Category: Space Sunday

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” →

It’s a mission that cost $650 million to mount, took 5 years of planning and building prior to spending 9.5 years in space as one of the fastest man-made objects yet built (and the fastest ever at launch); it has travelled some 4.76 billion kilometres to reach its destination, swinging by and studying Jupiter  (the first time we’ve done so close-up in over decade) in the process. All this for a close encounter which, due to the speed of the vehicle, could be measured in a mere hours.

But what an encounter!

I’m of course referring to NASA’s New Horizons mission which, on July 14th, 2015, after all of the above, flashed by the Pluto-Charon system precisely on target and just 72 seconds ahead of it’s  predicted arrival time of 11:49:59 UTC at its closest point to Pluto.

Obviously, the overall encounter has been going on for some time now, as I previewed in my  Space Sunday report of July 12th: what NASA called the “distant encounter phase” started in January 2015, and even now, as New Horizons heads away from Pluto and Charon, observations are still being made. But the mission has always been about the hours immediately either side of that point of closest approach, when New Horizons flashed by Pluto at a speed relative to the planet of 13.77 km/s (8.56 miles per second).

The close approach wasn’t something that could be followed in real-time, the time delay in transmissions from the probe to Earth being some 4.5 hours. This being the case, NASA kept people informed with images and information recorded in the hours leading-up to the period of closest approach, such as a stunning image of Pluto captured by New Horizon’s LORRI and Ralph instruments on July 13th. Since then, they’ve been releasing a steady stream of the initial images that have been returned by the probe.

Pluto also appears to be an active planet – more so than had been imagined – with distinct compositional difference across its surface, making understanding of some of its characteristics difficult, so it is going to be some time before a range of questions relating to Pluto’s formation, development, etc., are liable to be answered, as many of them are going to have to wait for the arrival of very high-resolution lossless images from the probe, some of may now be received until well into next year (transmission of all the data recorded by New Horizons will take some 16 months).

In particular, New Horizons focused on a bright region positioned towards the centre of the of Pluto’s sunlit side and initially dubbed “Pluto’s Heart” due to its shape (seen  most clearly in the image above left). Now informally christened “Tombaugh Regio”, after Pluto’s discoverer, Clyde Tombaugh,  the region has been of interest to the science team due to its apparent “youthful” appearance: it is relatively crater-free, suggesting the surface has undergone significant re-working compared to the surface features around it, which are far more heavily cratered.

The region is home to a series of intriguing features, including the “Norgay Montes”, named after Tenzing Norgay, Edmund Hillary’s companion on the 1953 ascent of Mount Everest. This is a range of mountains rising some 3,300 metres (10,000 feet) above the surrounding plains, and which are estimated to be around 100 million years old, making them one of the youngest surface features seen in the solar system (younger than the Appalachian Mountains in North America, for example). There are believed to be a exposed region of Pluto’s bedrock, itself likely to be heavily comprised of water ice.

Continue reading “Space Sunday: perfectly Pluto” →

Tuesday, July 14th promises to be a major day in the annals of space exploration, as the deep space probe New Horizons hurls through the Pluto-Charon system, making its closest approach to both, allowing us to gain our best views yet of this binary pairing of dwarf worlds and their little nest of moonlets.

The mission is already fast approaching the 10th anniversary of its launch (January 19th, 2006),  with the overall mission (from inception to the present day) already  almost 15 years old – although the planning for a Pluto mission goes back a lot further than that. Getting to the Pluto-Charon system has been a remarkable feat.

Originally, Voyager 1 had been provisionally scheduled to make a Pluto flyby as a part of its half of the “grand tour” of the solar system, using its encounter with Saturn to swing the probe on to a rendezvous with Pluto in 1986. In the end, Saturn’s Mighty moon Titan was considered a more valuable target for study, and the laws of celestial mechanics meant that a study of Titan and a swing-by of Saturn suitable to send the mission on to Pluto were mutually exclusive.

In the 1990s various missions to Pluto were proposed, ranging in size from the huge Mariner II mission, utilising an update on NASA’s veritable Mariner class probes, weighing two tonnes, down to the tiny Pluto 350, a comparatively tiny vehicle massing just 350 kilogrammes (772 pounds). These evolved, through short-lived programmes such as the Pluto Fast Flyby mission and the Pluto-Kuiper Express mission to eventually become New Horizons in 2001, a mission conceived and operated by the Applied Physics Laboratory, which often operates in partnership with NASA’s Jet Propulsion Laboratory.

At launch, New Horizons became the fastest spacecraft ever launched, using an Atlas V booster with no fewer than five strap-on solid rocket boosters. In addition, a high-powered third stage was used to boost it directly onto a solar escape trajectory – something which required the vehicle to achieve a velocity of over 16 kilometres per second (56,000 km/h or 37,000 mph) following launch. To put that in perspective, such was New Horizons’ velocity that it had passed beyond the orbit of the Moon (an average of 384,400 km / 238,900 miles from Earth) less than nine hours after launch.

Just under 3 months after launch, and travelling at over 21 kilometres a second, (76,000 km/h; 47,000 mph), New Horizons passed beyond the orbit of Mars, heading onwards for Jupiter, and a manoeuvre referred to a gravity assist.

Reaching the Jovian system in September, 2006, New Horizons was able to stretch its scientific legs, when it started observing Jupiter and its moons from a distance of 291 million kilometres (181 million miles). Over the next 6 months, the craft continued to close on Jupiter, gathering a huge amount of data along the way to add to our understanding of the biggest planet in the solar system, its complex weather systems and atmospheric composition, and its ever-growing system of smaller moons, many of which perform a vital role is “shepherding” Jupiter’s thin ring system.

This was the first real opportunity to observe Jupiter and its moons since the end of the Galileo mission in 2003, and New Horizons did so spectacularly well, passing within 2.3 million kilometres of the planet and using its gravity to further increase its speed by 14,000 km/h (9,000 mph), shortening the journey time to Pluto by some 3 years.

Following the Jupiter mission, the vehicle went into a hibernation mode, allowing it to reduce the power drain on its nuclear “battery”, the radioisotope thermoelectric generator (RTG) which provides the vehicle with all its electrical power (and which itself was the back-up unit for the Cassini mission which is still in operation around Saturn, 18 years after its launch).

During the vehicle’s hibernation, things were changing with regards to Pluto. Until the 1990s, it had always been classified as a planet – albeit one with an unusual orbit, which is both sharply inclined to the plane of the ecliptic in which the other planets of the solar system orbit, and highly elliptical, bringing it closer to the Sun than Neptune during certain periods.

Both of these factors, coupled with Pluto’s relatively small size, suggested that it was more of a “captured” object from the Scattered Disc, a region of the Solar System between Neptune and the Kuiper Belt  that is sparsely populated by icy minor planets (Pluto’s orbit around the Sun actually sits within the Scattered Disc).

In 2005, while New Horizons was sleeping,  astronomers at Mount Palomar Observatory imaged Eris, a Scattered Disc object, complete with a moon of its own (Dysnomia), which is some 27% more massive than Pluto. This discovery, coupled with the fact that the Scattered Disc may be the home of other objects of similar size, caused the International Astronomical Union to officially define the term “dwarf planet” in 2006, and downgrade Pluto’s status to match – although not without a certain amount of controversy and protest.

Continue reading “Space Sunday: Pluto – the history of a brief encounter” →