'The problem with trying to predict the gravitational interactions of many-body systems like the solar system or nearby stars is that they're chaotic, meaning they're impossible to predict with any certainty,' DiGiorgio said. So could their orbits grow unstable enough to one day influence Earth's orbit, hurling it closer to or farther from the sun? Or might some other rogue body pass close enough to the solar system to have a similar effect? Recent work suggests the orbits of Jupiter and other planets in the solar system have changed over time. 'This will render the Earth uninhabitable to humans long before the sun ever potentially swallows it.' Rogue influence The bigger thing to worry about 'is that as the sun evolves over the next 5 billion years, stellar evolution models predict that it will increase in brightness by about 6% every 1 billion years, slowly increasing Earth's temperatures and boiling off the oceans,' DiGiorgio said. Related: What's the maximum number of planets that could orbit the sun? 'This is relatively small compared to the normal variations in the sun's brightness that happen due to the Earth's elliptical orbit, so it's not much to worry about.' Given that Earth's distance from the sun may grow by 0.2% over the next 5 billion years, 'this dimming corresponds to a 0.4% reduction of solar energy hitting the Earth's surface,' he said. 'As the Earth moves away from the sun, the sun's light will become dimmer,' DiGiorgio said. Might Earth's growing distance from the sun influence Earth's climate? However, these tidal forces have a very weak effect on Earth's orbit: They cause Earth to move about 0.0001 inch (0.0003 cm) away from the sun every year, DiGiorgio calculated. (A similar effect is leading Earth's moon to slowly drift away from our planet (opens in new tab).) The bulge's mass has a gravitational pull associated with it, tugging Earth ahead on its orbit and slinging it farther from the sun, Scharringhausen noted. Because this is faster than the 365 or so days it takes for Earth to complete an orbit around the sun, the tidal bulge Earth generates on the sun sits ahead of Earth.

The sun rotates on its axis about once every 27 days, according to NASA (opens in new tab).

This stretches the side of the sun that faces Earth, resulting in a 'tidal bulge,' Britt Scharringhausen, an associate professor of physics and astronomy at Beloit College in Wisconsin, wrote for Cornell University's Ask an Astronomer (opens in new tab) page. Just as the moon's gravitational pull results in tides on Earth, so does Earth's gravity tug on the sun. 'This is pretty negligible, especially compared to the normal variation in Earth's orbital distance that happens because of its slightly elliptical orbit - about 3%,' DiGiorgio said. But we shouldn't throw the sun a bon voyage party just yet. Because the sun is losing mass, its pull on Earth is weakening, leading our planet to drift away from our star by about 2.36 inches (6 centimeters) per year, DiGiorgio said. The strength of an object's gravitational pull is proportional to how much mass it has. 'It's about the same amount of mass as Jupiter.' Jupiter, in turn, is about 318 times Earth's mass, according to the Exploratorium (opens in new tab) in California. Although 0.1% may not sound like a lot, 'this is a lot of mass,' DiGiorgio said.

Earths orbit