A survey magnetometer carried aboard the Air Force Pioneer I space probe obtained data over the interval 3.7 to 7 and 12.3 to 14.8 geocentric radii. The day was unusually quiet magnetically (AP∼ ) with a long quiet prior history. The data indicate an inverse‐cube‐field decrease in the region of 3.7 to 13.6 radii, where termination takes place, with a subsequent decrease to 5×10–5gauss. This value is examined in the light of possible interplanetary gas activity. The surprisingly distant geomagnetic cutoff suggests a very low gas pressure on the day of the flight. Increasingly large (fractionally) fluctuations were observed with increasing radii. A gross variability in the vestigial field would suggest hydromagnetic activity or a complex gas cloud s