According to a press statement from NASA on 18 January, our solar system’s beloved yellow star is slowly succumbing to the heartless process of time. As a result, our sun is losing mass, which makes its gravitational pull weaker.
This is causing the orbits of all the planets in our solar system to very slowly expand, not unlike “the waistband of a couch potato in midlife,” as NASA says.
A team of researchers from the Massachusetts Institute of Technology (MIT), University of Maryland, and the NASA Goddard Space Flight Center published a paper in Nature, which shows that our sun is acting in according with Albert Einstein’s theory of general relativity.
How did they figure this out? By studying Mercury.
Like humans, our Sun loses mass as it ages, weakening its gravitational pull. To study the dynamics of our aging star, @NASASun researchers have enlisted Mercury, the smallest, innermost planet in the solar system. See how: https://t.co/IaUqVgW9Zx pic.twitter.com/a8U55nPdsJ
— NASA (@NASA) January 19, 2018
In 2015, NASA’s MESSENGER probe crashed into Mercury (they do this a lot), putting an end to its probing. The seven years’ worth of data that it managed to gather before its murder-suicide has allowed the researchers to estimate the sun’s life cycle and apply the general theory of relativity to it.
“Mercury is the perfect test object for these experiments because it is so sensitive to the gravitational effect and activity of the sun,” says lead author Antonio Genova, an MIT researcher at NASA’s Goddard Space Flight Center.
In a nutshell, Einstein’s theory of general relativity posits that the gravitational fields of massive objects like the sun and other stars actually bend or distort spacetime, making gravity the geometric property of the observable universe.
As the New Scientist puts it: “Einstein proposed that objects such as the sun and the Earth change [spacetime’s] geometry. Although Earth appears to be pulled towards the sun by gravity, there is no such force. It is simply the geometry of space-time around the sun telling Earth how to move.”
“We’re addressing long-standing and very important questions both in fundamental physics and solar science by using a planetary-science approach,” Goddard geophysicist Erwan Mazarico said. “By coming at these problems from a different perspective, we can gain more confidence in the numbers, and we can learn more about the interplay between the sun and the planets.”
That bending or warping effect that Einstein predicted affects Mercury’s orbit, just as it affects the rest of the planets in the solar system.
The researchers found that general relativity predicts Mercury’s orbital path, proving Einstein right once again. Having said that, most things in science are open to critique and change. That’s how science is supposed to work, after all.
“The study demonstrates how making measurements of planetary orbit changes throughout the solar system opens the possibility of future discoveries about the nature of the sun and planets, and indeed, about the basic workings of the universe,” co-author Maria Zuber, vice president for research at MIT, said in the NASA statement.