New Horizons: The Pluto Story
Kamal Lodaya, The Institute of Mathematical Sciences, Chennai

The Amrican spacecraft New Horizons flew by Pluto, five billion kilometres away, on 14 July this year. The cover photo shows how glorious Pluto looks. We are used to thinking of Mars as the "red" planet (its surface has iron oxides), but to our surprise Pluto also looks brownish-orange.
Unlike at the asteroid Ceres, where another American spacecraft Dawn is in orbit (see elsewhere in this issue), and at the comet Churyumov-Gerasimenko which the European spacecraft Rosetta has been orbiting for a year now (see elsewhere in this issue), New Horizons did not stop at Pluto---it flew past taking pictures in a few hours. Think of the accuracy required to do this!
It might seem surprising to you but once New Horizons had attained a high speed, which it needed to cover 5 billion kilometres in ten years, it takes a huge amount of fuel to brake it to a speed low enough so it can go into orbit around Pluto. So it was decided not to place it into orbit, but to send it out of the solar system. The schematic shows the path of the spacecraft. 
Pluto is in the Kuiper Belt, a region of space just beyond Neptune's orbit, containing small bodies such as the three dwarf planets, Pluto, Haumea, and Makemake.
On its way out, four years later, New Horizons will fly past the Kuiper Belt object 2014 MU69, which is another billion and a half kilometres away. This is a small "Kuiper belt object" (KBO for short), perhaps 45 kilometres in diameter. Pluto is already the farthest object we have been to in the solar system, now we are trying to go to something even farther.
Pluto is among the largest Kuiper belt objects we know, 2360 kilometres in diameter. Just like we have thousands of asteroids between Mars and Jupiter (called the asteroid belt, with Ceres the largest, 950 kilometres in diameter), there are thousands of KBOs beyond the planet Neptune. Gerard Kuiper was a Dutch astronomer who thought such a second asteroid belt might exist, and now it is named in his honour.
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BOX on Asteroids
Last December the Japanese spacecraft Hayabusa 2 set off on a journey to a tiny 1-kilometre asteroid which goes by the name 1999 JU3. Japan has asked the public to send suggestions for naming the asteroid. This asteroid will be reached in 2018. The spacecraft will send down a small lander which will pick up surface samples which will eventually be returned to Earth.
China is also planning sending a spacecraft to some small asteroids. It already sent a mission Chang'e-2 which went into orbit around the Moon. Chang'e-2 was also sent to the small 5-kilometre asteroid Toutatis which it visited on 13 December 2012.
These asteroids (and the Moon) are rich in minerals, and one idea of the Japanese and Chinese missions is to see how feasible it is to get these minerals.
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Now that the large planets have all been visited, astronomers all over the world are trying to get their spacecraft to look at asteroids, comets and KBOs. The fascinating thing is that these seem to have features very different from what we saw on the planets.
Take Pluto for instance. What did we see there? The tell-tale orange colour is expected to be a sign of methane (CH4). We know that Pluto has a lot of nitrogen in its atmosphere (Earth has 70 per cent, but over 90 per cent of Pluto's surface is nitrogen ice) so we expect to find nitrogen compounds. In 2005, the American spacecraft Huygens (named after the Dutch astronomer who discovered it) visited Titan, one of Saturn's moons. It also has an orange look and its atmosphere has a lot of methane and nitrogen.
New Horizons also found a fair amount of carbon monoxide (CO) in Pluto's atmosphere. Unlike Earth, these compounds seem to be more concentrated in some areas of Pluto than in others. Some pictures show signs which suggest flowing, but we do not know what it is: solid, liquid or gas.
The greatest surprise so far has been mountains, as much as 3 kilometres high (which is big for Pluto's size).
As you may know, mountains on the Earth's suface are formed by geological processes taking place further down. But if you look at the Moon, it is mostly full of craters, so there is very little geology going on there. These processes owe a lot to the Sun's energy and at Pluto's distance no one expected much to be happening there. So finding all these is a surprise.
Pluto has moons, too (in fact five of them). Charon is nearly one-third its size (1200 km in diameter, which makes it bigger than the largest asteroid Ceres), both revolve around each other. It would be more realistic to call Pluto and Charon a binary KBO. Charon is grey in colour, like our Moon, but it has some amazing canyons on its surface. 
Since it revolves much closer to Pluto than our Earth does (it would appear seven times bigger in Pluto's sky) is it possible that the tides from Pluto have made these chasms? Or does Charon have some geology too?
New Horizons also got some pictures of two tiny moons of Pluto called Nix and Hydra. They have interesting shapes!
Another new world of the solar system has been opened to our eyes. Already people are asking why we cannot send more spacecraft to these faraway worlds so that we can learn about them. The main reason is that it takes a lot of fuel and a long time to get to them, and it also costs a lot of money. India has done well to develop an inexpensive way of reaching Mars. But Mars is only 20 crore kilometres away. Reaching 500 crore km is another matter!