C-type Asteroids Research Articles

Nucleus of active asteroid 358P/Pan-STARRS (P/2012 T1)

Context.The dust emission from active asteroids is likely driven by collisions, fast rotation, sublimation of embedded ice, and combinations of these. Characterising these processes leads to a better understanding of their respective influence on the evolution of the asteroid population.Aims.We study the role of fast rotation in the active asteroid 358P (P 2012/T1).Methods.We obtained two nights of deep imaging of 358P with SOAR/Goodman and VLT/FORS2. We derived the rotational light curve from time-resolved photometry and searched for large fragments and debris >8 mm in a stacked, ultra-deep image.Results.The nucleus has an absolute magnitude ofmR= 19.68, corresponding to a diameter of 530 m for standard assumptions on the albedo and phase function of a C-type asteroid. We do not detect fragments or debris that would require fast rotation to reduce surface gravity to facilitate their escape. The 10-h light curve does not show an unambiguous periodicity.

Exploring small bodies: Nano- and microlander options derived from the Mobile Asteroid Surface Scout

The MASCOT lander currently flying on-board of the Japanese Hayabusa2 spacecraft, both set to explore the C-type Near-Earth Asteroid (162173) Ryugu, is not the first, but certainly one of the more complex nanolander systems having been designed for being carried along a bigger interplanetary spacecraft. Other concepts and current missions have shown the attractiveness of the class of nanosystems now increasing its application range from Earth orbiting cubesats to interplanetary scientific exploration endeavors, from orbiting to landing missions. This paper is intended to investigate nanolander options derived based on the MASCOT lander concept. For this purpose we gather interesting target bodies and analyze their respective environmental properties as well as their influence on the nanolander design, for example the landing system, the surface mobility, the power subsystem and the communication architecture. Further, an expansion of the scientific objectives of the current MASCOT lander from geological surface scout to other scientific objectives opens a range of new possibilities. For deeper analysis on this, we provide an overview over possible alternative payloads to the ones already flying on MASCOT and analyze their influence on the system design as it is. Obviously, the experience that has been gained with MASCOT provides us with a head start for future missions, if it is properly exploited. With this paper we intend to recommend MASCOT type of nanolanders for a range of possible future applications.

Earth and moon observations by thermal infrared imager on Hayabusa2 and the application to detectability of asteroid 162173 Ryugu

Thermal Infrared Imager TIR on Hayabusa2 has proven its in-flight performance to detect celestial bodies during the cruise phase, especially by the observations of the Earth and the Moon before and after the Earth swing-by on 3rd of December 2015. The result indicates that the target C-type asteroid 162173 Ryugu will be detected from the distance of 3000 km at the beginning of the approach phase, and that a C-type small moon larger than 1 m will be detected from the home position, 20 km from the asteroid, if it orbits around the asteroid.

2004 EW95: A Phyllosilicate-bearing Carbonaceous Asteroid in the Kuiper Belt

Abstract Models of the Solar System’s dynamical evolution predict the dispersal of primitive planetesimals from their formative regions among the gas-giant planets due to the early phases of planetary migration. Consequently, carbonaceous objects were scattered both into the outer asteroid belt and out to the Kuiper Belt. These models predict that the Kuiper Belt should contain a small fraction of objects with carbonaceous surfaces, though to date, all reported visible reflectance spectra of small Kuiper Belt Objects (KBOs) are linear and featureless. We report the unusual reflectance spectrum of a small KBO, (120216) 2004 EW95, exhibiting a large drop in its near-UV reflectance and a broad shallow optical absorption feature centered at ∼700 nm, which is detected at greater than 4σ significance. These features, confirmed through multiple epochs of spectral photometry and spectroscopy, have respectively been associated with ferric oxides and phyllosilicates. The spectrum bears striking resemblance to those of some C-type asteroids, suggesting that 2004 EW95 may share a common origin with those objects. 2004 EW95 orbits the Sun in a stable mean motion resonance with Neptune, at relatively high eccentricity and inclination, suggesting it may have been emplaced there by some past dynamical instability. These results appear consistent with the aforementioned model predictions and are the first to show a reliably confirmed detection of silicate material on a small KBO.

