The final phase of the exploration began on February 12, 2019, when one of the Van Allen dual detectors began a series of orbit descent operations, lowering the lowest point of orbit from about 375 miles to only 190 miles from Earth. The lowest point of the orbit is called perigee. The probe eventually re-entered the Earth's atmosphere in about 15 years. Now the mission's goal is to use air drag to bring satellites into the atmosphere and eventually burn them out instead of becoming space debris.
In March, the second Van Allen probe will begin its orbit descent. Currently, the probe is in orbit in the Earth's radiation belt, which is filled with fast-moving particles that interfere with satellite electronic devices and pose a threat to astronauts passing through them. The size and shape of the radiation belt varies with solar activity.
The Van Allen probe took much longer to send back useful data to researchers than expected for two years. No spacecraft had been able to operate in dangerous radiation belts for more than two years before, but the two detectors have broken records, running for nearly seven years without accidents.