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 beginning my second year as a 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 two 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 planets and discs, which is reflected by the breadth of my projects. Some of the questions I am interested in include:

  • How do planets form in protoplanetary discs?
  • What are planetary atmospheres made of and how do they interact with planetary interiors?
  • Can planet formation in binary star systems give us important clues?
  • What methods can be employed to determine the key observables of exoplanets?
  • Finally, how should we synthesise our knowledge of the solar system and of exoplanetary systems to develop a unifying framework?
It is my goal to use observational, analytical, and numerical methods in my attempts to answer these questions. For more details, please take a look at the projects I am involved in.

Current and Past Projects



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


1. Chachan, Y. & Stevenson, D. J. 2018, On the Role of Dissolved Gases in the Atmosphere Retention of Low-Mass Low-Density Planets, ApJ, 854, 21, arXiv:1802.04296
2. Chachan, Y., Booth, R. A., Triaud, A. H. M. J., & Clarke, C. 2018, Dust accretion in binary systems: Implications for planets and transition discs (MNRAS, in revision)
3. Chachan, Y. & Stevenson, D. J. 2018, A linear approximation for the effect of cylindrical differential rotation on gravitational moments: Application to the non-unique interpretation of Saturn's gravity (Icarus, in revision)
4. Zhang, M., Chachan, Y., Kempton, E. M.-R., & Knutson, H. A. 2018, Forward modelling and retrievals with PLATON, a fast open source tool (PASP, in revision)

Full C.V.

Current and Past Projects

Planet Formation and Evolution

I use semi-analytical and numerical tools to study the formation and atmosphere-interior coupling in super-Earths as well as planet formation in binary star systems. (Chachan & Stevenson 2018, arXiv:1802.04296) (Chachan et al. 2018, MNRAS, submitted)

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Transmission Spectroscopy

Using Hubble Space Telescope and Spitzer data to characterise planetary atmospheres and develop forward models and retrievals to study their properties. (PLanetary Atmospheric Transmission for Observer Noobs: PLATON available on Github)

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Saturn's gravity field and Differential flow

We develop an intuitive understanding of how differential flow and gravitational moments are related and use our model to understand the degeneracy in flow properties in Saturn (Chachan & Stevenson 2018, Icarus, submitted).

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