Day: July 27, 2015

New Horizons is continuing outbound from the Pluto-Charon system, its primary mission  complete. A new phase of the mission has now begun: returning all the data gathered safely to Earth; a process that is going to take an estimated 16 months to complete. Even so, and as indicated in my last report, what has already been received has been enough to turn much of planetary science on its head.

During a mission briefing on July 24th, 2015, Alan Stern, the New Horizons principal investigator and members of the science team provided a further update on the mission, and revealed some of the more stunning images captured by the spacecraft during the close approach phase of the mission. One of the most striking of these was a picture snapped by New Horizons just seven hours after close approach, when it was already 2 million kilometres (1.2 million miles) from Pluto.

The image shows the dark disc of Pluto’s night side (which will not see the light of the Sun for another 20 years), surrounded by a halo of atmosphere, 130 kilometres (80 miles) thick, backlit by the distant Sun. Within the atmosphere sit two bands of thick haze, one around 50 kilometres (30 miles) altitude and the second at around 80 kilometres (50 miles) altitude.

These bands of haze are believed to be the result of ultraviolet sunlight striking the upper reaches of Pluto’s atmosphere, breaking apart the methane gas there, giving rise to more complex hydrocarbon gases such as ethylene and acetylene. These heavier gases then descend into the colder regions of Pluto’s atmosphere, condensing as ice particles, which are seen by New Horizon’s instruments as the bands of haze.

The ice particles are further acted upon by ultraviolet sunlight so that tholins are formed. Tholins are large complex organic aerosols thought to contain some of the chemical precursors of life. These gradually fall out of the atmosphere to mix with hydrocarbons on Pluto’s surface, giving it the distinctive colouring we see in images like those given below.

The July 24th briefing also revealed some of the most detailed images of Pluto’s sunlit side yet published, starting with the true colour image shown above. This shows Pluto in twice the level of detail as the July 13th image published by NASA, revealing surface features as small as two kilometres across (the ultra-high resolution images LORRI has captured will eventually reveal surface features as small as 50 metres across). Featured prominently and unmistakably in the image is Pluto’s light-coloured “heart”, informally named the “Tombaugh Regio” in honour of Pluto’s discoverer, Clyde Tombaugh.

This huge region is divided into two parts, defined by the two “lobes” of the heart. On the left (west side) is the relatively smooth expanse of the “Sputnik Planum”, roughly the size of Texas.The is largely composed of a thick layer of nitrogen, methane and carbon monoxide ice. That it is almost completely without craters suggests it is much younger than the rest of Pluto’s visible surface; but how it formed has yet to be determined.

The right side of the “heart” is also brightly-coloured, indicating the presence of ices similar in nature to those in “Sputnik Planum”, but it also shows a much rougher terrain as well. Further bright, icy material also extends from the “point” of the “heart” into the southern polar regions of Pluto, again mixing with rougher terrain.

While it is not clear what actually gave rise to the icy expanse of “Sputnik Planum”, it is not believed the same mechanism is responsible for the ice in either eastern lobe or which extends southwards from the “heart”. These are believed to be the result of material from “Sputnik Planum” being carried into these areas, where it is gradually “painting over” surface features there.

Continue reading “Space update: Pluto, Mars, and Earth’s big cousin” →