| The field of asteroid themophysical modeling is an important part in the study of asteroid.With the development of observational technology of space and ground based telescopes,a large amount of infrared data of asteroids have been observed,which has made this research field experienced an extraordinary growth in recent years.The thermal radiation emitted by an asteroid depends on thermophysical parameters such as the size,shape,albedo,thermal inertia,roughness,etc,of the asteroid.Thermophysical parameters of asteroids with various spectral types(C-type,V-type,etc.)and orbits(the main belt asteroids(MBAs),near-Earth asteroids(NEAs),etc.)have large differences.The value of thermophysical parameters can be obtained by calculating the theoretical radiant flux with certain thermal models and comparing with the corresponding infrared observational data.The scientific significance of studying the thermophysical properties of asteroids is multifaceted.For example,it can help us investigating asteroids’Yarkovsky effect and YORP effect,and predict the changes of their orbits and rotation states.Besides,thermal parameters are necessary to evaluate asteroid’s regolith grain size which can help us better study the asteroid’s surface compositional proper’ties.On the other hand,studying the thermophysical properties of asteroid families can further provide important clues for investigating the evolution mechanisms of asteroid belt and even the solar system.In this article,by combining the Advanced Thermophysical Model(ATPM)and mid-infrared observations,we studied a set of asteroids’thermal parameters mainly from the perspective of asteroid families,which include 10 Vesta family asteroids,Nysa-Polana complex asteroid(135)Hertha,Pallas family asteroid(531)Zerlina,3 Themis family members,as well as near-Earth asteroid(3200)Phaethon and(341843)2008 EV5.This work reveals the differences in thermal parameters between different asteroid families,as well as the similarities of the thermal parameters in the same asteroid family.The connections between NEAs and asteroid families are also discussed.Vesta family is one of the most numerous asteroid family in the asteroid belt,and is the fragments of asteroid(4)Vesta after a catastrophic cratering event.Previous studies showed that this family formed about 1 Gyr ago,thus can provide important clues to investigate the formation and evolution of the early stage of asteroid belt.In this work,we studied thermal parameters of 10 Vesta family members and obtained their mean thermal inertia of 42 Jm-2s-1/2K-1,mean geometric albedo of 0.328,and relatively low roughness.Besides,we analyzed the distribution characteristics of the thermal parameters according to our results including the relationship between thermal inertia and effective diameter.Considering the geometric albedos of other asteroids,the albedos of Vesta family members are relatively high.Besides,we studied the relations between thermal inertia and rotation period,however,we do not find obvious correlation between them,that’s probably because the sample size is too small.Furthermore,we evaluated the regolith grain sizes of these asteroids ranges from 0.006～1.673 mm.Asteroid(341843)2008 EV5 is an C-type Aten asteroid,and is also a potentially hazardous asteroid(PHA).It used to be the base-line target of ESA’s Maro-Polo-R spacecraft.Although the spacecraft did not fly to the asteroid,its physical properties,origin and evolution still have high scientific value.In 2010,WISE made a lot of thermal infrared observations,which provided key data for studying its thermophysical properties.In Chapter 5 we obtained its thermal inertia of Γ=110-10+30 Jm-2s-1/2K-1,geometric albedo of pv=0.095-0.003+0.016 and effective diameter Deff=431-33+6 m by using ATPM and WISE observations.Since its thermal inertia is relatively small compared to other near-Earth asteroids,we thus inferred that it originates from the main belt region.We integrate 1000 clone orbits of 2008 EV5 for 1 Myr in time backwards,and we obtained a probability of 6.1%that this asteroid comes from the main belt.Besides,we evaluate its regolith grain size ranges from 0.5～1.3mm.Previous studies showed that 2008 EV5 may comes from the Nysa-Polana family,thus we also studied physical properties of this asteroid family(135)Hertha,and obtained its thermal parameters as follows,Γ=30-21+35 Jm-2s-1/2K-1,pv=0.135-0.034+0.0182,and Deff=82.863-5.027+12.937 km.Asteroid(3200)is a quite popular asteroid in recent years,it is the target of spacecraft DESTINY+ of JAXA.Its special orbital shape(large eccentricity,small perihelion distance)causes large changes in temperature,giving it special physical characteristics.Besides,Phaethon is also the origin of the Gemini meteor shower.Previous investigations showed that Phaethon may originates from the Pallas family,although there are not many members of Pallas family,it is an important source of B-type asteroids in the main belt.In addition,most active asteroids are currently related to Pallas familly.In Chapter 6,we investigate the thermal properties of Pallas family asteroid(531)Zerlina and(3200)Phaethon together.We obtained the thermal inertia of these two asteroids are ΓPhaethon=550-290+920 Jm-2s-1/2K-1 and ΓZerlina=0-0+34 Jm-2s-1/2K-1,the geometric albedos are pv,Zerlina=0.1435-0.0325+0.0420,pv,Phaethon=0.1253-0.0020+0.0034,respectively.The differences in thermal parameters maybe caused by Phaethon’s outburst activities.When Phaethon is near the perihelion,its high surface temperature will change the physical properties of the materials on the surface.Observations also showed that Phaethon has mass loss events.Thus it turns to have different thermal properties with Pallas family asteroids.Themis family is also one of the most important families in the asteroid belt,named after the asteroid(24)Themis,and is distributed in the outer region of the asteroid belt.In this family,most of the asteroids are B-type and C-type asteroids.The material composition of these asteroids is relatively primitive,and most members may have water ice.Studying their thermal characteristics can provide us the parent body’s internal information,which in turn can provide an effective way to study the large B-type and C-type asteroid.In Chapter 7,we derived thermal parameters of 3 Themis family asteroids(62)Erato,(171)Ophelia and(222)Lucia by using WISE observations and ATPM.The value of the three asteroids’ thermal parameters are very close,which may indicate that they come from the same parent body.The asteroid family is an important contents to study the early evolution of the solar system.In the process of using the thermophysical model to derive the thermal parameters of the asteroid families,we proposed a new method for calculating the reflected sunlight contained in the observations and analyses the thermal parameters’ distribution characteristics.We derived a new set of thermal parameters of Vesta family members,and also investigated the relations between some NEAs and the main belt families.Besides,the results can improve the asteroid family classification method from the perspective of thermophysics and is also useful to study the target characteristics of the asteroid deep space exploration mission in the future. |
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