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Impact crater formation on comet surface and its implications for thermal history of comet nucleus

彗星表面撞击坑的形成及其对彗核热历史的影响

基本信息

批准号：
17340127
负责人：
ARAKAWA Masahiko
金额：
$ 10.67万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-17340127/
关键词：
Impact crater Comet Thermal history Sintering Scaling Law Fracture strength Impact disruption Gravity 衝突破片衝突融解圧縮強度

项目摘要

We carried out impact experiments on snow to simulate the impact crater found on the surface of comet nuclei. Especially, in order to clarify the relationship between the thermal history of the comet surface and the crater morphology, the impact experiments were conducted using sintered snow samples. The size of the impact crater was found to increase with the increase of the impact velocity up to 150m/s when the snow projectile was impacted on the snow with the porosity of 40% sintered at-10℃ during 15 min. These results show that the crater volume has a power law relationship to the projectile kinetic energy (Ek) with the power law index of 0.5 for the Ek. The crater size was found to decrease with the increase of the sintering time from 3 min. to 60 hrs. at -10℃. The crater volume has a power law relationship to the sintering time. A high velocity impact of a nylon projectile with the velocity of 2.7km was carried out on the snow with the porosity of 50%, and then we found that the outer edge of the crater was spalled out to form a ring like structure of the crater rim and the crater had a very spherical shape with the refrozen thin ice layer on the inner wall. This results show that the impact of the nylon projectile higher than 2.7km/s (impact pressure could be 3.9GPa) can induce impact melting of snow to spread it out on the crater wall. In order to estimate the temperature increase of the high velocity impact quantitatively, ice-on-ice impact experiments were conducted to measure the post shock temperature on the crater by using an infrared video camera. As a result, we found that the post shock temperature was measured to be from 2K to 9K when the ice projectile was impacted up to 300m/s. Thus, it was found that the projectile kinetic energy was partitioned into the crater heated at the post shock temperature with the partition coefficient of 1% to 10%.

我们对雪进行了撞击实验，以模拟彗星核表面发现的撞击坑。特别是，为了澄清彗星表面的热历史和陨石坑形态之间的关系，使用烧结雪样品进行了撞击实验。在-10 ℃烧结的孔隙率为40%的雪地上，当撞击速度达到150 m/s时，撞击坑的尺寸随着撞击速度的增加而增大，撞击时间为15 min。结果表明，撞击坑的体积与撞击动能Ek呈幂律关系，其幂律指数为0.5。在3 min ~ 60 h的烧结时间范围内，火山口尺寸随烧结时间的增加而减小。在-10℃下。火山口体积与烧结时间呈幂律关系。用尼龙弹丸以2.7km的速度高速撞击孔隙率为50%的雪，发现环形山外缘剥落，形成环形山边缘结构，环形山呈球形，内壁有再冻结的薄冰层。结果表明，尼龙弹丸的冲击速度大于2.7km/s（冲击压力可达3.9GPa），可使雪在撞击过程中融化并在火山口壁上扩散。为了定量估算高速撞击后的温升，利用红外摄像机进行了冰-冰撞击实验，测量了撞击后弹坑的温度。结果表明，当冰弹以300 m/s的速度撞击时，冲击后温度为2 ~ 9 K。因此，发现弹丸动能以1%至10%的分配系数分配到在冲击后温度下加热的弹坑中。