彗星塵:修订间差异
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== 成分 == |
== 成分 == |
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粉塵的成分通常為[[球粒隕石]]。其單體含有鎂鐵質矽酸鹽,如[[橄欖石]]和[[輝石]]<ref>{{cite journal |last1=Bradley |first1=J |last2=Brownlee |first2=D |last3=Veblen |first3=D |s2cid=4303275 |date=1983 |title=Pyroxene whiskers and platelets in interplanetary dust: evidence of vapor phase growth |journal=Nature |volume=301 |issue=5900 |page=473|doi=10.1038/301473a0 |bibcode=1983Natur.301..473B }}</ref>。矽酸鹽富含高冷凝溫度的{{link-en|鎂橄欖石|Forsterite}}和[[頑火輝石]]<ref name="brotsoual06">{{cite journal |last1=Brownlee |first1=D |last2=Tsou |first2=P |last3=Aléon |first3=J |s2cid=141128 |display-authors=etal |date=2006 |title=81P/Wild 2 Under a Microscope |journal=Science |volume=314 |issue=5806 |pages=1711–6 |doi=10.1126/science.1135840 |pmid=17170289 |url=https://digital.library.unt.edu/ark:/67531/metadc882789/ |hdl=1885/33730 |hdl-access=free }}</ref>。當這些顆粒迅速凝結時,它們往往會形成非常小的顆粒,而不是合併成液滴。 |
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與球粒隕石一樣,顆粒含有[[隕鐵| Fe(Ni)]]硫化物<ref name="zolze06">{{cite journal |last1=Zolensky |first1=M |last2=Zega |first2=T |last3=Yano |first3=H |last4=Wirick |first4=S |last5=Westphal |first5=A |last6=Weisberg |first6=M |display-authors=etal |s2cid=25539280 |date=15 Dec 2006 |title=Mineralogy and Petrology of Comet 81P/Wild 2 Nucleus Samples |journal=Science |volume=314 |issue=5806 |pages=1735–9 |doi=10.1126/science.1135842 |pmid=17170295 |bibcode=2006Sci...314.1735Z |hdl=1885/37338 |hdl-access=free }}</ref><ref>{{cite journal |last1=Zolensky |first1=M |last2=Thomas |first2=K |date=Nov 1995 |title=Iron and iron-nickel sulfides in chondritic interplanetary dust particles |journal=Geochimica et Cosmochimica Acta |volume=59 | issue=22 |page=4707|doi=10.1016/0016-7037(95)00329-0 |bibcode=1995GeCoA..59.4707Z }}</ref>和嵌入金屬和硫化物的玻璃(glass with embedded metal and sulfides,GEMS)<ref name="zolze06"/>。 |
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存在不同數量的有機物([[CHNOPS|CHON]])<ref>{{cite journal |last1=Kissel |first1=J |last2=Sagdeev |first2=R |last3=Bertaux |first3=J |s2cid=122405233 |display-authors=etal |date=1986 |title=Composition of comet Halley dust particles from Vega observations |journal=Nature |volume=321 |page=280 |doi=10.1038/321280a0 |bibcode=1986Natur.321..280K }} |
