ALL PLANETARY BODIES WITH INTRINSIC MAGNETIC FIELDS OR ATMOSPHERES POSSESS LONG MAGNETIC TAILS. IF THEY POSSESS THE SAME INTRINSIC MAGNETIC FIELD DIPOLE ORIENTATION AS EARTH THEN THE NORTHERN HALF OF THE TAIL IS COMPOSED OF OPEN MAGNETIC FIELDS ORIENTED BACK TOWARD THE PLANET AND THE SOUTHERN HALF HAS THE OPPOSITE ORIENTATION (SEE FIGURE 1 PANEL A). THE TWO LOBES OF THE TAIL ARE SEPARATED BY A SHEET OF HOT PLASMA DERIVED FROM THE SOLAR WIND AND IONS DERIVED FROM THE ATMOSPHERES OF THE PLANET AND ANY MOONS. THERE IS A CROSS-TAIL CURRENT SHEET THAT SEPARATES THE SUNWARD MAGNETIC FIELD IN THE NORTHERN LOBE FROM THE ANTI-SUNWARD FLUX IN THE SOUTHERN LOBE (I.E. THE CENTER OF THE PLASMA SHEET). THE INTRINSIC MAGNETOTAILS SUCH AS AT MERCURY EARTH AND THE OUTER PLANETS STORE MAGNETIC ENERGY IN THEIR TAIL LOBES AND THEN LATER CONVERT IT INTO PLASMA HEATING AND HIGH-SPEED JETTING THROUGH A PROCESS CALLED MAGNETIC RECONNECTION. MARS VENUS AND COMETS LACK GLOBAL INTRINSIC MAGNETIC FIELDS BUT MAGNETOTAILS STILL FORM AS A RESULT OF THE HELIOSPHERIC MAGNETIC FIELD LINES CARRIED BY THE SOLAR WIND DRAPING ABOUT THESE BODIES (SEE THE FIGURE PANEL B). THE VENERA 9 AND 10 AND PIONEER VENUS ORBITER MISSIONS TO VENUS FOUND THAT THE STRUCTURE OF ITS DRAPED FIELD MAGNETOTAIL HAS MANY SIMILARITIES TO THOSE OF MAGNETIZED PLANETS (SEE FIGURE 1). HOWEVER IT WAS NOT UNTIL MUCH FASTER FAR MORE COMPREHENSIVE PLASMA MEASUREMENTS BECAME AVAILABLE FROM THE VENUS EXPRESS MISSION THAT RECONNECTION WAS OBSERVED IN THIS PLANET S DRAPED FIELD TAIL. MORE RECENTLY THE MAVEN MISSION TO MARS HAS SHOWN THAT MAGNETIC RECONNECTION AT LOW ALTITUDES INVOLVING CRUSTAL MAGNETIC FIELD AND IN THE CROSS-TAIL CURRENT SHEET IS QUITE FREQUENT AND APPEARS TO HAVE IMPORTANT IMPACTS ON MARS UPPER ATMOSPHERE IONOSPHERE AND MAGNETIC TAIL. MAGNETIC RECONNECTION IS A FUNDAMENTAL PROCESS IN COSMIC PLASMAS THAT RECONFIGURES SHEARED MAGNETIC FIELDS SEPARATED BY THIN CURRENT SHEETS WITH A TRANSFER OF ENERGY TO THE CHARGED PARTICLES. INTENSIVE EXPERIMENTAL AND THEORETICAL INVESTIGATIONS OF RECONNECTION IN THE EARTH S MAGNETOTAIL INCLUDING THE ON-GOING MAGNETOSPHERIC MULTISCALE (MMS) MISSION HAVE FOUND THAT IT TAKES PLACE WHEN THE CROSS-TAIL CURRENT SHEETS TO BECOMES THIN RELATIVE TO THE SCALE OF THE GYRO-MOTION OF THESE CHARGED PARTICLES AROUND THE MAGNETIC FIELD LINES. WHEN THIS POINT IS REACHED THE PLASMA IONS AND ELECTRONS ARE NO LONGER FROZEN ONTO THE FIELD LINES. MAGNETIC NULLS ( X-LINES ) FORM IN THE CURRENT SHEET AND MAGNETIC FIELD LINES FROM OPPOSITE SIDES COME TOGETHER AND EXCHANGE PARTNERS. THIS PROCESS IS REPEATED ACROSS THE CURRENT SHEET TO PRODUCE MULTIPLE X-LINES THAT RESULT IN THE FORMATION OF MAGNETIC FLUX ROPES (OR PLASMOIDS). THE FORMATION INTERACTION AND TRANSPORT OF THESE FLUX ROPES APPEARS CENTRAL TO THE RECONNECTION PROCESS AND IT SOMETIMES TERMED COLLECTIVELY THE PLASMOID INSTABILITY.