News Science

New Horizons, its 5 billion km journey to Pluto, and what to expect

We are just a few short days from New Horizons’ closest approach to Pluto.1 The NASA probe has been flying through the solar system for nearly the past nine and a half years to get to the Dwarf Planet, nee planet, system. After traveling a distance of nearly 5 billion km, the probe is set to pass within 12,500 km of Pluto on 14 July 2015. To give you an idea, that is just further than the distance between New York City and New Delhi, India. In a field where distances are utterly incomprehensible, 12,500 km is incredibly close. With that in mind, here is a look at the New Horizons craft itself, its journey to, and what to expect from the Pluto systems.

New Horizons Probe

The probe has just about the same dimensions as grand piano, but with a huge satellite dish on top, and weighs in at a little more than 1,000 pounds. The probe is powered by a single radioisotope thermoelectric generator (RTG), that converts the heat released by decaying radioactive material – Plutonium 238 dioxide in this case – into electrical energy. The RTG is the cylindrical  protrusion, just under REX in the image above. Perhaps the most interesting thing about the probe is how little electricity it uses. For the entire Pluto encounter, the probe will need less power than two 100-watt light bulbs.2 New Horizons is carrying a payload of seven scientific instruments to gather data and images from the Pluto system:

  • LORRI (Long Range Reconnaissance Imager): This has been the probe’s main imaging camera thus far. Every image you have seen of Pluto and Charon so far has been taken by LORRI. Essentially, LORRI is a digital camera with a large telephoto telescope. The device has no color filers, taking only grey scale images. The color data is added in with the information gathered by Ralph.
  • Ralph: A Visible and infrared imager/spectrometer. Ralph is used to add color to to the greyscale images collected by LORRI imager.
  • Alice: An Ultraviolet imaging spectrometer. Used mainly for analyzing the composition of Pluto’s atmosphere. Yes, you read that right, Pluto’s atmosphere.
  • REX (Radio Science EXperiment): Measures atmospheric composition and radiation levels.
  • SWAP (Solar Wind Around Pluto): A solar wind and plasma spectrometer, measuring Pluto’s interaction with the solar wind, as well as the rate at which the dwarf planet’s atmosphere is escaping.
  • PEPSSI (Pluto Energetic Particle Spectrometer Science Investigation): An energetic particle spectrometer, measuring the composition and density of plasma escaping Pluto’s atmosphere.
  • SDC (Student Dust Counter): Designed and operated by students at the University of Colorado at Boulder, the SDC measures the space dust hitting the probe over the course of its journey.3

Journey to Pluto


Atlas-V New Horizons, its 5 billion km journey to Pluto, and what to expect

Images Via Wikipedia 1 and 2

New Horizons was launched aboard a modified Atlas V rocket on 19 January 2006. This was the first Atlas V rocket to contain a third stage. The New Horizons launch was unique for a number of reasons. Firstly, New Horizons is the fastest craft ever launched. Currently, Voyager 1 is traveling faster, but New Horizons had the faster launch speed.4 Secondly, New Horizons is the only craft ever to be launched directly into a solar escape trajectory. Again, Voyager 1 is on a similar trajectory, but it required several gravitational slingshots to achieve escape speed.

Jupiter Flyby and Gravity Assist

Jupiter New Horizons, its 5 billion km journey to Pluto, and what to expect

This was one of New Horizons’ first images of Jupiter, taken with LORRI at a range of around 80 milliom KM. Two of the Galilean moons are visible in the image: the volcanic moon Io (to the left) and the icy moon – which was recently confirmed to have a subsurface ocean of salty water – Ganymede (to the right). Via Johns Hopkins Applied Physics Laboratory

In January of 2007, New Horizons became the first man-made object to encounter Jupiter since the end of the Galileo mission in 2003, and the 7th overall.5 The Jupiter flyby was planned from the very outset of the mission, and provided a speed boos of about 4 km/sec, effectively shaving 5 years of the travel time to Pluto. As the Jupiter encounter was always a major component of the mission, there were several scientific goals during the four month flyby; it also provided the probe an excellent test for all of the on board scientific equipment.

Little-Red-Spot New Horizons, its 5 billion km journey to Pluto, and what to expect

Jupiter’s Little Red Spot, a massive storm just about the size of the Earth. Via Johns Hopkins University Applied Physics Laboratory

One of the main scientific goals for the Jupiter flyby was a to observe and measure the planet’s atmospheric conditions, and to study the Little Red Spot in detail. The atmospheric data and images sent back from the encounter provided scientists with a great many new discoveries:

They [the New Horizons Team] saw clouds form from ammonia welling up from the lower atmosphere and heat-induced lightning strikes in the polar regions – the first polar lightning ever observed beyond Earth, demonstrating that heat moves through water clouds at virtually all latitudes across Jupiter. They made the most detailed size and speed measurements yet of “waves” that run the width of planet and indicate violent storm activity below. Additionally, New Horizons snapped the first close-up images of the Little Red Spot, a nascent storm about half the size of Jupiter’s larger Great Red Spot and about 70 percent of Earth’s diameter, gathering new information on storm dynamics.6

Io New Horizons, its 5 billion km journey to Pluto, and what to expect

The image on the left shows a violent eruption on Io, with plumes reaching more than 290 km above the surface. The image on the right shows Io and its volcanic activity in the background, with Europa in the foreground. Both images via Johns Hopkins University Applied Physics Laboratory.

