# # Program information file # PROGRAM_ID 2024A049 PROGRAM_TITLE Estimating the size and thermal properties of [163693] Atira PROGRAM_INV1 Eric MacLennan PROGRAM_INV2 Anne Virkki PROGRAM_INV3 Tracy Becker PROGRAM_INV4 Aaron Deleon PROGRAM_INV5 Sean Marshall PROGRAM_SCICAT near-Earth objects PROGRAM_ABSTRACT_BEG These proposed MIRSI and SpeX observations will be used to directly determine the size and taxonomic class of the binary asteroid, [163693] Atira, the largest asteroid with an orbit completely interior to Earth's orbit. Because of its unique location in the Solar System, it is extremely difficult to observe using ground-based telescopes. However, the unique capabilities of the IRTF allow for daytime thermal infrared observations of Atira, which will reach a solar elongation greater than 70 degrees in the upcoming semester. Thermal emission observations at 10 microns using MIRSI will be used to distinguish between two likely size and shape constraints from previous radar shape modeling efforts. A 5 km and a 7 km sized model yield unique thermal flux measurements during the observation window in which Atira is bright enough [greater than 1 Jy] to be detected in 2 minutes of integration time. We will collect thermal observations for 6 hours in three consecutive days to monitor the thermal emission variation. Shape effects from the rotation of the primary and potential detection of a mutual event [secondary transit and/or eclipse] will better constrain the characteristics of the system. Moreover, the spectral classification and albedo of Atira are uncertain. Previous work has shown that the color suggests an X, D, or C class and Atira is unlikely to be in the S, A, or V classes. By obtaining a low-resolution near-infrared spectrum with SpeX, we can resolve this ambiguity. These SpeX observations will be carried out during twilight hours using an integration time of 30 minutes to achieve a minimum signal-to-noise of 50. Because of the surface temperature and likely low albedo of Atira, a thermal excess 'tail' will be visible at longer wavelengths. Albedo estimation via thermal tail modeling will be used to further constrain the taxonomic class. PROGRAM_ABSTRACT_END