New Horizons Transforms Pluto from a Speck to a Sphere [Slide Show]
We get a whole new appreciation for New Horizons’ Pluto close-ups when we compare them with pics taken by even the best Earthbound telescopes
New Horizons snapped a close-up of Pluto on July 13, just before it went dark for the duration of its closest approach. Credits: NASA/APL/SwRI
First, one of the latest and greatest views from New Horizons: the spacecraft captured the above image of mountains near Pluto's equator just 90 minutes before its closest approach to the dwarf planet. Based on the lack of craters pockmarking this region, scientists estimate the mountains are probably only 100 million years old, which on a cosmic timescale means they're practically brand-new. In fact, they might still be growing, which is weird because scientists wouldn't necessarily expect a frigid world like Pluto to be geologically active. Some of the icy moons orbiting gas giants in the outer solar system are active because gravitational interactions with their host planets heat their interiors. But Pluto doesn't have a nearby giant planet to generate its geologic activity, so scientists aren't quite sure how these mountains were formed.
When he was just a new hire at the Lowell Observatory, Clyde Tombaugh was charged with the rather tedious task of examining thousands of photographic plates of the sky. His mission: find the outer solar system planet predicted by Percival Lowell 15 years earlier, which was thought to be responsible for anomalies in the orbits of Uranus and Neptune. Using a “blink microscope,” Tombaugh flipped back and forth between images of the same portion of the sky, scouring pictures for wandering solar system bodies against the stationary backdrop of stars. Fortunately for Tombaugh, his countless hours of labor (and probably serious eyestrain) were not in vain. On February 19, 1930, he spotted the tiny speck of Pluto among the sea of stars.
Lowell Observatory Archives
Almost half a century after Tombaugh's discovery of Pluto, images taken with the Kaj Strand Astrometric Reflector at the U.S. Naval Observatory Flagstaff Station provided the first glimpse of its largest moon, Charon. In 1978 a keen-eyed astronomer named James Christy was examining photographic plates of Pluto when he noticed something odd. In some of the images (like the one on the left) Pluto appeared as an elongated smudge, whereas in others (as on the right) Pluto appeared as a round dot. Christy realized that the images of an apparently elongated Pluto must actually be showing two separate, overlaid celestial bodies. Charon is actually about half the size of Pluto--so big that the pair is sometimes referred to as a double dwarf planet system.
Credit: U.S. Naval Observatory
On February 21, 1994, NASA's Hubble Space Telescope provided the clearest view yet of Pluto and its partner in crime, Charon. Astronomers were excited about the image because it shows the dwarf planet and its moon as two distinct objects. Getting an image of Pluto and Charon as separate disks had previously proved difficult because they're locked in such a tight orbit. In fact, if our moon crowded Earth as closely Charon does Pluto, it would appear as big in the sky as an apple held at arm's length. This picture allowed astronomers to calculate Pluto and Charon's individual diameters with reasonable accuracy for the first time, and also revealed that Charon is slightly bluer than Pluto, meaning that each object sports its own surface composition and structure.
Credit: Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA Advertisement
Sixty-six years after Pluto's initial discovery, astronomers were finally able to discern some of its surface features with the Hubble Space Telescope. Hubble snapped pictures as Pluto rotated over the course of nearly a week, revealing the dwarf planet's bright and dark spots as well as polar ice caps. Scientists found that Pluto has much richer surface variety than other icy objects in the outer solar system, distinguishing it from its closest analogue, the Neptunian moon Triton.
Credit: Alan Stern (Southwest Research Institute), Marc Buie (Lowell Observatory), NASA and ESA
The pictures above were constructed from multiple Hubble images taken in 2002–03. The dark orange, white and black terrain revealed that Pluto had undergone a dramatic change in color between 2000 and 2002, with its north pole getting brighter and the surface turning redder. According to scientists, the altered terrain was probably due to surface ices evaporating on the sunlit pole and refreezing on the opposite pole of the planet as Pluto transitioned into the next phase of its seasonal cycle.
