The piece of information the student is missing to be able to find the gravitational force is the gravitational constant, G. The formula for gravitational force is given by Newton's law of universal gravitation:
\[ F = \frac{G \cdot m_1 \cdot m_2}{r^2} \]
where \( F \) is the gravitational force, \( G \) is the gravitational constant (approximately \( 6.674 \times 10^{-11} , \text{N(m/kg)}^2 \)), \( m_1 \) and \( m_2 \) are the masses of the two objects (in this case, the Earth and the Sun), and \( r \) is the distance between the centers of the two masses. Without the value of \( G \), the student cannot calculate the gravitational force.