Pluto’s frozen heart was one of the first interesting features revealed in the initial images sent back from New Horizons during its approach. The image above was taken on July 13th, 2015 – one day before the flyby – when New Horizons was 768,000 kilometers (476,000 miles) from Pluto’s surface.
As the spacecraft neared closer to Pluto, more was learned about this unique feature. Informally known as Sputnik Planum, the heart-shaped geological feature is actually a nitrogen glacier. In fact, it is now the largest known glacier in the solar system.