January 27, 2015
Elizabeth Howell
NASA/New Horizons spacecraft
New Horizons is a NASA spacecraft on its way to the dwarf planet Pluto. It scooted by Jupiter in 2007, and will pass by Pluto in July 2015 before possibly heading farther into the Kuiper Belt — a massive zone of icy bodies beyond Neptune.
Known objects in the Kuiper belt beyond the orbit of Neptune (scale in AU; epoch as of January 2015).
Investigators with the Hubble Space Telescope have identified a few targets for the spacecraft after it zooms by Pluto and its moons, but the mission extension depends on how well New Horizons is performing at that time and if it can receive approval in NASA’s budget.
NASA/ESA HUbble
When the spacecraft reaches Pluto, it will be only the fifth one to head so far away from Earth (the other ones being Pioneer 10 and Pioneer 11, and Voyager 1 and Voyager 2, which are either in the outer solar system or in the case of Voyager 1, interstellar space.)
Pioneer 10
Pioneer 11
Voyager 1
Voyager 2
Pluto’s distance — about 3 billion miles (5 billion kilometers) from Earth — presented power challenges for New Horizon’s designers, since the sun’s rays are too weak to generate power. There will also be long communications delays for those staying in touch with the 1,054-pound spacecraft; at Pluto, it will take 4.5 hours for a one-way message to get there from Earth.
Further, our understanding of the Pluto system keeps changing. The planet was discovered in 1930 by astronomer Clyde Tombaugh at the Lowell Observatory.
Lowell Observatory
Since then, we’ve discovered new moons — which can also be seen as dangerous obstacles for a spacecraft, if not accounted for. And in 2006 — shortly after New Horizons launched — astronomers voted to demote Pluto from its planetary status. New Horizons carries some of Tombaugh’s ashes.
Design challenges for long missions
Spacecraft typically have a set design lifetime, similar to warranties on electronics or cars. Over time, solar particles, cosmic rays and other phenomena can degrade the surface of the spacecraft or mess up the electronics. This makes long missions such as New Horizons especially challenging.
“You’ve got to remember that it takes 9.5 years to even get to where we want to take the mission,” said Glen Fountain, the New Horizons mission project manager from Johns Hopkins University Applied Physics Laboratory, in a 2006 interview with NASA.
“So we need a highly reliable system,” he said. “So, we have built into the electronics nearly two of everything. We are redundant. We have two guidance control processors, computers. We have two command and data handling processors. We have two solid-state recorders. Even if there is a failure, you can switch from one to the other.”
Another question, Fountain acknowledged, was how to handle power when the sun is too weak to provide solar power. New Horizons carries nuclear power (more precisely, a radioisotope thermoelectric generator) on board to solve this problem.
Mission Control kept the spacecraft in deep hibernation after a quick pass by Jupiter in February 2007. New Horizons underwent periodic wakeups until a last emerging from hibernation for good in December 2014, which will last through the “Pluto encounter” of 2015.
NASA did a detailed systems check of the spacecraft once a year to make sure it’s working properly and to, if necessary, make adjustments to its path to Pluto. The spacecraft also ferried a basic signal back to Earth once a week.
Zipping by Jupiter
New Horizons launched Jan. 19, 2006, on an Atlas V rocket from Cape Canaveral Air Force Station in Florida. A power outage and high winds delayed two previous launch attempts, but New Horizons made it safely into space on the third try.
The spacecraft’s first destination was Jupiter, in February and March 2007. New Horizons passed by less than 1.4 million miles (2.4 million km) of the solar system’s largest planet, making it the first spacecraft to swing by since the Galileo probe finished its mission at Jupiter in 2003.
Galileo
Among New Horizons’ first pictures were some of Io, Jupiter’s volcanic moon. The spacecraft captured the clearest pictures ever of the Tvashtar volcano on Io, showing volcanic fallout that was bigger than the state of Texas.
Additionally, the spacecraft flew through a stream of charged particles swirling behind Jupiter. It found large bubbles of charged particles, or plasma, and also revealed variations in the stream.
At the time, astronomers said the observations could help with understanding the environment around “hot Jupiter” planets found at other stars.
Plans for Pluto
One of the principal aims of New Horizons is to figure out the origins of Pluto and its companion Charon, a moon that is more than half Pluto’s size. At the time, Pluto and Charon were considered a double planet (although the definition of Pluto changed, as will be explained below.)
