In 2021 and 2023, NASA will launch two space probes called Lucy and Psyche. Lucy will visit Trojan asteroids, while Psyche will fly to a lone asteroid of pure metal.
NASA is currently developing two space probes - Lucy and Psyche - whose mission is to educate us on how the solar system came to be, visiting a total of eight asteroids orbiting Jupiter from 2025 to 2033.
The names of the probes were not chosen by chance: "Lucy" is the name given to the remains of our very distant ancestor 3.2 million years old, and it is very suitable, explains the head of the "Lucy" project Harold Levison:
"These little asteroids are actually remnants from planetary formation, which is why we named our probe Lucy after one of our human ancestors."
The space probe "Psyche" got its name differently - in honor of that lonely asteroid, consisting almost exclusively of metal, to which it will fly.
Kingdom of Jupiter
Jupiter is the largest planet in the solar system with a huge gravity corresponding to its size. And with the help of this power, Jupiter controls asteroids for many kilometers around it.
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In the same orbit as Jupiter, only 60 degrees in front of and 60 degrees after the planet, there are many asteroids captured by Jupiter, which have accumulated in the so-called L4 and L5 Lagrange points (read about Lagrange points at the end of the article).
They were named "Trojan Asteroids" in honor of the Trojan War. The asteroids at the L4 Lagrange point are named after the Greek heroes, and those at the L5 point are named after the heroes of Troy. In total, both groups contain up to a million asteroids, whose magnitude exceeds a square kilometer.
Lucy will be the world's first space probe to visit Trojan asteroids, and this visit, scientists hope, will shed light on the formation of the solar system. Because, although the asteroids belong to the kingdom of Jupiter, they are strikingly different from their surroundings and from each other. This means that they most likely formed in various places in the solar system.
When the solar system was very young, the planets did not yet have their modern orbits, they just moved "at random." When large, heavy planets like Jupiter, Saturn, Uranus and Neptune passed by, they caused total chaos among the millions of large and small asteroids that were also in the solar system.
Many of these asteroids were generally thrown out of the solar system, and some of them were captured by the powerful Jupiter, and it is they who are now called Trojan asteroids.
The story of the solar system
Harold Levison of Project Lucy put it this way: “One of the striking features of Trojan asteroids is that they are very different. When we look at them through a telescope from here on Earth, we see that they have very different colors and spectra. And therefore, we believe they will tell us something about how the solar system came into being and developed. We believe that the diversity is due to the fact that asteroids formed in different places in the solar system with different physical characteristics. But during the evolution of the system, they traveled all over the place until they completed their journey in orbit around Jupiter."
Long journey "Lucy"
Believe it or not, the Lucy space probe will also visit Greek heroes at L4, and then Trojan heroes at L5. This is a great achievement, because L4 and L5 are located at a distance of a billion kilometers from each other, each group on its own side of Jupiter, so to speak.
The space probe will be launched in 2021 and en route to L4 in April 2025, it will fly past a small asteroid, just four kilometers in size, with the apt name 52246 Donaldjuhansson, which was dubbed after the archaeologist who found the remains of the hominid Lucy in Ethiopia in 1974. It seems that the trajectory of the flight has suddenly very well coincided with the name of the probe - but then I have a question, did the same team that is engaged in Project Lucy give the name to the small asteroid?
Some problem is that "Lucy" will fly by asteroids at a speed of over 20,000 km per hour. Therefore, there will be only very little time to inspect each individual asteroid.
The reason is that there is no way to give Lucy with it as much fuel as the probe would need to slow down and fly past. The space probe weighs 1,435 kg, and most of that weight is made up of instruments, radio transmitters and solar panels.
In 2027, Lucy will reach L4, where it will orbit four very different asteroids next year. The space probe will then leave L4 and continue on a powerful curve through the solar system from point L4 to point L5. It is not at all strange that this journey will take about five years, and in March 2033, the probe will be near two asteroids 100 square kilometers in size, orbiting each other.
Such binary asteroids are rarely found in the inner solar system, as a rule, they are located in the Kuiper belt, beyond the orbit of Neptune - so here Lucy may have the opportunity to look at asteroids that we would otherwise be very far away get.
Psyche - an asteroid made of metal
The journey to the asteroid Psyche has a different purpose. This cosmic body, a good 250 square kilometers in size, is located in the asteroid belt between Mars and Jupiter, it rotates in a slightly elongated orbit at a distance of 2.5 to 3.3 astronomical units (AU) from the Sun, which the asteroid orbits in five years …
It sounds amazing, but Psyche is the only known asteroid that is supposedly made of pure metal. There is a version that Psyche began its existence as the core of a small planet, which was at least 500 km in diameter, and possibly almost as large as Mars.
When the solar system was still quite a "child", there were many collisions between planets and asteroids, and there is a theory that the planet, of which Psyche was a part, after one or several major collisions lost its rocky shell, so that only the core remained.
The only problem with this otherwise remarkable theory is that the remnants of the shell should have been preserved in almost the same orbit as Psyche itself, resembling ordinary rock asteroids. But nothing of the kind was found.
Surface water and molten metal core
In any case, Psyche for us is a unique opportunity to see what the metal core of the planet looks like. We know that the Earth has a core of liquid metal that creates a magnetic field, but there is no way to go down to it. But we can send a space probe on a journey of 300 million kilometers.
The Psyche space probe will be launched in 2023 and will reach its target in five years. The probe will be guided by an ion drive, which will give it the ability to enter orbit around the asteroid Psyche and study it from 2028 to 2030.
It will be an exceptional experience, as we have never seen a pure metal planet before. What does an impact crater look like? Will the drops of molten metal, scattered on impact, have time to solidify again before they fall back?
It was surprising to find traces of water on the surface, but this may be due to collisions with small asteroids containing ice.
But the most important question, of course, is related to magnetism. Today, it is assumed that the magnetic field is born from the rotation of metal cores inside planets large enough to have at least part of the core metal melted.
Psyche with a high degree of probability remained from a rather small planet, which was unlikely to have sufficient size for a liquid core. Therefore, it is very interesting to find out whether she still has traces of a magnetic field from the days when she was still the center of the planet, or, as the expert in this field Lindy Elkins-Tanton put it: “Will Psyche turn out to be a small refrigerator magnet in the middle of space?"
Lagrange points
Like all planets in the solar system, Jupiter has five so-called Lagrange points. These are the places where the small body will follow the planet in such a way that from the planet it will appear motionless.
Those asteroids that Lucy will visit are located at points L4 and L5, 60 degrees before and 60 degrees after Jupiter, but in the same orbit as the planet itself.
Moving at the same speed as the planet
A common misconception is that the forces that affect a small body balance each other at Lagrange points.
This is not true. At each of the five points, a small body is subjected to gravity from both the planet (here - Jupiter) and the sun.
These five points differ in that the sum of these forces in them is just such that a small body begins to turn around the sun at the same speed as the planet and therefore follows it.
This, however, only works when the body is so small that its own gravitational force can be neglected - and this condition is perfectly fulfilled by asteroids.
L4 and L5 stable points
L1, L2 and L3 are unstable points, a small body can jump off them quite quickly. However, it is quite possible to return to them again if you use a little fuel.
L4 and L5 are stable, which means that if a small body does not quite accurately hit one of the two points, then it can orbit around the point.
That is why L4 and L5 in the Sun-Jupiter system are so large that they can accommodate over a million asteroids. Asteroids are not located at the points themselves, but in orbits around them.