The force of gravity between two objects is described by Newton's law of universal gravitation, which states that the gravitational force \( F \) between two masses \( m_1 \) and \( m_2 \) separated by a distance \( r \) is given by the formula:
\[ F = G \frac{m_1 m_2}{r^2} \]
where \( G \) is the gravitational constant.
If the mass of the planet is cut in half, the new gravitational force can be expressed as:
\[ F' = G \frac{(m_1/2) m_2}{r^2} = \frac{1}{2} G \frac{m_1 m_2}{r^2} = \frac{1}{2} F \]
This shows that the gravitational force would decrease to half of its original value.
Therefore, the correct response is: The force of gravity would decrease.