At only 8.27 million kilometers from the star, tidal forces would circularise the orbit unless another perturbing body exists in the system.

In order to determine the mass of the planet, measurements of the star's radial velocity variations were made by the N2K Consortium.

Combined with the known inclination of the orbit as determined by the transit observations, this revealed the mass of the planet to be 0.53±0.04 times that of Jupiter.

[7] As evidenced by its high mass and planetary radius, HAT-P-1b is a gas giant, most likely composed primarily of hydrogen and helium.

[9] Current theories predict that such planets formed in the outer regions of their solar systems and migrated inwards to their present orbits.