Institute of Astronomy

Dr Mihkel Kama


Office: Hoyle H36
Office Tel: (01223) 337504
More Info (Internal)



We now know of over 4000 exoplanets, yet the full range of their properties remains a mystery. What can the composition of a planet tell us about its formation history? Are habitable worlds like Earth common?

Planets form in protoplanetary disks, containing gas, ices, and tiny rocks. I'm interested in the physical and chemical conditions and processes in planet-forming environments, and in how those relate to the properties of planets and planetary systems. Most of my work deals with elemental abundances and volatiles in protoplanetary disks, employing powerful telescopes like ALMA and APEX, and physical-chemical disk models.

Most chemical abundance measurements in disks rely on sub-millimetre spectroscopy to derive the quantity of specific molecules in the gas, and I too use this staple technique (e.g. Kama et al. 2016b). During my time at IoA, I've spearheaded an effort to go beyond the state-of-the-art. We developed a new tool for measuring the full elemental composition of the main planet-forming zone in disks. The Contaminated A-stars Method (CAM, Jermyn & Kama 2018) relies on the relatively slow mixing in the envelopes of stars with over 1.4 Solar masses, which allows freshly accreted material to dominate the surface. The photospheric composition of the star, which is easily measured, becomes an almost one-to-one proxy for the inner disk elemental budget.

We have now applied CAM to the "missing sulfur problem" in disks, and found that (89+-8)% of all sulfur atoms are, in fact, locked in refractory compounds and therefore invisible to cold gas-phase spectroscopy. This provides a novel input to disk and planet formation models incorporating chemistry, and is only a first taste of the potential of CAM.

Selected papers

Abundant refractory sulfur in protoplanetary disks (where we measure for the first time the fraction of sulfur, zinc, and sodium locked in rocks; Kama, Shorttle, Jermyn et al. 2019)

Stellar photospheric abundances as a probe of discs and planets (the theory and applications of measuring the composition of circumstellar material with CAM; Jermyn & Kama 2018)

Volatile locking and release in protoplanetary disks (detailed modelling of molecular and atomic lines from TW Hya and HD 100546, confirming a factor 100 depletion of C and O in the TW Hya disk, and determining that C/O > 1; Kama et al. 2016b)

Observations and modelling of CO and [Ci] in protoplanetary disks (definitive detections of atomic carbon in disks and modelling which relates it to the level of carbon depletion; Kama et al. 2016a)

Fingerprints of giant planets in the photospheres of Herbig stars (young A-type stars hosting transitional disks have photospheres depleted of refractory elements -- matching the high gas-to-dust ratio in their dust-depleted gaps and cavities; Kama, Folsom & Pinilla 2015)

Inner rim structures of protoplanetary disks (numerical and analytical models of the dust sublimation region; Kama et al. 2009)


Marie Sklodowska-Curie Fellow, IoA, University of Cambridge, in collaboration with the groups of Nikku Madhusudhan, Cathie Clarke, Mark Wyatt, Oliver Shorttle (current)

Research Associate, Leiden Observatory, astrochemistry group of Ewine van Dishoeck (2013-2016)

PhD, University of Amsterdam, thesis advisor Carsten Dominik (2008-2013)

MSc (cum laude), University of Amsterdam, thesis advisor Carsten Dominik (2006-2008)

BS, University of Tartu, Estonia, thesis advisor Indrek Kolka (2003-2006)

Page last updated: 7 November 2019 at 16:10