Science objectives of the Millimetron Space Observatory for the study of small bodies of the Solar System
Abstract
Space IR observatories have produced a large amount of new data about small bodies of the Solar System. Asteroid diameters can be estimated by fitting observational data on their infrared emission with the models of their thermal emission. The radiometry technique has been the major contributor of asteroid diameters since the 1980s, when the Infrared Astronomical Satellite (IRAS) allowed two thousand asteroid diameters to be determined. Midcourse Space Experiment (MSX) in the 1990s provided modest addition of observational data on approximately 150 asteroids. Later there has been two major space-based all-sky surveys at thermal infrared wavelengths in the last ten years: AKARI and WISE/NEOWISE. The WISE/NEOWISE project increased the number by two orders of magnitude, providing observations of hundreds of near-Earth asteroids, more than a hundred thousand main belt asteroids (MBAs), and thousands of outer MBAs and Jupiter Trojans. The AKARI IRC all-sky survey provided more than twenty thousand thermal infrared observations of over five thousand asteroids. The IRC asteroid flux catalogue includes data in the ranges from 6.7 to 11.6 $\mu$m and from 13.9 to 25.6 $\mu$m. Millimetron Space Observatory (MSO) is planned to be launched in 2029. MSO has an ideal wavelength range for the studies of the small bodies of the Solar System. The main advantage of MSO compared to previously launched space observatories is the possibility of studying trans-Neptunian objects (TNO) and detecting Planet X, since the maximum intensity of thermal radiation falls into the main sensitivity range of the SACS (43--450 $\mu$m) and LACS-P (300--3000~$\mu$m) detectors. Extensive observations of small bodies with an MSO should be carried out close to the ecliptic plane. In this case it is possible to cover the main locations of the main belt asteroids and trans-Neptunian objects. They can be distinguished by velocities ($\sim 0.01-0.02$ arcsec/sec for the asteroids and $\sim 0.0001-0.0002$ arcsec/sec for the TNO) and the temperature (for the asteroids temperature is in the range of $\sim 200-300$ K, and for TNO -- dozens of Kelvins, depending on the albedo). The small bodies of the Solar System observations will allow discovering hundreds of thousands of new objects with sizes 1--2 orders smaller than available today. We believe that the following tasks in the study of small bodies can be solved based on observations of the MSO: -- Breakthrough in the research of NEOs and distant small bodies. -- Small bodies as the sources of the dust, volatiles, and organics in the Solar System. -- Determination of the small bodies' physical parameters. -- Determination of chemical and mineralogical properties of the small bodies' surfaces. -- Refinement of heliocentric distribution of different small bodies' types. -- Search for Planet X. -- Identification and study of the small bodies populations in extrasolar systems. Thermal sub-millimeter observations will provide an immediate measure of small bodies' albedo and diameters even without measurement of the small bodies' optical brightness. MSO will provide real values of albedo and diameters without bias which we have today. Thermal sub-millimeter observations with Millimetron and optical observations with Gaia will provide a measure of small body masses and bulk density. MSO will result in the accurate masses of small bodies for different taxonomic classes and hence, bulk density.
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.286K