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米（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，並故意讓一個航天器撞向雙衛一，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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