Scientists revealed recently that the dwarf planet could actually one giant comet or have formed from comets. It had always been believed that all our planets including the dwarf one were created at the start of the Solar System from rock material that merged into one large object.
Scientists analyzing data from both the New Horizons mission to Pluto and the information back from the Rosetta Space Probe discovered a few similarities which started off the interest in that Pluto could be a giant comet, one that is without a tail as it is too far away from the Sun to burn off and create a tail.
It had been reported in the journal Icarus that scientists from the Southwest Research institute, San Antonio, Texas had come up with this theory. The smooth heart shape area (Tombaugh Regio) on the surface of the dwarf planet contains materials that are similar to those found on P67 comet by Rosetta. Pluto would have had to have been hit by a large number of comets over time, an estimated billions comets to be precise.
The scientists took data from P67 and scaled up the nitrogren content which matched what they found on Pluto so the theory came about. How much nitrogen Pluto had at the start and how much it has lost is not know and could affect the theory.