History

Planetary exploration is a historic endeavor and a major focus of NASA. New Horizons is designed to help us understand worlds at the edge of our solar system by making the first reconnaissance of Pluto and Charon - a “double planet“ and the last planet in our solar system to be visited by spacecraft. The mission would then visit one or more objects in the Kuiper Belt region beyond Neptune. Plans for an extended mission include one to two encounters of Kuiper Belt Objects, ranging from about 25 to 55 miles (40 to 90 kilometers) in diameter. New Horizons would acquire the same data it collected at Pluto-Charon - where applicable - and follow a timeline similar to the Pluto-Charon encounter: • Closest Approach - 4 weeks: object observations • Closest Approach + 2 weeks: post-encounter studies • Closest Approach + 2 months: all data returned to Earth

Our solar system contains three zones: the inner, rocky planets; the gas giant planets; and the Kuiper Belt. Pluto is one of the largest bodies of the icy, “third zone“ of our solar system. The National Academy of Sciences placed the exploration of the third zone in general - and Pluto-Charon in particular - among its highest priority planetary mission rankings for this decade. New Horizons is NASA's mission to fulfill this objective.

In those zones, our solar system has three classes of planets: the rocky worlds (Earth, Venus, Mercury and Mars); the gas giants (Jupiter, Saturn, Uranus and Neptune); and the ice dwarfs of the Kuiper Belt. They have solid surfaces but, unlike the terrestrial planets, a significant portion of their mass is icy material (such as frozen water, carbon dioxide, molecular nitrogen, methane and carbon monoxide). The ice dwarfs are planetary embryos, whose growth stopped at sizes (200 to 2,000 kilometers across) much smaller than the full-grown planets in the inner solar system and the gas giants region. The ice dwarfs are ancient relics that formed over 4 billion years ago. Because they are literally the bodies out of which the larger planets accumulated, the ice dwarfs have a great deal to teach us about planetary formation. New Horizons seeks those answers.

There are far more ice dwarf planets than rocky and gas giant worlds combined - yet, no spacecraft has been sent to a planet in this class. The National Academy of Sciences noted that our knowledge of planetary types is therefore seriously incomplete. As the first mission to investigate this new class of planetary bodies, New Horizons will fill this important gap and round out our knowledge of the planets in our solar system.

Pluto's largest moon, Charon, is half the size of Pluto. The pair form a binary planet, whose gravitational balance point is between the two bodies. Although binary planets are thought to be common in the galaxy, as are binary stars, no spacecraft has yet explored one. New Horizons will be the first mission to a binary object of any type. Generally, New Horizons seeks to understand where Pluto and Charon “fit in“ with the other objects in the solar system.

Launch

Launch: January 19, 2006 Launch Vehicle: Atlas V 551 first stage; Centaur second stage; STAR 48B solid rocket third stage Location: Cape Canaveral Air Force Station, Florida Trajectory: To Pluto via Jupiter Gravity Assist New Horizons launched in January 2006. It will swing past Jupiter for a gravity boost and scientific studies in February 2007, and reach Pluto and its moon, Charon, in July 2015. Then, as part of an extended mission, the spacecraft would head deeper into the Kuiper Belt to study one or more of the icy mini-worlds in that vast region, at least a billion miles beyond Neptune's orbit. Sending a spacecraft on this long journey will help us answer basic questions about the surface properties, geology, interior makeup and atmospheres on these bodies.

Orbit

Summary

The Voyage

Early Cruise: The first 13 months included spacecraft and instrument checkouts, instrument calibrations, small trajectory correction maneuvers and rehearsals for the Jupiter encounter.

Jupiter Encounter: Closest approach occurred Feb. 28, 2007. Moving about 51,000 miles per hour (about 23 kilometers per second), New Horizons flew about 3 to 4 times closer to Jupiter than the Cassini spacecraft, coming within 32 Jupiter radii of the large planet.

