Spitzer Observations of Spacecraft Target 162173 (1999 JU3)

Abstract

Near-Earth asteroid 162173 (1999 JU3) is the primary target of the Hayabusa-2 sample return mission, and a potential target of the Marco Polo sample return mission. Earth-based studies of this object are fundamental to these missions. We present a mid-infrared spectrum (5-38 microns) of 1999 JU3 obtained with NASA's Spitzer Space Telescope in May 2008. These observations place new constraints on the surface properties of this asteroid. To fit our spectrum we used the near-Earth asteroid thermal model (NEATM) and the more complex thermophysical model (TPM). However, the position of the spin-pole, which is uncertain, is a crucial input parameter for constraining the thermal inertia with the TPM; hence, we consider two pole orientations. In the extreme case of an equatorial retrograde geometry we derive a lower limit to the thermal inertia of 150 J/m^2/K/s^0.5. If we adopt the pole orientation of Abe et al. (2008a) our best-fit thermal model yields a value for the thermal inertia of 700+/-200 J/m^2/K/s^0.5 and even higher values are allowed by the uncertainty in the spectral shape due to the absolute flux calibration. The lower limit to the thermal inertia, which is unlikely but possible, would be consistent with a fine regolith similar to wthat is found for asteroid 433 Eros. However, the thermal inertia is expected to be higher, possibly similar to or greater than that on asteroid 25143 Itokawa. Accurately determining the spin-pole of asteroid 162173 will narrow the range of possible values for its thermal inertia.

arXiv comment4 pages, 2 figures; to be published as a Letter in Astronomy and Astrophysics

References in corpus (6)

• The Spitzer Space Telescope Mission
• The Infrared Spectrograph on the Spitzer Space Telescope
• Thermal inertia of near-Earth asteroids and implications for the magnitude of the Yarkovsky effect
• Thermal inertia of main belt asteroids smaller than 100 km from IRAS data
• Thermal infrared observations of the Hayabusa spacecraft target asteroid 25143 Itokawa
• Spitzer Observations of Comet 67P/Churyumov-Gerasimenko at 5.5-4.3 AU From the Sun

Cited by in corpus (10)

• Hayabusa-2 Mission Target Asteroid 162173 Ryugu (1999 JU3): Searching for the Object's Spin-Axis Orientation
• Thermo-physical properties of 162173 (1999 JU3), a potential flyby and rendezvous target for interplanetary missions
• Rotational Characterization of Hayabusa II Target Asteroid (162173) 1999 JU3
• Optical Properties of (162173) 1999 JU3: In Preparation for the JAXA Hayabusa 2 Sample Return Mission
• Thermal Tomography of Asteroid Surface Structure
• Expected spectral characteristics of (101955) Bennu and (162173) Ryugu, targets of the OSIRIS-REx and Hayabusa2 missions
• Ground-based Characterization of Hayabusa2 Mission Target Asteroid 162173 Ryugu: Constraining Mineralogical Composition in Preparation for Spacecraft Operations
• Space-Based Thermal Infrared Studies of Asteroids
• A novel facility for reduced-gravity testing: a set-up for studying low-velocity collisions into granular surfaces
• Secular Light Curves of NEAs 2201 Oljato, 3200 Phaethon, 99942 Apophis, 162173 Ryugu, 495848, and 6063 Jason