Solution

For a circular orbit, the gravitational force provides the centripetal force:
$\frac{Gmm_1}{r^2}=m_1w^2 r$
where $G$ is the gravitational constant, $m$ is the mass of the Sun, $m_1$ the asteroid's mass, $r$ is the orbital radius and $w$ is the angular velocity
we get
$\frac{Gm}{r^2}=w^2 r$
and from that
$r=(\frac{Gm}{w^2})^1/3$