by whom?
The "New Horizons" spacecraft.
Pluto
The "New Horizons" spacecraft, which flew by Pluto in July 2015, is the first and so far only attempt to explore Pluto directly. 
what is pluto? A dwarf planet in the Kuiper belt. who discovered it? Clyde Tombaugh when? 1930 what is its origin? One early hypothesis was that Pluto was an escaped moon of Neptune. what is its mass? 17.7% that of the Moon. what is its size? Its surface area is , or roughly the same surface area as Russia. what kind of atmosphere does it have? It has a tenuous atmosphere consisting of nitrogen (N), methane (CH), and carbon monoxide (CO). does it have a moon? UNANSWERABLE does it have a relation with any other planet? Yes, with Neptune. what kind? Pluto is protected by its 2:3 orbital resonance with Neptune. does it have a solid surface? UNANSWERABLE how is it classified? It meets the classification whether it "looks" like a planet. is the classification done by any organization? UNANSWERABLE do you know how far from the sun is it? From 30 to 49 astronomical units. what orbit does it follow? Nearly circular orbits around the Sun close to a flat reference plane called the ecliptic. has it been explored? Yes, in July 2015.
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Pluto [SEP] Exploration
The "New Horizons" spacecraft, which flew by Pluto in July 2015, is the first and so far only attempt to explore Pluto directly. Launched in 2006, it captured its first (distant) images of Pluto in late September 2006 during a test of the Long Range Reconnaissance Imager. The images, taken from a distance of approximately 4.2 billion kilometers, confirmed the spacecraft's ability to track distant targets, critical for maneuvering toward Pluto and other Kuiper belt objects. In early 2007 the craft made use of a gravity assist from Jupiter. "New Horizons" made its closest approach to Pluto on July 14, 2015, after a 3,462-day journey across the Solar System.