Astronomy: Predicting Earth’s future becomes more difficult – 03/29/2024 – Science

Astronomy: Predicting Earth’s future becomes more difficult – 03/29/2024 – Science

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Regardless of what stock market analysts, researchers and astrologers may say, we cannot predict the future. In fact, we cannot even reconstruct the past.

In 1814, the French mathematician Pierre-Simon Laplace declared that, if it were possible to know the speed and position of each particle in the Universe at a specific moment — and all the forces acting on them —, “for such an intellect nothing would be uncertain, and the future, as well as the past, would be within reach of their eyes.”

Laplace’s dream has not yet come true because we cannot measure things with infinite precision, and so small errors propagate and accumulate over time, leading to greater and greater uncertainty.

In the 1980s, astronomers including Jaques Laskar of the Paris Observatory concluded that computer simulations of the planets’ motions were unreliable when applied more than 100 million years into the past or future — for comparison’s sake, the Universe is 14 billion years old and the Solar System is about 5 billion years old.

This has now become even more complicated. A new set of computer simulations, which take into account the effects of stars passing through our Solar System, have narrowed scientists’ ability to look back or forward by another 10 million years.

Previous simulations considered the Solar System in isolation, a mechanical cosmos in which the main perturbations in planetary orbits were internal, resulting from asteroids.

“Stars matter,” said Nathan Kaib, senior scientist at the Planetary Science Institute in Tucson, Arizona (United States). He and Sean Raymond of the University of Oklahoma published their results in the Astrophysical Journal Letters in late February.

Researchers found that a Sun-like star called HD 7977, which is now 247 light-years away in the constellation Cassiopeia, could have passed close enough to the Sun about 2.8 million years ago to shake up the largest planets. in their orbits.

This additional uncertainty makes it even more difficult for astronomers to look back more than 50 million years, to correlate temperature anomalies in the geological record with possible changes in Earth’s orbit.

Knowing this would be useful as we try to understand ongoing climate change. About 56 million years ago, Kaib said, Earth apparently passed through the Paleocene-Eocene Thermal Maximum, a period more than 100,000 years long during which average global temperatures rose by as much as 8 degrees Celsius.

Was this warm period triggered by some change in Earth’s orbit around the Sun? We may never know.

“I’m not an expert, but I think this is the hottest period in the last 100 million years,” Kaib said. “And it’s almost certainly not caused by Earth’s orbit itself. But we know that long-term climate fluctuations are linked to Earth’s orbital fluctuations. And if you want to understand climate anomalies, it helps to be confident about what Earth’s orbit Is doing.”

“The simulations are carefully done, and I believe the conclusion is correct,” said Scott Tremaine, an orbital dynamics expert at the Institute for Advanced Study in Princeton, New Jersey. “This is a relatively small change in our understanding of the history of Earth’s orbit, but it is a conceptually important change.”

The really interesting story, he says, is how chaos in Earth’s orbit could have left a mark on the paleoclimate record.

The ability to track the movements of stars just beyond the Solar System improved with the European Space Agency’s (ESA) Gaia space telescope in 2013.

“For the first time, we can actually see individual stars, project them back in time or forward, and figure out which ones are close to the Sun and which ones haven’t,” Kaib said. According to his calculations, about 20 stars come within 1 parsec (about 3.26 light years) of the Sun every million years.

In the case of the star HD 7977, gravitational effects from a closer encounter could have shaken the orbits of the outer giant planets, which in turn could have shaken inner planets like Earth.

“This is potentially powerful enough to alter predictions from simulations about what Earth’s orbit was like beyond approximately 50 million years ago,” Kaib said. As a result, he said, almost anything is statistically possible if you look far enough ahead. “You find that, for example, if you go forward billions of years, not all planets are necessarily stable. In fact, there is about a 1% chance that Mercury will hit the Sun or Venus over the next 5 billion years. “

Whatever happens, chances are we won’t be around to see it.

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