Astrophysicist and Planetary Scientist Ph.D. Candidate at University of California, Los Angeles NASA FINESST Grant Recipient
Hi! Thank you for visiting my webpage.
I'm an Astrophysicist and a Planetary Scientist, and currently a Ph.D. Candidate in
the Department of Earth, Planetary, and Space Sciences at the
University of California, Los Angeles (UCLA).
I am interested in understanding the processes that dictate how planets form and evolve and how this ultimately leads to an environment and ingredients suitable for life.
Specifically, my research entails the following topics: planet formation and evolution; atmospheric escape; radiative hydrodynamics; atmosphere-interior interactions; ab initio molecular dynamics; planetary dynamics and celestial mechanics; and planetary habitability.
Please visit the 'Research' or 'Publications' section to learn more about my research.
I began my Ph.D. at UCLA in 2017 under the supervision of my Prof. Hilke Schlichting.
I received MS in Planetary Science (Geophysics & Space Physics) in Summer 2019 and advanced to Candidacy in Fall 2019.
In 2020, I was awarded the three-year Future Investigators in NASA Earth and Space Science and Technology (FINESST) grant, which now supports my research.
In addition to my work with Prof. Schlichting, I am leading projects with Profs. Lars Stixrude (UCLA)
and Edward Young (UCLA), and have been collaborating on others with
Profs. James Owen (Imperial College of London, UK)
and Erik Petigura (UCLA) and James Rogers (Imperial College of London), Dakotah Tyler (UCLA) and others.
In 2016, I graduated from the Indian Institute of Technology (IIT), Kanpur,
with a Bachelor's and Master's (Dual Degree) in Aerospace Engineering. For my Master's thesis, I explored the dynamics of rings around non-spherical, minor planets
such as Chariklo with Prof. Ishan Sharma and Dr. Sharvari Nadkarni-Ghosh.
In addition, I worked on projects encompassing a wide range of other topics such as orbital mechanics, N-body simulations, kinetic/granular theory and designing & building Formula-One prototype cars.
For more details, please see my CV or visit the 'Contact' section to know how we could get in touch.
My research lies at the intersection of astrophysics, planetary geosciences and chemistry and explores how Earth-like
extrasolar planets (or exoplanets) form from gas and dust and evolve over billions of years.
In particular, I am interested in understanding the fundamental physical and chemical processes that dictate a planet's formation and subsequent evolution.
My work involves building mathematical models that encapsulate such physical or chemical processes and are motivated by the observations of the
thousands of planets we know today. In addition, I use quantum mechanics to perform computational experiments to understand how the primary building
blocks of such planets interact with each other. This is motivated by the far-reaching consequences of such interactions on the formation, evolution,
and structure of planets but a lack of experimental data due to extreme environments in which these building blocks interact.
Below, I list my current and past research projects. For an up-to-date record of my research, please see my curriculum vitae.
Origin of super-Earths and sub-Neptunes: understanding the radius valley as a by-product of planet formation
Investigating the interaction between planetary building blocks using ab-initio molecular dynamics
Understanding the geochemical evolution of planets
Dynamics and impacts: exploring the observed asymmetry in the distribution of Lunar cold-spots
Dynamics of planetary rings: minor planets and Saturn
Below, I give an overview of my current (those published) and past projects that I have led or where I made substantial contributions.
Origin of super-Earths and sub-Neptunes: Understanding the radius valley as a by-product of planet formation under the core-powered mass-loss mechanism
A video explaining how the radius valley can be understood as a by-product of planet formation under the core-powered mass-loss mechanism. Credits: Emilie Eshbaugh (UCLA undergraduate student) and Hilke Schlichting.
The video above by Emilie Eshbaugh (UCLA) gives a great introduction to this project. If you prefer a textual summary and would like further details, please read below or refer the papers listed at the end of this section.
Till 1995, we only knew about the eight planets in our Solar system. Since, we have discovered thousands of planets in our galaxy orbiting other stars, i.e. exoplanets
(4031 as of Aug 1 2019; see NASA Exoplanet Archive). These discoveries have revolutionized the field
of exoplanetary science and offer new insights into the formation and evolution of planets.
One of the key findings from recent observations has been that the abundant planets in our galactic neighborhood, to-date, are 1 to 4 Earth radii in size, i.e. larger than Earth and smaller than Neptune.
Intriguingly, further observations have revealed that there is a lack of planets of sizes 1.5 - 2.0 Earth radii, i.e. a radius 'valley', in
the size distribution of such small, short-period (<100 days) exoplanets. Moreover, a transition in planet density has been noted around
~1.6 Earth radii, with smaller planets having higher bulk densities, consistent with rocky Earth-like compositions while
larger planets having lower bulk densities, suggesting that these planets are engulfed in H/He atmospheres.
It has thus been suggested that this valley likely marks a transition regime between smaller rocky planets, i.e.
