5. As shown in Figure 5, the moving chord $AB$ of the parabola $y=x^{2}$ lies on a line that is tangent to the circle $x^{2}+y^{2}=1$. The two tangent lines to the parabola at points $A$ and $B$ intersect at point $M$. Find the equation of the locus of point $M$.

保留了原文的换行和格式。
(The equation of the line containing the chord $AB$ is $y+y_{M}=2 x_{M} x$. It is easy to know that $d=\frac{\left|y_{M}\right|}{\sqrt{1+4 x_{M}^{2}}}=1$, i.e., $y_{M}^{2}-4 x_{M}^{2}=1$. Substituting $y+y_{M}=2 x_{M} x$ into $y=x^{2}$, we get $x^{2}-2 x_{M} x+y_{M}=0$. Therefore, $\Delta=4 x_{M}^{2}-4 y_{M}=y_{M}^{2}-4 y_{M}-1>0$, and $y_{M}^{2} \geqslant 1$. Solving this, we get $y_{M}>2+\sqrt{5}$ or $y_{M} \leqslant-1$. Hence, the equation of the trajectory of point $M$ is $y^{2}-4 x^{2}=1(y \leqslant-1$ or $y>$ $2+\sqrt{5}):)$