Further study of Io, the Galilean moon closest to Jupiter, and its volcanic activity was also prioritized by the New Horizons team. Again, like the atmospheric study mentioned above, New Horizons was able to make many new discoveries about Io:

The mission’s investigations of Jupiter’s four largest moons focused on Io, the closest to Jupiter and whose active volcanoes blast tons of material into the Jovian magnetosphere (and beyond). New Horizons spied 11 different volcanic plumes of varying size, three of which were seen for the first time and one – a spectacular 200-mile-high eruption rising above the volcano Tvashtar – that offered an unprecedented opportunity to trace the structure and motion of the plume as it condensed at high altitude and fell back to the moon’s surface. In addition, New Horizons spotted the infrared glow from at least 36 Io volcanoes, and measured lava temperatures up to 1,900 degrees Fahrenheit, similar to many terrestrial volcanoes.

New Horizons’ global map of Io’s surface backs the moon’s status as the solar system’s most active body, showing more than 20 geological changes since the Galileo Jupiter orbiter provided the last close-up look in 2001. The remote imagers also kept watch on Io in the darkness of Jupiter’s shadow, noting mysterious glowing gas clouds above dozens of volcanoes. Scientists suspect that this gas helps to resupply Io’s atmosphere.7

Moons-1024x692 New Horizons, its 5 billion km journey to Pluto, and what to expect

A montage of the best images of Jupiter’s 4 largest moons. The Galilean moons. Via ohns Hopkins University Applied Physics Laboratory

After the Jupiter flyby, New Horizons spent much of the journey in hibernation mode, awaking annually for systems checks. After several years of sleeping peacefully, New Horizons was awoken on 6 December 2014.

Pluto approach, and the beginning of the encounter

Since January of 2015, New Horizons has been beaming back images of Pluto and its largest moon Charon with increasing detail. In a few short months, the images have gone from a few square pixels (above) to being able to make out surface features (below). And they will only get better.

Though the closest encounter will take place on 14 July 2015, it will take some time for New Horizons to send all of the data back to Earth. All of the data and images are sent back to Earth in a series of downlinks. During these downliks, the craft is unable to do anything else. Therefore, while the craft is closest to Pluto, it will prioritize data collection and imaging over downlinking. In fact, during the 24 hours of the closest approach, New Horizons will not communicate with Earth at all. Emily Lakdawalla of the Planetary Society laid out the downlinking process and the time-frame of the approach excellently:

On Sunday, July 12, New Horizons will transmit the last of its optical navigation data. Then, on Sunday and Monday, July 12 and 13, there will be a series of four “Fail Safe” downlinks. These are designed to return a minimum set of data from all instruments, just in case New Horizons does not survive the flyby. A last downlink ending overnight Monday July 13, called “E-Health 1,” will include one last pre-closest approach photo of Pluto.

Then there is a nail-biting 24-hour period of waiting while New Horizons concentrates on flyby science and does not communicate with Earth, followed by the much-anticipated beep of the “Phone Home” downlink on Tuesday night, July 14. Following closest approach, on Wednesday and Thursday, July 15 and 16, there will be a series of “First Look” downlinks containing a sampling of key science data. Another batch of data will arrive in the “Early High Priority” downlinks over the subsequent weekend, July 17-20. Then there will be a hiatus of 8 weeks before New Horizons turns to systematically downlinking all its data. Almost all image data returned during the week around closest approach will be lossily compressed — they will show JPEG compression artifacts. Only the optical navigation images are losslessly compressed.

The transmission of the High Priority data set will be complete on July 20, and then image transmission will pause. For nearly two months, until September 14, New Horizons will switch to near-real-time downlinking of data from other, so-called “low-speed” instruments while it transmits just housekeeping information for all of the rest of the data. No new images will arrive on the ground during this time.8

That said, these images should be amazing. To lean on the Planetary Society again – they really do excellent work and if you are at all interested in Pluto, check out their coverage – they did an excellent simulation of the quality of images that New Horizons will return from the closest encounter:

Sim New Horizons, its 5 billion km journey to Pluto, and what to expect

This is truly one of the greatest scientific and technological achievements of man. The flyby marks the end of the first age of solar system exploration, in which all of the 9 classical planets will have been visited and imaged by a probe. What a time to be alive!


Top image via NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

  1. I realize that we are a startup blog, but this is one of the largest technological achievements of humankind. And space is awesome.  
  2. NASA, Southwest Research Institute, Johns Hopkins University Applied Physics Laboratory, “New Horizons The First Mission to Pluto and the Kuiper Belt: Exploring Fronter Worlds (PDF),” pp. 14-15. 15 December 2005  
  3., New Horizons Mission, “Spacecraft and Instruments”  
  4. Voyager 1’s speed was increased by its flybys of Jupiter and Saturn, giving it a speed of more than 17 km/sec relative to the Sun.  
  5. That designation is kind of wrong. The third stage of the Atlas V rocket the launched New Horizons actually arrived at Jupiter a few hours before the probe. This third stage is also on an escape trajectory out of the solar system.  
  6. Johns Hopkins University Applied Physics Laboratory, “Pluto-Bound New Horizons Sees Changes in Jupiter System,” 9 October 2007  
  7. Johns Hopkins University Applied Physics Laboratory, “Pluto-Bound New Horizons Sees Changes in Jupiter System,” 9 October 2007  
  8. Emily Lakdawalla, Planetary Society, “What to expect when you’re expecting a flyby: Planning your July around New Horizons’ Pluto Pictures (version 2),” 24 June 2015