History Stories

After a journey of nine years and some 3 billion miles, NASA’s New Horizons spacecraft flew by the dwarf planet Pluto and its five moons yesterday morning.

As its spacecraft New Horizons prepared to make its history-making flyby with Pluto on the morning of Tuesday, July 14, NASA released a high-resolution image of the dwarf planet, captured by New Horizons before it went out of contact with Earth the previous night. Taken when the probe was some 476,000 miles away from Pluto, the image’s most striking feature is the large, bright area on the planet’s surface that has been dubbed “the heart.” The region measures 1,000 miles across, and according to a New Horizons-themed Q&A held on Twitter yesterday by NASA’s planetary science director, Jim Green, is most likely made up of snow created by some combination of nitrogen, carbon monoxide or methane gases.

Around 7:38 a.m. Eastern time, New Horizons passed through the plane of the Pluto system, which includes the dwarf planet and its five moons: Hydra, Kerberos, Charon, Nix and Styx. The spacecraft passed near Charon’s orbit in order to minimize the chance of hitting any debris. Because of its incredible speed—more than 30,000 mph—any collision, even with an object the size of a grain of rice, could incapacitate the probe.

New Horizons made its closet approach at 7:49 a.m., coming within 7,750 miles (12,000 kilometers) of Pluto, or the distance between New York City and Mumbai. As quoted in an official statement about the mission, NASA Administrator Charles Bolden announced: “Once again we have achieved a historic first. The United States is the first nation to reach Pluto, and with this mission has completed the initial survey of our solar system, a remarkable accomplishment that no other nation can match.”

In the early 20th century, American astronomer Percival Lowell launched a dedicated search for a ninth, distant planet, the existence of which had been suggested by some gravitational disturbances in the orbit of Uranus. Though Lowell died in 1916, the search continued at the observatory he founded in Flagstaff, Arizona. In 1930, a young amateur astronomer named Clyde Tombaugh, hired by the observatory to aid in the search, spotted Pluto in the constellation Gemini. The later discovery of Charon, Pluto’s largest moon and nearly half its size, led astronomers to conclude that Pluto was not in fact as massive as they had first thought. In 2006, the International Astronomic Union (IAU) voted to reclassify Pluto as a dwarf planet, after astronomers realized it was one of the larger objects in the Kuiper Belt, the region located past Neptune that contains debris left over from the formation of the solar system.

By the time of this reclassification, the U.S. space probe New Horizons had already begun its historic journey towards Pluto, having launched from Cape Canaveral, Florida on January 19, 2006. The probe carried a small amount of Tombaugh’s ashes; he died in 1997 at the age of 90. At the end of February, New Horizons flew past Jupiter, making observations of the planet, its moons and its ring system. The probe then entered a long period of electronic hibernation, transmitting status updates only once a week.

Five months ago, New Horizons began its planned study of the Pluto-Charon system.
Like our own moon, Charon was formed when a large body smashed into the young Pluto. By coming in such close proximity to the dwarf planet and its moons, the probe offers a better look than ever before at Pluto’s atmosphere and geology, and its observations are expected to provide scientists with a greater understanding of the rest of the Kuiper Belt and the formation of the early solar system.

In the end, New Horizons’ journey to Pluto took about one minute less than predicted. In order to reach its destination, the probe had to pass through a 36-by-57 mile (60 by 90 kilometers) window in space. As NASA reported in its statement yesterday, this is “the equivalent of a commercial airliner arriving no more off target than the width of a tennis ball.”

Yesterday evening, scientists at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, which managed the New Horizons mission, waited eagerly for the “phone home” signal letting them know New Horizons had emerged from its flyby safe and sound. As the probe was busily observing its surroundings, it couldn’t turn its antenna around in order to send the all-clear signal right away; signals from Pluto take four and a half hours to reach Earth, traveling at the speed of light. All told, it would be 13 hours after New Horizons made its closest approach before the team in Maryland received confirmation that the flyby was successful. When the call came, around 9 p.m. on Tuesday night, mission operations manager Alice Bowman reported “We have a healthy spacecraft, we’ve recorded data of the Pluto system, and we’re outbound from Pluto.”

Crowd of hundreds of journalists, VIP guests and others gathered at the laboratory cheered, clapped and waved American flags after the call came in. The first new images from the flyby are expected to come in today, and New Horizons will continue to transmit material from its decade-long mission until October 2016.

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