Arushi Nath.

On 4 October 2025, I had the honor of presenting my research during the 5th ExoClock Annual Meeting, held at the Polytechnic University of Madrid from 3–4 October 2025. The two-day event gathered over 100 citizen scientists and professional astronomers from around the world, working towards a common mission: refining exoplanet ephemerides in preparation for the ESA Ariel space telescope.

My talk, “Extending Exoplanet Ephemerides through TTV Analysis with NEPTUNE and Ground-Based Observations,” represented the latest results of a year-long project combining precise ground-based photometry and advanced computational modeling.. It was both humbling and encouraging that, as a high school student, I had the opportunity to share my findings alongside leading researchers whose work directly supports Ariel’s mission to study the atmospheres of distant worlds.

As both a presenter and participant, I gained invaluable insight into exoplanet research and the collaborative engine that powers ExoClock’s success. ExoClock is a citizen-science initiative that coordinates ground-based observations of exoplanet transits to maintain up-to-date orbital predictions—known as ephemerides—for targets of the upcoming Ariel mission. The meeting highlighted how ExoClock’s coordinated global network contributes to refining exoplanet timing data, improving models of stellar variability, and developing analysis pipelines that will enhance Ariel’s scientific return.

The conference opened with a keynote by Prof. Giovanna Tinetti, Principal Investigator of Ariel, who outlined the mission’s pioneering goal: to perform large-scale spectroscopic surveys of exoplanet atmospheres. Ariel aims to observe exoplanets across their full orbits, constructing phase curves that reveal variations in temperature, chemistry, and reflectivity over time—adding a time-dependent “fourth dimension” to our understanding of planetary systems.

Prof. Tinetti emphasized that accurate characterization of host stars is as vital as understanding their planets. Stellar variability, activity, and composition directly shape the interpretation of exoplanet data. She described ExoClock as a vital bridge between ground-based observers and space-based science. By providing continuously updated orbital predictions (ephemerides), ExoClock ensures that observations remain precisely timed and scientifically productive. It addresses a long-standing issue: many exoplanet observations still depend on outdated ephemerides, leading to inefficient use of valuable telescope time.

The ExoClock coordination team—Anastasia Kokori, Angelos Tsiaras, Alex Siakas, and Georgia Pandelidou—presented major updates to the project. The latest data release includes timing observations for 620 exoplanets, representing nearly a tenfold improvement in predictive accuracy. Impressively, about 45% of known exoplanets required updated ephemerides, underscoring ExoClock’s essential role in maintaining accurate orbital data for mission scheduling. I am honored to have contributed transit observations for over 20 exoplanets.

ExoClock has also become a global educational and research network, connecting universities, observatories, and independent observers. Its growing baseline of observations now reaches around 60% coverage across known targets—where coverage is defined as the percentage of years since discovery with at least one observation. This long-term temporal baseline has begun revealing subtle orbital phenomena such as apsidal precession, which provides clues about planetary interior structures and tidal interactions—and has directly helped me improve my own TTV modeling process.

While ExoClock’s core mission centers on timing precision, the meeting also highlighted the broader context of stellar characterization—understanding the stars behind the planets.

A recurring theme of the meeting was the importance of stellar characterization—understanding the properties and behavior of host stars to accurately interpret the planets that orbit them. Because stellar variability and activity can significantly influence transit measurements, detailed knowledge of both the star and its orbital dynamics is essential for robust exoplanet analysis.

Serena Benatti (INAF) presented how radial velocity measurements help identify stellar activity patterns that could otherwise mimic planetary signals. Her analyses explained apparent anomalies in transit depth and shape that might otherwise bias atmospheric retrievals, ensuring more reliable interpretations of planetary atmospheres.

Mayuko Mori (Astrobiology Center) investigated the influence of starspots—cool magnetic regions on stellar surfaces—on transit light curves. Using multi-filter (griz) photometry and multi-epoch modeling, she demonstrated how to separate temperature and positional degeneracies. Her work on TOI-3884 revealed recurring spot crossings that trace stellar rotation and activity cycles, deepening our understanding of host-star variability.

Simone Hagey (University of British Columbia) presented her research on Transit Timing Variations (TTVs) in the TrES-1b system. TTVs can arise from several mechanisms—including orbital decay, apsidal precession, or the gravitational influence of an additional, unseen planet—making their interpretation both complex and informative. By integrating TTV and radial velocity data, she found that the best-fit model indicates orbital decay within a mildly eccentric system, providing an important clue about tidal evolution and energy dissipation in close-in exoplanets.

