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Neptune trojans are bodies in orbit around the Sun that orbit near one of the stable Lagrangian points of Neptune. They therefore have approximately the same orbital period as Neptune and follow roughly the same orbital path. Twelve Neptune trojans are currently known, of which nine orbit near the Sun–Neptune Lagrangian point 60° ahead of Neptune〔 and three orbit near Neptune's region 60° behind Neptune.〔 The Neptune trojans are termed 'trojans' by analogy with the Jupiter trojans. The discovery of in a high-inclination (>25°) orbit was significant, because it suggested a "thick" cloud of trojans (Jupiter trojans have inclinations up to 40°), which is indicative of freeze-in capture instead of in situ or collisional formation.〔 It is suspected that large (radius ≈ 100 km) Neptune trojans could outnumber Jupiter trojans by an order of magnitude.〔 E. I. Chiang and Y. Lithwick ''Neptune Trojans as a Testbed for Planet Formation'', The Astrophysical Journal, 628, pp. 520–532 ( Preprint )〕 In 2010, the discovery of the first known Neptune trojan, , was announced. Neptune's trailing region is currently very difficult to observe because it is along the line-of-sight to the center of the Milky Way, an area of the sky crowded with stars. It would have been possible for the ''New Horizons'' spacecraft to investigate , the only Neptune trojans discovered by 2014 detectable by ''New Horizons'', when it passed through this region of space en route to Pluto.〔 However, ''New Horizons'' may not have had sufficient downlink bandwidth, so it was decided to give precedence to the preparations for the Pluto flyby. == Discovery and exploration == In 2001, the first Neptune trojan was discovered, , near Neptune's region, and with it the fifth〔After the asteroid belt, the Jupiter trojans, the trans-Neptunian objects and the Mars trojans.〕 known populated stable reservoir of small bodies in the Solar System. In 2005, the discovery of the high-inclination trojan has indicated that the Neptune trojans populate thick clouds, which has constrained their possible origins (see below). On August 12, 2010, the first trojan, , was announced.〔 It was discovered by a dedicated survey that scanned regions where the light from the stars near the Galactic Center is obscured by dust clouds.〔 This suggests that large trojans are as common as large trojans, to within uncertainty,〔 further constraining models about their origins (see below). It would have been possible for the ''New Horizons'' spacecraft to investigate Neptune trojans discovered by 2014, when it passed through this region of space en route to Pluto.〔 Some of the patches where the light from the Galactic Center is obscured by dust clouds are along ''New Horizonss flight path, allowing detection of objects that the spacecraft could image.〔 , the highest-inclination Neptune trojan known, was just bright enough for ''New Horizons'' to observe it in end-2013 at a distance of 1.2 AU.〔 However, ''New Horizons'' may not have had sufficient downlink bandwidth, so it was eventually decided to give precedence to the preparations for the Pluto flyby.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Neptune trojan」の詳細全文を読む スポンサード リンク
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