Scientists Have Pinpointed the True Center of the Solar System

It’s not where you think.

  • Researchers are using a new software model to pinpoint the true center of the solar system.
  • Massive, bossy Jupiter pulls the center slightly out of true with its gravity field.
  • The true center is just outside of the sun’s surface, depending on where Jupiter is.

Even without third-generation GPS technology, scientists have pinpointed the center of our solar system. Yes, we revolve around the sun, but it’s not as simple as the center of the sun. Instead, the shape and interacting gravities in the solar system place the center just outside the sun’s surface.

Scientists using the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) are using the regular signals put out by dying stars called pulsars to help them calculate the distances required to make their location estimate. A massive group of researchers worked together on this project. They used new and better information to help add nuance to an existing model: the ephemeris.

When scientists look at the rotation and orbit of planets and other bodies in our solar system, they use a tool called an ephemeris. This is a centuries-old idea: a document where each known item is listed, along with where it will be at a particular time. It’s a snapshot of the solar system, basically, which sailors used to guide ships using celestial navigation.With a printed list in hand, they could compare what they saw in their instruments in realtime to where they believed the stars and planets should appear in the night sky at their position.

As technology has advanced, an ephemeris has gone from a handwritten table in a notebook to the “concentric circles” illustrations we’re used to seeing in books to computer models that react in realtime. Star Trek Voyager’s “astrometrics lab” uses ephemeris ideas. And for the group working with NANOGrav, the ephemeris was a great place to start.

“[R]ecent array data sets yield different gravitational-wave background upper limits and detection statistics when analyzed with different solar system ephemerides,” the group explains in its new paper, using the plural of ephemeris. “Crucially, the ephemerides do not generally provide usable error representations.”

So an ephemeris represents a best case with no wobbles—and the real solar system is packed with wobbles, because everything’s gravity pulls on everything else.

Most notably, the researchers say, Jupiter is a gravity bully that we still don’t understand well. Jupiter is very small compared to our sun, but it’s only a little smaller than the next closest star, Proxima Centauri. Jupiter is so massive that its gravity pulls on everything around it, and this makes Jupiter a great starting point for trying to quantify the missing wobbles.

“In this article, we describe the motivation, construction, and application of a physical model of solar system ephemeris uncertainties, which focuses on the degrees of freedom (Jupiter’s orbital elements) most relevant to gravitational-wave searches with pulsar-timing arrays,” the scientists explain.

To address the uncertainties, the researchers designed and built a new software model called BayesEphem. Using this software, they modeled the ephemerides that were causing problems in their gravitational wave measurements. And by adding a more accurate idea of the way Jupiter’s gravity influenced the movement of the celestial bodies around it, they found their gravitational wave measurements were harmonized as well.