The value of scientific progress risks being limited if researchers cannot clearly explain their findings and the attendant implications to other people. Thanks to a varied career spanning science and journalism, Steven Miller is now helping young scientists to meet this challenge.

Miller, a planetary scientist at University College London (UCL), started his career with a PhD in physical chemistry, which he received from Southampton University in 1975. He followed this up with a couple of postdoc jobs, but found full-time academic positions to be in short supply, so, in the early 1980s, he opted to change direction.

He helped Ken Livingstone, now the mayor of London, start up a left-wing newspaper to take on the conservative policies of then Prime Minister Margaret Thatcher. When he returned to science with a job at UCL a few years later, he realized that “many people couldn't communicate effectively to their colleagues, let alone to non-experts”. So he began teaching science communication to young scientists, knowing it would improve their work if they could “express more clearly why they thought what they thought”.

Although there is an obvious benefit to biomedical research being understood by the public, because it relates to human health, Miller argues that public engagement in astronomy is just as important. Pointing to the immense popularity of the Cassini-Huygens probe that landed on Titan, one of Saturn's moons, he notes, “astronomy lifts us above the daily grind”.

His research focuses on the atmospheres of exoplanets — those found outside our Solar system. One type that astronomers have identified is the Jupiter-like gas giant. These planets are huge, and some, such as HD209458b, which Miller and his co-workers chose to study, orbit incredibly close to their stars — at about 0.05 astronomical units (AU). One AU is the distance between Earth and the Sun.

Although Jupiter has a relatively thin atmosphere — equivalent in depth to about 10% of the planet's radius — the atmosphere of HD209458b measures between 200% and 300% of its radius. If Jupiter were moved in towards the Sun, Miller's group wondered, at what point might it begin to look like HD209458b?

The team created a three-dimensional model of this process and found that the change from a stable, Jupiter-like atmosphere to an expanded atmosphere with hydrogen gas escaping in a bulk outflow of 'planetary wind' occurs over a very short orbital distance. At 0.16 AU the atmosphere is stable, but at 0.14 AU the hydrogen breaks down, with catastrophic results.

Such a drastic and abrupt transition had never been modelled before and was rather unexpected. The group's three-dimensional model included a key aspect — the stabilizing effects on the planet of wind circulation, which distributes and dissipates heat (see page 845).

The finding provides insight into the evolution of gas-giant planets, which typically migrate in towards their stars during their lives. “Most form further out — such as where Jupiter is — and drift in over time. They probably cross a point where they go through this catastrophic breakdown,” says Miller. The giants in our Solar System are stable and are not moving towards the Sun, although we do not know why. But, as Miller says, “this is lucky for us, because these giants have a tendency to kick the little planets out of the way as they drift”.