A cold, slushy ocean lying deep beneath Pluto’s bright, heart-shaped Tombaugh Regio is the best explanation for features revealed by NASA’s New Horizons probe, according to new research. This cutaway image of Pluto shows a section through the area of Sputnik Planitia, with dark blue representing a subsurface ocean and light blue for the frozen crust. Image credit: Pam Engebretson. For several decades, researchers have observed that Tombaugh Regio...