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The Planetary Science Institute published this story on February 14, 2024. Edits by EarthSky.<\/p>\n
Stars that pass by our solar system have altered the long-term orbital evolution of Earth, and, by extension, modified our climate.<\/p>\n
That\u2019s according to Nathan A. Kaib, senior scientist at the Planetary Science Institute in Tucson, Arizona. Kaib is lead author of Passing Stars as an Important Driver of Paleoclimate and the Solar System\u2019s Orbital Evolution, a new paper published on February 14, 2024, in the peer-reviewed Astrophysical Journal Letters<\/em>. His work shows how perturbations caused by passing stars \u2013 minor deviations in Earth\u2019s path, caused by the pull of gravity from objects passing near \u2013 can alter Earth\u2019s path over the long term. And he said: <\/p>\n One reason this is important is because the geologic record shows that changes in the Earth\u2019s orbit accompany fluctuations in the Earth\u2019s climate. <\/p>\n If we want to best search for the causes of ancient climate anomalies, it\u2019s important to have an idea of what Earth\u2019s orbit looked like during those episodes.<\/p>\n<\/blockquote>\n EarthSky lunar calendars are back in stock! And we\u2019re guaranteed to sell out, so get one while you can. Your support means the world to us and allows us to keep going. Purchase here.<\/p>\n Sean Raymond at the Laboratoire d\u2019Astrophysique de Bordeaux also contributed to this work. And, according to their study: <\/p>\n One example of such an episode is the Paleocene-Eocene thermal maximum 56 million years ago, where the Earth\u2019s temperature rose 5-8 degrees Celsius (9-14 Fahrenheit). It has already been proposed that Earth\u2019s orbital eccentricity \u2013 how much Earth\u2019s orbit deviates from a perfect circle \u2013 was notably high during this event. <\/p>\n But our results show that passing stars make detailed predictions of Earth\u2019s past orbital evolution at this time highly uncertain, and a broader spectrum of orbital behavior is possible than previously thought.<\/p>\n<\/blockquote>\n Kaib and Raymond used backward-running computer simulations to predict the past orbital evolution of Earth and the sun\u2019s other planets. Like weather forecasting, this technique gets less accurate the longer the period of the forecast. Previously, these scientists did not consider the effects of stars passing near the sun in these \u201cbackwards forecasts.\u201d<\/p>\n As the sun and other stars orbit the center of the Milky Way, they inevitably can pass near one another, sometimes within tens of thousands of astronomical units (AU or Earth-sun units). These events are are known as stellar encounters<\/em>. <\/p>\n For instance, a star is thought to pass within 50,000 AU of our sun about every 1 million years. And a star is thought to pass within 10,000 AU of our sun about every 20 million years. This study\u2019s simulations include these types of events. In contrast, Kaib and Raymond said, most prior similar simulations did not.<\/p>\n Also, one major reason the Earth\u2019s orbital eccentricity fluctuates over time is because Earth is regularly pulled upon by the giant planets of our solar system: Jupiter, Saturn, Uranus, and Neptune. As stars pass near our solar system, they perturb the giant planet\u2019s orbits, which consequently alters the orbital trajectory of the Earth. <\/p>\n Thus, the giant planets serve as a link between the Earth and passing stars.<\/p>\n Kaib indicated that \u2013 when simulations include stellar passages \u2013 orbital uncertainties grow even faster. So, the time horizon beyond which these backwards simulations\u2019 predictions become unreliable is more recent than previously thought. <\/p>\n This means two things. First, there are past epochs in Earth\u2019s history where our confidence in what Earth\u2019s orbit looked like (for example, its eccentricity, or degree of circularity) has been too high. At times in the past, the real state of Earth\u2019s orbit is unknown. And, second, the effects of passing stars make regimes of orbital evolution (extended periods of particularly high or low eccentricity) possible and not predicted by past models. Kaib said: <\/p>\n Given these results, we have also identified one known recent stellar passage, the sun-like star HD 7977 which occurred 2.8 million years ago, that is potentially powerful enough to alter simulations\u2019 predictions of what Earth\u2019s orbit was like beyond approximately 50 million years ago.<\/p>\n<\/blockquote>\n And the current observational uncertainty of HD 7977\u2019s closest encounter distance is large, ranging from 4,000 AU to 31,000 AU. So Kaib concluded: <\/p>\n For larger encounter distances, HD 7977 would not have a significant impact on Earth\u2019s encounter distance. Near the smaller end of the range, however, it would likely alter our predictions of Earth\u2019s past orbit.<\/p>\n<\/blockquote>\n\n
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Simulations predict the past orbit of Earth<\/h3>\n
Dealing with orbital uncertainties<\/h3>\n
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Star HD 7977 Can Alter Earth\u2019s Orbit<\/h3>\n