New Horizons

New Horizons is an interplanetary space probe launched as part of NASA's New Frontiers program. It was launched in 2006 and became the first spacecraft to study Pluto up close in 2015. This mission was very important because Pluto is a mysterious dwarf planet far from the Sun, and before New Horizons, we only knew a little about it from faraway observations.

The spacecraft was built by scientists at Johns Hopkins University’s Applied Physics Laboratory and the Southwest Research Institute, led by Alan Stern. New Horizons was the fastest human-made object ever launched from Earth, speeding away at about 16 kilometers every second. It flew by Jupiter in 2007, using the planet’s gravity to get even faster before continuing its journey.

In July 2015, New Horizons made its historic flyby of Pluto, taking the first detailed pictures of its surface and learning much about its atmosphere and moons. After Pluto, the probe traveled onward to visit another distant object called 486958 Arrokoth in 2019. As of April 2026, New Horizons continues to explore the distant region known as the Kuiper belt, sending back valuable information about the outer edges of our solar system.

History

Main article: Exploration of Pluto

In 1992, a scientist named Robert Staehle asked the discoverer of Pluto, Clyde Tombaugh, if he could visit the planet, which led to ideas for sending a spacecraft there.

In 2000, a team led by Alan Stern began working on a mission called New Horizons. In 2001, it was chosen as one of two possible missions to Pluto. After facing some challenges getting support, the mission was finally approved in 2002. The team began building the spacecraft, planning to launch it in 2006 and reach Pluto in 2015. Alice Bowman became the Mission Operations Manager.

Mission profile

New Horizons is the first mission in NASA's New Frontiers program. It cost about $700 million over 15 years. The spacecraft was built mainly by the Southwest Research Institute and the Johns Hopkins Applied Physics Laboratory. Alan Stern from the Southwest Research Institute leads the mission.

The spacecraft was originally meant to visit Pluto, which was still called a planet when New Horizons was launched. Later, Pluto was reclassified as a dwarf planet, but some team members still call it the ninth planet. Pluto’s moons, Nix and Hydra, have names that match the initials of New Horizons.

Mementos

Along with its science tools, New Horizons carries special items. These include a CD with the names of over 400,000 people, a CD with pictures of the project team, a piece of Scaled Composites's SpaceShipOne, a special stamp, and two copies of the Flag of the United States.

The spacecraft also carries about 30 grams of Clyde Tombaugh's ashes to honor his discovery of Pluto in 1930. It has a Florida state quarter and a Maryland state quarter on board, as well as a science instrument named after Venetia Burney, who, as a child, suggested the name “Pluto.”

Goal

The goal of the mission was to learn about how Pluto and the Kuiper belt formed, and how the early Solar System changed. The spacecraft collected information about the air, surfaces, and environments of Pluto and its moons. It also planned to study other objects in the Kuiper belt. It gathered much more data at Pluto than earlier missions did at the Red Planet.

Some questions the mission tried to answer include: What is Pluto's atmosphere made of and how does it change? What does its surface look like? Are there big geological features? How do solar wind particles affect Pluto's atmosphere?

The mission's science goals were to:

• Map the surface compositions of Pluto and Charon
• Study the geologies and shapes of Pluto and Charon
• Study the air around Pluto and how fast it escapes into space
• Look for an atmosphere around Charon
• Map surface temperatures on Pluto and Charon
• Search for rings and more moons around Pluto
• Do similar studies of one or more Kuiper belt objects

Design and construction

The spacecraft is about the size and shape of a grand piano, with a dish attached to one side like a satellite. It was inspired by the Ulysses spacecraft, which also had a dish and a special power source called a radioisotope thermoelectric generator (RTG).

The body of New Horizons is triangle-shaped and almost 0.76 meters thick. A strong aluminum tube runs through the middle, holding important parts like the fuel tank and the RTG. The structure is designed to protect sensitive equipment and keep its balance when spinning.

New Horizons can change its spinning and steady itself using small engines fed by a special fuel called hydrazine. It has computers that help it know its position and direction, using stars and the Sun for guidance.

