Story Highlights

• The goal of the New Horizons mission was simple — to explore the Pluto system, and perform a basic reconnaissance study about what is happening there
• On July 14, 2015, New Horizons flew by Pluto at a distance of 12,500km, giving scientists a 'golden window' to study and record everything they wanted to know
• New Horizons has much more to cover in its journey. After zipping past Pluto, it is now on its way to reach the Kuiper belt situated beyond Pluto

“We keep moving forward, opening new doors, and doing new things, because we’re curious and curiosity keeps leading us down new paths” — Walt Disney, as quoted in the ending credits of the movie Meet the Robinsons (2007).

It’s curiosity that has led us to explore new worlds beyond planet earth. We have reached space, sent missions and men to the moon, touched down on Mars, sent probes to the Saturnian system, unlocked the mysteries of the gas giant Jupiter. With space missions like Pioneer and Voyager, we are now trying to understand planets and celestial bodies far beyond Jupiter and Saturn. A new addition to this slew of missions is New Horizons, a Nasa initiative that is taking mankind to Pluto and beyond.

After years of planning and research, New Horizons was launched on January 19, 2006, on board the Atlas V 551 rocket from the Cape Canaveral Air Force Station in Florida, US. “The goal of the New Horizons mission was very simple — to explore the Pluto system, and perform a basic reconnaissance study about what is happening on Pluto,” said Dr Henry Throop, a planetary scientist at the Planetary Science Institute, Mumbai, who has been associated with the mission since its conception in 2002. He is also the developer of Geo-Viz, the tool used by the science team to plan and simulate New Horizons’ observations.

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It is not for the first time that we are trying to look at Pluto, which was first seen in 1930 and can still be seen with modest telescopes. Nasa’s Hubble Space Telescope (HST), which has succeeded in capturing galaxies very far away from us, could only capture extremely grainy images of Pluto in 2012 because of its small size. The images of Pluto taken by the HST are so small that the process of imaging the surface from the orbit was as challenging as attempting to view the markings on a soccer ball located 60km away! “With the Hubble Space Telescope, Pluto is barely one pixel across,” quipped Throop.

So, to observe Pluto more closely, Nasa selected to fly New Horizons, led by a team from Johns Hopkins University — Applied Physics Laboratory (JHU APL) and the Southwest Research Institute (SwRI), both in the US. “With New Horizons, we can now image Pluto with a resolution of 5000×5000 pixels,” said Throop, talking about the immense value of this mission in understanding the planet.

The New Horizons spacecraft weighs about 480kg, with a suite of different scientific instruments onboard. One of them is Alice, an ultraviolet spectrometer designed to measure the gas composition of Pluto’s atmosphere. Others include an infrared spectrometer to map the surface composition and geological features of the planet using a colour optical imager; a radio instrument used to measure atmospheric composition and temperature; a telescope to capture high-resolution images of Pluto’s surface; a plasma-sensing instrument designed to measure particles escaping its atmosphere; and another instrument to measure dust impact of the spacecraft during its journey to Pluto.

New Horizons — a long, hard journey

Getting to Pluto from earth, traversing a distance of approximately 5.9bn km (about 40 times the distance from the earth to the sun), was an incredibly difficult task in itself. And there was a sense of urgency to get there as soon as possible because scientists say that since 1989, Pluto’s elliptical orbit has been moving it further, which means, it gets lesser heat from the sun with each passing year. This could lead to the freezing of its atmosphere, and if we don’t get there soon enough, we might miss out on studying its present, relatively thicker, atmosphere. Another reason to observe the surfaces of Pluto and its moons as soon as possible is that parts of them face away from the sun for several years at a time, obstructing spacecraft from studying them.

On July 14, 2015, New Horizons flew by Pluto at a distance of about 12,500km, giving scientists a huge opportunity to study and record everything they wanted to know about the planet. For the mission members, this meant positioning the instruments on board accurately to be able to take the best possible images.

