Recently, the inner main belt asteroid (152830) Dinkinesh was identified as
an additional fly-by target for the Lucy mission. The heliocentric orbit and
approximate absolute magnitude of Dinkinesh are known, but little additional
information was available prior to its selection as a target. In particular,
the lack of color spectrophotometry or spectra made it impossible to assign a
spectral type to Dinkinesh from which its albedo could be estimated. We set out
to remedy this knowledge gap by obtaining visible wavelength spectra with the
Keck telescope on 2022 November 23 and with Gemini-South on 2022 December 27.
The spectra measured with the Keck I/Low Resolution Imaging Spectrometer (LRIS)
and the Gemini South/Gemini Multi-Object Spectrograph South (GMOS-S) are most
similar to the average spectrum of S- and Sq-type asteroids. The most
diagnostic feature is the ≈15±1% silicate absorption feature at
≈0.9-1.0~micron. Small S- and Sq-type asteroids have moderately high
albedos ranging from 0.17-0.35. Using this albedo range for Dinkinesh in
combination with measured absolute magnitude, it is possible to derive an
effective diameter and surface brightness for this body. The albedo, size and
surface brightness are important inputs required for planning a successful
encounter by the Lucy spacecraft.Comment: 7 pages, 1 figure. Under review in Icaru