Delivery of organics to Mars through asteroid and comet impacts

Given rapid photodissociation and photodegradation, the recently discovered organics in the Martian subsurface and atmosphere were probably delivered in geologically recent times. Possible parent bodies are C-type asteroids, comets, and interplanetary dust particles (IDPs).The dust infall rate was estimated, using different methods, to be between 0.71 and 2.96 × 106 kg/yr (Nesvorny et al., 2011; Borin et al., 2017; Crismani et al., 2017); assuming a carbon content of 10% (Flynn, 1996), this implies an IDP carbon flux of 0.07−0.3×106 kg/yr. We calculate for the first time the carbon flux from impacts of asteroids and comets.To this end, we perform dynamical simulations of impact rates on Mars. We use the N-body integrator RMVS/Swifter to propagate the Sun and the eight planets from their current positions. We separately add comets and asteroids to the simulations as massless test particles, based on their current orbital elements, yielding Mars impact rates of 4.34×10−3 comets/Myr and 3.3 asteroids/Myr.We estimate the delivered amount of carbon using published carbon content values. In asteroids, only C types contain appreciable amounts of carbon. Given the absence of direct taxonomic information on the Mars impactors, we base ourselves on the measured distribution of taxonomic types in combination with dynamic models of the origin of Mars-crossing asteroids.We estimate the global carbon flux on Mars from cometary impacts to be ∼ 0.013 × 106 kg/yr within an order of magnitude, while asteroids deliver ∼ 0.05 × 106 kg/yr. These values correspond to ∼4−19% and ∼17−71%, respectively, of the IDP-borne carbon flux estimated by Nesvorny et al., Borin et al. and Crismani et al. Unlike the spatially homogeneous IDP infall, impact ejecta are distributed locally, concentrated around the impact site. We find organics from asteroids and comets to dominate over IDP-borne organics at distances up to 150 km from the crater center. Our results may be important for the interpretation of in situ detections of organics on Mars.

Isotopic Dichotomy among Meteorites and Its Bearing on the Protoplanetary Disk.

Whole rock Δ17O and nucleosynthetic isotopic variations for chromium, titanium, nickel, and molybdenum in meteorites define two isotopically distinct populations: carbonaceous chondrites (CCs) and some achondrites, pallasites, and irons in one and all other chondrites and differentiated meteorites in the other. Since differentiated bodies accreted 1-3 Myr before the chondrites, the isotopic dichotomy cannot be attributed to temporal variations in the disk. Instead, the two populations were most likely separated in space, plausibly by proto-Jupiter. Formation of CCs outside Jupiter could account for their characteristic chemical and isotopic composition. The abundance of refractory inclusions in CCs can be explained if they were ejected by disk winds from near the Sun to the disk periphery where they spiraled inward due to gas drag. Once proto-Jupiter reached 10-20 M ⊕, its external pressure bump could have prevented millimeter- and centimeter-sized particles from reaching the inner disk. This scenario would account for the enrichment in CCs of refractory inclusions, refractory elements, and water. Chondrules in CCs show wide ranges in Δ17O as they formed in the presence of abundant 16O-rich refractory grains and 16O-poor ice particles. Chondrules in other chondrites (ordinary, E, R, and K groups) show relatively uniform, near-zero Δ17O values as refractory inclusions and ice were much less abundant in the inner solar system. The two populations were plausibly mixed together by the Grand Tack when Jupiter and Saturn migrated inward emptying and then repopulating the asteroid belt with roughly equal masses of planetesimals from inside and outside Jupiter's orbit (S- and C-type asteroids).

The on-ground calibration performances of the hyperspectral microscope MicrOmega for the Hayabusa-2 mission

The miniaturized near-infrared hyperspectral microscope MicrOmega, on board the MASCOT lander for Hayabusa-2 mission, is designed to perform in situ measurements at the grain scale of the C-type asteroid 1999 JU3 RYUGU. MicrOmega will observe samples with a field of view of a few millimeters with a spatial sampling of 25 μm and acquire near-infrared spectra by illuminating the sample sequentially with different wavelengths from 0.99 to 3.55 μm over two spectral channels with a typical spectral sampling of 20 cm−1. The on-ground calibration of MicrOmega requires a full characterization of the nominal range of operation of the instrument, both spectral (0.99–3.55 μm) and thermal (−40 °C to +40 °C) to derive the radiometric and spectral responses combined into a 4D transfer function to convert raw signal to calibrated reflectance. This specific 4D radiometric reference gives the instrument response according to the pixel location (x,y), the wavelength and the instrument temperature. This paper reports the complex computation of the 4D radiometric reference for the 0.9–2.5 μm channel. In this spectral range, the composition of the grains of a wide variety of minerals with relevance to solar system bodies can be identified through diagnostic spectral features: mafic (pyroxene, olivine…) as well as hydrated and altered minerals that are key phases for the solar system bodies’ exploration.

