00:00We could believe that the best way to get to a planet from Earth is to wait patiently for it to get as close as possible.
00:08Yes, here it is, and take off on a rocket oriented towards it.
00:12Great, hi mom, see you later.
00:14But why didn't this method work?
00:19First of all, planets, including ours, move constantly on their elliptical orbit at a speed of several tens of kilometers per second.
00:28Your rocket would therefore need to be placed on an elliptical orbit, wouldn't it?
00:32It's a bit like aiming at a moving target with an arrow or organizing a surprise party for a friend.
00:38You wouldn't want to shout surprise at the wrong time.
00:42Likewise, when we send space vehicles to other planets, we want to use as little energy as possible.
00:49And to reach any planet in the simplest way, you need a special trick called Hohmann transfer orbit.
00:58Let's imagine that you want to go to Mars.
01:01You have to wait for Earth and the red planet to be in the right position so as not to get lost or run out of fuel halfway.
01:09A trip using a transfer orbit would take about 259 days.
01:15Indeed, the transfer orbit between Earth and Mars takes 517 days, and the trip to Mars corresponds to half of this orbit.
01:27But couldn't we travel faster?
01:29Yes, but that would require a lot more fuel, which would complicate the launch because the rocket would be too heavy.
01:36In fact, it would be a bit like a dog biting its tail.
01:40If you could travel at the speed of light, the trip would take you 12.5 minutes.
01:46In addition, when your rocket finally reaches the other planet, it must still slow down to get into orbit around it or to land on its surface.
01:55This means that it will use even more energy, even if there are ways to save a little.
02:00For example, by using parachutes or the aerodynamic braking system.
02:05It's a bit like skateboarding and you have to stop.
02:09You wouldn't crash into a wall, you would use your foot or something else to slow down gradually.
02:17Travelling to Venus is a bit faster.
02:19It would take you about 146 days.
02:22It's not that bad, but the problem is that you would have to wait about 2 years before coming back to Earth.
02:29Indeed, the planets must be properly aligned so that the spacecraft can reach Earth's orbit.
02:36In total, a return trip to Venus would take about 2 years and a month, waiting time included.
02:43And this waiting time would not be very pleasant, since it is the warmest planet in our solar system.
02:50Let's say you wanted to go to Jupiter.
02:54How long will it take?
02:56It depends on a lot of things, especially its position.
02:59In addition, at what speed would you travel?
03:02If you want to use the best of current technology,
03:05know that it took a little more than a year for the fastest spacecraft ever built, New Horizons of NASA, to reach Jupiter.
03:13But don't forget that the New Horizons mission was just a simple overflight.
03:18The probe did not orbit around Jupiter.
03:21If you wanted to stay in orbit and explore Jupiter up close, it would take much longer.
03:27So it's certainly not a weekend trip.
03:32With the transfer of Oman, it would take you several years to reach Jupiter.
03:37Indeed, the transfer of Oman consists of transferring an object from one orbit to another.
03:42Jupiter is on an orbit higher than that of our planet.
03:45Thus, to make the transfer, your rocket will have to take a trajectory that will lead it to exceed the orbit of our gas giant.
03:53The rocket must therefore accelerate when it approaches Jupiter to avoid falling back to the sun,
03:58then slow down when it exceeds Jupiter to avoid flying into space.
04:03It's a bit like when a car accelerates to climb a hill and slows down to go down the other side.
04:10This is how the probe uses Jupiter's gravity to get into orbit around this planet.
04:17It is difficult to determine the exact distance between Jupiter and Earth.
04:21They both rotate around the sun following different oval trajectories.
04:26Sometimes they are very close to each other, and sometimes they are very far away.
04:31In short, they constantly play with cats and mice.
04:34But on average, they are 714 million kilometers from each other.
04:38When Jupiter is at its maximum distance from Earth, it is at 967 million kilometers.
04:45That's 24,000 times the Earth's circumference.
04:48But if you could go to Jupiter at the speed of light, you would get there in about 40 minutes.
04:54There is a very fast spacecraft that we must talk about.
04:57The Parker Solar Probe.
04:59Imagine that you are on Russian mountains that move at incredible speeds, and even difficult to conceive.
05:07These Russian mountains would actually be our Parker Solar Probe,
05:11which is getting closer and closer to the sun, beating speed records.
05:16During its 10th flight over the sun in November 2021,
05:21the Parker Solar Probe managed to reach a maximum speed of 586,000 kilometers per hour.
05:29This is equivalent to going around the Earth in just a few minutes.
05:33And listen carefully.
05:34When the spacecraft in question gets even closer to the sun in December 2024,
05:40it should reach a speed of 690,000 kilometers per hour.
05:44So it's better to eat light before embarking on such a trip.
05:48Imagine that you are aboard the Parker Solar Probe,
05:52and that you wish to make a detour to visit Jupiter.
05:56If you could travel in a straight line at the same speed as this probe during its 10th flight,
06:01it would only take you 42 days to reach Jupiter when its orbit is close to ours.
06:07At an average distance, it would take about 51 days.
06:11You must also take into account the duration of your trip.
06:15Your rocket can arrive on a planet in two ways.
06:18Either by orbiting around the planet, or by flying over it very quickly.
06:22If the spacecraft is to go into orbit, it must slow down as it approaches the planet.
06:28Imagine that it is gripped by the gravity of the planet,
06:31and that it begins to rotate around it.
06:33It is therefore better to slow down upon arrival.
06:35This means that you have to burn a lot of additional fuel,
06:39and this makes the trip longer.
06:41Here's something interesting.
06:43To travel faster, we can use what is called gravitational assistance.
06:48This means that we use the gravity of the planets and other objects in space
06:52to give us a little push and accelerate our precious rocket.
06:56This is how the traveled probes were able to reach Saturn and beyond.
07:01But even with gravitational assistance,
07:04it still takes a lot of time to travel to other stars.
07:08For example, the closest star to us is Proxima Centauri,
07:12and it is 4.2 light years away.
07:15Let's now change methods to compare with the previous examples.
07:20If we traveled at the same speed as Traveler U,
07:23it would take us 75,000 years to reach it.
07:26If you prefer to go to Uranus,
07:29know that the distance can reach 3 billion kilometers
07:32depending on where the planets are in their orbit.
07:35Traveler 2 took about 9.5 years to reach Uranus.
07:41But Uranus is cold,
07:43and as an ice giant, it does not even have a real surface to land on.
07:47Anyway, most of the planet is made up of turbulent fluids.
07:52Not only would you have nowhere to land,
07:55but your rocket would have trouble crossing the atmosphere of Uranus without a hitch.
07:59The temperatures and pressures there are extreme
08:02and would quickly destroy your precious ship.
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