The asteroid (3200) Phaethon is widely recognized as the parent of the Geminid meteoroid stream. However, it has never shown evidence for ongoing mass loss or for any form of comet-like activity that would indicate the continued replenishment of the stream. Following an alert by Battams & Watson, we used NASA's STEREO-A spacecraft to image Phaethon near perihelion, in the period UT 2009 June 17-22, when the heliocentric distance was near 0.14 AU. The resulting photometry shows an unexpected brightening, by a factor of two, starting UT 2009 June 20.2 ± 0.2, which we interpret as an impulsive release of dust particles from Phaethon. If the density is near 2500?kg?m–3, then the emitted dust particles must have a combined mass of ~2.5 × 108 a 1?kg, where a 1 is the particle radius in millimeters. Assuming a 1 = 1, this is approximately 10–4 of the Geminid stream mass and to replenish the stream in steady state within its estimated ~103 yr lifetime would require ~10 events like the one observed, per orbit. Alternatively, ongoing mass loss may be unrelated to the event which produced the Phaethon-Geminid complex. An impact origin of the dust is highly unlikely. Phaethon is too hot for water ice to survive, rendering the possibility that dust is ejected through gas drag from sublimated ice unlikely. Instead, we suggest that Phaethon is essentially a rock comet, in which the small perihelion distance leads both to the production of dust (through thermal fracture and decomposition cracking of hydrated minerals) and to its ejection into interplanetary space (through radiation pressure sweeping and other effects).
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机译：小行星（3200）Phaethon被广泛认为是双子座流星体的母体。但是，它从未显示出持续不断的质量损失或任何形式的彗星状活动的迹象，这些活动表明溪流的持续补充。在Battams＆Watson发出警报后，我们使用NASA的STEREO-A航天器在UT 2009年6月17日至22日期间拍摄了近日点附近的Phaethon，当时日心距接近于0.14 AU。从UT 2009年6月20.2±0.2开始，所得到的光度法显示出意想不到的增亮2倍，我们将其解释为从Phaethon冲出的灰尘颗粒。如果密度接近2500？kg？m-3，则发射的尘埃颗粒的总质量必须为〜2.5×108 a 1？kg，其中1为以毫米为单位的半径。假设1 = 1，大约是双子座流质量的10–4，要在估计的〜103年寿命内以稳态补充流，则每个轨道需要约10次事件，如观察到的事件。或者，持续的质量损失可能与产生Phaethon-Geminid复合物的事件无关。灰尘的冲击源极不可能。 Phaethon太热了，水冰无法生存，因此不太可能通过升华冰中的气体阻力喷射出灰尘。相反，我们建议Phaethon本质上是一颗岩石彗星，其中小的近日点距离既会产生粉尘（通过热裂和水合矿物的分解裂变），又会导致粉尘喷入行星际空间（通过辐射压力扫描等）效果）。
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