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</ref><ref>{{cite journal |last1=Kissel |first1=J |last2=Brownlee |first2=D |last3=Büchler |first3=K |s2cid=186245081 |display-authors=etal |date=1986 |title= Composition of comet Halley dust particles from Giotto observations|journal=Nature |volume=321 |page=336|doi=10.1038/321336a0 |bibcode=1986Natur.321..336K }}</ref><ref>{{cite journal |last1=Kissel |first1=J |last2=Kruger |first2=F |s2cid=4358568 |date=1987 |title= The organic component in dust from comet Halley as measured by the PUMA mass spectrometer on board Vega 1|journal=Nature |volume=326 |issue=6115 |pages=755–60|doi=10.1038/326755a0 |bibcode=1987Natur.326..755K }}</ref>。雖然有機物在宇宙中非常豐富,並且被廣泛預測存在於彗星中,但在大多數望遠鏡中,它們的光譜都是模糊的。僅在[[哈雷艦隊|哈雷飛越]]期間通過[[質譜法]]確認有機物的存在<ref>{{cite journal |last1=Lawler |first1=M |last2=Brownlee |first2=D |s2cid=4314100 |date=1992 |title=CHON as a component of dust from comet Halley |journal=Nature |volume=359 |issue=6398 |pages=810–12|doi=10.1038/359810a0 |bibcode=1992Natur.359..810L }}</ref><ref name="levasseuragarwal18">{{cite journal |last1=Levasseur-Regourd |first1=A |last2=Agarwal |first2=A |last3=Cottin |first3=H |last4=Engrand |first4=C |last5=Flynn |first5=G |last6=Fulle |first6=M |last7=Gombosi |first7=T |s2cid=189791473 |display-authors=etal |date=2018 |title=Cometary Dust |journal=Space Science Reviews |volume=214 |issue=3 |page=number 64|doi=10.1007/s11214-018-0496-3 |bibcode=2018SSRv..214...64L }}</ref>。一些有機物多以[[多環芳香烴]](PAHs)的形式存在<ref>{{cite journal |last1=Clemett |first1=S |last2=Maechling |first2=C |last3=Zare |first3=R |last4=Swan |first4=P |last5=Walker |first5=R |s2cid=24398934 |date=1993 |title= Identification of complex aromatic molecules in individual interplanetary dust particles|journal=Science |volume=262 |issue=5134 |pages=721–5 |doi=10.1126/science.262.5134.721 |pmid=17812337 |bibcode=1993Sci...262..721C }}</ref><ref name="greenbergli"/><ref>{{cite journal |last1=Lisse |first1=C |display-authors=etal |s2cid=3024593 |date=2006 |title= Spitzer spectral observations of the deep impact ejecta|journal=Science |volume=313 |issue=5787 |pages=635–40 |doi=10.1126/science.1124694 |pmid=16840662 |bibcode=2006Sci...313..635L |url=https://authors.library.caltech.edu/51944/7/Lisse.SOM.pdf }}</ref><ref>{{cite journal |last1=Sandford |first1=S |display-authors=etal |s2cid=2727481 |date=2006 |title= Organics captured from comet 81P/Wild 2 by the Stardust spacecraft|journal=Science |volume=314 |issue=5806 |pages=1720–4 |doi=10.1126/science.1135841 |pmid=17170291 |bibcode=2006Sci...314.1720S }}</ref><ref name="kellerba06">{{cite journal |last1=Keller |first1=L |last2=Bajt |first2=S |last3=Baratta |first3=G |last4=Borg |first4=J |last5=Bradley |first5=J |last6=Brownlee |first6=D |s2cid=35413527 |display-authors=etal |date=15 Dec 2006 |title=IR Spectroscopy of Comet 81P/Wild 2 Samples Returned by Stardust |journal=Science |volume=314 |issue=5806 |pages=1728–31 |doi=10.1126/science.1135796 |pmid=17170293 }}</ref>。 |
