Asteroids seen by JWST-MIRI: Radiometric Size, Distance and Orbit Constraints

Abstract

Infrared measurements of asteroids are crucial for the determination of physical and thermal properties of individual objects, and for the understanding of the small-body populations in the solar system as a whole. But standard radiometric methods can only be applied if the orbit of an object is known, hence its position at the time of the observation. We present MIRI observations of the outer-belt asteroid 10920 and an unknown object, detected in all 9 MIRI bands in close proximity to 10920. We developed a new method "STM-ORBIT" to interpret the multi-band measurements without knowing the object's true location. The method leads to a confirmation of radiometric size-albedo solution for 10920 and puts constraints on the asteroid's location and orbit in agreement with its true orbit. Groundbased lightcurve observations of 10920, combined with Gaia data, indicate a very elongated object (a/b >= 1.5), with a spin-pole at (l, b) = (178°, 81°), and a rotation period of 4.861191 h. A thermophysical study leads to a size of 14.5 - 16.5 km, a geometric albedo between 0.05 and 0.10, and a thermal inertia in the range 9 to 35 Jm-2s-0.5K-1. For the newly discovered MIRI object, the STM-ORBIT method revealed a size of 100-230 m. The new asteroid must be on a very low-inclination orbit and it was located in the inner main-belt region during JWST observations. A beaming parameter η larger than 1.0 would push the size even below 100 meter, a main-belt regime which escaped IR detections so far. These kind of MIRI observations can therefore contribute to formation and evolution studies via classical size-frequency studies which are currently limited to objects larger than about one kilometer in size. We estimate that MIRI frames with pointings close to the ecliptic and only short integration times of a few seconds will always include a few asteroids, most of them will be unknown objects.

arXiv comment17 pages, 10 figures, 4 tables, accepted for A&A publication on Nov 22, 2022

References in corpus (26)

• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Spitzer Space Telescope Mission
• ATLAS: A High-Cadence All-Sky Survey System
• The Dark Energy Camera
• astroquery: An Astronomical Web-Querying Package in Python
• Main Belt Asteroids with WISE/NEOWISE I: Preliminary Albedos and Diameters
• Asteroid thermophysical modeling
• The Mid-Infrared Instrument for the James Webb Space Telescope, III: MIRIM, The MIRI Imager
• Hayabusa-2 Mission Target Asteroid 162173 Ryugu (1999 JU3): Searching for the Object's Spin-Axis Orientation
• WISE/NEOWISE Observations of the Hilda Population: Preliminary Results
• NEOWISE Reactivation Mission Year One: Preliminary Asteroid Diameters and Albedos
• Asteroid phase curves from ATLAS dual-band photometry
• Systematic ranging and late warning asteroid impacts
• The AKARI IRC asteroid flux catalogue: updated diameters and albedos
• Survey Simulations of a New Near-Earth Asteroid Detection System
• Testing the inversion of asteroids' Gaia photometry combined with ground-based observations
• Asteroids and the James Webb Space Telescope
• Shaping Asteroids with Genetic Evolution (SAGE)
• Sizes and albedos of Mars-crossing asteroids from WISE/NEOWISE data
• Hubble Asteroid Hunter: I. Identifying asteroid trails in Hubble Space Telescope images
• Dependence of Lightcurves on Phase Angle and Asteroid Shape
• Infrared Absolute Calibration I: Comparison of Sirius with Fainter Calibration Stars
• Asteroid Distributions in the Ecliptic
• Modeling collision probability for Earth-impactor 2008 TC3
• Observing Near-Earth Objects with the James Webb Space Telescope
• ESASky SSOSS: Solar System Object Search Service and the case of Psyche

Cited by in corpus (4)

• JWST sighting of decameter main-belt asteroids and view on meteorite sources
• Astrometric follow-up of near-Earth asteroid 2024 YR4 during a Torino scale level 3 alert
• Inconsistencies in Simple Thermal Model Results for Near-Earth Asteroids between Infrared Telescope Facility SpeX and NEOWISE Data
• Orbits of very distant asteroid satellites