Studies of Thermophysical Parameters and Distribution Characteristics of Asteroid Families Based on Infrared Observations

JIANG Hao-xuan

(Purple Mountain Observatory,Chinese Academy of Sciences,Nanjing 210023)

The field of asteroid themophysical modeling is an important part in the study of asteroid.In recent years,with the development of infrared observation technology,this research field has experienced extraordinary growth.Thermal radiation emitted by an asteroid depends on thermophysical parameters such as the size,shape,albedo,thermal inertia,roughness,etc,of the asteroid.The scientific significance of studying the thermophysical properties of asteroids is multifaceted.For example,it can help us investigate asteroids’Yarkovsky effect and YORP (Yarkovsky-O’Keefe-Radzievskii-Paddackor) effect.Besides,thermal parameters are necessary to evaluate asteroid’s regolith grain size which can help us better study the asteroid’s surface compositional properties and provide important clues for investigating the evolution mechanisms of asteroid belt and even the solar system.In this work,by combining the Advanced Thermophysical Model (ATPM) and mid-infrared observations,we studied thermal properties of Vesta family asteroids,Nysa-Polana complex asteroid(135)Hertha,Pallas family asteroid(531)Zerlina,3 Themis family members,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 (Near-Earth Asteroids) and asteroid families are also discussed.

Vesta family is the fragments of asteroid (4) Vesta after a catastrophic cratering event.In this work,we studied thermal parameters of 10 Vesta family members and obtained their mean thermal inertia of 42 Jm−2·s−1/2·K−1,mean geometric albedo of 0.328,and relatively low roughness.Comparing with the geometric albedos of other asteroids,the albedos of Vesta family members are relatively high.Furthermore,we evaluated the regolith grain sizes of these asteroids ranges from 0.006 to 1.673 mm.Themis family is also one of the most important asteroid families in which the material compositions of the family members are relatively primitive,and most members may have water ice.We derived thermal parameters of 3 Themis family asteroids (62) Erato,(171) Ophelia and (222) Lucia by using WISE(Wide-field Infrared Survey Explorer) observations and ATPM.The values of the three asteroids’ thermal parameters are very close,which may indicate that they come from the same parent body.

Asteroid (341843) 2008 EV5 is a C-type Aten asteroid,and is also a potentially hazardous asteroid(PHA).It is used to be the base-line target of ESA’s Maro-Polo-R spacecraft.In this work,we obtained its thermal inertia of Γ=,geometric albedo ofpv=and effective diameterm 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 integrated 1000 clone orbits of 2008 EV5 for 1 Myr backwards,and we obtained a probability of 6.1% that this asteroid comes from the main belt.Previous studies showed that 2008 EV5 could come 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=

Asteroid(3200)is the target of spacecraft DESTINY+(Demonstration and Experiment of Space Technology for INterplanetary voYage Phaethon fLyby dUSt science) of JAXA(Japan Aerospace Exploration Agency).Its special orbital shape (large eccentricity,small perihelion distance)leads to a large range of temperature difference,giving it special physical characteristics.Besides,Phaethon is also the origin of the Gemini meteor shower.Previous investigations showed that Phaethon may originate 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 this work,we investigate the thermal properties of Pallas family asteroid(531) Zerlina and (3200) Phaethon together.We obtained the thermal inertia of these two asteroids arethe geometric albedos are,respectively.The differences in thermal parameters may be due to 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,making it have different thermal properties from other Pallas family asteroids.