Recursive method and memory problems

   private void DFSVisitting(Planet current, Planet old, bool[] visited, int len)
    {
        int length;
        length = len;
        visited[current.id] = true;
        if (!(current == old)) {
            foreach (Route route in gameScreen.board.routes) {
                if (!(route.color == color && route.built)) continue;
                if ((route.planet1 == current && route.planet2 == old) || (route.planet2 == current && route.planet1 == old)) length += route.costs;
            }
        }

        List<Planet> neighbours = adjacent[current.id];
        foreach (Planet p in neighbours) {
            if (!visited[p.id]) {
                DFSVisitting(p, current, visited, length);
                // returns here
                lengths.Add(length);
                length = 0;
            }
        }
        lengths.Add(length);
    }