From Fukushima to the darkest corners of the ocean, robots built for extreme environments and an appetite for discovery continue to enlighten our understanding of places too dangerous to tread. Those launched into deep space may be the most daring examples, continually pushing the limits of human ingenuity and expanding our understanding of the universe. In this series New Atlas will be profiling space probes, both past and present, tasked with pushing the boundaries of science by leading us into the great unknown. This week: the spacecraft with a ticket to the edge of the solar system, NASA’s New Horizons probe.
Name: New Horizons
Launched: 2006
Subject of study: Pluto (for main), Ultimate Thule (for dessert)
Current location: Blazing through the Kuiper Belt
As NASA scientists finalized their plans for the New Horizons mission in the mid 2000s, the US had already sent space probes to all of our neighboring planets between Mercury and Neptune. But dangling at very edge of the solar system was a dark and icy carrot named Pluto, the final item on a bucket list of planetary exploration. The space probe was the first designed to inspect this dwarf planet from close proximity, but as it would turn out, its observations would extend billions of miles beyond.
Discovered in 1930, we always knew Pluto to be a cold and distant world, orbiting the Sun amongst a ring of frigid objects beyond Neptune known as the Kuiper Belt. Observations from ground-based telescopes continued to inform our understanding of the dwarf planet, such as the detection of methane ice and the discovery of its largest moon Charon in the 1970s. But much mystery remained.
As the first spacecraft built to properly investigate the dwarf planet, mission scientists equipped New Horizons with spectrometers to measure its energetic particles and observe it in visible and infrared light, along with instruments to gauge the solar winds and plasma swirling around it. Also onboard were imaging instruments, a radio science experiment and a student-built tool to measure interplanetary dust as the spacecraft traveled across the solar system.
This suite of instruments, it was hoped, would help to answer some of the fundamental questions surrounding Pluto. What can be found on the surface? What makes up its interior and what else can we find out about its tenuous atmosphere?
In January of 2006, mission scientists pinned their hopes of finding answers to these queries to the top of an Atlas V rocket, which had been modified to provide an extra kick. That launch shot New Horizons away from Earth faster than any vehicle in history, slinging it out into space at a speed of 36,000 mph (58,000 km/h).
The spacecraft continued at this pace until it reached Jupiter, where a gravity assist added another 9,000 mph (14,500 km/h) to the speedometer. The science team also took this opportunity to test out their instruments on the Jupiter system, where New Horizons observed lightning near its poles and an erupting volcano on Io, its third largest moon.
New Horizons then traveled onward to Pluto, where it finally made its close flyby in July 2015, following a three-billion-mile journey lasting almost ten years. Mission scientists actually fired up its instruments around 200 days before this, allowing them to build up to the historic encounter through images and observations on approach that would bring the dwarf planet into unprecedented focus.
Over a period totaling six months in all, New Horizons trained its instruments on Pluto and its moons for an intense examination, the first in the history of space exploration. In doing so, it showed us a snakeskin-like surface, mountains capped with methane ice, dunes that seem to be made of methane sand and mountain lakes made of frozen nitrogen. It even hinted at the presence of a subsurface ocean.
One of the more compelling insights was the discovery of hazy atmospheric layers rising to around 80 mi (130 km) above Pluto’s surface. The first ever color images of this along with later analysis revealed them to be driven by winds blowing across its mountainous terrain and suspending haze particles up above the surface.
High-resolution images of Charon, meanwhile, revealed the Plutonian moon in stunning detail. These showed us a world topped by a reddish hue at its north pole and littered with all kinds of interesting surface features. These included large webs of canyons appearing like huge fractures and contrasting with large, unusually smooth regions, hinting at a violent history of geological instability.
While Pluto was the primary science target for the New Horizons probe, the engineers behind the spacecraft built to travel much further than that. Inside they packed spare hydrazine fuel, communications gear built to work well beyond the dwarf planet and instruments that can function with even less sunlight than that found in Pluto's immediate vicinity.
As New Horizon zipped across the solar system in 2014, the science team used the Hubble Space Telescope to search for some secondary targets for their mission, around a billion miles past Pluto. Ultimae Thule, or Kuiper Belt object 2014 MU69, was seen as the best candidate, and the team started to put the pieces in place for a mission extension.
NASA agreed to fund this mission extension in July of 2016 and began preparing for a flyby of the most distant world we’ve ever explored. New Horizons rendezvoused with Ultima Thule on New Year’s Day 2019, skimming past at a distance of just 2,200 mi (3,500 km). It soon began relaying images that were as fascinating as they were confounding.
Initially, these photos appeared to show a body not resembling a rocky ball, as expected, but something like a bowling pin. A snowman was the impression gained from an even closer images, before finally astronomers settled on a much flatter description of Ultima Thule, something like a “pancake” stuck to a “dented walnut.”
The data, which mission scientists will receive on the Ultima Thule flyby up until mid-2020, continues to paint a picture of a world far more complex than we imagined, with hills, troughs, craters and pits dotting its surface.
New Horizons is scheduled to explore the Kuiper Belt until at least 2021, where it continues to speed away from us at more than 30,000 mph (48,000 km/h). While it won’t get up close and personal with other Kuiper Belt objects like it did Ultima Thule, it is still expected to reveal interesting insights from afar by measuring things like the brightness of various objects, along with charged particle radiation and the dust particles in the region.
In next week's edition and the final installment of "Into the great unknown" we look at ExoMars 2020, a Russian and European-backed venture to hunt for signs of life on the Red Planet. For more on pioneering space probes, check out previous installments here.
