Researchers have a new method for measuring the masses of objects in the Solar System. They use pulsars from the International Pulsar Timing Array (IPTA). Pulsars are a type of fast-rotating neutron star that emit a beam of light, giving them a “pulsating” appearance. This pulsation can be used as an extremely precise clock. And in turn that can be used to measure the mass of objects.

As explained in the Monthly Notices of the Royal Astronomical Society, astronomers can measure the arrival time of pulses from distant stars within a couple of hundred nanoseconds over multiple decades. The values are so precise that the motion of the Earth and Solar System is the main factor affecting the prediction. Therefore by studying the discrepancies, it is possible to estimate the mass of objects in the Solar System.

In particular, the team estimated the mass of the dwarf planet Ceres, along with four other objects in the asteroid belt. Ceres is estimated to have a mass that's 1.3 percent the mass of the Moon. The method is precise enough to measure masses equivalent to just 0.0003 percent of Earth's, which is about 10 times less sensitive than what astronomers can get from probes. Given that many objects have not been visited by spacecraft, this gives us an important tool for mass estimation.

“We rely on the work of our colleagues working in planetary astronomy, which uses a wealth of data, including data from spacecraft fly-bys, to create solar-system ephemerides that describes orbits of the planets, moons, and asteroids,” lead author Dr Nicolas Caballero, from the Max Planck Institute for Radio Astronomy, said in a statement. 

By linking pulsar timing to the ephemerides, the positions of celestial bodies in the sky, researchers can also discover information about unknown objects. Or at least put limits on their mass, based on unaccounted discrepancies from the observations. A second paper about this approach was published recently.

“It is a pilot study and we only considered unknown bodies in unperturbed, eccentric orbits," said co-author Yanjun Guo from the Kavli Institute in Beijing. "Nevertheless, it shows the exciting possibilities that pulsar timing offers to study the Solar System, and impose restrictions on the parameters of theoretically proposed objects, from anything ranging from Planet Nine, to dark matter in the solar neighbourhood.”

Researchers hope to use the IPTA to study gravitational waves, but it's clear that it also has important implications for the study of the Solar System.