My presentation focused on extending exoplanet ephemerides through TTV analysis—combining precise timing data from ground-based telescopes with computational modeling to detect or validate gravitational interactions from unseen companions.

To support this project, I recently set up a remote telescope in Nerpio, Spain, dedicated to high-precision photometric monitoring of exoplanet transits. Over the last three months, I observed nearly 25 transit events, generating accurate light curves that I contributed to the ExoClock database. These observations help refine orbital ephemerides and strengthen the global dataset that underpins the Ariel mission.

Using archived transit data from missions such as Kepler and TESS, I developed NEPTUNE—an open-source computational framework that combines N-body simulations, Bayesian inference, machine-learning-informed priors, and multi-period analysis to detect and characterize unseen exoplanets through Transit Timing Variations. In validation tests using Kepler-46b data, NEPTUNE successfully reproduced the orbital period (57 days), eccentricity (0.01), and companion mass (~110 Earth masses) of Kepler-46c, matching NASA’s published parameters.

Work is now underway to analyze transit data for additional exoplanets, particularly those with long orbital periods or systems where only a single transit has been observed. I am also developing algorithms to integrate new data captured by ExoClock into NEPTUNE. This integration will help extend baseline coverage and fill existing data gaps, further improving the precision and robustness of my models.

This work exemplifies how citizen observatories and open data science can combine to refine exoplanet parameters, strengthen mission planning, and accelerate discovery. It aligns with ExoClock’s philosophy: rigorous science, open collaboration, and shared learning.

Technical sessions highlighted the rapid evolution of computational astrophysics. Gordon Yip presented an overview of the Ariel Data Challenge, a citizen-science initiative now in its sixth year. The challenge invites the public to contribute statistical and machine-learning tools that will form a crucial part of Ariel’s ground segment and data analysis pipeline. Each edition focuses on a specific problem—ranging from light-curve retrieval and atmospheric characterization to instrument noise modeling.

These hybrid approaches embed physical constraints within neural architectures, preserving interpretability while improving predictive precision. Insights from these community-driven efforts are now directly influencing the design of Ariel’s data-processing pipelines, demonstrating how open scientific collaboration can accelerate the development of robust, explainable algorithms for exoplanet characterization.

Nicolas Cowan discussed how the Ariel survey will move beyond studies of individual planets toward population-level analyses, for example comparing day-to-night temperature contrasts across hundreds of planets to infer global atmospheric circulation and wind patterns.

On the engineering side, Javier Pérez-Álvarez reported on the technical progress of the Ariel telescope assembly. Engineers have streamlined the design to minimize part count while preserving mechanical stability and thermal performance. Innovations such as black radiative coatings for enhanced heat management and off-axis parabolic optics are contributing to improved optical efficiency and reduced stray light—key factors for achieving Ariel’s high-precision spectroscopic goals.

Reports from partner observatories underscored the international scope of ExoClock. The Royal Observatory Greenwich is currently undergoing major redevelopment under its First Light project, preparing to rejoin the network with modernized facilities by 2028. In Japan, Ritsumeikan University’s 60-cm telescope continues to deliver high-quality transit observations, leveraging advanced CMOS cameras and custom optical filters to achieve exceptional photometric precision.

The meeting concluded with a shared vision for the years ahead. As Ariel approaches launch in 2029, the citizen-science community is methodically refining every component of the observational chain—from small ground-based telescopes to the spacecraft’s instruments in orbit. This combination of precise timing, improved stellar models, and coordinated infrastructure ensures that when Ariel begins its survey, each observation will rest on a foundation of years of synchronized effort and global collaboration.

Between sessions and in the evenings, I exchanged ideas with observers from Italy, Greece, and the UK, discussing calibration pipelines, error propagation, and timing synchronization. These conversations will help me improve my photometry techniques and enhance the scientific output of my remote observatory. I also had opportunities to discuss strategies for improving my ongoing TTV research and identifying possible exoplanet systems where I could apply my methods.

These informal exchanges were as valuable as the presentations themselves, reinforcing my belief that scientific progress depends on openness, dialogue, and shared curiosity.