Power comes from the RTG, which uses a special material called plutonium-238 to create electricity. This power source gives about 245 watts at launch and slowly decreases over time. The spacecraft stores data in solid-state memory and sends it back to Earth using radio signals, though it takes many months to send all the data because of the huge distance.

Instruments

The New Horizons spacecraft carries seven instruments to study space. These include tools to look at images, measure particles, sense dust, and study radio waves. They help scientists learn about the surface, atmosphere, and environment of Pluto and its moons. The instruments use only 21 watts of power, and they work one at a time.

Long-Range Reconnaissance Imager (LORRI)

Main article: Long Range Reconnaissance Imager

LORRI is a camera designed to take clear, detailed pictures from far away. It uses a special detector cooled to very low temperatures to see clearly. The camera’s mirrors are made from a strong, lightweight material to keep their shape in cold space.

Principal investigator: Andy Cheng, Applied Physics Laboratory, Data: LORRI image search at jhuapl.edu

Solar Wind Around Pluto (SWAP)

Main article: SWAP (New Horizons)

SWAP studies tiny particles blown by the Sun’s wind around Pluto. It is designed to work even where the Sun’s wind is very weak, far from Earth.

Principal investigator: David McComas, Southwest Research Institute

Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI)

Main article: Pluto Energetic Particle Spectrometer Science Investigation

PEPSSI measures high-energy particles near Pluto. It can detect particles with much more energy than SWAP and tell apart different types of particles.

Principal investigator: Ralph McNutt Jr., Applied Physics Laboratory

Alice

Main article: Alice (spacecraft instrument)

Alice looks at Pluto’s atmosphere using ultraviolet light, a type of light invisible to our eyes. It can find out what the atmosphere is made of by seeing which colors of ultraviolet light are present.

Principal investigator: Alan Stern, Southwest Research Institute

In August 2018, NASA shared results from Alice showing a “hydrogen wall” at the edge of our solar system, first seen in 1992 by the Voyager spacecraft.

Ralph telescope

Main article: Ralph (New Horizons)

The Ralph telescope is another camera system that sees in both normal and infrared light. It has two parts: one for regular colors and one for infrared, which helps study surface materials.

Principal investigator: Alan Stern, Southwest Research Institute

Venetia Burney Student Dust Counter (VBSDC)

The Venetia Burney Student Dust Counter is built by students to measure tiny bits of dust in space. It uses special panels that record when dust hits them, helping scientists learn about dust in the outer solar system.

Principal investigator: Mihaly Horanyi, University of Colorado Boulder

Radio Science Experiment (REX)

Main article: REX (New Horizons)

REX uses a very stable crystal to study radio signals. This helps scientists learn about Pluto’s space environment using the spacecraft’s communication system.

Principal investigators: Len Tyler and Ivan Linscott, Stanford University

Journey to Pluto

Launch

The spacecraft New Horizons was launched on January 19, 2006, from Cape Canaveral Air Force Station in Florida. It was sent on its journey by a powerful rocket called the Atlas V. The launch had to be delayed a few times because of weather and technical checks, but finally, it took off successfully. The spacecraft traveled very quickly, passing the Moon’s orbit in just nine hours!

Inner Solar System

After launch, New Horizons made several small adjustments to its path to stay on course. It also turned on some of its instruments for the first time to make sure everything was working well. In April 2006, it passed the orbit of Mars and continued its journey toward Pluto.

Jupiter encounter

In 2007, New Horizons flew past the planet Jupiter, using the planet’s gravity to speed up. This helped shorten the trip to Pluto by three years. During this flyby, the spacecraft took many pictures and collected data about Jupiter and its moons, which helped test its instruments for the upcoming Pluto visit.

Outer Solar System

After Jupiter, New Horizons entered a sort of “sleep mode” for most of the trip to save energy. It only woke up briefly each year for checks and to adjust its course. The spacecraft crossed the orbits of Saturn in 2008 and Uranus in 2011 before finally reaching Pluto in 2015.

Pluto approach

As New Horizons got closer to Pluto, it began taking more detailed pictures. By early 2015, Pluto and its largest moon, Charon, could be seen clearly. The spacecraft made sure to avoid any possible dangers, like unseen moons or rings, before its historic flyby.

