New Horizons is a NASA probe that carried out the first reconnaissance of Pluto in July 2015 and, on January 1, 2019, flew past the small Kuiper Belt object Arrokoth, the most distant world ever explored at close range. The mission is led by principal investigator Alan Stern and operated by the Johns Hopkins University Applied Physics Laboratory (APL).[2][3]
The spacecraft is about the size of a grand piano and weighed 478 kilograms at launch, drawing power from a radioisotope thermoelectric generator because sunlight in the outer solar system is far too weak for solar panels. Launched on January 19, 2006, it left Earth at roughly 16.26 kilometers per second, the fastest departure speed of any spacecraft at the time.[2]
New Horizons is now in an extended mission focused on heliophysics and Kuiper Belt science. As of April 2026 it was 64.45 astronomical units (AU) from the Sun, about 9.6 billion kilometers, and partway through the longest hibernation of its flight, with wake-up planned for late June 2026.[1][2]
Spacecraft and instruments
| Instrument | Function |
|---|---|
| LORRI | Long-focal-length visible-light imager |
| Ralph | Color imaging and infrared composition mapping |
| Alice | Ultraviolet spectrometer |
| REX | Radio science and atmospheric occultations |
| SWAP | Solar wind analyzer |
| PEPSSI | Energetic particle spectrometer |
| Venetia Burney Student Dust Counter | Dust impact detector, built by students |
The generator produced about 245 watts at launch and loses a few watts each year, so the mission team manages an ever-tighter power budget; the spacecraft is nonetheless expected to remain operable into the 2030s.[2][3]
Launch and journey to Pluto
New Horizons launched on an Atlas V 551 from Cape Canaveral and crossed the Moon's orbit in about nine hours. A Jupiter gravity assist on February 28, 2007, added nearly 4 kilometers per second and cut roughly three years from the cruise, while giving the team a full rehearsal: the spacecraft imaged Jupiter's atmosphere, its faint rings, and a volcanic eruption plume rising from the moon Io. For most of the remaining trip the probe traveled in spin-stabilized hibernation, waking annually for checkouts.[2][3]
Pluto flyby
On July 14, 2015, after a journey of nine and a half years and about 5 billion kilometers, New Horizons passed 12,500 kilometers above Pluto. The flyby transformed a point of light into a complex world. The most prominent feature, an ice-covered basin informally part of the heart-shaped Tombaugh Regio, is Sputnik Planitia: a nitrogen-ice glacier roughly 1,000 kilometers across whose churning surface shows no detectable impact craters, implying it renews itself and is geologically young. Around it stand mountains of water ice up to about 3,500 meters tall.[2][3]
The spacecraft also recorded roughly 20 layers of photochemical haze in Pluto's thin nitrogen atmosphere, which scatters light blue, along with possible cryovolcanoes and evidence of ancient glacial flow. As New Horizons crossed through Pluto's shadow, the REX radio experiment measured the temperature and surface pressure of that atmosphere directly. Pluto's large moon Charon displayed a dark red polar cap, informally Mordor Macula, colored by methane escaping from Pluto, and a vast equatorial canyon system. Because the probe sped past at about 14 kilometers per second and stored everything onboard, transmitting the full dataset across the solar system took until October 2016.[2][3]
Arrokoth flyby
NASA approved an extended mission to a second target found in 2014 by a dedicated search with the Hubble Space Telescope. On January 1, 2019, New Horizons flew 3,538 kilometers from the object now named Arrokoth, about 6.5 billion kilometers from the Sun, setting the record for the farthest close-up exploration of any body.[2]
Arrokoth proved to be a contact binary about 36 kilometers long: two flattened, reddish lobes joined at a narrow neck. Its smooth, lightly cratered surface and gentle geometry indicate the lobes formed near each other in a collapsing cloud of pebbles and merged at low speed, strong evidence for the "streaming instability" model of planetesimal formation and a snapshot of the solar system's original building blocks. The name Arrokoth, adopted in November 2019, means "sky" in the Powhatan/Algonquian language.[2][3]
Kuiper Belt extended mission and heliophysics
In 2023 NASA approved a second extended mission that runs until the spacecraft exits the Kuiper Belt, expected around 2028-2029, with an emphasis on heliophysics: New Horizons is the only functioning spacecraft taking in-situ measurements in this region between the Voyagers and everything closer to the Sun.[4]
Its particle instruments sample the solar wind and pickup ions in the outer heliosphere, and the student-built dust counter has recorded unexpectedly high dust levels beyond 55 AU, hinting that the Kuiper Belt may extend farther than models predicted. The spacecraft has also used its cameras for observations impossible from Earth, including a stellar parallax demonstration in 2020, the darkest measurements yet of the cosmic optical background, and an all-sky ultraviolet map of hydrogen glow. The team continues to search, so far without success, for another Kuiper Belt object within reach of a third flyby.[2][4]
Status in 2026
Flight controllers placed New Horizons into hibernation on August 7, 2025, after uploading upgraded fault-protection software. The sleep period is the longest of the mission, surpassing the previous record of 273 days, with wake-up planned for late June 2026. Hibernation is not idle: three instruments record the charged-particle and dust environment around the clock while the spacecraft spins quietly and sends a weekly beacon tone home through the Deep Space Network.[1][5]
The mission's future was debated during 2025, when the White House's fiscal year 2026 budget proposal targeted New Horizons among many operating science missions for termination. Congress continued funding for the mission in the final appropriation, keeping NASA's plan to operate it through its Kuiper Belt exit intact.[2][6] Receding at roughly 2.9 AU per year, with radio signals taking almost nine hours to travel each way, New Horizons could eventually return data from the region of the termination shock, the boundary zone the Voyager probes crossed at 84 and 94 AU, if it remains healthy into the 2030s.[2]
References
- NASA's New Horizons Enters Mission's Longest Hibernation Period - NASA Science.
- New Horizons - Wikipedia.
- New Horizons - NASA Science.
- Beyond Pluto, New Horizons Gets a Reprieve from NASA - Scientific American.
- New Horizons begins record hibernation in Kuiper Belt - Space Daily.
- NASA's New Horizons mission faces an uncertain future (op-ed) - Space.com.
