Saturn’s location now pinpointed 50 times more precisely

Saturn’s and its moons’ locations can now be poinpointed about 50 times more precisely than measurements achieved by ground-based optical telescopes, thanks to pairing of the National Science Foundation’s Very Long Baseline Array (VLBA) radio-telescope system with NASA’s Cassini spacecraft.

Scientists can now tell you exactly where our solar system’s second largest planet is, plus its moons, to within about 2 miles (3.21km).

According to astronomers at the Jet Propulsion Laboratory (JPL), Pasadena, California, “The feat improves astronomers’ knowledge of Saturn’s orbit and benefits spacecraft navigation and basic physics research.”

Study leader Dayton Jones and colleagues used the VLBA to pinpoint the position of Cassini as it orbited Saturn over the past ten years by receiving the spacecraft’s radio transmitter’s signal. VLBA is a massive array of radio-telescope antennas spread from the Virgin Islands to Hawaii.


Saturn. Image credit: NASA/JPL/Space Science Institute.

They combined these data with Cassini’s orbit information from NASA’s Deep Space Network. Both observations, when combined, allowed the astronomers to make the most accurate determinations to date of the positions of the center of mass (barycenter) of Saturn and its moons.

The team included scientists from the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico and NASA’s Jet Propulsion Laboratory in Pasadena, California. They presented their findings at the American Astronomical Society’s meeting in Seattle.

They said they had managed to make the precise measurement thanks to Cassini’s long-term presence in the Saturn system plus the VLBA’s ability to process and interpret extremely fine detail.

This means scientists now have a much improved table of predicted positions of masses in the Saturn system, known as ephemeris. An ephemeris is a key tool of astronomy.

Dayton Jones

Mr. Jones said: “This work is a great step toward tying together our understanding of the orbits of the outer planets of our solar system and those of the inner planets.”

These more accurate positional data will help improve precise navigation of interplanetary spacecraft and help enhance measurements of the masses of solar system objects, he added.

Scientists will also now be able to predict more accurately when Saturn and/or its rings will pass in front of background stars – events that “provide a variety of research opportunities for astronomers,” JPL informed.

According to JPL:

“VLBA measurements of Cassini’s position have even helped scientists who seek to make ever-more-stringent tests of Albert Einstein’s theory of general relativity by observing small changes in the apparent positions of actively feeding black holes, or quasars, as Saturn appears to pass in front of them on the sky.”

The navigation team that was charged with plotting Cassini’s course around Saturn, started using new positional data provided by the ongoing study in 2013. The new ephemeris means they can now design better maneuvers for the spacecraft, resulting in mission-enhancing savings in propellant.

The navigators previously carried out their own estimates of Saturn’s and its moons’ positions using data garnered by tracking Cassini’s radio signal during its communications with Earth. Their new calculations, enhanced by data from VLBA, are approximately 20 times more accurate.

The team plans to continue the joint observations with the VLBA and Cassini through the end of late 2017, when Cassini’s mission ends.

They plan to use similar techniques when observing NASA’s Juno spacecraft’s motion when it reaches Jupiter in mid-2016. They expect to improve the orbital knowledge of the largest planet in our solar system as well.

JPL is a division of the California Institute of Technology (Caltech). It manages the Cassini and Juno missions and the Deep Space Network of NASA.

The National radio Astronomy Observatory is part of the National Science Foundation.