Hayabusa2–Sample return and kinetic impact mission to near-earth asteroid Ryugu

The Japan Aerospace Exploration Agency launched the asteroid sample return spacecraft “Hayabusa2” on December 3, 2014. Hayabusa2 will reach the C-type asteroid 162173 Ryugu in 2018, and return back to the Earth in 2020. Sample collections from three sites, four surface rovers deployment and a 4 MJ-class kinetic impact crater forming are planned in the 1.5 years of the asteroid-proximity operation. The mission objective of Hayabusa2 has three aspects, science, engineering and exploration, all of which would be expanded by the successful round-trip journey. The objectives and technologies used in this mission is not a direct solution for the future planetary defense, but should contribute to this field by increasing general asteroid knowledge and enhancing human capabilities of small body-surface access/roving/sampling/impacting. This paper describes the outline of the Hayabusa2 mission, overviews the kinetic impact technology as an example of planetary defense-related technologies and the current flight status after the two and a half years of the interplanetary cruise.

Water Reservoirs in Small Planetary Bodies: Meteorites, Asteroids, and Comets.

Asteroids and comets are the remnants of the swarm of planetesimals from which the planets ultimately formed, and they retain records of processes that operated prior to and during planet formation. They are also likely the sources of most of the water and other volatiles accreted by Earth. In this review, we discuss the nature and probable origins of asteroids and comets based on data from remote observations, in situ measurements by spacecraft, and laboratory analyses of meteorites derived from asteroids. The asteroidal parent bodies of meteorites formed ≤4 Ma after Solar System formation while there was still a gas disk present. It seems increasingly likely that the parent bodies of meteorites spectroscopically linked with the E-, S-, M- and V-type asteroids formed sunward of Jupiter's orbit, while those associated with C- and, possibly, D-type asteroids formed further out, beyond Jupiter but probably not beyond Saturn's orbit. Comets formed further from the Sun than any of the meteorite parent bodies, and retain much higher abundances of interstellar material. CI and CM group meteorites are probably related to the most common C-type asteroids, and based on isotopic evidence they, rather than comets, are the most likely sources of the H and N accreted by the terrestrial planets. However, comets may have been major sources of the noble gases accreted by Earth and Venus. Possible constraints that these observations can place on models of giant planet formation and migration are explored.

Asteroid Redirection Mission Evaluation Using Multiple Landers

In this paper, a low-thrust tugboat redirection method is assessed using multiple spacecraft for a target range of small near-Earth asteroids. The benefits of a landed configuration of tugboat spacecraft in formation are examined for the redirection of a near-Earth asteroid. The tugboat method uses a gimballed thruster with a highly collimated ion beam to generate a thrust on the asteroid. The target asteroid range focuses on near-Earth asteroids smaller than 150 m in diameter, and carbonaceous (C-type) asteroids, due to the volatiles available for in-situ utilization. The assessment focuses primarily on the three key parameters, i.e., the asteroid mass redirected, the timeframe for redirection, and the overall system cost. An evaluation methodology for each parameter is discussed in detail, and the parameters are employed to determine the expected return and feasibility of the redirection mission. The number of spacecraft employed is optimized along with the electrical power needed for each spacecraft to ensure the highest possible return on investment. A discussion of the optimization results and the benefits of spacecraft formation for the tugboat method are presented.

Composition of Jupiter irregular satellites sheds light on their origin

Irregular satellites of Jupiter with their highly eccentric, inclined and distant orbits suggest that their capture took place just before the giant planet migration. We aim to improve our understanding of the surface composition of irregular satellites of Jupiter to gain insight into a narrow time window when our Solar System was forming. We observed three Jovian irregular satellites, Himalia, Elara, and Carme, using a medium-resolution 0.8-5.5 micro m spectrograph on the National Aeronautics and Space Administration (NASA) Infrared Telescope Facility (IRTF). Using a linear spectral unmixing model we have constrained the major mineral phases on the surface of these three bodies. Our results confirm that the surface of Himalia, Elara, and Carme are dominated by opaque materials such as those seen in carbonaceous chondrite meteorites. Our spectral modeling of NIR spectra of Himalia and Elara confirm that their surface composition is the same and magnetite is the dominant mineral. A comparison of the spectral shape of Himalia with the two large main C-type asteroids, Themis (D 176 km) and Europa (D 352 km), suggests surface composition similar to Europa. The NIR spectrum of Carme exhibits blue slope up to 1.5 microm and is spectrally distinct from those of Himalia and Elara. Our model suggests that it is compositionally similar to amorphous carbon. Himalia and Elara are compositionally similar but differ significantly from Carme. These results support the hypotheses that the Jupiter irregular satellites are captured bodies that were subject to further breakup events and clustered as families based on their similar physical and surface compositions.

