Understanding Giant Planet Formation
Ravit Helled occupies an office in the buildings of the Irchel campus, University of Zurich, Y11 building. She is with her son who is just a few weeks old, “although I could have been in the event organized by NASA for the arrival of Juno at Jupiter I could not go there, since I was expecting a baby”, explains Ravit while holding the baby in her arms, “this is a more important event!” Ravit made her Phd Thesis in Tel-Aviv University and spent four years at UCLA, Los-Angeles as a postdoc and researcher, already working in the Juno team.
PlanetS: What was your field of research in LA?
Ravit Helled: I worked there for 4 years, I was a postdoc and then a researcher, being a member of the Juno scientific team since 2007. The Juno science objectives and focus fitted very well with my field of research which concerns giant planet formation.
I came back to Israel where I got a professor position. I moved to Zurich in June where I am a professor and the Platform Leader Academic Coordination of the NCCR PlanetS.
What is Juno?
Juno is a spacecraft sent by NASA to Jupiter, it will orbit 37 times the main solar system planet, the end of mission is forseen for the 20.2.18. Juno will help us to better understand the origin of Jupiter, its composition and how this composition changes with depth. Although I am no longer in the USA, I am still involved in the project as a science team member.
What will we learn with Juno?
There are several instruments on the spacecraft to measure Jupiter’s gravitational and magnetic fields, the atmospheric composition, and to study the aurora and energetic particles. It’s really hard to predict what we will learn from Juno because there are always surprises. We hope to have a better knowledge of the gravitational field and of the internal structure, which is important for understanding giant planets. In the 90s the Galileo probe measured a very dry atmosphere, the concentration of water was lower than expected introducing challanges for theories of planet formation. The common explanation is that the probe entered a « hot spot », a dry region with a low water concentration. Juno will help to solve this mystery since it will measure the water abundance down to higher pressure and will cover the entire planetary surface.
Then we will mesure the magnetic field and the velocity of development of auroras, with the aim of a better understanding of this phenomenon, even on Earth.
What are the main questions about giant planets?
We do not really know how do giant planets form, and how their composition is linked to their formation history. In the case of Jupiter’s, we want to know : how, where, and how long ? Understanding giant planet formation is important because giant planets are the first planets to form, and since they are so massive they can lead to perturbations of small objets and affect the formation of other planets in the system. For example, a fast formation of Jupiter could drive water-rich objects (i.e., comets) into the inner part of the solar system, and deliver some water to Earth. Understanding giant planet formation is crucial for understanding the formation of planetary systems.
What’s your field of investigation?
I am interested in the determination of Jupiter’s gravity field and the measurement of the water abundance. Jupiter’s gravitational field affects the motions of the Juno spacecraft and by using the Doppler effect (shifts in the frequency of a radio signal received from and sent back to Earth), we can get information on the density distribution inside Jupiter, and therefore its composition. Combining information on the water abundance and nature of the magnetic field helps to better constrain Jupiter’s internal structure,
And planetary migration?
This is a bit harder, if we can put good constraints on the chemical composition of the atmosphere and determine the proportion of water then we may be able to show where the planet has formed. But there are many uncertainties, and this is inderred indirectly, so I don’t think there will be a unique conclusion.
With Cassini end-of-mission and now with Juno, we will have measurements of the two giant planets in the solar-system.
Saturn if often thought as a mini-Jupiter, but the core seems to be more massive in Saturn, we don’t really know what are the differences between both planets and what provoked them. However, Cassini and Juno will do very similar measurements when they will crash on their own planet in one year more or less (20.2.18 for Juno 15.9.17 for Cassini). So we expect to have very accurate mesurements that will allow us to compare the internal structures of these two planets.
With Jupiter (and Saturn) we have a test case that we can use as a giant planet prototype. This knowledge can be used to better understand the interior of giant exoplanets as well as their formation history.