Interplanetary Cruise: activities during the approximately 8-year cruise to Pluto include annual spacecraft and instrument checkouts, trajectory corrections, instrument calibrations and Pluto encounter rehearsals.

Pluto-Charon Encounter

The entire Pluto encounter will last for 14 months. Observations beginning five months before closest approach and the data downloaded nine months after closest approach. Closest approach will take place on: July 14, 2015.

Into the Kuiper Belt

Plans for an extended mission include one to two encounters of Kuiper Belt Objects, ranging from about 25 to 55 miles (40 to 90 kilometers) in diameter. New Horizons would acquire the same data it collected at Pluto-Charon - where applicable - and follow a timeline similar to the Pluto-Charon encounter:
• Closest Approach - 4 weeks: object observations
• Closest Approach + 2 weeks: post-encounter studies
• Closest Approach + 2 months: all data returned to Earth
As it braavely goes where no astronomy probe has gone before!

Overview

Intro

Spacecraft instruments are selected to meet a mission's science goals. On New Horizons, for example, NASA set out a list of things it (and the planetary science community) wanted to know about Pluto: What is its atmosphere made of, and how does it behave? What does the surface of Pluto look like? Are there big geological structures? How do particles ejected from the sun (known as the solar wind) interact with Pluto's atmosphere? The New Horizons team selected instruments that not only would directly measure NASA's items of interest, but also provide backup to other instruments on the spacecraft should one fail during the mission

Overview

The science payload includes seven instruments:
Ralph: Visible and infrared imager/spectrometer; provides color, composition and thermal maps.
Alice: Ultraviolet imaging spectrometer; analyzes composition and structure of Pluto's atmosphere and looks for atmospheres around Charon and Kuiper Belt Objects (KBOs).
REX: (Radio Science EXperiment) Measures atmospheric composition and temperature; passive radiometer.
LORRI: (Long Range Reconnaissance Imager) telescopic camera; obtains encounter data at long distances, maps Pluto's farside and provides high resolution geologic data.

SWAP: (Solar Wind Around Pluto) Solar wind and plasma spectrometer; measures atmospheric ”escape rate””and observes Pluto's interaction with solar wind.
PEPSSI: (Pluto Energetic Particle Spectrometer Science Investigation) Energetic particle spectrometer; measures the composition and density of plasma (ions) escaping from Pluto's atmosphere.
SDC: (Student Dust Counter) Built and operated by students; measures the space dust peppering New Horizons during its voyage across the solar system.

Power

Electrical power for the New Horizons spacecraft and science instruments is provided by a single radioisotope thermoelectric generator, or RTG, supplied by the Department of Energy. An RTG is used on missions that can not use solar power - yet require a proven, reliable power supply that can produce up to several kilowatts of power and operate under severe environmental conditions for many years. New Horizons' journey will take it more than 4 billion miles from Earth, where the Sun is just a very bright star in the dark sky. Besides taking longer than 4 hours to reach Pluto and nearby Kuiper Belt objects, light from the Sun is 1,000 times fainter there than at Earth

Details

RALF

Ralph's main objectives are to obtain high resolution color maps and surface composition maps of the surfaces of Pluto and Charon. The instrument has two separate channels: the Multispectral Visible Imaging Camera (MVIC) and the Linear Etalon Imaging Spectral Array (LEISA). A single telescope with a 3-inch (6-centimeter) aperture collects and focuses the light used in both channels.

MVIC

MVIC operates at visible wavelengths - using the same light by which we see - and has 4 different filters for producing color maps. One filter is tailored to measure the methane frost distribution over the surface, while the others are more generic and cover blue, red and near-infrared colors, respectively. MVIC also has two panchromatic filters, which pass essentially all visible light, for when maximum sensitivity to faint light levels is required. In all cases, the light passes from the telescope through the filters and is focused onto a charge coupled device (CCD). (Although the MVIC CCD is a unique, sophisticated device, virtually all consumer digital cameras use CCDs.)

