Presentation Information
[PPS03-P15]Light Curve Prediction of Long-Period Comets for Target Selection of the Comet Interceptor Mission
*Manami Kishi1, Seiji Sugita1, Hideyo KAWAKITA2 (1.Department of Earth and Planetary Science, School of Science, The University of Tokyo, 2.Department of Astrophysics and Atmospheric Sciences, Kyoto Sangyo University)
Keywords:
Comet
Comet Interceptor (CI) is a mission designed to perform a flyby observation of long-period comets (LPCs) near 1 AU, where cometary activity is expected to be high. LPCs are thought to have experienced limited thermal processing by the Sun and therefore to retain abundant volatile materials and highly primitive compositional information. However, because LPCs orbits are usually unknown, it is often impractical to design and launch a spacecraft after discovery. To overcome this limitation, CI adopts a strategy in which the spacecraft is launched before target selection and placed in a parking orbit near a Lagrange point. Once a suitable LPC is discovered by ground-based telescopes, the spacecraft will transfer to a flyby trajectory to conduct observations. (Snodgrass & Jones, 2019).
To identify suitable CI targets, all-sky surveys of distant comets are currently being conducted using facilities such as the Vera C. Rubin Observatory. Observations from 2000 to 2024 indicate that, on average, 3.5 LPCs per year satisfy the orbital criteria for CI targets (Sánchez et al., 2024). From an operational perspective, CI requires the discovery and selection of comets at heliocentric distances of 5-10 au using ground-based telescopes. However, at these distances, comets are typically faint, and compositional identification through spectroscopy at various wavelengths is challenging. Therefore, it is necessary to predict cometary activity near perihelion (-1 au) based on brightness evolution at large heliocentric distances (Ivanova et al., 2025).
Previous observations have revealed a trend in comet brightening rates. Comets that exhibit high activity at large heliocentric distances (-10 au) tend to show relatively small brightening rates from 10 au to 1 au, whereas comets with low activity at -10 au often display significant brightening as they approach the Sun (Lacerda et al., 2025). Furthermore, comparisons between radio spectroscopic and visible photometric observations suggest that comets with small brightening rates as a function of heliocentric distance tend to be rich in highly volatile species such as CO and CO2, while those with larger brightening rates are more likely dominated by H2O (Biver et al., 1998, 2002).
However, there have been no quantitative studies evaluating how specific ice compositions translate into brightening behaviors. Consequently, it remains unclear how accurately cometary composition can be inferred only from observed brightening rates. To address this issue, we modeled the evolution of comet light curves for different ice compositions using a photometric model.
We developed a model to calculate magnitude variations of LPCs driven by the sublimation of H2O, CO, and CO2 at large heliocentric distances, following the method of Meech et al. (2017). Using this model, we calculated comet magnitudes as a function of heliocentric distance. By varying the relative abundances of H2O, CO, and CO2, we found that the ratios of CO and CO2 relative to H2O play a dominant role in determining the characteristic evolution of cometary light curves.
To identify suitable CI targets, all-sky surveys of distant comets are currently being conducted using facilities such as the Vera C. Rubin Observatory. Observations from 2000 to 2024 indicate that, on average, 3.5 LPCs per year satisfy the orbital criteria for CI targets (Sánchez et al., 2024). From an operational perspective, CI requires the discovery and selection of comets at heliocentric distances of 5-10 au using ground-based telescopes. However, at these distances, comets are typically faint, and compositional identification through spectroscopy at various wavelengths is challenging. Therefore, it is necessary to predict cometary activity near perihelion (-1 au) based on brightness evolution at large heliocentric distances (Ivanova et al., 2025).
Previous observations have revealed a trend in comet brightening rates. Comets that exhibit high activity at large heliocentric distances (-10 au) tend to show relatively small brightening rates from 10 au to 1 au, whereas comets with low activity at -10 au often display significant brightening as they approach the Sun (Lacerda et al., 2025). Furthermore, comparisons between radio spectroscopic and visible photometric observations suggest that comets with small brightening rates as a function of heliocentric distance tend to be rich in highly volatile species such as CO and CO2, while those with larger brightening rates are more likely dominated by H2O (Biver et al., 1998, 2002).
However, there have been no quantitative studies evaluating how specific ice compositions translate into brightening behaviors. Consequently, it remains unclear how accurately cometary composition can be inferred only from observed brightening rates. To address this issue, we modeled the evolution of comet light curves for different ice compositions using a photometric model.
We developed a model to calculate magnitude variations of LPCs driven by the sublimation of H2O, CO, and CO2 at large heliocentric distances, following the method of Meech et al. (2017). Using this model, we calculated comet magnitudes as a function of heliocentric distance. By varying the relative abundances of H2O, CO, and CO2, we found that the ratios of CO and CO2 relative to H2O play a dominant role in determining the characteristic evolution of cometary light curves.