A quarter of Sun-like stars eat their own planets, new study finds

How rare is our solar system? In the roughly 30 years since planets were first discovered orbiting stars other than our Sun, we have discovered that planetary systems are common in the Galaxy. However, many of them are quite different from the solar system as we know it.

The planets in our solar system orbit the Sun in stable, almost circular paths, suggesting that the orbits haven’t changed much since the planets were formed. But many planetary systems orbiting other stars have suffered from a very chaotic past.

The relatively calm history of our solar system has fostered the flourishing of life here on Earth. In the search for alien worlds that may contain life, we can narrow down targets if we have a way to identify systems that have had an equally peaceful past.

Our international team of astronomers addressed this question in research published in Nature Astronomy. We have found that between 20% and 35% of Sun-like stars eat their own planets, the most likely figure being 27%.

This suggests that at least a quarter of the planetary systems orbiting stars similar to the Sun have had a very chaotic and dynamic past.

Chaotic stories and binary stars

Astronomers have seen several exoplanetary systems in which large and medium-sized planets have moved significantly. The gravity of these migrating planets may also have disrupted the trajectories of other planets or even pushed them into unstable orbits.

In most of these very dynamic systems, it is also likely that some planets have fallen into the host star. However, we didn’t realize how common these chaotic systems are compared to quieter systems like ours, whose orderly architecture has fostered the flourishing of life on Earth.

Even with the most accurate astronomical instruments available, it would be very difficult to determine this by directly studying exoplanetary systems. Instead, we analyzed the chemical makeup of stars in binary systems.

Binary systems are made up of two stars orbiting each other. The two stars were generally formed at the same time from the same gas, so we would expect them to contain the same mixture of elements.

However, if a planet falls into one of the two stars, it dissolves into the star’s outer layer. This can change the star’s chemical makeup, which means we see more of the elements that make up rocky planets – like iron – than we otherwise would.

Traces of rocky planets

We have inspected the chemical composition of 107 binary systems composed of stars similar to the Sun by analyzing the spectrum of light they produce. From there, we established how many stars contained more planetary matter than their companion star.

We also found three things that add up to unambiguously prove that the observed chemical differences between the binary pairs were caused by the diet of the planets.

First, we found that stars with a thinner outer layer have a higher probability of being richer in iron than their companion. This is consistent with eating planets, because when the planetary material is diluted into a thinner layer, it further changes the chemical composition of the layer.

Second, stars richer in iron and other elements in rocky planets also contain more lithium than their companions. Lithium is quickly destroyed in the stars, while it is stored in the planets. Thus, an abnormally high level of lithium in a star must have arrived after the star formed, which corresponds to the idea that lithium was carried by a planet until it was eaten by the star. .

Third, stars that contain more iron than their companion also contain more similar stars in the Galaxy. However, the same stars have Standard abundance of carbon, which is a volatile element and for this reason is not transported by rocks. Therefore, these stars were chemically enriched by rocks, either from planets or from planetary materials.

Hunt for Earth 2.0

These results represent a breakthrough for stellar astrophysics and the exploration of exoplanets. Not only have we discovered that eating planets can change the chemical makeup of Sun-like stars, but also that a significant fraction of their planetary systems have had a very dynamic past, unlike our solar system.

Finally, our study opens up the possibility of using chemical analysis to identify the stars most likely to harbor true analogues of our calm solar system.

There are millions of relatively nearby stars similar to the Sun. Without a method for identifying the most promising targets, the search for Earth 2.0 will be like the search for the proverbial needle in a haystack.