LEISA

LEISA operates at infrared wavelengths (it uses heat radiation), and its etalon acts like a prism to bend different wavelengths of light by different amounts so that each wavelength can be analyzed separately. Since quantum physics teaches us that different molecules emit and absorb light at different wavelengths, analysis of the different components of the light by LEISA can be used to identify the unique ”fingerprints” of these molecules. LEISA will be used to map the distribution of frosts of methane (CH4), molecular nitrogen (N2), carbon monoxide (CO), and water (H2O) over the surface of Pluto and the water frost distribution over the surface of Charon. LEISA data may also reveal new constituents on the surfaces that have not yet been detected.

Alice

Alice is an ultraviolet imaging spectrometer that will probe the atmospheric composition of Pluto. A ”spectrometer” is an instrument that separates light into its constituent wavelengths, like a prism, only better. An ”imaging spectrometer” both separates the different wavelengths of light and produces an image of the target at each wavelength. Alice has two modes of operation: an ”airglow” mode, which allows measurement of emissions from atmospheric constituents, and an ”occultation“mode, when either the Sun or a bright star is viewed through the atmosphere producing absorption by the atmospheric constituents. The Alice occultation mode will be used just after New Horizons passes behind Pluto and looks back at the Sun through Pluto's atmosphere.

REX

REX is an acronym for “radio experiment,“- it is really just a small printed circuit board, containing sophisticated electronics, integrated into the New Horizons radio telecommunications system. All communication with New Horizons, including the downlink of science data, takes place through the radio package, which makes it critical to mission success.

Using an occultation technique similar to that described above for the Alice instrument, REX can be used to probe Pluto's atmosphere. After New Horizons flies by Pluto, its 83-inch (2.1-meter) radio antenna will point back at Earth. On Earth, powerful radio transmitters in NASA's Deep Space Network (DSN) will point at New Horizons and send radio signals to the spacecraft. As the spacecraft passes behind Pluto, the atmosphere bends the radio waves by an amount that depends on the average molecular weight of the gas in the atmosphere and the atmospheric temperature. REX will record the detected radio waves and send the data back to Earth for analysis. REX also has a “radiometry“mode, which will measure the weak radio emission from Pluto itself. When this radiometry measurement is performed looking back at Pluto following the flyby, REX data can be used to derive a very accurate value for Pluto's nightside temperature.

LORI

The instrument that provides the highest spatial resolution on New Horizons is LORRI - short for Long Range Reconnaissance Imager - which consists of a telescope with a 8.2-inch (20.8-centimeter) aperture that focuses visible light onto a charge coupled device (CCD). LORRI has a very simple design; there are no filters or moving parts. Near the time of closest approach, LORRI will take images of Pluto's surface at football-field sized resolution, resolving features approximately 100 yards or 100 meters across.

SWAP

The Solar Wind Analyzer around Pluto (SWAP) instrument will measure charged particles from the solar wind near Pluto to determine whether Pluto has a magnetosphere and how fast its atmosphere is escaping.

PEPSSI

Another plasma-sensing instrument, the Pluto Energetic Particle Spectrometer Investigation (PEPSSI), will search for neutral atoms that escape Pluto's atmosphere and subsequently become charged by their interaction with the solar wind.

