Giant planet and Solar System formation through ALMA eyes (AST/2020/NAY)

Formation of planets in general, and giant planets in particular, is an area of active research with major uncertainties. In the classical Core Accretion paradigm, solid cores are assembled first by solids sticking together; gas giants then grow by accretion of gas onto the cores. The process is thought to take millions of years. In the Gravitational Instability scenario, giant planets are born immediately after the protoplanetary disc formation when the latter fragments onto massive gaseous clumps. The clumps are loosely bound and prone to gas and dust loss. The Solar System data, and the exoplanetary data from satellites such as Kepler, proved somewhat insufficient to break the deadlock between the theories. These data tell us about the end state of the systems when planet formation ended, but do not tell us directly what goes on while the planets and protoplanetary discs co-exist.

In late 2015 the ALMA radio telescope revolutionised the field, showing first hints of planets immersed in discs, orbiting same stars at the same time. We have learned that planets can be assembled much faster than envisioned previously; that while they are massive enough to grow by accretion of gas rapidly, they do not do so as predicted (Nayakshin et al 2019). In parallel to these developments, theoretical work and simulations (fig. 1; Humphries and Nayakshin 2018, Humphries and Nayakshin 2019) showed that giant planets assembled via Gravitational Instability can be very metal rich as required by the exoplanetary and the Solar System data, and that these planets can migrate inward and explain the closer-in data as well (Humphries et al 2019). These arguments tip the scales strongly in favour of forming at the least the distant population of planets, with masses from sub-Neptune to many times Jupiter, by the Gravitational Instability scenario.

One very recent ALMA result (fig. 2, TsukagoshiEtal19) is particularly striking, showing a Neptune mass planet discovered just outside of the nearly all mm-sized dust in the TW Hydra system. Our numerical simulations show that this is only possible if the planet is the source of the dust seen by ALMA: this is therefore the most direct to date evidence of how giant planets loose mass. This and other recent ALMA observations not only confirm but also constrain the modern Gravitational Instability theory or planet formation.

In the first phase of this PhD project, state-of-the-art numerical simulations with our in-house numerical tools will be employed to further detail the properties of planets formed in the Gravitational Instability scenario, such as their mass, composition, orbital separation, and planetary system multiplicity. We shall also detail observational appearance of these planet-disc systems during their evolution by building detailed simulations of dust and planet dynamics in the extended protoplanetary discs. The key new element of these simulations will be mass loss from the planets, in both the gas and the dust, which was hitherto neglected by most modellers.

In the second phase of this project we shall compare the predictions of these simulations with the properties of the outer Solar System. While we have no gaseous disc in the Solar System now to test the theories as directly as through ALMA observations, we have unique constraints on the structure, spins and magnetic fields of the four giant planets. Additional constrains on the models are provided by the giant planets satellite systems and their interaction with the Kuiper belt. This part of the project will aim at bridging the gap between our views on the formation of the exoplanetary systems and the Solar System.

We shall also utilise our on-going collaborations with ALMA observers to compare our simulations to the current and future ALMA data. This project could also incorporate constraints from the Direct Imaging observations of young planetary systems in the NIR/optical, and population synthesis calculations, depending on the candidate's scientific interests.
Entry Requirements
UK Bachelor Degree with at least 2:1 in a relevant subject or overseas equivalent.

The University of Leicester English language requirements apply.

Home/EU students only subject to residency requirements.
Application Instructions
When applying, please ensure we have received all of the following required documents by Wednesday 29th January 2020:

• Submit an online application form https://le.ac.uk/study/research-degrees/funded-opportunities/stfc-studentships
• 2 academic references
• STFC Research Interests Form
• CV
• Undergraduate transcripts
- If you have completed your undergraduate degree, we will also require your undergraduate degree certificate
- If you have completed a postgraduate degree, we will also require your transcripts and degree certificate

If we do not have the required documents by the closing date, your application may not be considered for the studentship.
Interview Dates
26th February 2020 – In person
27th February 2020 – Skype only
28th February 2020 – Skype only
2nd March 2020 – Skype only
3rd March 2020 – Skype only
4th March 2020 – In person