Because mass defect is a continuous and slow change, the revolution still keeps a circular orbit, so there is GMm/r? =mv？ R, where m is the mass of the sun and m is the mass of the earth.

In this process, angular momentum is conserved. If there is L=mvr, then v=L/mr, and bring it into the above formula, r=L? /GMm？ .

As can be seen from the above formula, the distance is inversely proportional to the mass of the sun. Then the mass of the sun decreases and the orbital radius becomes longer.

Furthermore, it can be inferred that the period becomes longer.