Internal structure of asteroid gravitational aggregates

The internal structure of small asteroids is fundamentally unknown due to lack of direct measurements. The only clues on this topic come from theoretical considerations and from the comparison between measured bulk densities of asteroids and their corresponding analogue meteorite densities. The mass distribution and the void space between components in a gravitational aggregate determine the structure of such objects. In this paper we study numerically the dynamical and collisional evolution of the reaccumulation process of the fragments created in catastrophic collisions of asteroids in the 500 m to 10 km size range. An effort to consider irregularly shaped fragments is made by taking advantage of the results of laboratory experiments that provide relative mass distributions and aspect ratios for fragment shapes. We find that the processes that govern the final properties of the resulting aggregates are mainly stochastic, however interesting patterns can be identified. This study matches estimated macro-porosities of S-type asteroids and finds a loose linear relationship between macro-prorosity of asteroid aggregates and the mass ratio of the largest component to the whole aggregate (for both S and C-types). As for observed C-type asteroids, we conclude that their interiors should be more fragmented than in the case of S-type asteroids, explaining the difference in the estimated macro-porosity of real C asteroids with respect to S-types. We also find that slow rotators may be interpreted as a natural result in the process of gravitational reaccumulation.

Initial inflight calibration for Hayabusa2 optical navigation camera (ONC) for science observations of asteroid Ryugu

Hayabusa2, the first sample return mission to a C-type asteroid was launched by the Japan Aerospace Exploration Agency (JAXA) on December 3, 2014 and will arrive at the asteroid in the middle of 2018 to collect samples from its surface, which may contain both hydrated minerals and organics. The optical navigation camera (ONC) system on board the Hayabusa2 consists of three individual framing CCD cameras, ONC-T for a telescopic nadir view, ONC-W1 for a wide-angle nadir view, and ONC-W2 for a wide-angle slant view will be used to observe the surface of Ryugu. The cameras will be used to measure the global asteroid shape, local morphologies, and visible spectroscopic properties. Thus, image data obtained by ONC will provide essential information to select landing (sampling) sites on the asteroid. This study reports the results of initial inflight calibration based on observations of Earth, Mars, Moon, and stars to verify and characterize the optical performance of the ONC, such as flat-field sensitivity, spectral sensitivity, point-spread function (PSF), distortion, and stray light of ONC-T, and distortion for ONC-W1 and W2. We found some potential problems that may influence our science observations. This includes changes in sensitivity of flat fields for all bands from those that were measured in the pre-flight calibration and existence of a stray light that arises under certain conditions of spacecraft attitude with respect to the sun. The countermeasures for these problems were evaluated by using data obtained during initial in-flight calibration. The results of our inflight calibration indicate that the error of spectroscopic measurements around 0.7 µm using 0.55, 0.70, and 0.86 µm bands of the ONC-T can be lower than 0.7% after these countermeasures and pixel binning. This result suggests that our ONC-T would be able to detect typical strength (∼3%) of the serpentine absorption band often found on CM chondrites and low albedo asteroids with ≥ 4σ confidence.

The spin-barrier ratio for S and C-type main asteroids belt

Asteroids of size larger than 0.15 km generally do not have periods P smaller than about 2.2 h, a limit known as cohesionless spin-barrier. This barrier can be explained by means of the cohesionless rubble-pile structure model. In this paper we will explore the possibility for the observed spin-barrier value to be different for C and S-type Main Asteroids Belt (MBAs). On the basis of the actual bulk density values, the expected ratio between the maximum rotation periods is PC/PS≈1.4±0.3. Using the data available in the asteroid LightCurve Data Base (LCDB) we have found that, as regards the mean spin-barrier values and for asteroids in the 4–20 km range, there is a little difference between the two asteroids population with a ratio PC/PS≈1.20±0.04. Uncertainties are still high, mainly because of the small number of MBAs with known taxonomic class in the considered range. In the 4–10 km range, instead, the ratio between the spin-barriers seems closer to 1 because PC/PS≈1.11±0.05. This behavior could be a direct consequence of a different cohesion strength for C and S-type asteroids of which the ratio can be estimated.

Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn’s rapid gas accretion

There is a long-standing debate regarding the origin of the terrestrial planets’ water as well as the hydrated C-type asteroids. Here we show that the inner Solar System’s water is a simple byproduct of the giant planets’ formation. Giant planet cores accrete gas slowly until the conditions are met for a rapid phase of runaway growth. As a gas giant’s mass rapidly increases, the orbits of nearby planetesimals are destabilized and gravitationally scattered in all directions. Under the action of aerodynamic gas drag, a fraction of scattered planetesimals are deposited onto stable orbits interior to Jupiter’s. This process is effective in populating the outer main belt with C-type asteroids that originated from a broad (5-20 AU-wide) region of the disk. As the disk starts to dissipate, scattered planetesimals reach sufficiently eccentric orbits to cross the terrestrial planet region and deliver water to the growing Earth. This mechanism does not depend strongly on the giant planets’ orbital migration history and is generic: whenever a giant planet forms it invariably pollutes its inner planetary system with water-rich bodies.

Hayabusa2 Mission Overview

The Hayabusa2 mission journeys to C-type near-Earth asteroid (162173) Ryugu (1999 JU3) to observe and explore the 900 m-sized object, as well as return samples collected from the surface layer. The Haybusa2 spacecraft developed by Japan Aerospace Exploration Agency (JAXA) was successfully launched on December 3, 2014 by an H-IIA launch vehicle and performed an Earth swing-by on December 3, 2015 to set it on a course toward its target Ryugu. Hayabusa2 aims at increasing our knowledge of the early history and transfer processes of the solar system through deciphering memories recorded on Ryugu, especially about the origin of water and organic materials transferred to the Earth’s region. Hayabusa2 carries four remote-sensing instruments, a telescopic optical camera with seven colors (ONC-T), a laser altimeter (LIDAR), a near-infrared spectrometer covering the 3-μm absorption band (NIRS3), and a thermal infrared imager (TIR). It also has three small rovers of MINERVA-II and a small lander MASCOT (Mobile Asteroid Surface Scout) developed by German Aerospace Center (DLR) in cooperation with French space agency CNES. MASCOT has a wide angle imager (MasCam), a 6-band thermal radiator (MARA), a 3-axis magnetometer (MasMag), and a hyperspectral infrared microscope (MicrOmega). Further, Hayabusa2 has a sampling device (SMP), and impact experiment devices which consist of a small carry-on impactor (SCI) and a deployable camera (DCAM3). The interdisciplinary research using the data from these onboard and lander’s instruments and the analyses of returned samples are the key to success of the mission.

Detection of the Yarkovsky effect for C-type asteroids in the Veritas family

The age of a young asteroid family can be determined by tracking the orbits of family members backward in time and showing that they converge at some time in the past. Here we consider the Veritas family. We find that the membership of the Veritas family increased enormously since the last detailed analysis of the family. Using backward integration, we confirm the convergence of nodal longitudes $\Omega$, and, for the first time, also obtain a simultaneous convergence of pericenter longitudes $\varpi$. The Veritas family is found to be $8.23^{+0.37}_{-0.31}$~Myr old. To obtain a tight convergence of $\Omega$ and $\varpi$, as expected from low ejection speeds of fragments, the Yarkovsky effect needs to be included in the modeling of the past orbital histories of Veritas family members. Using this method, we compute the Yarkovsky semi-major axis drift rates, ${\rm d}a/{\rm d}t$, for 274 member asteroids. The distribution of ${\rm d}a/{\rm d}t$ values is consistent with a population of C-type objects with low densities and low thermal conductivities. The accuracy of individual ${\rm d}a/{\rm d}t$ measurements is limited by the effect of close encounters of member asteroids to (1) Ceres and other massive asteroids, which cannot be evaluated with confidence.

Confirmation of Large Super-fast Rotator (144977) 2005 EC127

Abstract (144977) 2005 EC127 is a V-/A-type inner-main-belt asteroid with a diameter of 0.6 ± 0.1 km. Asteroids of this size are believed to have rubble-pile structure, and therefore cannot have a rotation period shorter than 2.2 hr. However, our measurements show that asteroid 2005 EC127 completes one rotation in 1.65 ± 0.01 hr with a peak-to-peak light-curve variation of ∼0.5 mag. Therefore, this asteroid is identified as a large super-fast rotator. Either a rubble-pile asteroid with a bulk density of g cm−3 or an asteroid with an internal cohesion of 47 ± 30 Pa can explain 2005 EC127. However, the scenario of high bulk density is very unlikely for asteroids. To date, only six large super-fast rotators, including 2005 EC127, have been reported, and this number is very small when compared with the much more numerous fast rotators. We also note that none of the six reporting large SFRs are classified as C-type asteroids.

