💫 The tragic fate of planets around dying stars

A recent study published in the Monthly Notices of the Royal Astronomical Society reveals an impressive phenomenon concerning aging stars. By analyzing nearly half a million stars that have begun their transformation into red giants, astronomers have discovered that giant planets orbiting too close to their star seem to gradually disappear. This research identified 130 planets and potential candidates around these evolving stars, including 33 new discoveries.

The mechanism responsible for this planetary destruction lies in gravitational tidal forces. Just as the Moon influences Earth's oceans, planets exert an attraction on their host star. When the star begins to swell as it ages, this interaction becomes more intense, gradually slowing the planet and reducing its orbit. Dr. Edward Bryant, the study's lead author, emphasizes the surprising efficiency of this process that leads planets to spiral toward their star until their complete destruction.



Data collected by NASA's TESS satellite were crucial for this discovery. Researchers analyzed more than 15,000 potential signals before confirming the 130 objects of interest. The study clearly shows that the further a star advances in its evolution, the less likely it is to host nearby giant planets. The occurrence rate drops to only 0.11% for the most evolved red giants.

This research gives us a glimpse into the distant future of our own Solar System. In about five billion years, our Sun will also begin its transformation into a red giant. Dr. Vincent Van Eylen, co-author of the study, specifies that Earth could technically survive this phase, being farther away than the giant planets studied, but conditions would become uninhabitable for any form of life.

The next step for researchers is to precisely determine the mass of these candidate planets. This measurement will help better understand the exact mechanisms that cause their death spiral. Astronomers use for this purpose the tiny oscillations of stars, betraying the gravitational influence of their planetary companions.

These observations open a new window on the dynamics of planetary systems at the end of their lives. They remind us that the Universe is in perpetual change, where even the most stable systems eventually undergo radical transformations over billions of years.

The transformation of stars into red giants

The life cycle of stars follows a well-defined path that depends mainly on their initial mass. For stars similar to our Sun, the main phase of their existence lasts several billion years, during which they transform hydrogen into helium in their core. This period of stability allows the development of planetary systems and, in some cases, the emergence of life.

When nuclear fuel begins to deplete, the star enters a phase of spectacular transformation. Its core contracts while its outer layers expand considerably, potentially reaching hundreds of times their original size. This expansion is accompanied by surface cooling, giving the star that characteristic red color that earns it the name red giant.


This stellar metamorphosis spans several million years, creating radically different conditions in the planetary system. The closest planets see their environment completely disrupted, with temperatures increasing dramatically and gravitational forces changing. The star becomes literally unrecognizable compared to what it was during its youth.

Understanding this process helps us anticipate the fate of our own Solar System. Astronomers estimate that in five billion years, the Sun will undergo this same transformation, probably engulfing Mercury and Venus, while Earth will see its oceans evaporate and its atmosphere dissipate into space.

The role of tidal forces in orbital evolution

Tidal forces represent a subtle but powerful gravitational phenomenon that profoundly influences celestial bodies. On Earth, we observe their most visible effects in the movement of oceans, where lunar attraction creates the ebb and flow of tides. This same principle applies on a planetary scale, where gravitational interactions between celestial bodies gradually modify their trajectories.

In a planetary system, each body exerts an attraction on the others, creating mutual deformations. These deformations, although minute, generate internal friction that dissipates energy. This energy dissipation results in a transfer of angular momentum, slowly but surely changing the orbital parameters of the concerned bodies over astronomical timescales.

When a star ages and swells, its gravitational influence on nearby planets intensifies considerably. Tidal forces then become strong enough to slow planetary rotation and gradually reduce their orbital distance. This process can accelerate exponentially as the planet approaches, creating an infernal spiral toward the star.

The study of exoplanetary systems now allows us to concretely measure these effects. Astronomers observe that giant planets close to their star become increasingly rare around older stars, testifying to the destructive efficiency of these interactions over the long term.