Observations from NASA and the European Space Agency telescopes have made possible the discovery of a new exoplanetary system 116 light years from Earth. According to research by an international team led by the University of Warwick published in the journal Science, this new “solar system” has a peculiarity: its architecture contradicts the standard model of planetary formation.
In short, based on the astrophysics we know, it should not exist. We do not know if it will force us to rewrite current theories, but we do know that we will urgently review them.
The discovery. The LHS 1903 system is made up of four planets orbiting a red dwarf, the most common and longest-lived type of star in the universe. The question is how they are arranged: the innermost planet is rocky, the next two are gaseous and surprisingly, the outermost planet (LHS 1903 e) is also rocky.
That planet shouldn’t be there. LHS 1903 e is a large super-Earth (it has 1.7 times the radius of the Earth and 5.79 Earth masses, thus achieving a similar density) located on the periphery, but of course, it should not be in that position, according to current models. It is not a minor anomaly: it breaks the paradigm from the foundations.
This arrangement contradicts the usual pattern we see in all known planetary systems: rocky planets (refractory materials) are in the hot zone and gas giants in the cold outer zone, beyond the “snow line”, where ice makes it possible for large nuclei to grow that capture hydrogen. The canonical example is our solar system: rocky Mercury, Venus, Earth and Mars orbit closer and gaseous Jupiter, Saturn, Uranus and Neptune orbit further away.
And Pluto? In our solar system, those large, gaseous planets formed first and then the four rocky planets in the innermost orbits. However, Pluto is further away. Tomas Wilson, professor at the University of Warwick and lead author of the study, explains the existence of rocky bodies beyond Neptune: unlike LHS 1903 e, they are much smaller, rich in ice and probably formed much later than the rest of the planets in the Solar system, caused by collisions.
Why is it important. According to theory, a planet as large as LHS 1903 e in that cold zone should have devoured gas until it became a giant like Jupiter. But there is another reading: that the formation model fails and is not the only recipe that explains how exoplanetary systems form.
But as we mentioned above, red dwarfs are the most abundant stars in the galaxy and if the model fails in this system, it is plausible that it will not hit the mark in much of the cosmos either. There may be other “inverted” systems pending interpretation or that we have misinterpreted.
A possible explanation. What the research team proposes is the gas-poor formation mechanism hypothesis. In short, the important thing is not so much where but when. Thus, the planets were formed one after another in the opposite order to our solar system, starting first with the innermost one and going outwards from there.
When planets form, they consume the gas available in the disk that surrounds the star. LHS 1903 was formed last, when there was no more gas left, so it could no longer become the gas giant that might have been expected. As the lead researcher explains: “It means that the outermost planet formed millions of years after the innermost one. And since it formed later, there was actually not enough gas and dust left in the disk to build this planet.”
The research method. The data analyzed by the international team comes from the collaboration of NASA’s TESS telescopes and ESA’s CHEOPS exoplanet characterization satellite: the first detects planets with the in-transit method and the second studies them in depth, which allows it to obtain information such as size, mass and, from there, density. Among the alternative hypotheses considered is its birth from impacts between planets or the loss of its gaseous envelope, which they ended up discarding.
Astrophysics has pending subjects. Beyond finding a clear mechanism, what seems evident is that observing this system of exoplanets opens up a range of possibilities about how planets form around stars that will last for years. Néstor Espinoza, an astronomer at the Space Telescope Science Institute in Baltimore who was not involved in the study, explains it to CNN: “This system provides a very interesting piece of information that planetary formation models will try to explain for years, and I am sure that we will learn something new about the planetary formation process once they are compared to each other.”
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