I believe you have all seen the pictures of the solar system, based on the earth's orbit (ecliptic plane), although some planets have some small angles between the orbital plane and the ecliptic plane, but these angles are not large, and the overall look is still flat, so if the probe launched by human beings flies up or down, won't it be easy to fly out of the solar system?

This idea sounds plausible, but in fact our impression of the solar system as "flat" is largely misguided, because none of these images are drawn at a 1:0 scale and have undergone a lot of simplification, so that they look like a two-dimensional plane, which is not the case with the solar system.

To find out if a probe can fly out at will, you first have to understand how big the solar system really is. Before the 20th century, astronomers believed that the solar system was the sun plus the known large planets. With advances in observational technology, Pluto was discovered, and later the Kuiper Belt – a ring-like region filled with small icy objects – that expanded the boundaries of the solar system considerably.

However, the true edge of the solar system is the Oort cloud, which is made up of small icy objects left behind by the birth of the sun, covering an area of about 2 to 0 light years, like a huge sphere that envelops the entire solar system.

Since the Oort cloud is a spherical structure, it means that the solar system is not simply a flat plate, but more like a system surrounded by spheres. Therefore, whether the probe is flying upward, downward, or in other directions, the distance to cross the Oort cloud is actually about the same, and there is no such thing as a "shortcut".

Because the sun's gravitational pull is uniform in all directions, it is not feasible for the probe to quickly break free from the gravitational shackles by choosing one direction. When it comes to "flying out of the solar system", there are actually two understandings: one is to fly out of the Oort cloud and completely leave the gravitational range of the solar system; The other is to fly to the place where the Sun's gravity no longer dominates, that is, to enter interstellar space, that is, the junction of the solar wind and the interstellar medium.

目前，人类发射的探测器，比如旅行者1号和2号，已经飞出了太阳风影响的区域，进入了柯伊伯带，距离太阳大约162个天文单位（1天文单位是地球到太阳的距离，约1.5亿公里），然而，它们离奥尔特云还远得很，还得上万年才能接近。

奥尔特云的内边缘估计在2000到5000天文单位，外边缘甚至能达到10万天文单位（约1.6光年）。所以，飞出赫利奥圈只是迈出了第一步，要穿越奥尔特云才是真正的起点。

Since the direction does not affect the distance out of the solar system, why do most probes choose to fly within the ecliptic plane? There are two main reasons. First of all, the planet's gravitational slingshot effect can help the probe accelerate and steer, save fuel and run faster. Secondly, the main targets of planets, moons, and asteroids are near the ecliptic plane, so it is convenient to fly in this direction to explore at close range.

Secondly, if you build a probe simply to "fly out of the solar system" without any scientific tasks, it is no different from throwing a stone into the depths of the universe, and there will be no echo in the next tens of thousands of years, which is meaningless to human beings, so the main purpose of the current artificial probe is to explore the celestial bodies in the solar system, collect data, and fly out of the solar system is just a side result.

For example, Voyager 2 and 0, the original mission was also to explore the outer planets, and after completing the mission, they continued to fly outside the solar system because they could not be recovered, but the Voyager carried a gold-plated record on it, which recorded the sounds and images of the Earth, and scientists hope that it will be discovered by alien civilizations one day in the future.

In general, no matter which direction the probe flies, it flies the same distance out of the solar system, and there is no such thing as "flying upwards faster". But flying along the ecliptic plane is different, the probe can be accelerated by the planet's gravitational slingshot, and it can also save fuel. Therefore, most of the probes launched by humans choose this path, which can not only complete scientific tasks, but also go as far as possible.