Research
Hao Cao's group studies how magnetic fields and gravity reveal the otherwise hidden interiors, deep fluid motion, and space environments of planets and moons. The work connects spacecraft observations with geophysical theory, numerical modeling, and magnetometer development, so the same physical signals can be used to understand both planetary structure and the environments through which spacecraft travel.
Planetary Interiors and Deep Fluid Dynamics
Giant planets are natural laboratories for fluid dynamics at scales that cannot be reproduced on Earth. The group uses gravity measurements, magnetic constraints, and dynamical modeling to ask how far atmospheric jets extend below the clouds, how deep winds interact with conducting interiors, and what those signals reveal about the structure and evolution of Jupiter and Saturn.
Related context links and videos
- Hao Video Giant Planet Interior Dynamics: Recent Progress and Open Questions IPAM/MathInstitutes video of Hao Cao's January 31, 2025 talk on giant-planet interior dynamics.
- Mission NASA Juno mission overview Juno mission context for Jupiter's interior, atmosphere, gravity, and magnetosphere measurements.
- Mission Juno findings: Jupiter's jet-streams are unearthly NASA/Juno summary of deep atmospheric winds inferred from spacecraft data.
- Paper Strong resemblance between surface and deep zonal winds inside Jupiter Peer-reviewed gravity analysis connecting Jupiter's visible winds to deep interior flow.
Planetary Magnetic Fields and Secular Variation
Planetary magnetic fields are generated by moving electrically conducting fluids, and their shapes and time variation carry information about deep interiors. Hao's research combines spacecraft magnetometry from missions such as NASA's Juno and Cassini with dynamo theory to study Jupiter, Saturn, Mercury, and Earth, including how magnetic secular variation can trace fluid motion below the surface.
Related context links and videos
- Hao Video The Magnetic Fields of Mercury, Ganymede, and Saturn Public INI/Newton Institute seminar video by Hao Cao on comparative planetary magnetic fields.
- Mission NASA's Juno finds changes in Jupiter's magnetic field NASA/JPL overview of Jupiter magnetic secular variation and its likely connection to deep winds.
- Video Jupiter Magnetic Tour NASA Scientific Visualization Studio tour of Jupiter's dynamo and magnetic field.
- Paper A rapidly time-varying equatorial jet in Jupiter's deep interior Nature paper connecting Jupiter's changing magnetic field to a deep equatorial jet.
- Mission Cassini Grand Finale overview NASA context for Saturn gravity and magnetic-field measurements close to the planet.
Ocean Worlds and Coupled Interior-Space Environments
Icy moons can respond electromagnetically to their parent planets and surrounding plasma, turning magnetic measurements into probes of subsurface oceans, ice shells, and space environments. The group's mission-connected work includes Europa and the Jupiter system, including the European Space Agency's JUpiter ICy moons Explorer (JUICE) and broader Europa-focused geophysical context.
Related context links and videos
- Mission Jupiter and its complex surroundings: what will Juice reveal? ESA overview of Juice science across icy moons, Jupiter's magnetic environment, and coupled plasma systems.
- Mission Induced magnetic field from Europa's subsurface ocean NASA explanation of how Europa's induced magnetic response constrains ocean and ice-shell properties.
- Video Testing Europa Clipper's magnetometer JPL video on the instrument that will measure Europa's magnetic environment.
- Paper Geophysical characterization of Ganymede, Callisto, and Europa by Juice Space Science Reviews paper on Juice investigations of icy-moon interiors.
Lunar and Planetary Surface Magnetometry
Long-duration surface magnetometry can help reveal the electrical structure, thermal state, and plasma interaction of planetary bodies. Hao is Principal Investigator for NASA's Development and Advancement of Lunar Instrumentation (DALI) L-MAG project, which is developing a miniaturized, low-power fluxgate magnetometer system for lunar surface observatories.
Related context links and videos
- Mission NASA Development and Advancement of Lunar Instrumentation awards NASA DALI context for L-MAG and lunar surface instrument development.
- UCLA How to study water on the Moon UCLA overview of Hao Cao's NASA-funded lunar magnetometer technology work.
- Video The Moon passes through Earth's magnetotail NASA visualization of the lunar space environment relevant to long-duration surface magnetometry.
Space-Weather Measurements and Instrument Development
The same magnetic-field measurements that probe planetary interiors also matter for near-Earth space weather. Hao is Deputy Instrument Lead and Co-Investigator for the fluxgate magnetometer (MAG) on NASA's Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission, which studies how Earth's magnetosphere responds to the solar wind.
Related context links and videos
- Mission NASA TRACERS mission overview NASA mission page for studying magnetic reconnection and space-weather effects near Earth.
- UCLA NASA launches UCLA instrument into space UCLA story on the TRACERS fluxgate magnetometer designed and built by the UCLA team.
- Video TRACERS science animations NASA Scientific Visualization Studio animations of TRACERS sampling the polar cusp.
- Paper The TRACERS Fluxgate Magnetometer (MAG) Space Science Reviews paper on the TRACERS magnetic-field instrument.