NASA believed Charon formed when Pluto hit another big object long ago, creating debris that circled around Pluto and eventually formed Charon. It’s a similar theory to how Earth’s moon formed, so the scientists hoped to understand the creation of our moon better by looking at Charon’s origins.
Scientists are also eager to learn about the visual differences between Charon and Pluto. From Hubble observations, researchers deduced Pluto is far more reflective than Charon, and that Pluto has an atmosphere while Charon does not.
NASA further speculated that Pluto might even have volcanic activity, because the Voyager 2 spacecraft spotted possible volcanoes (to researchers’ surprise) on Triton, a moon of Neptune that is of a similar size and composition.
New Horizons crossed Neptune’s orbit in August 2014, and in September, the spacecraft team released pictures that the machine took of a small moon called Hydra that summer. The goal was not only to take the pictures, but to do a simulated “satellite search” — it’s possible there are other moons of Pluto that are just waiting to be discovered, when the spacecraft gets closer.
The spacecraft emerged from hibernation again in December 2014, representing the first of a series of milestones as New Horizons approaches Pluto. “Technically, this was routine, since the wake-up was a procedure that we’d done many times before,” said Glen Fountain, New Horizons project manager at the Johns Hopkins Applied Physics Laboratory, in a statement. “Symbolically, however, this is a big deal. It means the start of our pre-encounter operations.”
Pluto’s planetary status changes
Ten years can be a long time in planetary science, and that is particularly true of Pluto. Since New Horizons left our planet in 2006, we’ve discovered another moon nearby Pluto. Planners have made course corrections to keep the spacecraft away from Pluto’s moons.
Further, Pluto was demoted from its position as the ninth planet in our solar system. In August 2006, members of the International Astronomical Union (IAU) — the global body that governs astronomy names and other matters — met in a general assembly to decide on the definition of a planet.
This vote was called in response to the recent discoveries of large bodies in the Kuiper Belt, an area beyond Neptune believed to contain trillions of objects.
On Aug. 24, 2006, IAU representatives determined three features all planets must possess:
They must orbit the sun (and not another body, as a moon orbits a planet).
They must have enough mass to form a round shape.
They must be large enough to clean out bits of rock and other matter in the area around their orbits.
Pluto didn’t meet all the classifications, and was reclassified as a dwarf planet.
The decision drew fire from Alan Stern, the principal investigator of the New Horizons mission. “I’m embarrassed for astronomy. Less than 5 percent of the world’s astronomers voted,” he said in a 2006 interview with Space.com. “This definition stinks, for technical reasons.”
The decision is still controversial, years later. Little is known about Pluto because it is so far away from Earth, but we have been able to increase our understanding of it by peering at the planet with the Hubble Space Telescope and other observatories. More fuel may be added to the debate as NASA’s Dawn spacecraft gets close-up to Ceres this year, one of the largest members of our solar system’s asteroid belt.
NASA/Dawn
An overhead view of the New Horizons spacecraft’s path across Uranus’ orbit.
Credit: NASA, JHU/APL
Post-Pluto
It is expected that New Horizon’s arrival at Pluto will give us more data about its surface, its moons and its environment, which can better refine our knowledge of the dwarf planet and its system.
Over the northern hemisphere summer of 2014, investigators used the Hubble Space Telescope to see if there were any Kuiper Belt objects within reach of New Horizons after it concludes its Pluto mission. Scientists identified three candidates, with each of them at least 1 billion miles (1.6 billion kilometers) beyond the dwarf planet.
The team plans to make a pitch to NASA for extended operations in 2016, to take a closer look at one of these worlds. Meanwhile, even after the mission ends, a group of scientists, artists, engineers and more are proposing placing a sort of message from Earth on the free hard drive space on the New Horizons spacecraft.
“When New Horizons gets past Pluto, [and] has done all its data and is going on the slow boat to the heliopause [the boundary between the solar system and interstellar space], then it might be possible to just reprogram about 100 megabytes of its memory and upload a new sights and sounds of Earth that are not created by a small group of scientists but, in fact, are globally crowdsourced,” said Jill Tarter, who is the co-founder of the SETI (Search for Extraterrestrial Intelligence) Institute, in 2013.
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