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The proof of Einstein’s theory confirms that the Sun is losing mass

Image: NASA's Goddard Space Flight Center

The best planet, Mercury, is in the middle of telling us something important about our sun: it's losing mass.

Mercury, the planet closest to the sun, has a history of helping us study gravity. Albert Einstein showed that Newton's laws of motion are broken when dealing with very large masses. He created his theory of general relativity to explain this: gravity is a manifestation of the deformation of space-time caused by massive bodies like the sun. Mercury's orbit shows this deformation more clearly, and, in fact, before Einstein's work, scientists were baffled by its strangeness, even attributing it to the gravitational effects of an invented planet called Vulcan. Now, a team of researchers in the USA. UU You are using new measurements of Mercury's orbit to learn more about the sun and more about Einstein's theory.

The researchers set out to perform the largest test of something called the Einstein equivalence principle. As Antonio Genova, the author of the MIT study, described the principle: "You are not able to distinguish between a uniform gravitational field and an accelerated frame of reference". It's like when you're in an elevator: you can feel gravity is pulling you more or less, but you're really accelerating.

Testing this principle requires comparing two ways of calculating mass: one, which is based on how an object behaves in the uniform gravitational field, and another, which is based on how much force is needed to push that object. That's basically comparing how much you weigh on Earth versus if you were on a rocket accelerating to perfectly reproduce the Earth's gravity (approximately 10 meters per second squared).

If those mass values ​​are the same, Einstein's equivalence principle is true. In this case, the researchers were interested in the center of mass of the solar system, the point at which everything, even the center of the sun, travels around. The principle of equivalence would be maintained if we measured the location of the center to be in the same place that would be predicted by the combined gravitational force of the sun on itself and the other planets on the sun. If these locations were different, it would imply that the mass of the bodies he used to calculate the location should differ in some way, and that Einstein's equivalence principle would be incorrect.

Mercury, being so affected by the sun's gravity, offers a way for scientists to discover small differences between the theoretical predictions of the sun's gravity and what we actually observe, by measuring Mercury's orbit for a long time. Fortunately, we have the MESSENGER probe orbiting Mercury to do these calculations.

The MESSENGER data showed that Einstein is still not wrong, of course. With better equipment, scientists may one day perform these tests with even more precision, and perhaps find a place where the measurements differ slightly from their theories. However, that has not happened yet.

The MESSENGER team could also determine how the sun's gravity changes over time, depending on how it loses mass and how that lost mass causes the orbits of the planets to widen. Seven years of data, combined with observations of how the sun consumes its hydrogen fuel, reveal that the sun is fading slowly and slightly on Mercury. This was one of the "first experimental observations of solar mass loss," according to the article recently published in Nature Communications.

Such an effect is minuscule and could cause a widening of the Earth's orbit equal to less than one inch per year. That is practically nothing and it does not matter in your daily life. "This type of information is not a cause for concern," Genova said, "but it could be very useful for monitoring the sun itself." Maybe I could give researchers another way to measure the behavior of the sun's interior.

Astrophysicist Konstantin Batygin of CalTech thought the newspaper was "very sweet," according to an email to Gizmodo. He especially liked that there was virtually no change in the gravitational constant, G, in the different measurements, another proof of the consistency of gravity. Once again, our theories have been confirmed by new precision measurements.

As a reminder, all this data comes with an extension: scientists can always achieve a better certainty of the data with more measurements and better equipment.

More importantly, this should remind you that Mercury is an amazing and useful planet that you must not forget. After all, monitoring continues to support the accuracy of one of the most important theories in physics: the one that describes gravity.

[Nature Communications]

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