A question of mass
Charbonneau, who was not involved in the latest research, points out that the masses of the 18 objects were not measured directly. Models used to generate the results rely in part on age estimates of nearby stars to predict a mass, so there is some uncertainty in the findings. According to the study, the objects are anywhere from five to 15 times as massive as Jupiter.
Because of the large masses, Charbonneau told SPACE.com he "might be hesitant to call them planets, or at least I would want to make it clear that these objects are much more massive than any of the planets in our solar system."
The team of researchers acknowledges that the objects might be brown dwarfs, but they say other research shows it is unlikely that 18 brown dwarfs would be concentrated in such a relatively small portion of space.
"If planets can only exist around a star, then our candidates are very low-mass brown dwarfs," said Zapatero Osorio. "But if planets must be a certain mass, then these objects are planets."
Zapatero Osorio and her colleagues say the work points to another interesting possibility: Many stars in the Milky Way Galaxy are thought to have formed in star clusters like the one in Orion, which means there could be lots of homeless planets populating the back roads of our galaxy.
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