Comets have captivated the curiosity of scientists for millennia. Not only are they among the most fascinating phenomena in the night sky, but their puzzling properties and variability continue to present unresolved challenges for researchers today.
Many observational, laboratory and modeling research programs have been devoted to comets and most prominently, they have been studied in situ by multiple space missions. A key motivation behind these efforts is the notion that comets preserve pristine material, providing direct insight into the conditions during solar system formation. Comets are traditionally considered to be well-preserved planetesimals that have spent billions of years beyond the orbit of Neptune and have therefore retained their primordial properties. However, recent studies, especially ESA’s Rosetta mission to comet 67P/Churyumov–Gerasimenko, have challenged this idea. It is now established that most comets have been significantly altered and that tracing their evolution is key for understanding the conditions in the solar system throughout its history.
Today’s comets formed as planetesimals beyond the giant planets' orbits. During planetary migration ~4 billion years ago, millions of them were scattered outward to the trans-Neptunian region and the Oort cloud. In the current epoch, some of the trans-Neptunian objects (TNOs) interact gravitationally with the outer planets and re-enter the middle solar system, as Centaurs or as active comets. Once they transition to cometary orbits, they lose material continuously, and undergo noticeable surface changes with every orbit until they disintegrate or reach dormancy. The individual phases of the comet life-cycle stages have been studied extensively over the past few decades. However, the findings about the different populations are rarely combined and a complete model of the changes experienced by comet nuclei from re-entering the inner solar system until their gradual end is still missing.
Building a comprehensive understanding of comet evolution requires integrating evidence from various research techniques across all evolutionary stages. This proposal addresses this challenge by focusing on a versatile method applicable consistently across all populations. We will utilize multi-band photometric observations in visible wavelengths, specifically targeting inactive comet nuclei and comparing them with inactive objects from all related object classes. Such spectrophotometric observations from ground and space telescopes are optimal for population-wide studies. However, collecting sufficiently large samples of observed objects from each population has not been possible until now. Even though photometric observations are technically straightforward, they require large amounts of precious observing time on large 2- to 8-meter telescopes.
The data scarcity, however, is about to be alleviated. Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST) will begin in 2025 and will scan the whole sky observable from the southern hemisphere every few nights. This wealth of data is poised to shift the field of small-body research into the realm of big data. The proposed research project is designed to utilize this transition period and to combine existing and proposed observations from other telescopes with LSST in order to test some of the most compelling hypotheses for comet evolution.
This work will be completed by the PI, two PhD students and two scientists with a PhD. Additionally the project will be supported by a network of international collaborators who have already worked together in the framework of an ISSI International team led by the applicant. To guarantee the continuous exchange with experts focusing on complementary techniques, the project envisions a series of workshops hosted in Bulgaria where the evolving team of experts will sustain the multi-disciplinary approach and extend the project findings towards a comprehensive model of solar system evolution.