In Search of a 'Big Picture' for the climate of Planets and Exoplanets

Tuesday 21st October, 2014

According to our speaker, Professor Peter Read from Oxford University, his talk could have been entitled "How the Study of Planetary Atmospheres Needn't (Only) Be Rocket Science" whereas the actual title he gave was the similarly long "In Search of a Big Picture for the Climate of Planets and Exoplanets". This alternative title applied as, instead of primarily using the data obtained from spacecraft visiting the planets, he uses computers with the Met Office's software to model planetary atmospheres and climate.

Prof Read gained a PhD in Radio Astronomy at Cambridge University and from that moved straight to the Met Office when the Voyager spacecraft were actively touring the Solar System. He is currently a Professor in the Department of Physics at Oxford University but still has links with the Met Office as he chairs the Oxford-Met Office Academic Partnership which promotes collaboration between Oxford researchers and the Met Office.

Using Met Office software, he and his team are aiming to produce a generic model for any planetary atmosphere. This would not only allow scientists to understand planets both within and outside our Solar System but it would have far-reaching benefits to understanding the Earth's climate and its future behaviour.

He began his talk by explaining that he defines climate as being the average state of an atmosphere and how it varies. The majority of planets have their atmospheric variation driven by the energy they receive from solar radiation plus any internal heat that originated from their formation. To model this, the software splits the shell of an atmosphere around a planet into a three-dimensional spherical grid. Each of these "boxes" simulates the exchange of radiation from the Sun versus the infrared energy radiated back into space. The model also needs to take into account other processes that occur at various boundary layers in the atmosphere as well as the presence of clouds and moisture.

In the Solar System there are eight planets with substantial atmospheres — the four gas giants (Jupiter, Saturn, Uranus and Neptune), the rocky inner planets (Venus, Earth and Mars), plus Titan a moon of Saturn. Once his team has predictions from the modelling software he compares these with actual data from spacecraft that have studied the planets in depth.

In some respects the atmospheric systems on these worlds are a puzzle. For example, Venus and Titan spin very slowly but their atmospheres rotate much faster and Mars, Venus and Titan lack the jet streams that are seen on Earth. However, some features seen in the planetary atmospheres are replicated in both physical and software models.

Back in 1981, both Voyager spacecraft spotted a persistent hexagonal cloud pattern around Saturn's north pole that was confirmed by the Cassini spacecraft and the Hubble Telescope. This phenomena has been successfully reproduced in both experimental laboratory models and using the software model. In fact, Prof Read commented that by varying different parameters such as the rotation speed they can produce stable vortices with any number of sides from triangles through octagons to regular polygons with a great many sides.