The New Horizons Science Instrument Suite
Instrument NamePIWavelength/
Energy/
Mass Range
Field of View
(milliradians)
Angular resolution
(milliradians / pixel)
Wavelength/
Energy/
Mass Res/pixel
Alice:Ultraviolet
mapping spectrometer
Alan Stern, SwRI52-180nm1.7x 70 (slit)
35 x 35 (solar occultation aperture)
1.7 x 5.20.183 nm
LORRI:Long-Range
Reconnaissance Imager
Andy Cheng, APL350-850nm5.08 x 5.080.00496 N/A
Ralph MVIC:Multispectral
Visible Imaging Camera
Alan Stern, SwRI450 - 1000nm (Pan)
425 - 550nm (Blue)
540 - 700nm (Red)
780 - 1000nm (IR)
860 - 910 nm (CH4)
Multicolor: 100 x N (pushbroom)
OpNav, pan only: 100 x 2.6 (framing)
0.02See filter bandpasses
Ralph LEISA
(Linear Etalon Imaging Spectral Array):
Infrared spectrometer
Alan Stern, SwRI1250-2500 nm15.9 x 15.90.062 Full spectral range: R=300 (~6.5 nm / pixel)
2100 - 2250 nm: R=600 (~3.7 nm / pixel)
REX: Radio Science
Experiment
Len Tyler
Stanford
4.1 cm2020Radiometry mode: N/A
Occultation mode:
3 x 10-13 in Δf/f
SDC: Student Dust CounterMihaly Horanyi,
U.Colorado
4x10-12 - 4x10-9 g~pN/A ~ factor of 2 in mass
PEPSSI (Pluto Energetic Particle
Spectrometer Science Investigation):
Medium energy particle spectrometer
Ralph McNutt, APL52-180nm1.7x 70 (slit)
35 x 35 (solar occultation aperture)
1.7 x 5.20.183 nm
SWAP (Solar Wind Around Pluto):
Low energy plasma instrument
Dave McComas, SwRI30 eV - 7.7 keV270 deg x 10 deg
(deflection angles up to +15 deg additional)
N/A 1 eV (< 2 keV)
9% (›2 keV)
Introduction

Planetary exploration is a historic endeavor and a major focus of NASA. New Horizons is designed to help us understand worlds at the edge of our solar system by making the first reconnaissance of Pluto and Charon - a “double planet” and the last planet in our solar system to be visited by spacecraft. Then, as part of an extended mission, New Horizons would visit one or more objects in the Kuiper Belt region beyond Neptune.

Our solar system contains three zones: the inner, rocky planets; the gas giant planets; and the Kuiper Belt. Pluto is one of the largest bodies of the icy, “third zone” of our solar system. The National Academy of Sciences placed the exploration of the third zone in general - and Pluto-Charon in particular - among its highest priority planetary mission rankings for this decade. New Horizons is NASA's mission to fulfill this objective.

In those zones, our solar system has three classes of planets: the rocky worlds (Earth, Venus, Mercury and Mars); the gas giants (Jupiter, Saturn, Uranus and Neptune); and the ice dwarfs of the Kuiper Belt. There are far more ice dwarf planets than rocky and gas giant worlds combined - yet, no spacecraft has been sent to a planet in this class. The National Academy of Sciences noted that our knowledge of planetary types is therefore seriously incomplete. As the first mission to investigate this new class of planetary bodies, New Horizons will fill this important gap and round out our knowledge of the planets in our solar system.

As the first voyage to a whole new class of planets in the farthest zone of the solar system, New Horizons is a historic mission of exploration. The United States has made history by being the first nation to reach every planet from Mercury to Neptune with a space probe. The New Horizons mission to Pluto and the Kuiper Belt - the first NASA launch to a “new” planet since Voyager more than 30 years ago - allows the U.S. to complete the reconnaissance of the solar system.

Mission Objectives

General Objectives

• Map surface composition of Pluto and Charon
• Characterize geology and morphology (“the look”) of Pluto and Charon
• Characterize the neutral atmosphere of Pluto and its escape rate
• Search for an atmosphere around Charon
• Map surface temperatures on Pluto and Charon
• Search for rings and additional satellites around Pluto
• PLUS... conduct similar investigations of one or more Kuiper Belt Objects

Summary

Pluto and Charon are widely considered to be among the largest objects in the Kuiper Belt, a vast reservoir of icy objects located just outside of Neptune's orbit and extending out to about 50 astronomical units from the Sun. The Kuiper Belt is thought to be the source of most short-period comets - those with orbits shorter than 200 years - so scientists really want to compare the composition and surface properties of Pluto and Charon to those of cometary nuclei. Pluto and Charon are truly part of the current “frontier” in planetary science. No spacecraft has ever explored them, yet they promise to tell us much about the origins and outskirts of our solar system.

