About me

To describe my love for astronomy,
I will resort to a few words by Vera Rubin:
"I became an astronomer because I could not imagine
living on Earth and not trying to understand how the Universe works."

I am a ffith year graduate student in planetary science at Caltech. I have had the privilege of pursuing my long held childhood interest in astronomy and planetary science for the last five years. I grew up in Delhi and finished high school in Singapore on a SIA Youth Scholarship. I then moved to the U.K. to do my undergraduate study at the University of Cambridge, where I finished my bachelors in physics and masters in astronomy.

Research Interests

I have a broad interest in planetary atmospheres, planet formation, and protoplanetary discs, which is reflected by the breadth of my projects. More specifically, I am interested in:

  • Dust evolution in protoplanetary disks and consequences for planet formation
  • Planet formation and accretion of envelopes onto cores
  • Planetary atmospheric composition and its provenance
  • Atmosphere-interior interaction and its observable consequences
I use observational, analytical, and numerical methods in my attempts to study these areas. For more details, please take a look at the projects I am involved in.

Current and Past Projects

C.V.

Education

PhD, California Institute of Technology, 2017-
Advisors: Heather Knutson and Dave Stevenson
M. Sci, Institute of Astronomy, University of Cambridge, 2016-17
Advisors: Cathie Clarke, Amaury Triaud, Richard Booth
B. A., Natural Sciences (Physics), University of Cambridge, 2013-16

Recipient of: Institute of Astronomy Prize, Dirac Prize,
Cambridge Commonwealth Trust Scholarship,
SIA Youth Scholarship

Publications on ADS Full C.V.

Current and Past Projects

Spectroscopic Characterization of Exoplanetary Atmospheres

I reduce and analyze data from the Hubble and Spitzer Space Telescopes to characterize planetary atmospheres. In particular, I studied the quintessential warm-Neptune HAT-P-11b in detail and found that its atmosphere is atypically poor in heavy elements (Chachan et al. 2019). I also used Hubble data to study the super-puff Kepler79d and argue that high altitude hazes can explain the spectra and mass loss histories of super-puffs (Chachan et al. 2020). To interpret atmospheric spectra, I co-developed the open source forward and retrieval modelling code PLATON with Michael Zhang (Github, Zhang et al. 2019, Zhang et al. 2020).

Dust in protoplanetary disks and planet formation

I am particularly intrigued by the evolution of dust in protoplanetary disks and its consequences for planet formation. Currently, I am studying the formation of cold gas giants with inner super-Earths in the pebble accretion paradigm. In Chachan, Lee, & Knutson 2021, I showed that changes in material properties of grains across the water ice line creates strong radial gradients in the dust-to-gas ratio of the disk, which could explain why 1) giant planets preferrentially form at intermediate distances, 2) super-Earths do not undergo runaway accretion, and 3) super-puffs likely formed beyond the ice line and migrated in. I also studied the dynamics of dust in binary star systems and its consequences for formation of circumbinary planets in Chachan et al. 2019.

Atmosphere-Interior Interaction

I use semi-analytical and numerical tools to model the atmosphere-interior coupling and evolution of super-Earths. In Chachan & Stevenson 2018, I showed that an enormous amount of hydrogen can be stored in the interiors of super-Earths due to hydrogen's solubility in magma oceans.

Older Projects

I have dabbled in various research projects over the years. These includes studies on Saturn's differential flow and gravitational moments (Chachan & Stevenson 2019), Venus' circumsolar ring (Github), phase transformations of oxides of Iron, and moleculer spintronics.