Rotational Light Curve, phase, and visible colors of (52246) Donaldjohanson throughout Lucy Mission Flyby
A.C. Souza-Feliciano, F.L. Rommel, B.E. Morgado, L.M. Catani
Icarus, In Press, Journal Pre-proof, Available online 20 August 2025
” Highlights
- We confirm that (52246) Donaldjohanson is a very slow rotator asteroid and refine its rotation period to 253.1 ± 2.6 h.
- We obtained the color of this asteroid in different rotational phases and found indications of heterogeneity on the surface of (52246) Donaldjohanson compatible with aqueous alteration.
- For an observer on Earth, Lucy’s flyby happened at the rotational phase of 0.30 (zero phase set at JD 2458198.8677584), an intermediate phase between a bright and a faint peak.
- The angle between the SOAR telescope, the object, and the spacecraft at the moment of the flyby was 102 degrees. In that case, depending on the object’s orientation, we may have seen it almost in quadrature.”
“The main belt asteroid (52246) Donaldjohanson was visited on April 20th of 2025 by the Lucy spacecraft. We took this opportunity to observe the object with the SOAR telescope, aiming to create synergy between ground- and space-based observations. Our goal includes refining the rotational period of (52246) Donaldjohanson, determining the rotational phase of the flyby observation, and obtaining the photometric colors of (52246) Donaldjohanson in the SDSS and Bessell-Johnson system. To achieve our goals, we used photometric observations of (52246) Donaldjohanson from three datasets: obtained in (i) during the week of Lucy flyby on the SOAR Telescope using r- and i- filters of the SDSS system in five different nights; (ii) August 2019, also on the SOAR Telescope using R- and V- filters of the Bessell-Johnson system on two nights; and (iii) between 2018 and 2025 on the r-, g-, and i- filters of the ZTF survey. Using the ZTF database and SOAR observations, the Lomb-Scargle periodogram confirms its long rotational period of 253.1 ± 2.6 h. The rotational light curve has an amplitude of 1.03 ± 0.03 mag, in agreement with an elongated asteroid. No signal of a secondary object is found in the residual fit at a limit of 0.2 mag. The colors r i and V R agree with a Cg-type asteroid for most of the phases analyzed. Some small variations in colors are found and they could be explained by some heterogeneity on Donaldjohanson’s surface. The angle between the spacecraft, Donaldjohanson, and the SOAR Telescope at the moment of the flyby was estimated to be 102 degrees. The results discussed here could serve as a reference and would support further analyses of the Lucy mission data. The comparison and combination of spacecraft and ground-based observations could allow the extension of the knowledge obtained here to an uncountable number of asteroids that will not have the opportunity to be visited by spacecraft.”
