Ageing Sun causing changes in planets

Loss of the star’s gravitational grip is making planets in solar system expand their orbits

The orbits of planets in our solar system are expanding as the Sun ages and loses its gravitational grip, say scientists who have observed changes in the trajectory of Mercury to measure the mass loss of our star. The new values improve upon earlier predictions by reducing the amount of uncertainty.

That is especially important for the rate of solar mass loss, because it is related to the stability of G, the gravitational constant, researchers said. Although G is considered a fixed number, whether it is 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 Antonio Genova, researcher at Massachusetts Institute of Technology (MIT) in the US.

The study, published in the journal Nature Communications, began by improving Mercury's charted ephemeris – the road map of the planet's position in our sky over time. For that, the team drew on radio tracking data that monitored the location of NASA's MESSENGER spacecraft while the mission was active.

The scientists worked backward, analysing subtle changes in Mercury's motion as a way of learning about the Sun and how its physical parameters influence the planet's orbit. For centuries, scientists have studied Mercury's motion, paying particular attention to its perihelion, or the closest point to the Sun during its orbit. –PTI