RESEARCH

Modirrousta-Galian is a theoretical exoplanetologist specializing in super-Earths, sub-Neptunes, and their interactions with their host stars. His research builds on and connects principles from the atmospheric, geologic, and astrophysical fields to provide a theoretical explanation for observable phenomena.

super-Earth

Super-Earths (R ≲ 1.75R   ): Most super-Earths do not have hydrogen-rich atmospheres, so atmospheric spectroscopy is currently challenging. Because of this, it is common for researchers to constrain their compositions from mass and radius models even though the resultant degeneracies are large.  Modirrousta-Galian's research concerns with further constraining these bodies by considering their reflectivities. Different reflectivities could indicate different surface geochemistries, which can then be used to narrow down the bulk planetary composition. Furthermore, Modirrousta-Galian has focused on atmosphere-interior exchange and how this can lead to surprisingly large effects such as magma oceans dissolving large amounts of hydrogen.

sub-Neptune

Sub-Neptunes (1.75R   ≲ R ≲ 3.50R   ): Sub-Neptunes are exoplanets that typically have large primordial atmospheres and total masses less than ~10M   . Because of their hydrogen-rich atmospheres, spectroscopy is much more feasible than for super-Earths. This allows for their atmospheric constituents to be determined, but what does this mean? The atmospheric enrichment could be from (1) the original protoplanetary disc, (2) planetesimal accretion, or (3) erosion from the central embryo. These choices are not mutually exclusive, but determining which is the major source of enrichment can help constrain the bulk planetary composition. For example, if the atmosphere were rich in icy species due to the erosion of the central embryo, then the embryo would most probably be ice-rich. Considering the above, Modirrousta-Galian creates atmosphere-interior models and simulations in order to better understand sub-Neptunes.

Sun

Star-planet interactions: It is essential to consider the way stars and planets interact in order to get a thorough understanding of the evolution of exoplanetary bodies. One such interaction is the X-ray and ultraviolet irradiation from host stars onto their exoplanets. When this is considered in conjunction with thermal effects, most close-orbiting small exoplanets can lose the entirety of their primordial atmospheres within a few million years. This can have several effects on the evolution and observed properties of certain bodies. For instance, if the original primordial atmosphere were large enough, the interior embryo may have become compressed resulting in an ultra-dense 'remnant core'.