavelengths using the instrument Near-Infrared Integral Field Spectrometer (NIFS), breaking new ground in astrophysical studies, and allowing unprecedented levels of measurement accuracy.
Scientists have determined that both planets are encased by three layers of aerosol photochemical haze where fine particles from sunlight are suspended in a gas and interact with and break down atmospheric elements. The difference lies in the thicker middle layer of Uranus, which masks the deeper colour behind the haze as well as hiding dark spots. Uranus has 13 rings and Neptune has five, with four ring arcs.
The differences lie in the thicker middle layer of Uranus, which masks the deeper colour behind the haze
The Hubble space telescope’s reliability and ‘unique vantage point’ have enabled astronomers to take regular annual ‘maps’ of our distant planets to track changes in the concentration of atmospheric methane gas, characteristics of haze particles, and atmospheric flow patterns as the Outer Planets Atmospheres Legacy program, or OPAL.
The atmospheres of planets are controlled by interacting forces that result in unstable and ever-changing compositions, however Neptune’s atmosphere is much more turbulent than that of Uranus, with the fastest winds in the solar system at up to 1300 mph. Researchers isolated the factor of methane snow, that pulls haze particles deeper into the atmosphere, as being more efficient on Neptune and maintaining the lower opacity of the middle layer (Aerosol-2).
Neptune’s atmosphere is much more turbulent than that of Uranus, with the fastest winds in the solar system at up to 1300mph
The blue colour is created by Rayleigh scattering of electromagnetic radiation through atmospheric molecules, as red colours are more absorbed by the methane rich (3%) atmosphere of Neptune and Uranus.