海王星环
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海王星环总共包含5个主要的行星环,且它们最早是由天文学家帕特里斯·布歇、莱因霍尔德·哈夫纳和让·曼弗雷德于1984年在智利拉西拉天文台发现的。[1][2]而这些环的第一张照片则是于1989年由旅行者2号飞船拍摄的。[3]十分微弱,由尘土构成,很像木星环或天王星环,但要比木星环纤细得多。这5个环后来分别以对发现海王星作出重大贡献的5个人命名。他们分别是约翰·戈特弗里德·伽勒、于尔班·勒威耶、威廉·拉塞尔、弗朗索瓦·阿拉戈和约翰·柯西·亚当斯。[3]
海王星环的组成物质非常黑暗,类似于天王星环。[4]环里的灰尘比例较高[4],且其光学深度较低,小于0.1。[5]亚当斯环分为五个环弧,又逆时针方向分别被命名为博爱,平等1和平等2,自由,和勇气。[4]弧占据范围狭窄,轨道经度非常稳定。环弧如何保持稳定仍在进行辩论。[6]
发现
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威廉·拉塞尔于1846年首次提及了围绕海王星的环。天文学家在1968年通过恒星掩星首次观测到天王星环,但是遭到忽视。[3]天王星环直到1977年时才被发现。天王星环发现后不久,维拉诺瓦大学哈罗德学者Reitsema团队开始寻找围绕海王星环。他们在1981年5月24日观测海王星的一次掩星,然而没有发现任何环带。[3]
海王星在1983年9月12日出现另一次掩星,但是地面观测结果无法确定。旅行者2号在1989年飞越海王星时确认海王星环存在。[3]
最亮的环(亚当斯环和勒威耶环)已经被哈勃太空望远镜和地面望远镜拍摄[7][8],但昏暗的环仍然远远低于能见度门槛。[9]2022年,詹姆斯韦伯太空望远镜对这些环进行了近红外相机拍摄,这是自航海者2号探测以来首次观察海王星环。[10]
特征
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海王星拥有五个不同的环[4],从内向外依次是:伽勒环、勒威耶环、拉塞尔环、阿拉戈环和亚当斯环。[11]勒威耶环和伽勒环之间也许还存在更暗弱的延伸。[4][6]海王星的另三个环很窄,宽度约100公里或100公里以下[5][6],与此相反,宽广的伽勒环和拉塞尔环宽度为2000至5000公里。[4]亚当斯环拥有五个明亮的环弧[4],按逆时针数分别是:博爱、平等1、平等2 、自由和勇气。[6][12]“博爱、平等、自由”是法国大革命的口号。[13]
海王星环包含了大量细小的灰尘:灰尘占环横截面面积的20%和70%。[6]它们类似木星环,灰尘量50-100%,但土星环和天王星环,它们含有的尘埃很少(小于0.1%)。[11][6] 海王星环的粒子是的黑暗物质;可能是冰与有机物的混合物。[11][4]整体而言,海王星环类似于木星环[4];两个环系统都由微弱、狭隘、广泛的尘埃环组成。[6]
海王星的环和天王星一样,被认为是比较年轻的。[4]这些环的年龄很可能大大地低于它们自己的年龄。[6]另外,像天王星一样,海王星的环可能是由于一个小卫星碎裂而产生。[4]
伽勒环
伽勒环是海王星最内侧的环,它大约2000公里宽,距海王星约41,000-43,000公里。[11]这环里的尘埃估计比例为40%-70%。[4][14]
勒威耶环
勒威耶环的轨道半径约为53,200公里[11],但它是狭窄的,宽度约113公里[5],尘埃比例为40%-70%。[6][14]而它是海王星的环里很亮的环。海王星的小卫星海卫五,其轨道半径约为52,526公里,因此能够发挥自己的作用,成为勒威耶环的牧羊犬卫星。[11]
拉塞尔环
拉塞尔环是海王星的最宽广的环[6],其轨道半径约为57,200公里。[11]这是一个微弱的环,尘埃比例约是20%-40%。[14]与勒威耶环和阿拉戈环挨得很紧。[11]
阿拉戈环
阿拉戈环很窄,很暗,但比拉塞尔环亮多了。[11]然而,许多出版物并没有提及阿拉戈环的存在。[6]
亚当斯环
外侧的亚当斯环轨道半径约为63,930公里[11],是最有名的和最值得研究的海王星环。这个环是狭窄的[14],稍有偏心和倾斜,总宽度约为35公里[5]。环的尘埃比例是在20%-40%。[14]海王星的小卫星海卫六,它的轨道在亚当斯环内,是一个牧羊犬卫星,通过42:43的轨道共振[12]使亚当斯环稳定。[12]
环弧
亚当斯环最亮的部分是环弧。[3]弧是离散区域内的环,其中的粒子神秘聚集在一起。亚当斯环已知包括五个短弧,博爱、平等1、平等2、自由和勇气,最亮最长的弧是博爱,而最暗的则是勇气。[15]亚当斯环的弧有些类似土星G环的弧。[16][11]弧的结构相当稳定,但一些变化已经被注意到。[17]自1986年以来,弧的整体亮度下降。勇气弧向前跃升了294°[18],而自由弧在2003年几乎已经消失了。博爱和平等(1和2)弧表现出相对亮度的不规则变化。[18]
性质
环 | 半径(公里)[11] | 宽度(公里) | 当量深度(公里)[19] | 正常光学厚度[20] | 灰尘比例(%)[14] | 偏心率 | 斜度(°) | 注释 |
---|---|---|---|---|---|---|---|---|
伽勒环(N42)[21] | 40,900–42,900 | 2,000 | 0.15[4] | ~ 10−4[4] | 40–70 | ? | ? | 广阔暗淡的环 |
勒威耶环(N53)[22] | 53,200 ± 20 | 113[5] | 0.7 ± 0.2[5] | 6.2 ± 1.5 × 10–3[5] | 40–70 | ? | ? | 狭窄的环 |
拉塞尔环[23] | 53,200–57,200 | 4,000 | 0.4[4] | ~ 10−4[4] | 20–40 | ? | ? | 拉塞尔环是从阿拉戈环延伸出来的一个薄弱的环 |
阿拉戈环[24] | 57,200 | <100[4] | ? | ? | ? | ? | ? | |
亚当斯环(N63)[25] | 62,932 ± 2 | 15–50[5] | 0.4[4] 1.25–2.15[5](环弧) |
0.011 ± 0.003[5] 0.03–0.09[4](环弧) |
20–40 40–70 (环弧) |
4.7 ± 0.2 × 10–4[12] | 0.0617 ± 0.0043[12] | 有五个明亮的环弧[26] |
- 问号表示参数未知。
相关条目
参考文献
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