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可能會發現非常小的[[太陽前顆粒]](presolar grains,PSG)夾雜物<ref name="brotsoual06"/><ref name="kellerba06"/>。 |
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== 塵埃和彗星的起源 == |
== 塵埃和彗星的起源 == |
2022年6月5日 (日) 17:45的版本
彗星塵是指起源於彗星的宇宙塵埃,它可以提供彗星起源的線索。當地球通過彗星塵埃軌跡時,它會產生流星雨。
物理性質
大小
彗星活動產生的塵埃大部分為次微米級[1]至微米的大小[2][3]。然而,這一部分是短暫的,會因為輻射壓導致它們被吹出太陽系[4][5],或因為坡印廷–羅伯遜效應而螺旋向內[6][7]。
下一個尺寸等級是"蓬鬆的"("fluffly")[4][5]或"羣集類型"("cluster-type")[8],是前述顆粒的聚合物。它們的大小通常為20-100微米,但可以觀察到尺寸不是任意的[9],這是由於多孔的聚合物容易斷裂 [10] or compact.[8][11][12]。
更大的粒子是微流星體[13][14],不再是塵埃了[15][16]。在國際天文學聯合會(IAU)沒有定義的情况下[17][18],各小組設計了自己的粉塵定義:小於100微米[19]、50[20]、40[21] 30,[22]、和20微米[23] 還有<10微米[24][25][26][16]。其中一些塵埃/微流星體的定義是近似的或模棱兩可的[27][28][29],有些還重疊或自相矛盾(衝突)[30][23][22]。
IAU於2017年發佈了一份正式聲明。流星體為30微米至1米,塵埃較小,且不鼓勵使用"微流星體"一詞(儘管不是微流星體)[31]。國際流星組織 (IMO)雖然注意到了新的定義[32],但仍在其網站上顯示先前的定義[33],即0.001cm[34]。美國流星學會(AMS)也沒有給出嚴格的定義[35][36]。
成分
粉塵的成分通常為球粒隕石。其單體含有鎂鐵質矽酸鹽,如橄欖石和輝石[37]。矽酸鹽富含高冷凝溫度的鎂橄欖石和頑火輝石[27]。當這些顆粒迅速凝結時,它們往往會形成非常小的顆粒,而不是合併成液滴。
與球粒隕石一樣,顆粒含有 Fe(Ni)硫化物[38][39]和嵌入金屬和硫化物的玻璃(glass with embedded metal and sulfides,GEMS)[38]。
存在不同數量的有機物(CHON)[40][41][42]。雖然有機物在宇宙中非常豐富,並且被廣泛預測存在於彗星中,但在大多數望遠鏡中,它們的光譜都是模糊的。僅在哈雷飛越期間通過質譜法確認有機物的存在[43][44]。一些有機物多以多環芳香烴(PAHs)的形式存在[45][19][46][47][48]。
可能會發現非常小的太陽前顆粒(presolar grains,PSG)夾雜物[27][48]。
塵埃和彗星的起源
彗星起源的模型有:[49]
彗星的體積大小的特性,像是密度以及化學成分,可以區分模型之間的不同。例如,彗星和星際塵埃的同位素比率非常接近,顯示兩著有著一個共同的起源。
在1),星際塵埃模型說冰在濃厚雲氣的塵埃粒子上早於太陽形成。冰和塵埃混合,然後聚合成彗星,化學性質沒有明顯的改變。J. Mayo Greenberg在1986年率先提出這種想法。
在2) 太陽系模型,在星際雲中形成的冰首先揮發成為圍繞著原始太陽的塵埃和氣體吸積盤中的一部分。揮發的冰稍後在凝結成固體,並成為彗星的一部分。 The vaporized ices later resolidified and assembled into comets. 所以彗星在這個模型中會與由星際冰直接形成的彗星有著不同的組成。.
在3) 原始碎石堆模型說彗星是在木星形成的區域內凝聚成形。
星塵號發現在威爾德二號彗星的彗星塵內有矽酸鹽的結晶,這意味著塵埃形成的溫度超過[玻璃熔點]] (>1,000K),是在環繞著年輕恆星盤面的內側高溫地區,然後混合著太陽星雲從恆星內側向外輻射很遠的距離,或是塵埃粒子凝結在發展中紅巨星或超巨星向外流動。威爾德二號彗星的塵埃與新形成恆星吸積盤外側發現的顆粒相似[50]。
彗星和它的塵埃讓我們可以研究太陽系主要行星軌道以外的區域。彗星的區別在於它們的軌道,長週期彗星的軌道週期超過200年,有著很長的橢圓軌道,與太陽系平面的傾斜是隨機的。短週期彗星與太陽系平面的傾斜通常都小於30度,環繞太陽公轉的方向如同行星一樣,都是逆時針的,並且週期少於200年。
一顆彗星遍歷它的軌道時將體驗一系列不同的條件。對長週期彗星,大部分的時間都在遠離太陽的場所,因為溫度太低而不會發生冰蒸發的情況。當它經過類地行星的區域,蒸發將快速到足以將小顆粒帶走,但較大的顆粒仍會受到抑制而留在彗核,並開始形成塵埃層。越靠近太陽,熱和蒸發的速率越高,因此將沒有塵埃柯粒可以留存。所以,覆蓋著彗核的塵埃層厚度可以顯示彗星會接近太陽到多近,以及經過近日點次數的多寡。如果一顆彗星有著厚厚的塵埃層,它可能已經頻繁的經過近日點,但並沒有過度的接近太陽。
塵埃層累積的厚度,可能可以對所有的短周期彗星做最佳的描述,短週期彗星彗核表面上塵埃層的厚度被認為可以達到公尺的等級。積累的塵埃層隨著時間的推移會改變短週期彗星的物理性質。塵埃層不僅會抑制太陽對彗星冰的加熱 (塵埃對太陽光中的熱是固若金湯的不良導體),也會使彗核內氣體流失的速率減緩。A典型的短週期彗星彗核在軌道上會快速的減緩它的蒸發速率,到達某一個點時會無法檢測到彗髮和彗尾的活動,天文學家就會將它們看成是低反照率的近地小行星。
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- ^ ([//web.archive.org/web/20171124175241/http://arxiv.org/abs/astro-ph/0603554 页面存档备份,存于互联网档案馆) [astro-ph/0603554] The Circumstellar Environments of Young Stars at AU Scales]
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