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What to Expect in the Leadup to New Horizons' Historic Flyby of Pluto

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After a nerve-wracking hiccup this weekend, NASA’s New Horizons mission is all systems go: We are now just a week away from the space probe’s long-awaited encounter with Pluto. Here’s what to expect over the course of the next seven days.

After 3,455 days and nearly 3-billion miles, New Horizons is now less than a week away from its historic encounter with Pluto and its moons. NASA says the spacecraft is back on track after its main computer became overloaded due to a timing conflict in the probe’s command sequence. New Horizons’ computer was tasked with receiving a large command load while it was simultaneously trying to compress science data. The main computer responded exactly as it was supposed to, going into safe mode while switching on the backup computer.


The temporary disruption was scary, but it only resulted in a loss of of 30 photographs out of a planned 500.


LORRI images taken of Pluto from July 1 to 3, 2015. (NASA/JHUAPL/SWRI)

“We’re delighted with the New Horizons response to the anomaly,” noted NASA’s director of planetary science Jim Green in a statement. “Now we’re eager to get back to the science and prepare for the payoff that’s yet to come.”


No doubt, things are about to get incredibly exciting over the next seven days. Here’s how things are scheduled to go down.

Tools of the Trade

New Horizons is equipped with seven different instruments, including three optical instruments, two plasma instruments, a dust sensor, and a radio science receiver/radiometer:

  • LORRI: Long-range and high-resolution visible mapping
  • SWAP: Solar wind
  • PEPSSI: Energetic particle spectronomy
  • Alice: Ultraviolet imaging spectroscopy
  • Ralph: Visible mapping, infrared spectroscopic mapping
  • SDC: Student-built dust counter
  • Rex: Radio science and radiometry

(NASA/New Horizons)

Among other things, these tools will be used to study the geology of Pluto and its moons. The probe will map surface composition, and measure temperature, atmospheric pressure, and the escape rate of Pluto’s atmosphere.


Indeed, the Pluto-Charon system has a lot to offer scientists; Pluto, as the largest known body in the Kuiper Belt, is theorized to have an extensive nitrogen atmosphere, complex seasons and surface features, an ice-rock interior that may harbor a subterranean ocean, and at least five moons for studying, namely Charon, Hydra, Nix, Styx, and Kerberos. It’s early yet, but these moons look incredibly interesting in their own right.

New Horizons’ optical instruments will allow it to detect any object down to 2 km (1.2 miles) in diameter. It’s possible, therefore, that the system will yield previously undetected moons. Possibly even rings. The probe is expected to map the surfaces of Pluto and Charon with an average pixel scale of one kilometer (0.6 miles).


(NASA/New Horizons)

Here’s NASA’s complete list of science objectives for the mission:

Required (Primary Goals)

  • Characterize the global geology and morphology of Pluto and its moons
  • Map surface composition of Pluto and Charon
  • Characterize the neutral atmosphere of Pluto and its escape rate

Important (Secondary Goals)

  • Characterize the time variability of Pluto’s surface and atmosphere
  • Image Pluto and Charon in stereo
  • Map the terminators (day/night boundary) and compositions of selected areas of Pluto and Charon in high resolution
  • Characterize Pluto’s ionosphere and solar wind interaction
  • Search for atmospheric hydrocarbons and nitriles
  • Search for an atmosphere around Charon
  • Determine albedos and surface temperatures on Pluto and Charon

Desired (Tertiary Goals)

  • Characterize the energetic particle environment of Pluto and Charon
  • Refine bulk parameters (radii, masses, densities) and orbits of Pluto and Charon
  • Search for additional satellites, rings and magnetic fields

The Encounter

New Horizons is currently traveling at 14.56 km/s (9.05 miles/s) relative to the Sun. At a distance of 32.85 AU, it’s now taking about 4.5 hours for radio signals to travel from the spacecraft to Earth. That’s a round-trip of 9 hours, so two-way communications is quite awkward.


In about three days, the probe’s long-range scans will start to include the mapping of Pluto and Charon to 40 km (25 mile) resolution. This will allow enough time for the craft to image all sides of both bodies. During this time, scientists will be on the lookout for signs of cryovolcanism, among other things.


Above tweet: A simulation of the flyby, via Nasa’s Eyes on the Solar System app.

The spacecraft is expected to make its closest approach to Pluto, a distance of approximately 12,500 km or 7,750 miles, on July 14 at 11:50 UTC. During this brief window of time, the probe’s cameras will map the entire surface structure of the sunlit faces of both Pluto and Charon and also map surface composition. LORRI is expected to acquire images at resolutions as high as 50 m/px, while the MVIC (Multispectral Visible Imaging Camera) on Ralph should obtain four-color global dayside maps at about 1.6 km (1 mile) resolution. The spectral near-infrared maps will be at about 7 kilometers per pixel (4.4 miles/px), and at times as good as 0.6 km/pixel. In other words, the images will be gloriously detailed.


Using audio from NASA’s briefings and social media web chats and his own animation, filmmaker James Malcolm made a short film about the New Horizons mission to the Pluto System. This should get you pumped if you aren’t already.


Afterwards, as New Horizons streams away from Pluto, it will turn around and map the dwarf planet’s night side, which will be softly illuminated by Charon’s moonlight. During this phase of the mission, the probe’s antenna will receive a powerful radio beam from Earth, aimed in such a way that it will pass through Pluto’s atmosphere. The resulting measurements will allow scientists to map the temperature, density, and composition of the atmosphere right down to the surface.


From there, New Horizons will continue to snap pictures as best it can as it heads deeper into the Kuiper Belt. The mission will continue well into the 2020s as the probe (hopefully) encounters more distant objects.

[ NASA | New Horizons ]

Contact the author at and @dvorsky. Top image by NASA/JHUAPL/SWRI: The most recent high-resolution image sent by NASA’s New Horizons spacecraft, a shot that includes one of four mysterious dark spots. The image was captured by the LORRI camera prior to the July 4 anomaly that sent the probe into safe mode..