“We built a small spacecraft and put it on top of a very powerful launch chic, so we get out there in 9.5 years, travelling at ~16 km/sec (around 58,000 km/hr), one of the fastest spacecrafts ever launched. Now, once we have got there, we’re still going quickly. There is no way to slow down the spacecraft. But, because we were still moving very quickly, our observations had to be planned very carefully. We had about 24 hours of ‘golden’ observations at Pluto. And by the time that period was over, we were well on our way past Pluto, and outbound into the Kuiper belt,” said Throop about their fight against time.

Throop’s brainchild, the software GeoViz, short for Geometry Visualizer, played a very important role in helping scientists precisely plan all the image and data acquisition exercises during this ‘golden window’. “The GeoViz system essentially operates to show the science team what sort of observations are possible at a given time. It’s kind of a spacecraft simulator that can predict at a given position and time what will we be seeing on Pluto, which regions will be captured on the cameras, where the sun is, what stars are in the background, where the earth is, and so forth. It makes planning the observations easy, since you can graphically visualise where you are and what to look at,” explained Throop.

But why did the scientists decide to study Pluto? “The main reason we went out to visit Pluto is that we haven’t been there before. Pluto is far from the sun, and we have eight planets we’ve explored with spacecraft before. They’re all inwards of Pluto. And Pluto is a bit further out, and totally different from the others,” remarked Throop.

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There is a particular interest in studying the planet because it is unlike other gas giants found in its neighbourhood. “Pluto is not like the inner planets. And it’s certainly not like the gas giants — Jupiter, or Neptune, for instance. It’s really its own new class of bodies. We think of Pluto as the largest known in this third class of bodies — the ‘ice planets’. It’s so cold at Pluto’s location that the gases in our atmosphere on earth — nitrogen, CO2, water vapour, methane, and so on — freeze out. They all turn solid near Pluto’s surface temperature of around 40 K (~ -233oC),” explained Throop.

A treasure trove of data from the horizon

The researchers are elated that New Horizons is delivering all its mighty promises. Its superior imaging capability has shown that Pluto is an active world. “There is geology happening there right now. Something is keeping its core warm, so there are mountains being formed, nice ice flowing, and craters eroding away, and so forth. This was totally unexpected. Nearly everyone thought that Pluto would be cold, and old, and geologically ‘dead’,” said Throop.

“If you look at the inner planets in our solar system, Mercury and Mars, for instance, they look like they’ve cooled off in the 4.5 billion years since they were formed, so there is very little active geology happening there now. And this is what we expected. But somehow, something on Pluto is keeping its core warm, so it is active,” he explained.

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But New Horizons has much more to cover in its journey. After zipping past Pluto, it is now on its way to reach the Kuiper belt situated beyond Pluto. “Right now, we are in New Horizons’ Extended Mission, which means Nasa is supporting the mission for several more years, to let us plan and operate a second major flyby in the outer solar system. New Horizons will do distant flybys of more than a dozen Kuiper Belt Objects (KBOs) — celestial bodies found in the Kuiper belt. We are really excited to have identified a KBO in the vicinity — called 2014 MU69 — and we have made a change to the spacecraft’s trajectory, such that we will intersect this KBO’s orbit on January 1, 2019,” said Throop, hinting that 2014 MU69 will be given a more romantic name at some point.

KBOs are interesting in their own right and the New Horizons team is all excited about the impending face-off with 2014 MU69. “This body is cold and icy — like Pluto. But it’s much smaller than Pluto, with a diameter of maybe 30km, versus Pluto’s 2,400 km. Being much smaller, we expect it will look far different than Pluto. Physical processes will work much differently there than Pluto. It’s going to be a whole new world, and I can’t wait to get there,” said Throop, visibly excited.

Like earlier space missions, New Horizons is helping space agencies and scientists gain valuable knowledge about the planetary bodies and beyond. “We’d love to come back to the Kuiper belt, but there are also so many other great places in the solar system that we’d like to visit — Europa, Enceladus, and Titan being among the places I’m most interested in seeing visited up close. Luckily, the number of space-faring countries is growing. With Isro’s recent successes on Mars and the moon, in addition to its orbital missions such as Astrosat, I hope it won’t be long before India itself starts exploring the outer solar system,” signed off Throop.

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