Orbital Insertion

The Italian-French mathematician Joseph-Louis Lagrange discovered five special points in the vicinity of two orbiting masses where a third, smaller mass can orbit at a fixed distance from the larger masses. More precisely, the Lagrange Points mark positions where the gravitational pull of the two large masses precisely equals the centripetal force required to rotate with them. Of the five Lagrange points, three are unstable and two are stable. The unstable Lagrange points - labeled L1, L2 and L3 - lie along the line connecting the two large masses. The stable Lagrange points - labeled L4 and L5 - form the apex of two equilateral triangles that have the large masses at their vertices.

The L1 point of the Earth-Sun system affords an uninterrupted view of the sun and is currently home to the Solar and Heliospheric Observatory Satellite SOHO. The L2 point of the Earth-Sun system is home to the WMAP spacecraft and (perhaps by the year 2014) the James Webb Space Telescope. The L1 and L2 points are unstable on a time scale of approximately 23 days, which requires satellites parked at these positions to undergo regular course and attitude corrections.

Science

Comming Soon

Overview

The compact New Horizons spacecraft carries a payload of seven science instruments for examining the geology, composition, surface, temperature and atmospheric structure of the planet and its moon. Flybys of one or more of the icy objects in the Kuiper Belt may be scheduled thereafter, during a mission extension. The New Horizons payload is incredibly power efficient, with the instruments collectively drawing only about 28 watts. The payload consists of three optical instruments, two plasma instruments, a dust sensor and a radio science receiver/radiometer.

Other News
Other News

What color is Pluto? The answer, revealed in the first maps made from New Horizons data, turns out to be shades of reddish brown.

Although this is reminiscent of Mars, the cause is almost certainly very different. On Mars the coloring agent is iron oxide, commonly known as rust. On the dwarf planet Pluto, the reddish color is likely caused by hydrocarbon molecules that are formed when cosmic rays and solar ultraviolet light interact with methane in Pluto's atmosphere and on its surface.

Pluto's reddish color has been known for decades, but New Horizons is now allowing the correlation of the color of different places on the surface with their geology and eventually with their compositions, making computer modeling of how Pluto has evolved to its current state.

Experts have long thought that reddish substances are generated when Lyman-alpha series ultraviolet light from the sun strikes molecules of the gas methane (CH4) in Pluto's atmosphere, powering chemical reactions that create complex compounds called tholins. The tholins drop to the ground to form a reddish material.

Recent measurements with New Horizons' Alice instrument reveal that a diffuse Lyman-alpha glow falling on Pluto from all directions in interplanetary space is strong enough to produce almost as much tholin as the direct rays of the sun. This means Pluto's reddening process occurs even on the night side where there's no sunlight, and in the depths of winter when the sun remains below the horizon for decades at a time.

Tholins have been found on other bodies in the outer solar system, including Titan and Triton, the largest moons of Saturn and Neptune, respectively, and made in laboratory experiments that simulate the atmospheres of those bodies.

The mission's first map of Pluto is in approximate true color. Pluto's largest dark spot is significantly redder than the majority of the surface, while the brightest area appears closer to neutral gray.

New Horizons Reveals Pluto’s Extended Atmosphere

Scientists working with NASA’s New Horizons spacecraft have observed Pluto’s atmosphere as far as 1,000 miles (1,600 kilometers) above the surface of the planet, demonstrating that Pluto’s nitrogen-rich atmosphere is quite extended. This is the first observation of Pluto’s atmosphere at altitudes higher than 170 miles above the planet’s surface (270 kilometers).

