Today, we will talk about the second satellite of the earth. Some people say it's just a moon. In fact, there is another celestial body called the Trojan asteroid, which is also bound by the planet's gravity and orbits the planet. So what is the confirmed Trojan asteroid of the earth?
Satellite of the solar system
The solar system is a very magical place. Although we are in the solar system, there are still many unsolved mysteries. Especially, in the inner part of the solar system, think about the gas giant planets in our solar system (such as Jupiter), whose mass ranges from tens to hundreds of times that of the earth.
Above, from left to right: Jupiter, Saturn, Uranus and Neptune
These giant gaseous planets are surrounded by all kinds of interesting and mysterious celestial bodies, ranging from massive satellites with atmosphere, such as Saturn's Titan (left), to captured objects in the Kuiper Belt, such as Neptune's big satellite, Triton (middle), and then to ordinary natural satellites formed around the planets.
national aeronautics and space administration (NASA); Cassini/Huygens (left), Voyager 2 (middle), Cassini (right).
in a word, if we look at all the satellites in the solar system, these gas giants monopolize the satellites in the solar system, both in quality and quantity. If we observe satellites with a diameter of more than 1 kilometers, there are 7 satellites in Jupiter, 11 satellites in Saturn, 8 satellites in Uranus, 6 satellites in Neptune, and even Pluto, which is not a planet, has one, which is the same as the number of satellites in the whole solar system, because only the satellites of the earth in the solar system belong to this category.
Mercury and Venus have no satellites, the earth has only one big satellite, and Mars has two captured asteroids (but each is below 25 kilometers), which we generously call satellites. In contrast, Jupiter has at least 49 satellites less than 25 kilometers, while Saturn has at least 63 satellites, including 2 satellites less than 5 kilometers in diameter, which were discovered this year.
If there are captured asteroids on Mars, our neighbor, is it possible to have captured asteroids on Earth? To understand this problem, we must first understand two different types of capture that may occur.
Trojan Asteroids of Planets
The gravitational interaction between a low-mass celestial body, a planet and the sun may lead to great changes in the orbits of low-mass celestial bodies, and of course, there will be occasional gravitational capture. But gravity capture not only refers to the asteroid's orbit around the planet, but also can move stably (or quasi-stably) at two independent positions before and after the planet's orbit, such as the L4 and L5 Lagrangian points marked above.
Take Jupiter as an example. Jupiter is a typical particle. Although it captures many celestial bodies orbiting itself, there are also a large number of celestial bodies orbiting the L4 and L5 gravitational points of the sun, which share the same orbit with Jupiter and are called Troyes asteroids. (or in more ancient poetic terms,? Trojans? And? Greek? One in L4 and one in L5. )
Troyes asteroids L4 and L5 are shown in green. The above picture shows how Jupiter and these asteroids move in orbit.
The above picture is minus Jupiter's orbital motion
In fact, if any planet is lucky enough, that is to say, if an asteroid breaks into the L4 and L5 points of a planet, it may be captured by the planet's gravity and orbit the planet * * *, then there may be these Trojan asteroids in the orbit of this planet. There are no Mercury and Venus. Mars always has seven candidate Trojan asteroids, four of which have been confirmed!
so you may ask, are there really asteroids in the earth's orbit? Of course, the earth has only one natural satellite orbiting our planet, but what if the earth and other celestial bodies orbit the sun together at (L4) or (L5)?
satellites of the earth? The second moon
3753 Cruithne in p>21. Astronomer Duncan? Waldron discovered this dim asteroid in a photographic negative on October 1th, 1986. This picture was taken by the British Schmidt telescope at the Saidingquan Observatory in Australia.
you may have heard of 3753 Cruithne, which is considered as? The second moon of the earth? . 3753 Cruithne is a rock only 5 kilometers wide, and its orbit follows the orbit of the earth!
what does this mean? It takes about 365 days for the earth to move around the sun. Where is 3753 Cruithne? 364 days! This is a very close number! From the sun's point of view, both celestial bodies are elliptical orbits, the sun is in a focus, and from the earth's point of view, this trailing asteroid is a horseshoe-shaped orbit. Please look at the animation below.
the above picture shows the perspective of the sun. The orbit of 3753 Cruithne has a certain inclination with the orbit of our earth. The picture below shows the perspective of the earth.
but technically speaking, it isn't? Earth's satellite? Because it is not bound by the gravity of the earth and does not orbit the earth. So it's not even a real Trojan asteroid, and 3753 Cruithne is expected to be thrown out of Earth's orbit thousands of years later. 3753 Cruithne will approach the Earth in 2292, and there will be a gravitational encounter between this asteroid and the Earth. By then, the orbit of 3753 Cruithne will change by 5, kilometers. The earth's orbit will change by 1.3 cm.
Is there a satellite in orbit on Earth? In 21, the first and only real Trojan asteroid was discovered!
asteroid 21 TK7! Its diameter is only 3 meters (not kilometers, but meters), which was discovered by NASA's Wide Area Infrared Detector (WISE) in October 21. Yes, it was found with an infrared space telescope!
it runs in a horseshoe orbit around the lagrange point L4 of the earth. if we fly over the solar system and compare it with the earth, the following figure shows its running route.
So, strictly speaking, we don't have a second moon, but we finally have a Trojan asteroid, which moves in a horseshoe-shaped orbit in the earth's orbit under the gravity of the earth, and orbits with the earth. It belongs to our earth.
So the Trojan asteroid is not 3753 Cruithne. It's 21 TK7!