Small bodies and their evolution
Comets, Centaurs, asteroids, and icy planetesimals: how they formed, how they change, how their orbits evolve, and what present-day activity can tell us about their history.
Earth & planetary science · remote sensing
I work with models and measurements, from comets to Earth-observing satellites.
I’m an Earth and planetary scientist. On the Earth-observation side, I work on calibration of MODIS and VIIRS. On the planetary side, I’ve worked on comets, asteroids, Centaurs, planet formation, and mission-related science. The common thread is simple: understand the physics, understand what is actually measured, and make sure the two tell a consistent story.
I am a Senior Research Scientist at Science Systems and Applications, Inc. (SSAI), supporting NASA Goddard. My current work includes MODIS reflective-solar-band calibration and VIIRS day–night-band calibration.
At a glance
Current work and background
Now: satellite calibration and performance analysis. Ongoing: planetary science, research collaborations, and scientific computing. Ph.D. in Geosciences — Planetary Sciences, Tel Aviv University (2010).
Research
The two sides of my work are closer than they look.
In both fields, I’m trying to infer a physical system from measurements that have limits and uncertainties. Sometimes the system is a comet or asteroid. Sometimes it is the instrument itself. Models tell us what to expect; data tell us where the model needs work.
Instrument calibration
On-orbit calibration and characterization of MODIS reflective solar bands and the VIIRS day–night band, especially long-term changes that matter for the science data record.
Models and analysis
Numerical models, time-series analysis, and research software in Python, C/C++, Fortran, shell, Linux, and Git.
Observations
A few of the things behind the plots.
Satellite images and spacecraft observations sit at the end of a long chain of geometry, instrument response, calibration, modeling, and interpretation. These three examples come from the systems and targets discussed elsewhere on this site.
Selected work
A few projects that show the range.
The examples below span satellite calibration, comet dynamics, and asteroid ejecta. Each starts with a concrete measurement or modeling problem.
MODIS after orbital drift
Terra and Aqua are now sampling solar-diffuser geometries outside much of the range characterized early in the missions. My 2022 first-author study examined calibration options for that regime; later team work used additional Aqua yaw maneuvers to characterize the changing geometry.
Why it matters: the goal is to keep reflective-solar-band calibration reliable as these long-running missions move into a new part of their orbital life.
VIIRS day–night-band calibration
I support day–night-band calibration for NOAA-20 and Suomi NPP. The work includes tracking calibration behavior across the DNB’s large dynamic range; collaborative publications also cover NOAA-21 performance.
Why it matters: stable calibration is what makes low-light measurements comparable over time rather than just visually striking.
The Centaur gateway to Jupiter-family comets
Numerical orbital integrations identified a short-lived, low-eccentricity region just outside Jupiter through which many objects pass on their way from the Centaur population to Jupiter-family comet orbits.
Why it matters: the Gateway gives us a specific place to study the dynamical transition and the onset of comet-like physical activity together.
Didymos and ejecta in a binary system
A 2024 study simulated 72 variations of the Didymos system and grouped the resulting ejecta distributions and surface-return times to see which system properties most strongly control the outcome.
Why it matters: the work provides a baseline for predicting how a binary system’s configuration changes where impact ejecta goes and how quickly material returns to a surface.
Publications
Selected papers.
A short list from both sides of my research, with first-author work marked on the publications page. Full records are available through Google Scholar, ORCID, ResearchGate, and ADS.
2026
Terra MODIS Mission Operation, Calibration, and Performance ↗Xiong et al. (including G. Sarid) · Journal of Applied Remote SensingEarth observation
2024
Categorization of Spatial and Temporal Ejecta Outcomes in Binary Systems Based on Variations of the Didymos System ↗Larson, Fernández & Sarid · The Planetary Science JournalPlanetary science
2019
29P/Schwassmann–Wachmann 1, A Centaur in the Gateway to the Jupiter-Family Comets ↗Sarid et al. · The Astrophysical Journal LettersPlanetary science · first author
Consulting & collaboration
I’m open to exploratory conversations.
If you have a scientific or technical problem that overlaps with my background, I’m happy to talk and see whether I can be useful. I’m not promising current availability, and any outside work would need to be compatible with my employer obligations.
What I can help with →