'super-Earths' to larger planets with significant atmospheres, i.e. 'sub-Neptunes'.
Radius valley in the distribution of small, close-in planets separating populations of super-Earths and sub-Neptunes.
Plot based on data from Fulton et al. 2017.
Typically, atmospheric erosion due to high-energy radiation from the host stars, i.e. photoevaporation, is suggested as an explanation to these observations.
Recently, however, Ginzburg et al. 2018 and my advisor and I (Gupta & Schlichting 2019, 2020) have demonstrated that atmospheric loss due to a planet's own cooling luminosity, i.e. core-powered mass-loss,
can also explain the observed radius valley, even without photoevaporation.
Furthermore, we have demonstrated that planetary evolution under this mechanism can explain a multitude of trends observed in the planet size distribution
with orbital period, insolation flux and stellar mass, metallicity, age (Gupta & Schlichting, 2020).
Schematic demonstrating how the core-powered mass-loss mechanism results in super-Earths and sub-Neptunes and thus the radius valley. See Gupta & Schlichting, 2019 for details.
It is likely that the observed planet distribution was not just sculpted by core-powered mass-loss and photoevaporation, but by a multitude of processes over their lifetime such as giant impacts or different planet formation pathways (icy planets, formation in gas depleted disks or after dispersal of gas disks). Nevertheless,
our work shows that the valley in the size distribution of exoplanets is an inevitable by-product of the planetary formation process, i.e. through the core-powered mass-loss mechanism.
Rings around small, non-spherical planetary bodies
Artistic rendition of the triaxial shaped dwarf planet Haumea with its surrounding ring.
Image credit: Wikipedia user 'Tomruen'.
For years, we have known of the rings around the giant planets of our Solar System.
Rings are also expected to exist around extrasolar planets but have not been detected so far.
However, what was not expected was the existence of rings around much smaller, non-spherical bodies of our Solar System.
This changed in 2014 with the discovery of rings around a small body named Chariklo, followed by another discovery in 2017, of rings around the dwarf planet, Haumea.
These discoveries suggest that the ring systems are much more common in our Solar System than previously thought,
and their existence has challenged our understanding of their evolution and formation.
In collaboration with my former group
from IIT Kanpur (Prof. Ishan Sharma, Dr. Sharvari Nadkarni-Ghosh, Shri B. Bharath and others), I have been trying to understand the dynamics
of rings around non-spherical bodies through N-body simulations.
To know more, please refer:
⚬A. Gupta, S. Nadkarni-Ghosh & I. Sharma, 2018. Icarus 299, 97-116. [ADS]
Investigating the observed asymmetry in the distribution of Lunar cold-spots
We have known for some time that our Moon has a spatial (longitudinal and latitudinal) asymmetry in the distribution of craters.
This asymmetry is due to our Moon's synchronous motion around Earth and is also observed around other natural satellites like in the Galilean system.
Since these observations, this problem has been investigated and explained using analytical, semi-empirical and numerical models.
However, recent observations of the distribution of lunar 'cold-spot' craters by the Lunar Reconnaissance Orbiter (LRO)
have revealed that their longitudinal asymmetry is higher than that previously observed.
These 'cold-spot' craters are the recently formed lunar craters which show distinctly low night-time temperatures around
them thus allowing them to be observed by LRO's thermal instruments.
These are estimated to be a million years old or younger and to have sizes between ~ 50 - 2000 m -- much younger and smaller than the craters observed previously.
Therefore, this discrepancy in the distribution of cold-spot craters raises questions, for example,
about the assumptions and inferences made by the previous studies when investigating the older observations regarding the impactor size distribution
or the source of these craters.
Through this project, we are trying to answer such questions. While I was leading this project in its earlier stages, it is currently being led by Sophia Turner who is a senior-year undergrad at UCLA.
Saturn's F-ring: dynamics under continual formation and disruption of aggregates
Cassini image shows Saturn's potato-shaped moon, Prometheus, dynamically and physically interacting with the F-ring.
Image credit: NASA/JPL/Space Science Institute.
Saturn's F-ring is one of the most beautiful and dynamically active systems in our Solar system.
This is due to the continual formation and disruption of aggregates in this ring which is because it is located near Saturn's Roche limit.
Under Prof. Heikki Salo's (University of Oulu, FI) guidance, who is an expert on numerical simulations of planetary rings,
I investigated the dynamics of this ring system using N-body simulations and also the mechanism of confinement in rings due to the shepherding satellites.
⚬ J. Owen et. al. (nine authors including A. Gupta). 2022. In review.
[ADS] ⚬ E. Estrela, M. Swain, A. Gupta, C. Sotin and A. Valio 2020. ApJ. 898, 104.
[ADS] ⚬ Adaptively optimized trajectories for rendezvous with an asteroid
If you have any questions, comments or suggestions regarding my work and publications or would like to collaborate, or want to connect for outreach events, please do get in touch. I’d love to hear from you!