雙衛一

雙衛一
	攝於2022年9月
發現
發現者	Petr Pravec（英語：Petr Pravec） et al.
發現日期	2003年11月20日
編號
其它名稱	S/2003 (65803) 1
軌道參數
	曆元 7.5 2011年1月 (儒略日 2455873.0)
半長軸	1.19±0.03 km (撞擊前)
離心率	≤ 0.03
軌道週期	11.9216262±0.0000027 hr (11h 55m 18s; 撞擊前); 11h 23m ± 2m (撞擊後)
平均軌道速度	0.174 m/s (撞擊前)
平近點角	89.2°±1.8°
軌道傾角	168.6°±1.8° 相對於黃道
隸屬天體	雙生星
物理特徵
大小	208 米 × 160 米 × 133 米
質量	~5×109 kg (推測)
自轉週期	潮汐鎖定?
反照率	0.15±0.04
光譜類型	S-型小行星
絕對星等(H)	21.3±0.2

雙衛一是近地天體雙生星的一顆衛星。它的直徑為170公尺（560英尺），與羅馬鬥獸場相當，重約480萬噸。它與雙生星中心相距約1190米^[7]。2003年，有人在翁德熱約夫天文台發現了雙衛一。2020年6月，國際天文聯會將這顆小行星衛星命名為雙衛一^[8]。2022年9月，美國國家航空暨太空總署在開展雙小行星改道測試時將雙衛一列為撞擊目標，並故意讓一個太空飛行器撞向雙衛一，目的是改變雙衛一的軌跡^[9]。

備註

^ Astronomers involved in the discovery of Dimorphos include Petr Pravec（英語：Petr Pravec）, L.A.M. Benner, M.C. Nolan, P. Kusnirak, D. Pray, J.D. Giorgini, R.F. Jurgens, 史蒂文·J·奧斯特羅, J.-L. Margot, C. Magri, A. Grauer, and S. Larson. The discovery used lightcurve and radar observations from the 噴氣推進實驗室, Pasadena, 加利福尼亞州; 阿雷西博天文台, Arecibo, 波多黎各; and 翁德熱約夫天文台, Ondřejov, 捷克. ^[1]
^ Orbital parameters are those after the impact of DART, which changed the 軌道周期 by 32 minutes. Other possibly changed parameters remain to be reevaluated.^[3]
^ Scheirich and Pravec (2022) give the Dimorphos's orbit pole orientation in terms of 黃道坐標系, where $λ$ is 黃道坐標系 and $β$ is 黃道坐標系.^[4]^{（p. 4）} $β$ is the angular offset from the 黃道, whereas 軌道傾角 $i$ with respect to the ecliptic is the angular offset of the 黃極 from the 黃極, at $β$ = +90° ; $i$ with respect to the ecliptic would be the 角 of $β$ .^[5] Therefore, given $β$ = –78.6° , $i$ = 90° – (–78.6°) = 168.6° from the ecliptic.

參考文獻

^ ^1.0 ^1.1 ^1.2 (65803) Didymos. www.johnstonsarchive.net. [2021-11-11]. （原始內容存檔於2020-10-23）.
^ ^2.0 ^2.1 Naidu, Shantanu P.; Chesley, Steven R.; Farnocchia, Davide; Moskovitz, Nick; Pravec, Petr; Scheirich, Petr; Thomas, Cristina; Rivkin, Andrew S. Anticipating the DART impact: Orbit estimation of Dimorphos using a simplified model. The Planetary Science Journal. October 2022, 3 (10): 234. Bibcode:2022PSJ.....3..234N. S2CID 252815897. arXiv:2210.05101 . doi:10.3847/PSJ/ac91c0.
^ ^3.0 ^3.1 Dunbar, Brian. NASA Confirms DART Mission Impact Changed Asteroid's Motion in Space. NASA. 11 October 2022 [2022-10-11]. （原始內容存檔於2023-03-07）（英語）.
^ Scheirich, P.; Pravec, P. Preimpact Mutual Orbit of the DART Target Binary Asteroid (65803) Didymos Derived from Observations of Mutual Events in 2003–2021. The Planetary Science Journal. July 2022, 3 (7): 12 [2023-01-21]. Bibcode:2022PSJ.....3..163S. S2CID 250650906. doi:10.3847/PSJ/ac7233. 163. （原始內容存檔於2022-07-19）.
^ Coordinate transformations. Astronomy and Astrophysics. European Southern Observatory. January 1998 [17 June 2022]. （原始內容存檔於17 June 2021）.
^ ^6.0 ^6.1 Nakano, Ryota; Hirabayashi, Masatoshi; Brozovic, M.; Nolan, M. C.; Ostro, S. J.; Margot, J. L.; et al. NASA's Double Asteroid Redirection Test (DART): Mutual Orbital Period Change Due to Reshaping in the Near-Earth Binary Asteroid System (65803) Didymos. The Planetary Science Journal. July 2022, 3 (7): 16 [2023-01-21]. Bibcode:2022PSJ.....3..148N. S2CID 250327233. doi:10.3847/PSJ/ac7566. 148. （原始內容存檔於2022-09-27）.
^ 觀網財經. 人类首次行星防御演习，成功了. [2023-01-21]. （原始內容存檔於2023-03-08）.
^ Temming, Maria. An asteroid's moon got a name so NASA can bump it off its course. Science News. 29 June 2020 [1 July 2020]. （原始內容存檔於2021-09-12）.
^ Rincon, Paul. NASA DART asteroid spacecraft: Mission to smash into Dimorphos space rock launches. BBC News. 2021-11-24 [2021-11-25]. （原始內容存檔於2022-01-01）（英國英語）.