The new information was gathered by New Horizon’s Alice imaging spectrograph during a carefully designed alignment of the sun, Pluto, and the spacecraft starting about an hour after the craft’s closest approach to the planet on July 14. During the event known as a solar occultation, New Horizons passed through Pluto’s shadow while the sun backlit Pluto’s atmosphere.

Alice Solar Occultation

This figure shows how the Alice instrument count rate changed over time during the sunset and sunrise observations. The count rate is largest when the line of sight to the sun is outside of the atmosphere at the start and end times. Molecular nitrogen (N2) starts absorbing sunlight in the upper reaches of Pluto’s atmosphere, decreasing as the spacecraft approaches the planet’s shadow. As the occultation progresses, atmospheric methane and hydrocarbons can also absorb the sunlight and further decrease the count rate. When the spacecraft is totally in Pluto’s shadow the count rate goes to zero. As the spacecraft emerges from Pluto’s shadow into sunrise, the process is reversed. By plotting the observed count rate in the reverse time direction, it is seen that the atmospheres

Pluto Wags its Tail: New Horizons Discovers a Cold, Dense Region of Atmospheric Ions Behind Pluto

Artist’s concept of the interaction of the solar wind (the supersonic outflow of electrically charged particles from the Sun) with Pluto’s predominantly nitrogen atmosphere

New Horizons has discovered a region of cold, dense ionized gas tens of thousands of miles beyond Pluto — the planet’s atmosphere being stripped away by the solar wind and lost to space. Beginning an hour and half after closest approach, the Solar Wind Around Pluto (SWAP) instrument observed a cavity in the solar wind — the outflow of electrically charged particles from the Sun — between 48,000 miles (77,000 km) and 68,000 miles (109,000 km) downstream of Pluto. SWAP data revealed this cavity to be populated with nitrogen ions forming a “plasma tail” of undetermined structure and length extending behind the planet.

Similar plasma tails are observed at planets like Venus and Mars. In the case of Pluto’s predominantly nitrogen atmosphere, escaping molecules are ionized by solar ultraviolet light, “picked up” by the solar wind, and carried past Pluto to form the plasma tail discovered by New Horizons. Prior to closest approach, nitrogen ions were detected far upstream of Pluto by the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument, providing a foretaste of Pluto’s escaping atmosphere.

Plasma tail formation is but one fundamental aspect of Pluto’s solar wind interaction, the nature of which is determined by several yet poorly constrained factors. Of these, perhaps the most important is the atmospheric loss rate.

NASA’s Hubble Finds Pluto’s Moons Tumbling in Absolute Chaos

Comprehensive analysis of data from NASA’s Hubble Space Telescope shows that two of Pluto’s moons, Nix and Hydra, wobble unpredictably.

This set of computer modeling illustrations of Pluto’s moon Nix shows how the orientation of the moon changes unpredictably as it orbits the “double planet” Pluto-Charon.

The moons wobble because they’re embedded in a gravitational field that shifts constantly. This shift is created by the double planet system of Pluto and Charon as they whirl about each other. Pluto and Charon are called a double planet because they share a common center of gravity located in the space between the bodies. Their variable gravitational field sends the smaller moons tumbling erratically. The effect is strengthened by the football-like, rather than spherical, shape of the moons. Scientists believe it’s likely Pluto’s other two moons, Kerberos and Styx, are in a similar situation.

Prior to the Hubble observations, nobody appreciated the intricate dynamics of the Pluto system. This data provides important new constraints on the sequence of events that led to the formation of the system.

Three of Pluto’s moons are presently locked together in resonance, meaning there is a precise ratio for their orbital periods. Styx orbiting Pluto twice for every three orbits made by Hydra.

Hubble data also reveal the moon Kerberos is as dark as a charcoal briquette, while the other frozen moons are as bright as sand. It was predicted that dust blasted off the moons by meteorite impacts should coat all the moons, giving their surfaces a homogenous look, which makes Kerberos’ coloring very surprising.