Pluto system encounter

The New Horizons spacecraft came closest to Pluto on July 14, 2015, at a distance of about 12,500 kilometers from the surface. We learned that the spacecraft was healthy and working well when we received its signals on Earth the next day.

The mission had three main goals. The most important goal was to learn about the surfaces and atmospheres of Pluto and its large moon, Charon. Other goals included studying how Pluto’s surface and atmosphere change over time, mapping the day-night borders, and looking for more moons or rings around Pluto. All of these goals were met successfully.

Post-Pluto events

After flying by Pluto in July 2015, New Horizons shared that it was doing well and had successfully recorded science data about Pluto and its moon Charon. The spacecraft began sending back the huge amount of information it collected, which took some time because it was very far from Earth.

By October 2016, all the data from the Pluto flyby had been sent back to scientists. Later, New Horizons traveled to study another object in space called Arrokoth in 2019 and continued its journey, moving farther away from the Sun.

Mission extension

The New Horizons team asked for and got permission to keep the mission going until 2021 to explore more objects in the Kuiper Belt. They found enough money for this on July 1, 2016. During this time, the spacecraft flew close to 486958 Arrokoth and planned to watch several other distant objects, maybe even flying by another one.

Kuiper belt object mission

Target background

The team wanted to find objects between 50 and 100 km (30 to 60 mi) wide for New Horizons to fly by, just like it did with Pluto. But finding the right object was hard. The path set by the Pluto flyby limited where New Horizons could go, and the spacecraft only had 33 kg (73 lb) of hydrazine propellant left. The object had to be within a narrow path close to Pluto and not too far from the Sun, about 55 times farther than Earth is from the Sun. It also needed to stand out in color compared to Pluto and maybe have a small moon.

KBO Search

In 2011, scientists started looking for these objects using big telescopes on Earth, like the Magellan Telescopes in Chile and the Subaru Observatory in Hawaii. People helped by looking at pictures online in a project called Ice Hunters. They found about 143 objects, but none were in the right place. Then, in 2014, they used the Hubble Space Telescope, which could see much farther, to look for a good target. There was about a 95% chance they would find one.

Suitable KBOs

In October 2014, Hubble found three possible objects, called PT1, PT2, and PT3. PT1 was picked to be the target and later named 486958 Arrokoth. These objects were small, between 30 and 55 km (19 to 34 mi) wide, and far from the Sun, about 43 to 44 times farther than Earth. They were different from Pluto because they were part of a group called "cold" classical Kuiper belt objects.

PT1 was the best choice because it was easier to reach with New Horizons' remaining fuel. Changing the path to reach it used about 35% of the fuel left for adjusting the path. PT3 might have been brighter and possibly bigger, but reaching it would have used too much fuel.

After learning more about their paths, scientists gave the three objects official names: 2014 MU₆₉ (which became 486958 Arrokoth), 2014 OS393 (PT2), and 2014 PN70 (PT3). A fourth object, 2014 MT69, was ruled out later. PT2 was also not chosen before the flyby of Pluto.

KBO selection

On August 28, 2015, 486958 Arrokoth (known temporarily as (486958) 2014 MU₆₉ and nicknamed Ultima Thule) was chosen as the flyby target. The spacecraft changed its path with four engine firings between October 22 and November 4, 2015. The flyby happened on January 1, 2019, at 00:33 UTC.

Observations of other KBOs

Besides flying by 486958 Arrokoth, New Horizons was set to watch and study between 25 and 35 different objects in the Kuiper Belt. It also planned to learn about the gases, dust, and plasma in the Kuiper Belt until 2021.

On November 2, 2015, New Horizons took pictures of 15810 Arawn from 280 million km away. It took more pictures in April 2016 from 111 million km away. These pictures helped scientists learn more about [15810 Arawn]'s location and how it spins.

In July 2016, New Horizons took pictures of Quaoar from about 2.1 billion km away. These pictures helped scientists study how light reflects off Quaoar.

