Lagrange Points - Space Fly Fly

    "They are often called" a place where there is no gravity. " Huge outer spaces, millions of kilometers long, where gravity does not work, areas that capture and do not release any object that gets there. Astronomers call them Lagrange points or, briefly, L4 and L5. ” Under the cut - a huge article about them, darlings.

    (Article by Stuart Clark, New Scientist ), rather large. Shortened translation)

    For 4.5 billion years since the formation of the solar system, everything - from dust clouds to asteroids and hidden planets - could collect and accumulate in them. Some semi-scientific publications even claim aliens who have hidden in L4 and L5 and have been observing the Earth from their saucers.

    If we ignore the green men for a second, even the very presence at the points of old cosmic rock fragments can make many scientists happy. “I think in L4 and L5 you can really find a whole“ population ”of diverse objects,” says astrophysicist Richard Gott of Princeton University.

    After a century of scientific speculation, we finally came to find out what is hidden at the points of Lagrange. This year, a little later, two spacecraft that are still engaged in the study of the Sun, reached spaces L4 and L5.

    Astronomers plan to use the instrumentation aboard NASA's STEREO A and B space probes to search for celestial bodies that are supposedly hidden in the areas of the Lagrange points. Their findings could significantly affect our understanding of how the Solar System was formed, of those colossal interactions that formed the Moon and, perhaps, to warn us against future collisions.

    The Lagrange points were first discovered in 1772 by the mathematician Jose Louis Lagrange. He calculated that the gravitational field of the Earth should neutralize the gravitational attraction of the Sun in five areas of space - in fact, the only areas where the object can really become weightless.
    Of the five points, L4 and L5 are the most intriguing. They are the only stable areas if the satellite enters L1 or L2, after a few months it “lets go” and it flies further, but any object that comes into view of L4 or L5 will remain there for a very long time, if not forever. They are located at a distance of 150 million km from the Earth, on the plane of the Earth’s orbit, with L4 orbiting the Sun 60 degrees ahead of the Earth, and L5 is at exactly that angle behind the planet.

    Around other planets, evidence of the same areas is observed. In 1906, Max Wolf discovered an asteroid located beyond the main belt between Mars and Jupiter, and realized that it was in L4 of Jupiter. Wolf called him Achilles, and thus founded the tradition of naming such asteroids by the names of participants in the Trojan War. The realization that Achilles might fall into such a trap lifted a wave of searches for additional examples. Now about 1000 asteroids caught by the Jupiterian points of Lagrange are known.

    The search for "Trojan" asteriods near other planets is not very successful so far. Near Saturn, they could not be found; near Neptune they found exactly one. And, naturally, they became interested in the Earth.
    The only problem is that points L4 and L5 are difficult to observe from Earth. They are located close to the Sun, so that at night the L5 region is above the horizon and quickly falls, and L4 is eclipsed by the dawn rays.

    Which did not stop Paul Weigert from the University of Eastern Ontario, Canada, from conducting a series of searches in the 1990s using the Franco-Hawaiian telescope on Mount Mae Kea, Hawaii. This was a rather difficult task, since L4 and L5 occupy more visible areas in the sky than the Moon on the full moon. Unfortunately, the Weigert team was not able to find any interesting things.

    Closer to our time, an automatic search such as the Lincoln Near Earth Asteroid Research project has also begun to focus on the Lagrange areas, but so far nothing has been discovered there. “This line of research has faded away because everyone is sitting and waiting for someone else to make a discovery,” says Weigert.

    STEREO KA can change things - even though the probes were not specifically designed to search for asteroids. They were launched in 2006, one in front of the Earth, the other behind, so now they can explore the space between the Earth and the Sun, mainly studying solar storms that could damage orbiting satellites or equipment on Earth. Just L4 and L5 are very successful “observation points” for solar activity “We even talked about stopping the probes when they reach these areas, because anyway it takes several days for accurate recordings,” says Michael Keyser of the Space Center flying to Goddard in Greenbelt, Maryland, is also a member of the STEREO project.
    In fact, the STEREO project team believes that stopping their probes in zones L4 and L5 requires too much fuel consumption. Therefore, the probes will tune to a very slow "span", though not so slow as to fall into a gravitational trap.

    In this regard, Richard Harrison of the Rutford Appleton Laboratory in Oxfordshire came up with the idea that the probes can be loaded with another task. He explored all the possibilities and realized that the tools designed to obtain heliospherical images can be reconfigured to search for asteroids. Even in this case, it will be very difficult to find a Trojan asteroid, since it will be a point moving against the background of thousands of stars. Fortunately, a team of volunteers has already formed who will study the pictures in detail.

    If the asteroid is still found, by changing the sunlight reflected on its surface, it will be possible to determine its rotation and predict the location of other asteroids at the Lagrange points. And then, perhaps, the answer to the question will appear: why does the Earth have such a massive satellite? Now most scientists are sure that the moon was formed from space debris, or rather, the debris left after an object the size of Mars crashed into the Earth about 4 billion years ago. The problem is to explain where he could come from. Because, as computer models of the situation show, all objects of this size entering the solar system would have to destroy the Earth in a collision, instead of decaying into pieces themselves and forming satellites. So such an object should have arisen “near”, not to have enough time to accelerate before the collision. Another confirmation of the proximity of such a body is the discovery in the lunar matter of the same amount of oxygen isotopes that is characteristic of the Earth. Mars, for example, is characterized by a different ratio. But it remains unclear how such a large celestial body could form close to the Earth and not collide with it. If only the formation did not occur at the points of Lagrange. And as soon as the object reached a certain size, the attraction of other planets, for example, Venus, tore it from this area and forced it to crash into the Earth. “The same amount of oxygen isotopes with the Earth could be explained by the fact that its formation occurred close to the Earth,” Gott says. In addition, being in the same orbit, both planets could not differ too much in speed, when the collision occurred. And, if at the Lagrange points near the Earth it will be possible to detect the remnants of the formation of such a planet and prove that their oxygen isotope content is common with the earth, in fact, the theory will be almost proved.

    If asteroids are found, they are unlikely to be more than a kilometer in diameter, says Weigert. Despite the fact that the average size of the asteroids of the main belt is 100 kilometers.

    In the end, you can add a little yellowness to the expectations of the discovery: some astronomers suggest that a whole planet may be hiding at the points of Lagrange. “No way,” says Paul Weigrt. “There isn’t the right amount of substance to form such a large body,”
    But 4.5 billion years ago the situation was different: the planets were formed from a mixture of dust and gas, and L4 and L5 were just the right “batteries" for large celestial bodies to appear there. Nothing of planetary size, but Richard Gott believes that threatening asteroids might still be hiding there. “If we could find something big enough, it would be like a wound bomb,” because the gravitational influence of other planets, especially Venus, could “ pull away ”such an asteroid just enough distance to bring it out of the Lagrange point. And send it to Earth.

    “If we see a big enough asteroid there, we just blow it up and take the wreckage,” Gott says.

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