NASA’s New Horizons spacecraft, may help settle the question of the asphalt-black moon, as well as the other oddities uncovered by Hubble.

The turmoil within the Pluto-Charon system offers insights into how planetary bodies orbiting a double star might behave. For example, NASA’s Kepler space observatory has found several planetary systems orbiting double stars.

Chaos may be a common trait of binary systems. It might even have consequences for life on planets if found in such systems.”

Clues to the Pluto commotion first came when astronomers measured variations in the light reflected off Nix and Hydra. Analyzing Hubble images of Pluto taken from 2005 to 2012, scientists compared the unpredictable changes in the moons’ brightness to models of spinning bodies in complex gravitational fields.

This illustration shows the scale and comparative brightness of Pluto’s small satellites. The surface craters are for illustration only and do not represent real imaging data.

Pluto's moons are believed to have been formed by a collision between the dwarf planet and a similar-sized body early in the history of our solar system. The smashup flung material that consolidated into the family of moons observed around Pluto today. Its binary companion, Charon, is almost half the size of Pluto and was discovered in 1978. Hubble discovered Nix and Hydra in 2005, Kerberos in 2011, and Styx in 2012. These little moons, measuring just tens of miles in diameter, were found during a Hubble search for objects that could be hazards to the New Horizons spacecraft as it passes the dwarf planet in July.

Researchers say a combination of Hubble data monitoring and New Horizon’s brief close-up look, as well as future observations with NASA’s James Webb Space Telescope will help settle many mysteries of the Pluto system. No ground-based telescopes have yet been able to detect the smallest moons.

New Horizons 'Captures' Two of Pluto's Smaller Moons

Pluto's moon Nix (left), shown here in enhanced color as imaged by the New Horizons Ralph instrument, has a reddish spot that has attracted the interest of mission scientists. The data were obtained on the morning of July 14, 2015, and received on the ground on July 18. At the time the observations were taken New Horizons was about 102,000 miles (165,000 km) from Nix. The image shows features as small as approximately 2 miles (3 kilometers) across on Nix, which is estimated to be 26 miles (42 kilometers) long and 22 miles (36 kilometers) wide.

Pluto's small, irregularly shaped moon Hydra (right) is revealed in this black and white image taken from New Horizons' LORRI instrument on July 14, 2015 from a distance of about 143,000 miles (231,000 kilometers). Features as small as 0.7 miles (1.2 kilometers) are visible on Hydra, which measures 34 miles (55 kilometers) in length.

While Pluto's largest moon, Charon, has grabbed most of the lunar spotlight, two of Pluto's smaller and lesser-known satellites are starting to come into focus via new images from NASA's New Horizons spacecraft.

Nix and Hydra – the second and third moons to be discovered – are approximately the same size, but their similarity ends there.

New Horizons' first color image of Nix, in which colors have been enhanced, reveals an intriguing region on the jelly bean-shaped satellite, which is estimated to be 26 miles (42 kilometers) long and 22 miles (36 kilometers) wide.

Although the overall surface color of Nix is neutral grey in the image, the newfound region has a distinct red tint. Hints of a bull's-eye pattern lead scientists to speculate that the reddish region is a crater. There has not been time to analyze the data to gain more details of the processes involved.

Meanwhile, the sharpest image yet received from New Horizons of Pluto's satellite Hydra shows that its irregular shape resembles the state of Michigan. The new image was made by the Long Range Reconnaissance Imager (LORRI) on July 14, 2015 from a distance of 143,000 miles (231,000 kilometers), and shows features as small as 0.7 miles (1.2 kilometers) across. There appear to be at least two large craters, one of which is mostly in shadow. The upper portion looks darker than the rest of Hydra, suggesting a possible difference in surface composition. From this image, mission scientists have estimated that Hydra is 34 miles (55 kilometers) long and 25 miles (40 kilometers) wide.

Images of Pluto's most recently discovered moons, Styx and Kerberos, are expected to be transmitted to Earth no later than mid-October.

