Illustration of spacecraft flying past a world far from the Sun,

Artist's impression of the New Horizons spacecraft encountering a Kuiper Belt Object. Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)

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Jan. 1, 2019: NASA's New Horizons spacecraft flew past Ultima Thule in the early hours of New Year's Day, ushering in the era of exploration from the enigmatic Kuiper Belt, a region of primordial objects that holds keys to understanding the origins of the solar system.

Fuzzy peanut-shaped space object.
A composite of two images reveal the best indication of Ultima Thule's size and shape so far. Credit: Credits: NASA/JHUAPL/SwRI

"Congratulations to NASA's New Horizons team, Johns Hopkins Applied Physics Laboratory and the Southwest Research Institute for making history yet again. In addition to being the first to explore Pluto, today New Horizons flew by the most distant object ever visited by a spacecraft and became the first to directly explore an object that holds remnants from the birth of our solar system," said NASA Administrator Jim Bridenstine. "This is what leadership in space exploration is all about."

Signals confirming the spacecraft is healthy and had filled its digital recorders with science data on Ultima Thule reached the mission operations center at the Johns Hopkins Applied Physics Laboratory (APL) today at 10:29 a.m. EST, almost exactly 10 hours after New Horizons' closest approach to the object.

On July 14, 2015, New Horizons became the first spacecraft to explore Pluto and its five moons up close. The successful flyby revealed Pluto as a dynamic, complex world. The science results were beamed back to Earth over 16 months. New Horizons has now explored its second science target—(486958) 2014 MU69—and will be sending the data back to Earth for months.

Launch Date Jan. 19, 2006 | 19:00 UT
Launch Site Cape Canaveral, Florida, USA | Launch Complex 41
Destination Pluto, Kuiper Belt, Beyond Our Solar System
Type Flyby
Status Successful—Extended Mission in Progress
Nation United States
Alternate Names 2006-001A

Key Dates

Jan. 19, 2006 | 19:00 UT: Launch

July 14, 2015 | 11:49:58 UT: Pluto Flyby

Jan. 1, 2019 | 5:33 UT: MU69 Flyby


Launch Vehicle: Atlas V

Spacecraft Mass: 850 pounds (385 kilograms)

Spacecraft Instruments:

  1. Visible and infrared imager/spectrometer (RALPH)

  2. Ultraviolet imaging spectrometer (ALICE)

  3. Radio science experiment for studying atmospheres (REX)

  4. Telescopic camera (LORRI)

  5. Solar wind and plasma spectrometer (SWAP)

  6. Energetic particle spectrometer (PEPSSI)

  7. Space dust counter (SDC)

Spacecraft Dimensions: The primary structure is 0.7 m (27 inches) tall, 2.1 m (83 inches) long and 2.7 m (108 inches) at its widest.

Spacecraft Power: One Radioisotope Thermoelectric Generator

Max Power: 240 watts

Antenna Diameter: 2.1-m (83-inch)

In Depth

New Horizons is a mission sent to study the dwarf planet Pluto, its moons, and other objects in the Kuiper Belt, a region of the solar system that extends from about 30 AU, near the orbit of Neptune, to about 50 AU from the Sun.

The first mission of NASA’s New Frontiers program—a medium-class, competitively selected, and Principal Investigator-led series of missions—that also includes Juno and OSIRIS-REx, New Horizons was the first spacecraft to encounter Pluto, a relic from the formation of the solar system. By the time of its Pluto system encounter, the spacecraft had to travel farther away and for a longer time period (more than nine years) than any previous deep space spacecraft ever launched.

The design of the spacecraft was based on a lineage traced back to the CONTOUR and TIMED spacecraft, both also built by the Applied Physics Laboratory at Johns Hopkins University. Besides its suite of scientific instruments, New Horizons carries a cylindrical radioisotope thermoelectric generator (RTG), a spare from the Cassini mission, that provided about 250 W of power at launch (decaying to 200 W by the time of the Pluto encounter).

After reaching initial Earth orbit at 167 × 213 kilometers, the Centaur upper stage fired (for a second time) for 9 minutes to boost the payload out to an elliptical orbit that stretched to the asteroid belt. A second firing of the Star 48B solid rocket accelerated the spacecraft to a velocity of 58,536 kilometers/hour, the highest launch velocity attained by a human-made object relative to Earth. It was now set on a trajectory to the outer reaches of the solar system.

Controllers implemented mid-course corrections on 28 and 30 January and 9 March 2006, and a month later, on 7 April, New Horizons passed the orbit of Mars. A fortuitous chance to test some of the spacecraft’s instrumentation—especially Ralph—occurred on 13 June 2006 when New Horizons passed by a tiny asteroid named 132524 APL at a range of 101,867 kilometers.

The spacecraft flew by the solar system’s largest planet, Jupiter, for a gravity assist maneuver on 28 February 2007 with a closest approach at 05:43:40 UT. The encounter increased the spacecraft’s velocity by 14,000 kilometers/hour, shortening its trip to Pluto by three years. During the flyby, New Horizons carried out a detailed set of observations over a period of four months in early 2007. These were both designed to gather new data on Jupiter’s atmosphere, ring system, and moons (building on research from Galileo) and to test out instruments.

