2. Let $P$ be any point inside a regular tetrahedron $ABCD$ with edge length $\sqrt{2}$, and let the distances from point $P$ to the four faces be $d_{1}, d_{2}, d_{3}, d_{4}$. Then the minimum value of $d_{1}^{2}+d_{2}^{2}+d_{3}^{2}+d_{4}^{2}$ is $\qquad$