Nix and Hydra were both discovered in 2005 using Hubble Space Telescope. New Horizons' findings on the surface characteristics and other properties of Nix and Hydra will help scientists understand the origins and subsequent history of Pluto and its moons.

NASA’s New Horizons Team Selects Potential Kuiper Belt Flyby Target

NASA has selected the potential next destination for the New Horizons mission to visit after its historic July 14 flyby of the Pluto system. The destination is a small Kuiper Belt object (KBO) known as 2014 MU69 that orbits nearly a billion miles beyond Pluto.

This remote KBO was one of two identified as potential destinations and the one recommended to NASA by the New Horizons team. Although NASA has selected 2014 MU69 as the target, as part of its normal review process the agency will conduct a detailed assessment before officially approving the mission extension to conduct additional science.

Like all NASA missions that have finished their main objective but seek to do more exploration, the New Horizons team must write a proposal to the agency to fund a KBO mission. That proposal – due in 2016 – will be evaluated by an independent team of experts before NASA can decide about the go-ahead.

Path of NASA's New Horizons spacecraft toward its next potential target, the Kuiper Belt object 2014 MU69, nicknamed "PT1" (for "Potential Target 1") by the New Horizons team. Although NASA has selected 2014 MU69 as the target, as part of its normal review process the agency will conduct a detailed assessment before officially approving the mission extension to conduct additional science.

Early target selection was important; the team needs to direct New Horizons toward the object this year in order to perform any extended mission with healthy fuel margins. New Horizons will perform a series of four maneuvers in late October and early November to set its course toward 2014 MU69 – nicknamed “PT1” (for “Potential Target 1”) – which it expects to reach on January 1, 2019. Any delays from those dates would cost precious fuel and add mission risk.

2014 MU69 is just the kind of ancient KBO, formed where it orbits now, that the Decadal Survey would like to target. This KBO costs less fuel to reach [than other candidate targets], leaving more fuel for the flyby, for ancillary science, and greater fuel reserves to protect against the unforeseen.”

New Horizons was originally designed to fly beyond the Pluto system and explore additional Kuiper Belt objects. The spacecraft carries extra hydrazine fuel for a KBO flyby; its communications system is designed to work from far beyond Pluto; its power system is designed to operate for many more years; and its scientific instruments were designed to operate in light levels much lower than it will experience during the 2014 MU69 flyby.

The 2003 National Academy of Sciences’ Planetary Decadal Survey (“New Frontiers in the Solar System”) strongly recommended that the first mission to the Kuiper Belt include flybys of Pluto and small KBOs, in order to sample the diversity of objects in that previously unexplored region of the solar system. The identification of PT1, which is in a completely different class of KBO than Pluto, potentially allows New Horizons to satisfy those goals.

But finding a suitable KBO flyby target was no easy task. Starting a search in 2011 using some of the largest ground-based telescopes on Earth, the New Horizons team found several dozen KBOs, but none were reachable within the fuel supply aboard the spacecraft.

The powerful Hubble Space Telescope came to the rescue in summer 2014, discovering five objects, since narrowed to two, within New Horizons’ flight path. Scientists estimate that PT1 is just under 30 miles (about 45 kilometers) across; that’s more than 10 times larger and 1,000 times more massive than typical comets, like the one the Rosetta mission is now orbiting, but only about 0.5 to 1 percent of the size (and about 1/10,000th the mass) of Pluto. As such, PT1 is thought to be like the building blocks of Kuiper Belt planets such as Pluto.

Unlike asteroids, KBOs have been heated only slightly by the Sun, and are thought to represent a well preserved, deep-freeze sample of what the outer solar system was like following its birth 4.6 billion years ago.

There’s so much that can be learned from close-up spacecraft observations that cannot be learned from Earth. The detailed images and other data that New Horizons could obtain from a KBO flyby can revolutionize our understanding of the Kuiper Belt and KBOs.