Nevertheless, during 52 hours of data recorded by the MIT probe before battery power ran out, Rossi's group found a transition between two distinct regions around Earth. Near Earth, there were fairly strong and well organised magnetic fields, but no indication of interplanetary protons. At 22 Earth radii, the spacecraft entered a region where magnetic fields were weaker and more irregular, and where a substantial flux of protons was observed coming from the general direction of the Sun. On several occasions during the rest of the flight, this flux disappeared and then reappeared again, which indicated that the spacecraft was flying close to the boundary between the two regions and that this boundary was moving irregularly. Eventually, this boundary became known as the magnetopause.