7 Scientific Instruments 'New Horizons' Uses to Study Pluto

NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute / NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Just 10 minutes ago, NASA’s New Horizons spacecraft made the closest encounter with Pluto the human race has ever had—a flyby for the record books. After its science payload gathers reams of data just 7800 miles above the surface, New Horizons spins around and begins collecting data on Pluto’s night side, which will be softly illuminated by Charon, its largest moon. In addition to unlocking the mysteries of Pluto, the data collected by New Horizons will help explain the origins of the outer solar system and how planet-satellite systems evolve.

We'll have more updates for you once NASA releases the first images from the flyby, which should arrive at Johns Hopkins University's Applied Physics Laboratory (APL), mission headquarters, at 9:02 p.m. ET. In the meantime, learn about the seven scientific instruments aboard New Horizons that are exploring the Pluto system for us.

1. Alice

Alice is the spacecraft’s ultraviolet imaging spectrometer. Its job is to figure out the atmosphere of Pluto, and gain some insight into the atmosphere around Charon. Alice will analyze the atomic and molecular makeup of the atmosphere, determining what’s there and in what quantities, and probe its density and temperature. It'll also determine if Pluto has an ionosphere, or upper atmosphere.

2. Ralph

Ralph is the spacecraft’s mapping instrument. Its job is to create composition and temperature maps of the surfaces of Pluto, its moons, and any Kuiper Belt objects to be encountered years from now. The instrument also records geology and morphology. Ralph’s resolution is about 10 times better than the human eye and uses less than half the power of a child’s nightlight. The APL describes Ralph as the “main ‘eyes’ of New Horizons.” Together, Ralph and Alice are named for the Kramdens on the 1950’s television series The Honeymooners.

3. REX

Short for Radio Science Experiment, REX will determine the sizes and densities of Pluto, Charon, and a future Kuiper Belt object, and measure the temperature (both during the day and at night) and density of Pluto’s atmosphere down to the surface. It will also measure the density of Pluto’s ionosphere.

REX is especially exciting in that it will use a technique called an “uplink radio experiment.” Here’s how it works: As the probe passes behind Pluto, NASA’s Deep State Network will send powerful radio signals to REX. The radio waves will pass through Pluto’s atmosphere on the way to New Horizons, and will bend certain ways depending on the temperature and molecular weights of gasses encountered. This is the opposite of how such scans are normally performed; until now, it’s the spacecraft that would send the radio signals to Earth. Because of the mindboggling speed and distance involved with New Horizons, that would be impossible. REX is a huge advance in outer planetary exploration.


The Long Range Reconnaissance Imager, or LORRI, "is essentially a digital camera with a large telephoto telescope—only fortified to operate in the cold, hostile environs near Pluto,” according to the New Horizons team. LORRI is so powerful that on closest approach, it was able to resolve features as small as football fields. The instrument began snapping shots of the Pluto system at the start of 2015 and is responsible for pretty much every shot we’ve seen so far. The camera only takes black-and-white photographs; color filters were left out of the design in order to keep things simple, and to ensure an extremely high light-sensitivity level. (Light levels are 1000 times lower in the Pluto system than on Earth.) The Ralph instrument provides the color data for LORRI images.


Solar Winds at Pluto, or SWAP, measures the interaction of Pluto with the charged particles from the Sun. The instrument will record the rate at which the atmosphere escapes from Pluto. (Because of the planet’s relatively weak gravity acceleration, it is thought that around 165 pounds of material escape per second.) Such measurements help planetary scientists determine the density and structure of Pluto’s atmosphere.


PEPSSI, short for Pluto Energetic Particle Spectrometer Science Investigation, is both a missed sponsorship opportunity and the companion instrument to SWAP. Once neutral atoms escape Pluto, they are charged by the Sun and swept away by the solar winds. Like SWAP, PEPSSI will help scientists determine the escape rate of Pluto’s atmosphere, and figure out the atmosphere’s composition.

7. SDC

The Venetia Burney Student Dust Counter, or SDC, was created by students at University of Colorado at Boulder. Collisions involving asteroids, comets, and Kuiper Belt objects produce microscopic dust particles. Likewise, dust in the Pluto system can come from objects impacting Pluto’s moons. By counting and measuring space dust along the way, scientists can model collision rates and activity in the outer solar system. According to APL, this is the first time students have designed, built, and flown an instrument on a NASA planetary mission. The SDC is named for Venetia Burney, who in 1930, as an 11-year-old girl, gave the planet newly discovered by Clyde Tombaugh a name: Pluto.