Washington, Jan 22 (IANS): Changes in the orbit of Mercury -- the planet closest to the Sun in the solar system -- has demonstrated the repercussions of an ageing Sun.

Like humans, the Sun is losing mass as it ages, weakening its gravitational pull. As a result, the orbits of planets in the solar system are expanding.

In the study, scientists at the National Aeronautics and Space Administration (NASA) and the Massachusetts Institute of Technology (MIT) indirectly measured this mass loss and other solar parameters by looking at changes in Mercury's orbit.

They found key details to monitor the rate of solar mass loss, because it's related to the stability of G, the gravitational constant.

Although G is considered a fixed number, whether it's really constant is still a fundamental question in physics.

"Mercury is the perfect test object for these experiments because it is so sensitive to the gravitational effect and activity of the Sun," said lead author Antonio Genova, a researcher at MIT, working at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

For long, scientists have studied Mercury's motion, and have also charted a road map of Mercury's orbit, called "ephemeris" to study its closest point to the Sun and its farthest point from the Sun.

Other factors that could change Mercury's orbit include Albert Einstein's theory of general relativity, which proves that as a result of the Sun's own gravity, it is capable of warping space time, causing a shift in Mercury's orbit.

The Sun's interior structure and dynamics, one of which is its oblateness -- a measure of how much it bulges at the middle -- rather than being a perfect sphere, can also impact Mercury's orbit.

In the study published in the journal Nature Communications, the team developed a novel technique that simultaneously examined the orbits of Mercury and MESSENGER spacecraft, which probed Mercury till its death in 2015, to learn more about the interplay between the Sun and the planets.