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The incredible things that had to go just right for Juno to reach Jupiter

Akshat Rathi
By Akshat Rathi

Senior reporter

“We just did the hardest thing NASA has ever done,” said Scott Bolton, the lead investigator on the Juno mission. After a five-year journey, the spacecraft Juno managed to enter the perfect orbit around Jupiter. Soon, it will start revealing secrets of the solar system’s biggest and most unchanged planet.

But to get Juno there, NASA had to overcome incredible challenges.

The spacecraft has a diameter of about 3.5 meters (12 feet) and weighs some 3,600 kg (roughly 8,000 lb). That’s huge—for things put in space. So it had to be launched on one of NASA’s biggest rockets, the Atlas V. Fortunately, space launches have become fairly safe. Atlas rockets have a success rate of about 90%.

Next, Juno had to survive its five-year, 1.7-billion-mile journey to reach Jupiter. In doing that, it had to cross the perilous asteroid belt between Mars and Jupiter. Fortunately, each of the millions of asteroids is surrounded by billions of cubic meters of space. So, it turns out the probability of hitting an asteroid while passing through the belt is quite low. So low, in fact, that it is not something NASA needed to worry about.

Finally, as Juno approached Jupiter, it entered the riskiest phase of its mission. The spacecraft would have be traveling at incredible speeds, while being accelerated by Jupiter’s gravity. This would have happened at the same time as Juno was blasted with crazy amounts of radiation produced by Jupiter and tried to dodge debris around the planet.

The spacecraft would have reached a top speed of 165,000 mph before being slowed down. (For reference, a bullet on Earth can reach a speed of about 1,700 mph.) To achieve the right speed, Juno’s main engine fired for about 35 minutes and  slowed it down by only about 1,200 mph. That was just enough to let Jupiter’s enormous gravity capture the probe in an orbit around it.

Jovial spacecraft.

In effect, NASA achieved to throw a tiny object through 1.7 billion miles of space into an area that is only about tens of kilometers wide. It’s like throwing a basketball from London to New York and managing to hit the backboard perfectly to land the ball in the basket.

NASA has not yet revealed if all systems are functional. So we don’t know if the spacecraft’s delicate scientific instruments are intact after dealing with radiation and debris. These scientific instruments have been designed to measure radiation, magnetic fields, tiny differences in gravity, and even take pictures. The data from these instruments will start to pour in over the next few weeks.

The spacecraft is also carrying a plaque with words from the astronomer Galileo, who discovered the first moons of Jupiter, and three Lego mini-figures of Galileo and the Roman gods Jupiter and Juno. Juno is, in fact, an apt name for the mission. According to Roman mythology, Jupiter drew a veil of cloud around himself to hide his mischiefs. But Juno, his wife (and, oddly, his sister), found a way to peer under those clouds. The spacecraft Juno is going to try and do the same thing, under the gassy layer of Jupiter.

What it will reveal will tell us not just fascinating things about our 400-year-old obsession with Jupiter but also the origins of our own planet, which formed about the same time as Jupiter. There is also a chance that Juno might find more moons of Jupiter, adding to the 67 we already know about.

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