Ravit Helled

Today, we know that planets are common and diverse astronomical objects. We still don't know, however, how planets form. In addition, we still need to understand whether our Solar System is unique. My research deals with planetary formation focusing on the formation of gaseous-rich planets inside and outside the Solar System. In particular, I try to understand the formation of the outer planets. I investigate what are the predicted compositions of giant planets formed by different mechanisms, and how the planetary composition depends on its birth environment. I also explore the connection between the planetary formation process and the long-term (thermal) evolution of the planets.

Another aspect of my research is planetary interiors. The aim is to determine the composition and internal structures of planets. Key questions I try to answer include: What are the compositions and internal structure of the outer planets? Do giant planets have cores, and if yes, and are they "fuzzy"? Do giant planets have distinct layers or are they homogeneously mixed? What is the dominate heat transport mechanism in gaseous planets? How can we link planetary composition with planet formation and evolution? Modelling planets in the solar system and exoplanets is different. By nature, extrasolar planet research is more statistical and covers a much larger parameter range while studies of Solar System's planets that are constrained by very accurate measurements focus more on detailed physical/chemical processes. In both cases, we need to understand the behaviour of materials at extreme, linking planetary science with high-pressure physics.

Today, more than 4000 exoplanets have been discovered. A key question in exoplanetary science is to characterise these planets, i.e., understand what they are made of. In our research we concentrate on planets that have measured masses and radii and infer their mean density, and bulk composition. We explore the behaviour of the Mass-Radius (M-R) diagram for various model assumptions, equations of state, etc. In addition, we search for trends and correlations in exoplanetary data such as how the composition depends on stellar properties, the relation between orbital period and planetary radius, and the behaviour of the M-R for different planet masses. We then use these information to better understand planet formation and evolution.