[2] Astronomers involved in the discovery of Dimorphos include Petr Pravec（英語：Petr Pravec）, L.A.M. Benner, M.C. Nolan, P. Kusnirak, D. Pray, J.D. Giorgini, R.F. Jurgens, 史蒂文·J·奧斯特羅, J.-L. Margot, C. Magri, A. Grauer, and S. Larson. The discovery used lightcurve and radar observations from the 噴氣推進實驗室, Pasadena, 加利福尼亞州; 阿雷西博天文台, Arecibo, 波多黎各; and 翁德熱約夫天文台, Ondřejov, 捷克. ^[1]

[5] Orbital parameters are those after the impact of DART, which changed the 軌道周期 by 32 minutes. Other possibly changed parameters remain to be reevaluated.^[3]

[pole-8] Scheirich and Pravec (2022) give the Dimorphos's orbit pole orientation in terms of 黃道坐標系, where $λ$ is 黃道坐標系 and $β$ is 黃道坐標系.^[4]^{（p. 4）} $β$ is the angular offset from the 黃道, whereas 軌道傾角 $i$ with respect to the ecliptic is the angular offset of the 黃極 from the 黃極, at $β$ = +90° ; $i$ with respect to the ecliptic would be the 角 of $β$ .^[5] Therefore, given $β$ = –78.6° , $i$ = 90° – (–78.6°) = 168.6° from the ecliptic.

[johnston-1] 1.0 ^1.1 ^1.2 (65803) Didymos. www.johnstonsarchive.net. [2021-11-11]. （原始內容存檔於2020-10-23）.

[Naidu2022-3] 2.0 ^2.1 Naidu, Shantanu P.; Chesley, Steven R.; Farnocchia, Davide; Moskovitz, Nick; Pravec, Petr; Scheirich, Petr; Thomas, Cristina; Rivkin, Andrew S. Anticipating the DART impact: Orbit estimation of Dimorphos using a simplified model. The Planetary Science Journal. October 2022, 3 (10): 234. Bibcode:2022PSJ.....3..234N. S2CID 252815897. arXiv:2210.05101 . doi:10.3847/PSJ/ac91c0.

[DartPressUpdateNASA-4] 3.0 ^3.1 Dunbar, Brian. NASA Confirms DART Mission Impact Changed Asteroid's Motion in Space. NASA. 11 October 2022 [2022-10-11]. （原始內容存檔於2023-03-07）（英語）.

[Scheirich2022-6] Scheirich, P.; Pravec, P. Preimpact Mutual Orbit of the DART Target Binary Asteroid (65803) Didymos Derived from Observations of Mutual Events in 2003–2021. The Planetary Science Journal. July 2022, 3 (7): 12 [2023-01-21]. Bibcode:2022PSJ.....3..163S. S2CID 250650906. doi:10.3847/PSJ/ac7233. 163. （原始內容存檔於2022-07-19）.

[coordstransform-7] Coordinate transformations. Astronomy and Astrophysics. European Southern Observatory. January 1998 [17 June 2022]. （原始內容存檔於17 June 2021）.

[Nakano2022-9] 6.0 ^6.1 Nakano, Ryota; Hirabayashi, Masatoshi; Brozovic, M.; Nolan, M. C.; Ostro, S. J.; Margot, J. L.; et al. NASA's Double Asteroid Redirection Test (DART): Mutual Orbital Period Change Due to Reshaping in the Near-Earth Binary Asteroid System (65803) Didymos. The Planetary Science Journal. July 2022, 3 (7): 16 [2023-01-21]. Bibcode:2022PSJ.....3..148N. S2CID 250327233. doi:10.3847/PSJ/ac7566. 148. （原始內容存檔於2022-09-27）.

[10] 觀網財經. 人类首次行星防御演习，成功了. [2023-01-21]. （原始內容存檔於2023-03-08）.

[Temming-2020-06-29-11] Temming, Maria. An asteroid's moon got a name so NASA can bump it off its course. Science News. 29 June 2020 [1 July 2020]. （原始內容存檔於2021-09-12）.

[Rincon-2021-11-24-12] Rincon, Paul. NASA DART asteroid spacecraft: Mission to smash into Dimorphos space rock launches. BBC News. 2021-11-24 [2021-11-25]. （原始內容存檔於2022-01-01）（英國英語）.

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