Tombaugh Regio is the largest bright surface feature of the dwarf planetPluto. It is just north of the equator, to the northeast of Cthulhu Macula and to the northwest of Krun Macula, which are both dark features. Its western lobe, a 1000 km-wide plain of nitrogen and other ices lying within a basin, is named Sputnik Planitia. The eastern lobe consists of high-albedo uplands thought to be coated by nitrogen transported through the atmosphere from Sputnik Planitia, and then deposited as ice. Some of this nitrogen ice then returns to Sputnik Planitia via glacial flow. Named after Clyde Tombaugh, the discoverer of Pluto, it is nicknamed the "heart" after its shape.
Description
Tombaugh Regio is a large, light-colored region about across. The two lobes of the feature are geologically distinct. The western lobe, Sputnik Planitia, is smoother than the eastern, and they are of slightly different colors. Early speculation was that the western lobe may be a large impact crater filled with nitrogen snow. Bright spots within the region were initially speculated to be mountain peaks. Photos, released on 15 July 2015, revealed mountains made of water ice in the feature; they also showed no craters in this same region. Subsequent data indicated that the center of Sputnik Planitia is rich in nitrogen, carbon monoxide, and methane ices, and that features near the edges of the region show evidence of ice flow such as glaciers, and light material overlying the darker material at the eastern edge of Cthulhu Macula. The surface of Sputnik Planitia is divided into polygonal convection cells and is less than 10 million years old, indicating that Pluto is geologically active. The feature had been identified as a bright spot for six decades prior to the New Horizonsflyby, although it was impossible to image it with enough resolution to determine its shape. Over these six decades the spot had been observed to be dimming. In 2020, it was found that Tombaugh Regio controlled the wind circulation of Pluto, and could sculpt the landscape on its surface.
Naming
Tombaugh Regio was first identified in the initial image of Pluto returned after the New Horizons probe recovered from an anomaly that temporarily sent it into safe mode. NASA initially referred to it as a "heart" in reference to its overall shape. On 15 July 2015, the region was provisionally named "Tombaugh Regio" by the New Horizons team in honor of astronomer Clyde Tombaugh, the discoverer of Pluto, regio being Latin for 'region'. On 7 September 2017, the name was officially approved by the International Astronomical Union, together with names for 13 other surface features on Pluto. Some people find the feature also resembles the Disney character Pluto, an animated non-anthropomorphic dog which shares the name of the dwarf planet, facing eastward. The Walt Disney Company acknowledged this perceived likeness in a short animation.