Although observing the moons from distances much farther than Galileo, New Horizons was still able to return impressive pictures of Io (including eruptions on its surface), Europa, and Ganymede. Following the Jupiter encounter, New Horizons sped its way towards the Kuiper Belt, performing a mid-course correction on 25 September 2007.

It was in hibernation mode from 28 June 2007 during which time the spacecraft’s on-board computer kept tabs on mission systems, transmitting special codes indicating that operations were either nominal or anomalous. During hibernation, most major systems of New Horizons were deactivated, revived only about two months every year. The second, third, and forth hibernation cycles were activated on 16 December 2008, 27 August 2009, and 29 August 2014.

It passed the halfway point to Pluto on 25 February 2010. The discovery of new moons (Kerberos and Styx) around Pluto during the mission added to suspicions that there might be debris or dust around Pluto. Mission planners devised two possible contingency plans in case debris increased as the spacecraft approached Pluto, either using its antenna facing the incoming particles as a shield, or flying closer to Pluto where there might be less debris.

On 6 December 2014, ground controllers revived New Horizons from hibernation for the last time to initiate its active encounter with Pluto. At the time, it took 4 hours and 25 minutes for a signal to reach Earth from the spacecraft. The spacecraft began its approach phase towards Pluto on 15 January 2015, its trajectory adjusted with a 93-second thruster burn on 10 March. Two days later, with about four months remaining before its close encounter, New Horizons finally became closer to Pluto than Earth is to the Sun.

Pictures of Pluto began to reveal distinct features by 29 April, with detail growing literally week by week into its approach. A final 23-second engine burn on 29 June accelerated New Horizons towards its target by 27 centimeters/second, also fine-tuning its trajectory. There was a minor concern on 4 July when New Horizons entered “safe mode” due to a timing flaw in the spacecraft command sequence.

Fortunately, the spacecraft returned to fully nominal science operations by 7 July. Three days later, data from New Horizons was used to conclusively answer one of the most basic mysteries about the dwarf planet: its size. Mission scientists concluded that Pluto is 2,370 kilometers in diameter, slightly larger than prior estimates. Charon was confirmed to be 1,208 kilometers in diameter. Finally, at 11:49 UT on 14 July 2015,

New Horizons flew by about 7,800 kilometers above the surface of Pluto. About 13 hours later, at 00:53 UT on 15 July, a 15-minute series of status messages was received at mission operations at Johns Hopkins University’s APL (via NASA’s Deep Space Network) confirming that the flyby had been fully successful. Besides collecting data on Pluto and Charon (flyby at 28,800 kilometers range), New Horizons also observed Pluto’s other satellites, including Nix, Hydra, Kerberos, and Styx.

The download of the entire set of data collected during the Pluto/Charon encounter—about 6.25 gigabytes of data—took over 15 months, and officially completed at 21:48 UT on 25 October 2016. Such a lengthy period was necessary because the spacecraft was roughly 4.5 light-hours from Earth and it could only transmit 1–2 kb/second.

Data from New Horizons clearly indicated that Pluto and its satellites were far more complex than imagined, and scientists were particularly surprised by the degree of “current activity” on Pluto’s surface. The atmospheric haze and lower-than-predicted atmospheric escape rate forced scientists to fundamentally revise earlier models of the system.

Pluto, in fact, displays evidence of vast changes in atmospheric pressure and possibly past presence of running or standing liquid volatiles on its surface. There are hints that Pluto could have an internal water-ice ocean today. Photographs clearly showed a vast thousand-kilometer-wide heart-shaped nitrogen glacier (called Sputnik Planitia) on the surface, undoubtedly the largest known glacier in the solar system.

On Charon, images showed an enormous equatorial extension tectonic belt, suggesting a long-past water ice ocean.

In the fall of 2015, after its Pluto encounter, mission planners began to redirect New Horizons for a flyby on 1 January 2019 with 2014 MU69, a Kuiper belt object that is approximately 6.4 billion kilometers from Earth. Four course corrections were implemented in the fall while a fifth was carried out on 1 February 2017.

The goal of the encounter is to study the surface geology of the object, measure surface temperature, map the surface, search for signs of activity, measure its mass, and detect any satellites or rings. As of 3 April, the spacecraft was halfway from Pluto to its target.

Soon after, on 10 April, New Horizons entered hibernation mode, when much of the vehicle remained in unpowered mode for “a long summer’s nap” that lasted until 11 September. During this time, the flight computer broadcast a weekly beacon-status tone back to Earth, and another data stream once a month on spacecraft health and safety data.

On the first anniversary of its Pluto/ Charon flyby, on 14 July 2017, the New Horizons team unveiled new detailed maps of both planetary bodies. As of 4 November 2017 New Horizons was AU (6.03 billion kilometers) from Earth and traveling at approximately 14.22 kilometers/second (relative to the Sun) heading generally in the direction of the constellation Sagittarius. The mission is currently ext40.31 ended through 2021 to explore additional Kuiper belt objects.

Additional Resources

NASA: New Horizons

Johns Hopkins University Applied Physics Laboratory: New Horizons

National Space Science Data Center Master Catalog: New Horizons

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