Looking at Mercury Reveals How the Sun is Losing Its Mass

Sunday, 21 January 2018 - 3:19PM
Space
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Sunday, 21 January 2018 - 3:19PM
Looking at Mercury Reveals How the Sun is Losing Its Mass
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NASA Goddard
The sun is losing mass very, very slowly. This is mostly normal -  as it goes about its nuclear fusion process, it gradually converts mass into energy and then radiates that energy out into the solar system.

So what does this mean for the rest of the solar system? Eventually it's going to have some Earth-destroying implications, but that's a few billion years down the line. For now, it's beginning to throw some orbits out of whack, according to a group of researchers at NASA and MIT who thought they could use a planet's orbit to learn more about the sun.

Mercury, being the closest planet to the sun, is showing the most signs of change as its own orbit begins shifting. The researchers, who just published their findings in Nature Communications, have been charting a road map of Mercury's orbit (which is called an "ephemeris") and studying various changes in that road map, especially its closest point to the sun and its farthest point from the sun.

These two points, called the perihelion (when it's closest to the sun) and aphelion (farthest from the sun) can be altered by other planets in the solar system, who exert their own gravitational pull over tiny Mercury, but those aren't strong enough to account for all the changes. Something else must be messing with Mercury, and the pull of other planets had to be removed from the equation. 




There are plenty of other factors that could change Mercury's orbit as well, including factors related to Einstein's theory of general relativity: because the sun is so massive, it's capable of warping spacetime to the point that this, too, can impact Mercury's orbit. So all of these factors had to be separated, if anyone wanted to get a specific look at how much the sun's loss of mass was impacting all this.

Eventually the researchers did separate it all, creating a new process where they examined both Mercury's orbit, and the orbit of the MESSENGER probe that circled Mercury until its fiery death back in 2015, when it crashed into the planet's surface. Using all this data, they could get a look at how the sun's internal workings were shifting and impacting Mercury. According to Goddard geophysicist Erwan Mazarico:

Opening quote
"We're addressing long-standing and very important questions both in fundamental physics and solar science by using a planetary-science approach. 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."
Closing quote


In the end, the researchers found that Mercury's changing orbit meant the sun was losing 0.1 percent of its mass over a period of ten billion years - a very small amount, but significant enough to shuffle things around the solar system just because the sun is so massive. This matches up with previous predictions, but it had never been observed like this before.

So how does the sun losing that tiny amount of its mass change things? It means that every planet, Earth included, could be pushed back by up to half an inch per year.

Like we said, a tiny loss of mass in our giant local star can make ripples throughout our solar system, so we should know what's going on.
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