Billions of years from now, the Sun will swell into a red giant, swallowing Mercury, Venus, and Earth. But that’s not the only way our planet could meet its demise. A new simulation points to the menacing threat of a passing field star that could cause the planets in the solar system to collide or fling Earth far from the Sun.
When attempting to model the evolution of the solar system, astronomers have often treated our host star and its orbiting planets as an isolated system. In reality, however, the Milky Way is teeming with stars that may get too close and threaten the stability of the solar system. A new study, published in the journal Icarus, suggests that stars passing close to the solar system will likely influence the orbits of the planets, causing another planet to smack into Earth or send our home planet flying.
In most cases, passing stars are inconsequential, but one could trigger chaos in the solar system—mainly because of a single planet. The closest planet to the Sun, Mercury, is prone to instability as its orbit can become more elliptical. Astronomers believe that this increasing eccentricity could destabilize Mercury’s orbit, potentially leading it to collide with Venus or the Sun. If a star happens to be nearby, it would only make things worse.
The researchers ran 2,000 simulations using NASA’s Horizons System, a tool from the Solar System Dynamics Group that precisely tracks the positions of objects in our solar system. They then inserted scenarios involving passing stars and found that stellar flybys over the next 5 billion years could make the solar system about 50% less stable. With passing stars, Pluto has a 3.9% chance of being ejected from the solar system, while Mercury and Mars are the two planets most often lost after a stellar flyby. Earth’s instability rate is lower, but it has a higher chance of its orbit becoming unstable if another planet crashes into it.
“In addition, we find that the nature of stellar-driven instabilities is more violent than internally driven ones,” the researchers wrote in the paper. “The loss of multiple planets in stellar-driven instabilities is common and occurs about 50% of the time, whereas it appears quite rare for internally driven instabilities.”
The probability of Earth’s orbit becoming unstable is hundreds of times larger than prior estimates, according to the study. Well, that just gives us one more thing to worry about.