About me

I am a postdoctoral researcher in the Department of Astrophysics at the University of Zürich. I previously did my PhD at the Observatoire de la Côte d'Azur, in Nice. I grew up in Boulogne-Billancourt, near Paris.

Research

My research focuses on the internal structures of giant planets. I have developed interior and evolution models of Jupiter, Saturn, Uranus, Neptune and also exoplanets, from hot-Jupiters to sub-Neptunes. Below are some highlights from my work.

A dilute core inside Jupiter

Contrary to the idea that Jupiter had a dense, compact core at its center, the Juno mission revealed that its core is actually diluted. It was previously thought that most of the heavier elements, like rocks and ices, were concentrated in a dense core, well separated from the surrounding hydrogen and helium envelope. However, thanks to Juno’s extremely precise measurements of Jupiter’s gravitational field, interior models now suggest that these heavier elements are gradually mixed with hydrogen and helium over a large part of the planet. This diffuse structure challenges traditional models of giant planet formation. A key question is the precise extent of the dilute core, which is crucial for reconciling Jupiter’s formation, evolution, and current structure — a topic I have been actively working on. [link]
Interior of Jupiter

Helium rain in Jupiter and Saturn

Hydrogen and helium, the main constituents of gas giants, become immiscible within these planets. This phase separation leads to the formation of helium droplets which sink in the deep interior. This phenomenon has been confirmed by the Galileo probe (1995) which measured a depletion of helium in Jupiter's atmosphere. By coupling evolution models of Jupiter and Saturn with phase diagrams of hydrogen and helium, I investigated the effect of helium rain on the planetary internal structure and thermal evolution. I confirmed that helium rain is modest in Jupiter but drastic in Saturn (which is colder). Both planets have different internal structures, with a large helium gradient and a potential helium ocean inside Saturn. [link]
Helium rain in Jupiter and Saturn

Hydrogen-water demixing in sub-Neptunes

A phase separation between hydrogen and water is expected in cold, water-rich planets. Uranus and Neptune are likely to be subject to this phenomenon. With the recent detection of cold/temperate sub-Neptunes like K2-18b and TOI-270d, it is crucial to assess whether hydrogen-water demixing can occur in those planets. We find that this process occurs in both exoplanets and leads to a complete depletion of water in K2-18b's atmosphere but only a partial depletion in TOI-270d's atmosphere, in agreement with the recent observations from the James Webb Space Telescope. [link]
Hydrogen-water demixing in sub-Neptunes

Publications

Here you can find a list of refereed publications that I contributed to:

First author

Co-author

A nice review about giant planets

Conferences

Media

  • Article about our A&A paper on the Juno website [link]

  • (In French) Article sur la mission Juno dans l'encyclopédie Universalis [link]

  • Astrophysics Seminar at the University of Zurich [video on Youtube]

  • (In French) Présentation à la semaine scientifique Lagrange (Observatoire de la Côte d'Azur)

    • Contact

    You can contact me at: saburo.howard@uzh.ch