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A voyage to Pluto with New Horizons

Photo Credit : The National Aeronautics and Space Administration, USA

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“We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths” – said Walt Disney. And that is exactly true with our thirst to explore new worlds beyond our planet Earth. We reached the space, sent missions and men to the Moon, reached Mars, sent probes to the Saturnian system, unlocked the mysteries of the gas giant Jupiter, and with 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 illustrious fleet of space missions is ‘New Horizons’ that is taking mankind to Pluto and beyond.

“The goal of the New Horizons mission was very simple -- explore the Pluto system, and perform basic reconnaissance study about what is happening on Pluto”, says Dr. Henry Throop, a planetary scientist at the Planetary Science Institute, Mumbai, who has been associated with the New Horizons mission since 2002. He is also the developer of GeoViz, the tool used by the science team to plan and simulate New Horizons’ observations.

It is not the first time that we are trying to look at Pluto. The Hubble Space Telescope (HST) succeeded in capturing extremely grainy images of Pluto, so small that the process of imaging the surface from the orbit is as challenging as attempting to view the markings on a soccer ball located 60 kilometers away! “With the Hubble Space Telescope, Pluto is barely one pixel across”, quips Dr. Throop. To observe Pluto more closely, NASA selected to fly the New Horizons mission, led by a team from the Southwest Research Institute (SwRI) and Johns Hopkins University - Applied Physics Laboratory (JHU APL). “With New Horizons, we can now image Pluto with a resolution of 5000 x 5000 pixels”, he adds talking about the immense value this mission holds in understanding Pluto like never before.

After years of planning and research, New Horizons was launched on 19th January 2006, on board an Atlas V 551 rocket from Cape Canaveral in Florida, USA. But why did 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 8 planets we've explored with spacecraft before. They're all inward of Pluto. And Pluto is a bit further out, and totally different from the others”, remarks Dr. Throop.

But Pluto has its own specialties. “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 - they freeze out. They all turn solid near Pluto's surface temperature of around 40 K (~-233oC)”, explains Dr. Throop.

The New Horizons spacecraft weighs about 480 kilograms with a suite of different scientific instruments on-board of which Alice, an ultraviolet spectrometer designed to measure the gas composition of Pluto's atmosphere, is one. Others include an infrared spectrometer to map the surface composition and geological features 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 Pluto's atmosphere and another instrument to measure dust impacts of the spacecraft during its journey to Pluto.

New Horizons – reaching the horizon of the Solar System

Getting to Pluto from here, traversing a total distance of approximately 5.9 billion kilometers (about 40 times the distance from Earth to Sun), is an incredibly difficult task in itself. And there was a sense of urgency to get there as soon as possible because Pluto’s elliptical orbit has been moving it further out from the Sun, which means, it gets lesser heat from the Sun with each passing year. This could lead to the freezing of its atmosphere quite soon 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 the system never face the Sun for several years at a time, obstructing the spacecraft from studying them.

On July 14, 2015, New Horizons flew by Pluto at a distance of about 12,500 kilometers, giving a huge opportunity for scientists to study and record everything they wanted to know about Pluto. And for the mission members, this meant positioning the instruments on board accurately to snap the best images of Pluto. “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, traveling at ~16 km/sec (around 58,000 km/hr), one of the fastest spacecraft 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," describes Dr. Throop about their fight against time.

Dr. Throop’s brainchild, GeoViz, short for 'Geometry Visualizer', played a very important role in helping scientists to precisely plan all the image and data acquisition exercise 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 is kind of a 'spacecraft simulator' that can predict 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 visualize where you are and what to look at,” explains Dr. Throop.

A treasure trove of data from the horizon

Lo and behold, New Horizons has delivered all its mighty promises! New Horizons' 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'”, reveals Dr. 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 explains.

New Horizons has so much to cover in its journey. After zipping past Pluto, it is now on its way to the Kuiper Belt situated beyond Pluto. “Right now we are in New Horizons' ‘Extended Mission’, which means that 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 Kuiper Belt Object 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 1 Jan 2019”, shares Dr. Throop hinting that '2014 MU69' will be suggested 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 30 km, vs. Pluto's 2400 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," shares Dr. Throop with excitement in his eyes.

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 at Mars and the Moon, in addition to its orbital missions such as Astrosat, I hope that it won't be too long before India itself starts exploring the outer Solar System,” opines Dr. Throop, signing off with a sense of adventure that awaits him in the near future.