Understand how Earth's neighboring stars changed the planet's orbit

Year after year, we learn that the planets in our solar system (like our beloved Earth) move slowly around the sun in what appears to be an unchanging motion. However, the Sun, planets, major moons, and dwarf planets (such as Pluto) are in a constant exchange of gravitational energy and can subtly change their orbits every thousand or millions of years.

How scientists can understand such changes determines how reliably they can track planetary orbits. This is known as the time horizon.

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“There is a certain period after that The watch can no longer be returned“, explained Sean Raymond, an astronomer at the Astrophysical Laboratory of Bordeaux and the University of Bordeaux (France), to Eos.

The most accurate calculations of the time horizon on our planet Requires more precise measurements Of the objects in our solar system. Everything from the Sun's slightly non-spherical shape, to the sizes of other objects here (such as planets, dwarf planets, large asteroids, and moons) needs to be accounted for.

Recently, based on a study published in Astrophysical Journal LettersAstronomers have proven this There is another factor that needs to be considered When calculating the Earth's time horizon: Other stars traveling at amazing speeds are close to our home.

The gravitational paths they produce Capable of shortening Earth's time horizon by up to 10%.or Seven million yearsThe study says.

Given this information, it is vital We precisely know Earth's orbital past to understand the architectural history of our solar system and Earth's climate, (also) affected by subtle changes in our planet's orbit.

Verify Earth's orbit by going back in time

• It is known that going back in time (even theoretically) requires accuracy.
• Lead author Nathan Cape, a planetary scientist at the Planetary Science Institute in Tucson, Arizona (USA), and the University of Oklahoma in Norman, explains:
  • Even the smallest doubts On the current mass or position of the body It will grow dramatically Since the orbit goes back millions of years, even previous orbits become very chaotic, Untraceable;
• This principle also applies to weather forecasts: even the smallest uncertainties surrounding weather forecast models mean unreliable forecasts beyond a few days in advance.

Sometimes, astronomers know the positions of objects in the solar system to an accuracy of one meter, but “an error of one meter is spread across Jupiter's position, and in this way, It is impossible to return as much as we want“says Raymond, co-author of the study.

Time horizon

The so-called Earth time horizon currently being considered is 60 million to 70 million years ago. Moreover, the orbit of our planet Too uncertain to be traceableas well as for paleoclimatologists to consider it as a cause of major climate changes.

Despite this situation, the most accurate calculations of the time horizon assume that our solar system exists in isolation, and is not affected by events in the Milky Way, according to Cape.

But astronomers know that the Sun does receive “visits” from other stars and they estimate that on average there are 20 stars about three light-years away from our main star every million years.

However, it is still uncertain how much influence gravity would have on the solar system, and thus how it would affect our time horizon.

study

Using computer simulations, the study team traced what Earth's orbit would have been like 150 million years ago, taking into account the gravitational effects of the solar system's planets, as well as Pluto and several related asteroids.

From here, they were able to discover that the Earth's orbit had become too uncertain, thus preventing it from being tracked after about 67 million years, confirming the time horizon calculations made previously.

They then placed the solar system they simulated in the “sol neighborhood” and let the stars pass through it, as they would in real life. It was then discovered that if the passing star was large enough, moved slowly enough, or was several light-years away from the Sun, its gravity would disrupt the orbits of the exoplanets.

These instabilities affected the Earth's orbit and shortened its time horizon by between five million and seven million years, or between 7% and 10%.

Check out an example of the simulation in the video below:

“The study is interesting and suggests that passing stars may have to be added to the list of small influences on the orbital evolution of the solar system,” said Richard Zippy, a physicist at the University of Hawaii at Manoa, Honolulu (USA). Who did not participate in the study.

Current models of orbital evolution already include small impacts from asteroids, solar quadrupole moments, tidal dissipation, and solar mass loss, according to Zippy.

The horizon remains unchanged

The authors of the research were able to prove that a chance encounter between the Sun and another star could, at least in theory, change the Earth's orbit. Let's see if this really happened:

Recent data collected by the European Space Agency's (ESA) Gaia mission, which has mapped the positions and movements of millions of stars in our galaxy, show that a Sun-like star, called HD 7977, passed through our solar system about 2.8 million years ago.

We don't know how close it was to the Sun, but there is a 5% chance that it passed within 3,900 AU of our main star, or about 100 times the distance between the Sun and Pluto.

In other words, if HD 7977 passed close to the Sun, simulations conducted during the study showed that the gravity of the “visiting” star would resonate across the solar system, slightly extending and shortening Earth’s orbit. Its time horizon is only 50 million years.

This modified time horizon, generally a limit on how far scientists can estimate the influence of Earth's orbit on its climate, places it within a range of ancient climate change called the Paleocene-Eocene Thermal Maximum (PETM).

Geological records from about 55 million years ago indicate an increase of more than 5°C in Earth's average temperature which may have been caused by a change in the planet's orbit.

The idea that passing stars are important drivers of ancient climate should be viewed with caution. Opportunities to meet stars [como] With HD 7977 to be relevant to our calculations or understanding of PETM is too small.

Richard Zippy, physicist at the University of Hawaii at Manoa, Honolulu (USA), in an interview with Eos

“Maybe including stellar encounters in astronomical models could make a little difference in the calculations, but not in the data,” according to Zippy, which also suggests that the geological data from the event clearly describe what happened.

According to Cape and Raymond, although post-encounter simulations with HD 7977 showed consistency with the PETM geological record, the star did not cause the warm climatic period, nor did they state that the calculated time horizon should be accepted as is.

They also emphasized that the model lacks many fine details, such as tides and a non-spherical Sun or Moon, found in more complex time horizon calculations.