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12. Pluto Flyby Today, 14 July 2015!
John Austin
images of dwarf planet pluto

Composite image from 12 July, showing Pluto and Charon (in the distance) from a distance of about 2 million kilometres. Image Credit: NASA[1].

Today, 14 July 2015, at 11.50 pm UT (1 hour behind BST), the New Horizons spacecraft passes Pluto at a distance of less than 12,500 km. After its 9 year journey from Earth, the spacecraft will pass the Pluto system at 13.8 km/s, and in the short time available, it will obtain the best information yet of the dwarf planet and its moons.

The Route to Pluto

The New Horizons spacecraft was launched on 19 January 2006 and passed by Jupiter on 28 Feb 2007. The flyby of Jupiter enabled the spacecraft to be accelerated by an additional 4 km/s from its 16 km/s Earth launch speed.

An early July engine burn was used to optimise the flight path for its close encounter. The engines to not have the power to reduce the speed of the spacecraft by enough to be captured by the relatively weak Pluto gravity. Instead, the spacecraft will pass by the Pluto system at some 13.8 km/s. This still leaves sufficient time for data collection, assuming that all the instruments work on board as planned. Pluto is currently 4.8 billion km from Earth, so a radio signal from Earth would take 4.4 hours to reach Pluto. Last minute course corrections or to camera pointing will therefore not be possible. Everything has therefore been planned in meticulous detail by mission control to ensure that the instruments are pointing in the right direction at all times. It wouldn't be much use for the cameras to be pointing into space at critical moments!

Information About Pluto

Until New Horizons[1], very little was known about Pluto[2]. It is too distant from Earth for it to appear other than a point of light in Earth-based telescopes. The Hubble space telescope has managed to resolve some of Pluto's surface features, and indeed has expanded our knowledge of the system to include the 5 moons of Pluto. By the end of May, New Horizons had already produced higher resolution images of Pluto than are available from Hubble. As the distance to the dwarf planet has rapidly reduced, so the quality of images has improved. At the shortest distance, images will be several thousand times better than images from Hubble, with a best resolution of up to 50m on the planet surface per pixel. It will be several months or even years before all the data from the seven science instruments on New Horizons can be analysed. At the moment, interest is being focused on the pattern of light and dark regions spread around the equator of the dwarf planet.

The Latest Images

images of dwarf planet pluto

This view, captured by New Horizons on 11 July 2015, shows linear features which may be cliffs as well as possible impact craters. Rotating into view is the heart-shaped feature while around the dwarf planets equator is a series of dark regions which will have rotated out of view by the time of closest approach. Image Credit: NASA[1].

At a distance of 2.5 million kilometres, the surface of Pluto has already revealed some amazing features[1], not seen on any other solar system object, primarily the pattern of light and dark spots around the equator. Because of the 6-day rotation period, 11 July was the last opportunity to view the region in full prior to the flyby. During the flyby itself, little data will be sent to Earth as the spacecraft will be collecting data. Information will be sent to Earth at a later time.

The visit to Pluto completes the overview of the solar system, initially begun at the start of the space age in the late 1950s. All the planets have now been observed at close quarters, and two dwarf planets (Ceres and Pluto) have been observed closely, as well as comets and several objects in the Asteroid belt. Of course Pluto was an important part of that collection, as it used to part of the group of "classical" planets and may yet be upgraded once more.

More Information About Pluto

NASA[3] has had regular updates on New Horizons and Pluto, while the BBC[4] has been reporting, primarily using NASA resources. For UK residents, there is also a BBC Sky at Night TV programme on the Pluto close encounter on 20 July 2015[5]; other countries may also be planning similar broadcasts. This is an historic occasion: enjoy it!


Article initially prepared 14 July 2015

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Website revised by John Austin, 14/7/2015. © Enigma Scientific Publishing, 2015.