The New Horizons probe took this photograph of Pluto that shows a heart-shaped bright spot on its surface.
On July 14, after a journey of about 3 billion miles, NASA’s New Horizons probe finally passed by Pluto. It took the piano-sized spacecraft more than nine years to reach the dwarf planet. Dwarf planets are celestial bodies that are generally smaller than the planet Mercury. Unlike planets, they share their orbits around the sun with comets, asteroids, or other dwarf planets. Scientists, engineers, and other spectators at the New Horizons operations center at Johns Hopkins University cheered as the probe flew within 7,750 miles of Pluto’s surface. New Horizons flew closer to the dwarf planet than any other spacecraft had before.
When New Horizons was launched in January 2006, Pluto was still considered a planet. It was reclassified as a dwarf planet in August of that year by the International Astronomical Union (IAU) at the urging of astronomers such as Neil deGrasse Tyson. Pluto is located in a largely unexplored region of our solar system known as the Kuiper (KY•per) Belt, which lies beyond the planet Neptune’s orbit. This disc-shaped region is home to comets, asteroids, and other dwarf planets.
New Horizons collected data and captured high-resolution images as it sped by Pluto at about 31,000 miles per hour. Because Pluto is so far away, it took about 4 1/2 hours for the probe’s signals to reach Earth. The probe also took pictures of Charon, Pluto’s largest moon, from about 17,000 miles away. Scientists who have studied the photos from New Horizons have noted a large heart-shaped bright spot on Pluto’s surface. NASA referred to it as a “love note” from Pluto and estimated it to be 1,000 miles across. Scientists expected to see many impact craters on the dwarf planet’s surface, but surprisingly very few were spotted.
During its 10-hour flyby, New Horizons recorded the extremely cold temperatures around Pluto, took measurements of its atmosphere, and mapped the dwarf planet and its moons. The probe’s data showed that Pluto is larger than once thought. At about 1,472 miles in diameter, it is the largest known object in the Kuiper Belt. As New Horizons travels deeper into the Kuiper Belt, scientists expect the probe to encounter hundreds of other dwarf planets and other, smaller celestial bodies.