By Sabine Stanley, Ph.D., Johns Hopkins University
NASA thought that Pluto’s atmosphere may condense on Pluto’s surface as it moved further away from the Sun. They wanted to study Pluto’s atmosphere at its most active; hence, New Horizon, the fastest ever spacecraft was launched. How did the New Horizons’ race against time go?
The Fastest Ever Spacecraft: New Horizons
NASA decided that it was important to send a mission to Pluto early in the twenty-first century, because Pluto would soon be much farther away from the Sun. And, thus, the New Horizons mission was born.
The New Horizons spacecraft was launched in January 2006. At the time, its launch speed of 10 miles per second—that’s over 36,000 miles per hour—made it the fastest spacecraft ever launched. About 13 months after launch, the spacecraft flew by Jupiter to get a gravity assist, which sped up the spacecraft to around 50,000 miles per hour. That boost knocked 3 years off New Horizon’s unassisted flight time to Pluto.
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Discovery of Pluto’s Moons and the Consequent Fear of Debris
After the Jupiter flyby, the spacecraft spent about 7.5 years in hibernation en route to Pluto. It only woke up periodically to test its instruments. However, during this time, scientists were still studying Pluto from Earth. In fact, two of Pluto’s tiny moons, Kerberos and Styx, were discovered by astronomers using the Hubble Space Telescope in 2011 and 2012. These moon discoveries actually caused mission planners to start worrying that the New Horizons spacecraft might encounter more debris in the Pluto system than initially thought.
A combination of telescope observations and computer simulations determined that there was about a 0.3% chance that the spacecraft would experience a catastrophic collision. In December of 2014, about seven months later, New Horizons woke up from its final hibernation and began preparing for an encounter with Pluto.
A Technical Glitch before the Flyby
All was going as planned until 10 days before its closest approach to Pluto. On July 4, 2015, the spacecraft suddenly went into safe mode! A spacecraft goes into safe mode when it has detected some anomaly with its systems and shuts down all instruments to keep them safe.
When this happens, engineers and scientists on Earth try to determine what triggered the safe mode. The New Horizons scientists and engineers worked tirelessly and quickly determined it to be a software glitch, which could be fixed in a couple of days. The Pluto mission was restored from safe mode to full capability just days before the closest approach.
This is a transcript from the video series A Field Guide to the Planets. Watch it now, Wondrium.
Other Technical Challenges with the Mission
As New Horizons approached Pluto, the combination of Pluto’s inclined orbit and large spin axis tilt meant that the orbital plane of Pluto’s moons was almost face-on to the spacecraft. New Horizons was going to treat the Pluto system as a dartboard with Pluto at the center and Charon almost 20,000 kilometers from Pluto.
New Horizons passed Pluto about 12,500 kilometers above its surface and within the orbit of Charon. To make matters more nerve-racking, scientists weren’t able to communicate with the spacecraft during the encounter. This wasn’t just because the light travel time between Pluto and Earth is around five hours. No; an even bigger delay here was because, in order for the instruments on the spacecraft to give their full attention to Pluto and take measurements, the communications system had to be pointed away from Earth. So communication with the spacecraft wasn’t possible.
The Success of the New Horizon Mission
Scientists waited through 22 hours of planned radio silence as New Horizons focused all its attention on Pluto. But after those 22 hours of successful flyby, on July 15, 2015, data from the Pluto encounter began to be received. New Horizons had collected over 6 gigabytes of data. Now, we had to get that data back to Earth, so scientists could analyze it, and this took longer than one might think.
Owing to the extreme distance between New Horizons and Earth, data could only be transmitted at about 1 or 2 kilobits per second. It took about 15 months to download all six gigabytes of collected data. So what did New Horizons find?
Learn more about exploring the Earth-Moon system.
The Discoveries of the Mission
The mission revealed Pluto in splendid detail. The surface is covered in frozen nitrogen, with some methane, carbon monoxide, and water ices too. The surface appears reddish in certain regions. The red material is a dusting of complex organics, possibly Carl Sagan’s ‘tholins’. Tholins are produced from sunlight’s breakdown of methane in the atmosphere. Similar reddish material is seen at Saturn’s moon Titan and Neptune’s moon Triton.
Some regions are redder than others. We think this is an indicator of the age of the surface. The regions that are more red have been around longer and so have a thicker coating of organics. The whiter regions are younger, and thus, the layer of organics is thinner. When we use crater counting to determine the relative ages of the whiter and redder regions, we find the same result: The regions with reddish organic coating have more craters than the regions with less coating.
Common Questions about a Race against Time: New Horizon Mission
The devised mission of NASA’s New Horizons spacecraft was to study the dwarf planet Pluto, its moons, and also the other objects present in the Kuiper Belt.
Yes, New Horizons is still sending data. But, now it is sending the data concerning the Kuiper Belt.
New Horizons was the fastest ever spacecraft with the launch speed of 36,000 mph.
New Horizons communicates with earth via its 2.1-meter wide high-gain antenna, while smaller antennas help with the backup communication.