In a paper just published by the Astrophysical Journal, Schlaufman has set the upper boundary of planet mass between four and 10 times the mass of the planet Jupiter.
Schlaufman, an assistant professor in the university’s Department of Physics and Astronomy, says setting a limit is possible now mainly due to improvements in the technology and techniques of astronomical observation. The advancements have made it possible to discover many more planetary systems outside our solar system and therefore possible to see robust patterns that lead to new revelations.
“While we think we know how planets form in a big-picture sense, there’s still a lot of detail we need to fill in,” Schlaufman said. “An upper boundary on the masses of planets is one of the most prominent details that was missing.”
The conclusions in the new paper are based on observations of 146 solar systems, Schlaufman said. Almost all the data he used was measured in a uniform way, he said. The data are more consistent from one solar system to the next, and so more reliable.
Defining a planet, distinguishing it from other celestial objects, is a bit like narrowing down a list of criminal suspects. It’s one thing to know you’re looking for someone who is taller than 5-foot-8, it’s another to know your suspect is between 5-foot-8 and 5-foot-10.
In this instance, investigators want to distinguish between two suspects: a giant planet and a celestial object called a brown dwarf. Brown dwarfs are more massive than planets, but less massive than the smallest stars. They are thought to form as stars do.
For decades brown dwarfs have posed a problem for scientists: how to distinguish low-mass brown dwarfs from especially massive planets? Mass alone isn’t enough to tell the difference bzween the two, Schlaufman said. Some other property was needed to draw the line.
In Schlaufman’s new argument, the missing property is the chemical makeup of a solar system’s own sun. He says you can know your suspect, a planet, not just by itssize, but also by the company it keeps. Giant planets such as Jupiter are almost always found orbiting stars that have more iron than our sun. Brown dwarfs are not so discriminating.