This manuscript analyzes forced photometry data of the dwarf planets Pluto and Eris obtained by the ATLAS network between 2015 and 2023 using the o- and c-band filters. The phase curves of Pluto and Eris show no noticeable opposition effect. Eris shows no changes in its absolute magnitudes between 2016 and 2022, and its weighted mean absolute magnitudes are H=o−1.35±0.03\documentclass[12pt]{minimal}
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\begin{document}$_{o}=-1.35 \pm 0.03$\end{document} and H=c−1.01±0.02\documentclass[12pt]{minimal}
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\begin{document}$_{c}=-1.01 \pm 0.02$\end{document}. Pluto’s absolute magnitudes in the o and c filters show temporal variations between 2017 and 2022 Pluto and Eris show temporal variations in their phase coefficients β\documentclass[12pt]{minimal}
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\begin{document}$\beta $\end{document} in the o and c filters related to “phase reddening.’ This effect is more pronounced for Eris than for Pluto. The absolute color Hc-Ho of Eris is 0.34±0.05\documentclass[12pt]{minimal}
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\begin{document}$0.34 \pm 0.05$\end{document}. The absolute colors of Pluto are systematically redder than those of Eris. The absolute color and relative phase coefficients of Pluto in the o- and c-filter show a significant anti-correlation on an annual basis, which is a direct result of “phase reddening”. The relationship between these two variables is not obvious in Eris because of the small annual variations in absolute color. Eris and Pluto show no comet-like outbursts during the observation period studied here.
