Astrophysicist David Kipping has discovered that in special cases, we can directly measure the mass of the star by looking at the movement of the planets orbiting it.
By measuring the amount of light blocked by a planet, astronomers found they could calculate its weight relative to the star it orbits. But without its exact dimensions, the actual mass of the planet remained a mystery. Although computer models give a good guess, they are not as accurate as real measurements.
Kipping realised that if a planet has a moon big enough for us to see, then by measuring the amount of light both bodies block, the data could be plugged into Kepler’s Third Law-which acts like a theoretical cog in the machine of planetary motion. By taking the results and studying the star’s wobble caused by the planet’s gravitational tug, scientists could figure out the its mass directly.
“If there was no moon, this whole exercise would be impossible,” said Kipping, who works at the Harvard-Smithsonian Center for Astrophysics, in Massachusetts. “No moon means we can’t work out the density of the planet, so the whole thing grinds to a halt.”
Kipping hasn’t put his method into practice yet, as no observed star fits the criteria. However, NASA’s Kepler spacecraft, a huge orbiting telescope, could discover such set-ups. The new data will be vital in studying the origin, development and ultimate fate of the universe.