D/H ratios of the inner Solar System.

The original hydrogen isotope (D/H) ratios of different planetary bodies may indicate where each body formed in the Solar System. However, geological and atmospheric processes can alter these ratios through time. Over the past few decades, D/H ratios in meteorites from Vesta and Mars, as well as from S- and C-type asteroids, have been measured. The aim of this article is to bring together all previously published data from these bodies, as well as the Earth, in order to determine the original D/H ratio for each of these inner Solar System planetary bodies. Once all secondary processes have been stripped away, the inner Solar System appears to be relatively homogeneous in terms of water D/H, with the original water D/H ratios of Vesta, Mars, the Earth, and S- and C-type asteroids all falling between δD values of −100‰ and −590‰. This homogeneity is in accord with the ‘Grand tack’ model of Solar System formation, where giant planet migration causes the S- and C-type asteroids to be mixed within 1 AU to eventually form the terrestrial planets.This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’.

Thermal Imaging Performance of TIR Onboard the Hayabusa2 Spacecraft

The thermal infrared imager (TIR) is a thermal infrared camera onboard the Hayabusa2 spacecraft. TIR will perform thermography of a C-type asteroid, 162173 Ryugu (1999 JU3), and estimate its surface physical properties, such as surface thermal emissivity \(\epsilon \), surface roughness, and thermal inertia \(\varGamma \), through remote in-situ observations in 2018 and 2019. In prelaunch tests of TIR, detector calibrations and evaluations, along with imaging demonstrations, were performed. The present paper introduces the experimental results of a prelaunch test conducted using a large-aperture collimator in conjunction with TIR under atmospheric conditions. A blackbody source, controlled at constant temperature, was measured using TIR in order to construct a calibration curve for obtaining temperatures from observed digital data. As a known thermal emissivity target, a sandblasted black almite plate warmed from the back using a flexible heater was measured by TIR in order to evaluate the accuracy of the calibration curve. As an analog target of a C-type asteroid, carbonaceous chondrites (\(50~\mbox{mm} \times 2~\mbox{mm}\) in thickness) were also warmed from the back and measured using TIR in order to clarify the imaging performance of TIR. The calibration curve, which was fitted by a specific model of the Planck function, allowed for conversion to the target temperature within an error of 1 ∘C (\(3\sigma \) standard deviation) for the temperature range of 30 to 100 ∘C. The observed temperature of the black almite plate was consistent with the temperature measured using K-type thermocouples, within the accuracy of temperature conversion using the calibration curve when the temperature variation exhibited a random error of 0.3 ∘C (\(1\sigma \)) for each pixel at a target temperature of 50 ∘C. TIR can resolve the fine surface structure of meteorites, including cracks and pits with the specified field of view of 0.051∘ (\(328 \times 248~\mbox{pixels}\)). There were spatial distributions with a temperature variation of 3 ∘C at the setting temperature of 50 ∘C in the thermal images obtained by TIR. If the spatial distribution of the temperature is caused by the variation of the thermal emissivity, including the effects of the surface roughness, the difference of the thermal emissivity \(\Delta \epsilon \) is estimated to be approximately 0.08, as calculated by the Stefan-Boltzmann raw. Otherwise, if the distribution of temperature is caused by the variation of the thermal inertia, the difference of the thermal inertia \(\Delta \varGamma \) is calculated to be approximately \(150~\mbox{J}\,\mbox{m}^{-2}\,\mbox{s}^{0.5}\,\mbox{K}^{-1}\), based on a simulation using a 20-layer model of the heat balance equation. The imaging performance of TIR based on the results of the meteorite experiments indicates that TIR can resolve the spatial distribution of thermal emissivity and thermal inertia of the asteroid surface within accuracies of \(\Delta \epsilon \cong 0.02\) and \(\Delta \varGamma \cong 20~\mbox{J}\,\mbox{m}^{-2}\,\mbox{s}^{0.5}\,\mbox{K}^{-1}\), respectively. However, the effects of the thermal emissivity and thermal inertia will degenerate in thermal images of TIR. Therefore, TIR will observe the same areas of the asteroid surface numerous times (\({>}10\) times, in order to ensure statistical significance), which allows us to determine both the parameters of the surface thermal emissivity and the thermal inertia by least-squares fitting to a thermal model of Ryugu.