Credit: NASA, ESA, and M. Buie (Southwest Research Institute)
In 2005 two new members were added to Pluto's far-flung little family: Nix and Hydra. New Horizons team members discovered the two moons using the Hubble Telescope. Nix and Hydra remained hidden for so long because they are thousands of times fainter than Pluto and don't hug their host planet as closely as Charon does, orbiting two to three times farther out.
These two pictures were taken a couple weeks apart during the summer of 2011 by scientists using--you guessed it--the Hubble Space Telescope. The green circle marks the spot of Pluto's newest moon, then designated P4 but later rebranded as Kerberos after the hellhound from classical mythology, in accordance with the tradition of giving Pluto's satellites names associated with the god of the underworld. Kerberos is a puny moon--only about 13 to 34 kilometers across--that loops around Pluto once every 32 days between the orbits of Nix and Hydra.
Credit: NASA, ESA, and M. Showalter (SETI Institute) Advertisement
A year after Kerberos's discovery, Hubble hit on Pluto's fifth and final moon, Styx in 2012. The team of scientists that found Styx were actually scouring Pluto's neighborhood for objects that might prove hazardous to New Horizons during its flyby. With New Horizons hurtling past Pluto at approximately 48,000 kilometers per hour, a collision with debris in the Plutonian system could spell the spacecraft's doom.
Credit: NASA / ESA / M. Showalter / SETI Institute
New Horizons captured this composite image as it was closing in on Pluto and Charon on July 11, showing the two bodies in unprecedented detail. The picture gives us a new appreciation for the distinct color and brightness differences between Pluto and its largest moon.
New Horizons snapped a close-up of Pluto on July 13, just before it went dark for the duration of its closest approach. For technical reasons, the spacecraft was out of touch with Earth on July 14 as it collected data, but this image sheds new light on Pluto’s surface features. Pluto’s primary characteristic in the image above has been informally dubbed the “heart” and spans about 1,600 kilometers, bordering darker terrains near the equator. For the first time we can see that some regions of Pluto are scarred with impact craters that could be billions of years old. In contrast, the heart’s smooth terrain probably indicates that there are geologic processes at work on Pluto. Signs of erosion and fractures in Pluto’s crust are also testaments to a complex geologic history.
This picture of Nix might not look like much compared to the spectacular images New Horizons is getting of Pluto's terrain. But the fact that Nix shows up as a conglomerate of pixels rather than just one lone dot is pretty incredible. Scientists think we're looking at one end of an elongated moon, probably about 40 kilometers in diameter, and this image shows surface features on Nix as small as small as six kilometers across.
Credit: NASA/JHUAPL/SWRI Advertisement
From only 77,000 kilometers, on July 14 New Horizons could discern surface features on Pluto a mere kilometer across. In the left center of Pluto’s “heart,” north of the icy mountains, lies a vast, smooth plane that appears to be upwards of 100 million years old. The region, informally christened Sputnik Plain, might still be geologically active. The frozen terrain is separated into misshapen patches that are girded by narrow troughs, and there also appear to be groups of mounds and fields of small pits on the surface.
This week the Internet is flush with photos of Pluto from the New Horizons mission. To someone who is not necessarily a Plutophile, it might be kind of difficult to see what all the hype is about. After all, the Hubble Space Telescope has shown us galaxies near the edge of the observable universe. What’s so exciting about seeing a dwarf planet in our own solar system?
Setting aside the fact that New Horizons’ safe arrival means that scientists successfully guided a piano-size robot across the solar system for nearly a decade, the New Horizons flyby is momentous because the spacecraft is churning out photos that show Pluto in unprecedented detail. To really appreciate how striking our new views of Pluto are, let’s take a look back at photos of the former ninth planet, now Kuiper Belt object, from the earliest glimpses to the New Horizons pictures.
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