Since the discovery of the first exoplanet in the mid-1990s, astronomy has undergone a true revolution that has led to the discovery of more than six thousand planets orbiting distant stars.
However, one question remained unanswered: Where are the moons of those planets? Although scientists are convinced that planets in other star systems must have moons, just like in our solar system, no confirmed discovery of any of them has been announced to this day.
Today, an international team of researchers may have come closer to solving this mystery, after observing a strange celestial object in a star system known as CD-35 (CD-35 2722). However, the surprise is that this object does not quite fit the traditional definitions of a moon or a planet, which has opened a wide door for scientific debate.
The CD35 star system is located about 73 light-years from Earth and contains a star with a mass roughly half that of the Sun. What makes it unique, however, is that it is orbited by another object, a brown dwarf. Brown dwarfs form in the same way as stars, but they lack the mass to ignite hydrogen fusion in their cores, and are therefore sometimes described as "failed stars."
Brown dwarfs typically have masses between 13 and 80 times that of Jupiter, meaning they are larger than giant planets, but smaller than the smallest stars.
An illustration of the improbable planetary system including the massive brown dwarf TOI-201 c, the warm Jupiter TOI-201 b, the rocky super-Earth TOI-201 d, and the host star TOI-201. (Image credit: INAF)
After three decades of research... Is it the first moon outside the solar system, or a new class of objects? (Italian National Institute for Astrophysics)
Using the Very Large Telescope of the European Southern Observatory in Chile, researchers discovered a huge gaseous object orbiting this brown dwarf, not the star itself, which made its classification a complicated matter.
Is it a moon, a planet, or something new?
The new object is similar to moons in that it orbits another body, but it differs from all known moons because the body it orbits is not a planet, but a brown dwarf.
Team leader Kevin Hoy, from the University of Diego Portales and the Millennium Center for Young Exoplanets and Their Moons in Chile, said:
"It is difficult to describe this system using familiar words such as planet or moon, as this object has enough mass to be a planet, but it does not orbit a star, rather it orbits an object which in turn orbits a star."
He added that its existence as the "third wheel" in this system leads scientists to consider it a moon, despite its significant difference from the small rocky moons we know in the solar system.
Researchers believe this discovery may necessitate a re-examination of the boundaries between planets, moons, and brown dwarfs—boundaries that were once clear in our solar system but have become less so when studying distant star systems.
A brown dwarf is a celestial body that falls between the ranks of planets and stars, as it does not have enough mass to initiate nuclear fusion reactions like stars (NASA).
Although the team cannot yet confirm that it is the first moon outside the solar system, it confidently asserts that it is the first exoplanet to be observed with such clarity.
"The satellite we observed is a huge gaseous body orbiting a massive companion, several times larger than Jupiter," said researcher Alice Zorlu of Diego Portales University. "In the solar system, it is easy to distinguish between the sun, planets, and moons, but here the boundaries between stars, planets, and moons have become blurred."
Tags:
science
