‘Intruder’ stars have changed Earth’s climate over aeons
Stars intruding into the Sun’s cosmic backyard could have shifted
Earth’s orbit in the distant past, triggering major climate events in our planet’s history. The gravitational influence of these intruder stars has also impacted the orbits of other planets in the Solar System, causing minor deviations called perturbations. “Perturbations – a minor deviation in the course of a celestial body caused by the gravitational attraction of a neighbouring body – from passing stars alter the longterm orbital evolution of the Sun’s planets, including Earth,” research team leader Nathan Kaib, a senior scientist at the Planetary Science Institute in Arizona, said. “One reason this is important is because the geologic record shows that changes in Earth’s orbital eccentricity accompany fluctuations in Earth’s climate. If we want to best search for the causes of ancient climate anomalies, it’s important to have an idea of what Earth’s orbit looked like during those episodes.”
As the Sun and other stars orbit the centre of the Milky Way, they occasionally pass each other relatively closely, cosmically speaking. Over the course of the 4.6 billion years that the Solar System has existed, it has been influenced by many of these stellar encounters.
The new research is the first to factor such events into the ‘backward forecasts’ of our planet’s orbit and climate, used to predict the past orbital evolution of Earth and the other Solar System planets. Stars passing the Solar System perturb the orbits of these giant planets, and this in turn alters Earth’s trajectory around the Sun. This means that the giant planets act as links between passing stars and the orbit of Earth.
Like forward-looking weather forecasts, the more time that backward climate models attempt to cover, the larger uncertainties grow. Kaib and his team found that when factoring in stellar encounters, orbital uncertainties grow rapidly and models quickly become unreliable.
There are two major outcomes of this, according to the researchers. First, scientists have been too confident when predicting Earth’s orbit and its eccentricity accurately at certain points in our planet’s history. Second, there are points during Earth’s history when stellar encounters have made possible certain orbital regimes – extended periods of particularly high or low eccentricity – that aren’t seen in current models. One example of such an episode could be the Paleocene-Eocene Thermal Maximum that occurred around 56 million years ago, during which Earth’s temperature rose by five to eight degrees Celsius (9 to 14 degrees Fahrenheit).