Jonty Marshall

Jonty-Marshall-full-image-wJonty is a Vice Chancellor’s Postdoctoral Research Fellow at UNSW Australia working with the Exoplanetary Science group to better understand the planet formation process through links between stars, their attendant planets, and remnant dusty debris.

My primary research interest is circumstellar dust discs as evidence of planetary systems around mature, main-sequence stars.  These discs are the tenuous, dusty remnants of the gas-rich, primordial protoplanetary discs that surround stars during their formation, the birthplace of planetary systems like our own. They are composed of rocky and icy bodies ranging from micron-sized dust grains to kilometre-sized planetesimals (asteroids and comets). The dust grains are the remnants of collisions between larger bodies in the disc; these systems are therefore known as debris discs.

We most commonly observe debris discs as excesses above their host stars photospheric emission at infrared wavelengths, produced by thermal emission from dust grains, but have also observed them at optical and near-infrared wavelengths by the light they scatter from their host star. We have identified around 20 +/- 2 % of nearby, sun-like stars with excess consistent with the presence of cool debris analogous to the Edgeworth-Kuiper belt.

Through hierarchical growth, dust grains present in a primordial protoplanetary disc stick together in collisions, becoming pebbles, boulders, and eventually planetesimals. It is these planetesimals that constitute the building blocks of planets. We might therefore surmise that the presence (and properties) of dusty debris and planets around another star should be correlated. Indeed, we find a higher incidence of planets around systems with debris and have further identified an anti-correlation between planet mass and debris disc brightness.

As an easily visible remnant of the planet formation process, a debris disc is therefore an ideal marker of a planetary system existing around another star. For sun-like stars, these planetary systems represent alternative outcomes of the same planet formation process that produced our own solar system with its two debris belts (the Asteroid belt and Edgeworth-Kuiper belt) and eight planets. By studying such systems in detail we thus obtain an understanding of the formation timescales, range of outcomes, and incidence of planetary systems like our own.

Research area(s)  Exoplanets, Debris Disks, Formation and evolution of planetary systems (Planets), Astrobiology

Email: jonty.marshall@unsw.edu.au

Tel: (02) 9385 5572

Institution: University of New South Wales Australia