by Stars interfering with the sun’s cosmic backyard may have shifted Earth’s orbit in the distant past, triggering major climatic events in our planet’s history.
The gravitational influence of these invading stars also affected the orbits of the other planets in the solar system, causing minor deviations known as perturbations.
New research looks at the effect of these encounters between the sun and other stars on backward forecasts of the Earth’s orbit around its star and the climate effects resulting from changes in that orbit and the orientation of our planet.
“Perturbations vary – a small deviation in the course of a celestial body, due to the gravitational attraction of a neighboring body – from stars passing over the long-term orbit of the sun’s planets, including the Earth,” said the head of the research team Nathan Kaib, a senior scientist at the Planetary Science Institute in Tucson, Arizona, in a statement.
“One reason this is important is because the geological record shows that changes in the Earth’s orbit are accompanied by fluctuations in the Earth’s climate,” Kaib said. “If we want to do the best search for the causes of ancient climate anomalies, it is important that we have an idea of what the Earth’s orbit looked like during those events.”
Related: Climate change: Causes and effects
As the sun and other stars orbit the center of the Milky Way galaxy, they occasionally pass each other in close proximity, cosmetically speaking.
The sun is thought to come within 50,000 AU of another star every million years or so, and within 20,000 AU of a neighbor every 20 million years or so, on average. (One AU, or astronomical unit, is the average distance of the Earth-Sun – about 93 million miles, or 150 million kilometers.)
So, over the 4.6 billion years that the solar system has existed, it has been affected by many of these interstellar encounters. The new research is the first to include such events in the “reverse forecasts” of our planet’s orbit and climate that are used to predict the orbital evolution of Earth and the other solar system planets.
The orbits of the Solar System’s giant planets, Jupiter, Saturn, Uranus and Neptune, play a role in the Earth’s orbit — the amount it pulls around the sun on the balanced circle.
Stars passing the solar system disturb the orbits of these giant planets and this, in turn, changes the Earth’s trajectory around the sun. This means that the giant planets act as links between the passing stars and the Earth’s orbit.
Like forward-looking weather forecasts, the more time backward climate models try to cover, the more uncertainties grow. Kaib and his team found that when interstellar interactions are factored in, orbital uncertainties grow rapidly and models quickly become unreliable.
This has two major consequences, according to the researchers. First, scientists were overconfident in predicting the Earth’s orbit and eccentricity accurately at certain points in our planet’s history. Second, there are points in Earth’s history when stellar encounters may have involved certain orbital regimes — long periods of very high or low eccentricity — that are not seen in current models.
Kaib said the Paleocene-Eocene Thermal Maximum that occurred about 56 million years ago may be one example of such an event, when Earth’s temperature rose 9 to 14 degrees Fahrenheit (5 to 8 degrees Celsius).
“It has already been suggested that Earth’s orbital eccentricity was extremely high during this event, but our results show that passing stars make detailed predictions of Earth’s orbital evolution in the past very uncertain, and that a wider spectrum of orbital behavior is possible than previously thought. ,” explained Kaib.
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Kaib and his colleagues were able to identify a recent stellar encounter between the sun and a star entering the solar system’s cosmic neighborhood. There is great uncertainty about how far the star HD 7977 passed the sun about 3 million years ago, with estimates ranging from 4,000 AU to 31,000 AU. But, if it was something close to the encounter, it is possible that forecasts back from the Earth’s orbit would be even more unreliable.
That encounter was “powerful enough to change the predictions of Earth’s orbit simulations about 50 million years ago,” Kaib concluded. “At larger contact distances, HD 7977 would not have a significant impact on Earth’s contact distance. Near the smaller end of the range, however, it is likely to change our predictions of Earth’s orbit in past.”
The team’s research was published online February 14 in Astrophysical Journal Letters.
