14 DAY TRIAL // In our own solar system, assessing the differences between planets and stars is a fairly easy procedure. We look at the Sun, and then at Jupiter or Saturn (the largest planets), and the difference is immediately obvious. But things are not as simple in the Universe. Astronomers have discovered over the years exoplanets that simply blur the difference between a planet and a star, to the point where defining a star as a celestial body that can sustain thermonuclear reactions is no longer enough. Some experts believe that these new bodies may represent the “missing link” between stars and planets, Space reports.
“Taken together, these discoveries are going to change what we call a planet. Until now people have been arguing about how big can an object be and still be a planet,” Massachusetts Institute of Technology (MIT) astrophysicist Sara Seager says. Some of the exoplanets that have been spotted through ground- or orbit-based telescopes are so large that they dwarf Jupiter, a gas giant that makes the Earth look like a grain of sand in solar orbit.
The most hazy definitions of stars and planets revolve around the formations known as brown dwarfs. Reaching up to 70 Jupiter masses, they have the appearance of stars that are unable to sustain thermonuclear fusion. They are very hot at times, which seems to confirm that they have stellar connections, while some are cooler, and resemble planets such as Jupiter or Saturn more than they do a star. Determining the category in which these bodies fall is a hot topic of debate in scientific groups.
Creating definitions to encompass these formations may, however, be a futile effort, some believe, simply because new discoveries could throw the classification in disarray at any time, such as it was the case with the recently found exoplanets. They ruined the former classification, which held that exoplanets could only grow to be about 13 Jupiter masses in size anywhere in the Universe. “No one is writing a law or rule that you have to call them this or that,” Seager adds. More than 300 exoplanets have been discovered to this point, orbiting stars in the Milky Way and beyond.