On December 5, 2017, while New Horizons was 40.9 times farther from Earth than the Sun is, it took a picture of the Wishing Well cluster. This was the farthest picture ever taken by a spacecraft, breaking a record that had stood for 27 years. Two hours later, New Horizons broke its own record by taking pictures of the Kuiper belt objects 2012 HZ₈₄ and 2012 HE₈₅ from about 0.50 and 0.34 AU away. As of February 2018, these were the closest pictures ever taken of a Kuiper belt object besides Pluto and Arrokoth.

The dwarf planet Haumea was observed from far away by New Horizons in October 2007, January 2017, and May 2020, from distances of 49, 59, and 63 times farther than Earth is from the Sun. New Horizons also watched the dwarf planets Eris (2020), Haumea (2007, 2017, 2020), Makemake (2007, 2017), and Quaoar (2016, 2017, 2019), as well as the large KBOs Ixion (2016), Máni (2016, 2017, 2019), and 2014 OE₃₉₄ (2017, 2018). It also observed Neptune's largest moon Triton in 2019, which is similar to Pluto and Eris.

By December 2023, New Horizons had discovered about 100 Kuiper belt objects and flew close enough to about 20 of them to learn about their shapes, how they spin, if they have moons, and what their surfaces are made of. Since 2021, Canadian scientists have used machine learning to make it faster to find more objects for New Horizons to visit.

Encounter with Arrokoth

See also: 486958 Arrokoth § Exploration

The New Horizons spacecraft visited an object named Arrokoth as part of its mission. Scientists wanted to study Arrokoth to learn about its surface, temperature, and how it formed. They also looked for any tiny moons or rings around it.

New Horizons flew very close to Arrokoth, about three times closer than it did when it visited Pluto. The spacecraft took pictures and collected information during its quick flyby. The closest point happened on January 1, 2019. After the flyby, New Horizons began sending the collected data back to Earth, a process that took many months to complete.

Post-Arrokoth events

In April 2020, New Horizons joined with telescopes on Earth to capture images of stars like Proxima Centauri and Wolf 359. These images, taken from very far apart, helped scientists see how stars move — the first easy way to show this movement.

Using cameras on New Horizons far from the Sun, scientists studied the darkness of space. They found the sky looked ten times darker than what we see from Earth because there is less glow from the Sun’s light out there. This helped them learn about how much light all the galaxies in space give off.

On April 17, 2021, New Horizons reached a point 50 AU from the Sun — a distance only four spacecraft had reached before. The team kept using New Horizons to learn about the space around the Sun and to study objects in the Kuiper Belt.

In 2025, scientists made the first map showing a special kind of light from the Milky Way galaxy using data from New Horizons.

Plans

After flying by Arrokoth, New Horizons still has power and may work until the 2030s. There might be a chance to fly by another object in the Kuiper Belt in the 2020s, but scientists are still looking for a good target. Starting in 2025, New Horizons will focus more on studying space weather. It might also take a picture of Earth from far away, but only after finishing other planned tasks, because pointing the camera toward Earth could damage it.

Speed

New Horizons is known for being the fastest spacecraft ever launched, leaving Earth at 16.26 kilometers per second (58,536 km/h; 36,373 mph). It was the first spacecraft to go straight out of the Solar System, needing a speed of about 16.5 km/s (59,000 km/h; 37,000 mph) near Earth. As of May 2, 2024, it is 58.80 AU (8.796 billion km; 5.466 billion mi) from the Sun, moving at 13.68 kilometers per second (49,200 km/h; 30,600 mph).

Although very fast, it is not the fastest spacecraft to leave the Solar System. As of July 2023, that title belongs to Voyager 1, moving at 16.985 km/s (61,146 km/h; 37,994 mph) because it got a boost from Jupiter and Saturn. When New Horizons reaches 100 AU from the Sun, it will be traveling about 13 km/s (47,000 km/h; 29,000 mph), which is slower than Voyager 1 at that distance. The Parker Solar Probe can also be considered very fast, reaching speeds of up to 191 km/s (690,000 km/h; 430,000 mph) when it gets closest to the Sun.