We report the first evidence for a large-scale reconnection exhaust newly initiated in the solar wind using observations from three spacecraft:ACE,Wind and ARTEMIS P2.We identified a well-structured X-line exhaust using measurements from ARTEMIS P2 in the downstream solar wind.However,in the upstream solar wind,ACE detected the same current sheet that corresponds to the exhaust identified by ARTEMIS P2 data without showing any reconnection signals.We cannot either find any reconnection signals from Wind that was located between ACE and ARTEMIS P2.Within the exhaust,a magnetic island is identified,which is not consistent with the quasi-steady feature as previously reported and gives further evidence for that the reconnection is newly initiated.Our observations show that the entering of energetic particles probably from Earth's bow shock makes the crucial difference between the non-reconnecting current sheet and the exhaust.Since no obvious driving factors are responsible for the reconnection initiation,we infer that these energetic particles probably play an important role in the reconnection initiation.Theoretical analysis also shows supports for this potential mechanism.
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