Research

Why are comets interesting to us? 

Comets are among the oldest objects in our solar system, representing the leftover materials from which planets and moons were built. These fragments of ice and rock were scattered to the cold outer reaches of the solar system, far beyond the Sun’s influence. There, they have remained dormant for billions of years, preserving the pristine building blocks of the solar system. In this way, comets serve as cosmic time capsules, offering invaluable clues to the origins of planet formation process and even life itself.

Occasionally, one of these pristine objects is nudged into the inner solar system, where Jupiter's gravity shapes their orbits—these are known as Jupiter Family Comets (JFCs). As some of the most accessible reservoirs of primordial material, JFCs offer invaluable insights into the solar system’s formation and early evolution. However, as these comets approach the Sun, their near-surface ices sublimate, driving active processes that transform their once-pristine surfaces. To truly understand the value of comets as a window into the formation of the solar system, it is essential to first explore how these processes alter their surfaces.

Moreover, comets provide a unique environment to study landscape evolution. With no atmosphere, very low gravity (~100,000x less than Earth), and a material yield stress similar to a powdery snow, at first it’s hard to imagine any physical mechanisms that can effectively erode a comet’s surface into recognizable landforms other than just a large, flat plain. And yet, when we look at comets, we see very dramatic topography, with landscapes that look, without context, rather familiar to those we see here on Earth (Fig. 1). My research seeks to uncover the forces behind the formation of these striking landscapes, shedding light on how surface evolution unfolds in one of the most extreme and fascinating environments in the solar system.

A New Era of Small Body Geology 

Prior to Rosetta, all missions to comets were flyby missions at relatively large distances from their target nuclei (Fig. 2). The Rosetta mission to comet 67P revolutionized our understanding by providing the highest-resolution spatial and temporal data of any comet, allowing us to directly observe the processes driving cometary surface evolution and opening the doors to the field of small body geology.

Rosetta revealed two distinct landscapes on the surface–"smooth" and "rough" terrains. The rough terrains represent the nucleus's consolidated 'bedrock,' retaining substantial relief—though how they remain intact is still a mystery. Sublimation of ices acts as an active weathering process, generating loose, transportable sediment. While some of this sediment accumulates at the base of cliffs, the comet’s low gravity allows sublimating gases to loft particles and transport them across the surface. This widespread sediment transport creates the smooth terrains, which are extensive deposits of centimeter-to-decimeter sized, water ice-rich particles.

Venus is often called Earth’s “sister planet” due to their nearly identical sizes and densities. Yet, despite these similarities, Venus has taken a vastly different evolutionary path. By studying Venus’s interior, we can gain insights into when and why Earth’s and Venus’s paths diverged. This research also has implications for astrobiology; understanding Venus’s evolution could help us address a fundamental question: what makes a planet habitable?

On Venus’s surface, we find a variety of deformational features in distinct patterns and scales. My work focused on tectonic deformations along canali—long, dried-out lava channels with nearly constant widths found across Venus’s plains. Stratigraphic evidence suggests that these canali formed in the last phases of extensive plains volcanism, possibly during a global resurfacing event around 300 million years ago. Originally, these channels would have followed downhill gradients, allowing lava to flow, but post-formation tectonic forces have warped them into nearly periodic topographic features (Fig. 5). The dominant scales of this deformation provide clues to Venus’s lithospheric structure and mantle dynamics, helping us better understand the planet’s unique geologic history and internal processes.

Topography is a powerful tool for understanding landscapes, revealing the relationships between different landforms, the history of a region, and the interactions of processes shaping its evolution. Saturn’s moon Titan is an Earth-like world with a range of familiar landforms, including lakes, rivers, dunes, seas, and mountains. Although these features formed under conditions vastly different from Earth’s, the processes that shaped them are strikingly similar, allowing us to apply the principles of terrestrial geomorphology to Titan’s surface. To fully leverage these techniques, however, we need accurate topographic data.

The Cassini mission provided some radar altimeter data for Titan, but since the spacecraft orbited Saturn, not Titan, coverage was limited. To address this, we used radar stereogrammetry with overlapping radar images from Cassini to generate high-resolution topographic maps (e.g., Fig. 6). This technique allows us to better understand Titan’s diverse terrain and gain insights into the processes shaping its landscapes.