Question

What dwarf planets has NASA sent probes to?

Answer 1

I remember only one the new horizon to Pluto.

Explanation:

New horizon to Pluto.

Answer 2

NASA has sent probes to the dwarf planets Ceres and Pluto.

Explanation:

A dwarf planet is a body which meets 2 of the 3 criteria for being a planet. It must be orbiting the sun and almost spherical. The 3rd criterion for a planet is that it must have cleared its orbit of other bodies except moons.

Ceres is in the asteroid belt and got upgraded to dwarf planet status. It was visited by the NASA Dawn space probe which reached Ceres in March 2015.

Pluto is a trans Neptunian object which got demoted from planet to dwarf planet when the rules changed. The NASA New Horizons space probe visited Pluto in July 2015.