NASA planning orbiter mission to Pluto

The Southwest Research Institute, in collaboration with NASA, is exploring the feasibility and cost of a long-term Pluto Orbiter mission. The mission aims to send an unmanned spacecraft to study Pluto and two other Kuiper Belt objects over two years. The new spacecraft will feature a larger payload and more advanced instruments than the New Horizon probe. Although specific instruments are not detailed, the mission builds on the success of the New Horizon mission, which flew past Pluto and its moons, reaching the farthest object visited, Ultima Thule.

Describe the previous mission led by the Southwest Research Institute and its significance.

What was the farthest object visited by the New Horizon probe, and what is its significance?