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Telescopes and space missions

Pluto comes into focus as New Horizons nears the dwarf planet

09 Jul 2015 Hamish Johnston
Pluto's heart: image of the dwarf planet taken by New Horizons

Stunning images of Pluto have been acquired over the past few days by the New Horizons spacecraft as it approaches the dwarf planet 7.5 billion km from Earth. The NASA mission will come within 12,500 km of Pluto – which has never before been visited by a spacecraft – on Tuesday 14 July before it ventures deeper into the Kuiper Belt.

Launched in 2006 to study Pluto and the Kuiper Belt, New Horizons is carrying seven scientific instruments including visible, infrared and ultraviolet imagers and spectrometers. The Long Range Reconnaissance Imager (LORRI) was used to take the above image of Pluto on 7 July, when the spacecraft was 8,000,000 km from the dwarf planet. The image includes several features of interest to planetary scientists including the elongated dark feature at the equator, which has been dubbed the “whale”. The large heart-shaped bright region to the right of the whale measures about 2000 km across.

‘Incredible’ images expected

“The next time we see this part of Pluto at closest approach, a portion of this region will be imaged at about 500 times better resolution than we see today,” says Jeff Moore, geology, geophysics and imaging team leader of NASA’s Ames Research Center. “It will be incredible!”

Also on board New Horizons is the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI), which will study material such as nitrogen and carbon monoxide that escapes from Pluto’s atmosphere and is then ionized by ultraviolet light from the Sun. NASA heliophysicist Nikolaos Paschalidis helped design and build low-energy integrated circuits for PEPSSI – a technology that has since been upgraded and used on several subsequent missions.

“The challenge with this mission, and the PEPSSI instrument in particular, was making it as small as possible, and capable of taking highly reliable measurements using low power, under extreme environmental conditions,” says Paschalidis. Indeed, he points out that PEPSSI is the most compact, lowest-power energetic particle spectrometer ever to be flown on a space mission.

Communication breakdown

While the mission appears to be going to plan, NASA scientists had a scare last week when communications with New Horizons were lost for more than an hour on 4 July. The mission’s autopilot recognized that something was going wrong and placed the spacecraft in safe mode while engineers determined that a flaw in the timing of the spacecraft’s command sequence had caused the problem.

According to the mission’s principle investigator Alan Stern of the Southwest Research Institute, about 30 planned scientific observations were not made while the spacecraft was in safe mode. However, he points out that some of these were preliminary observations that were not expected to deliver useful data because of the large distance between the spacecraft and Pluto. Stern says that the lost data account for less than 1% of the information that New Horizons will acquire during its flyby of the dwarf planet and therefore their loss is not significant.

The spacecraft is now operating normally and Stern and colleagues looking forward to analysing data from the nearly 500 observations that New Horizons will make as it passes Pluto.

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