Riddle of exoplanets around 55 Cancri solved

New simulations reveal how 55 Cancri's impossible planets maintain stable orbits

Published: April 25, 2014 at 12:00 pm

Researchers have solved the mysteries surrounding one of the most fascinating nearby planetary systems. Credit: Center for Exoplanets and Habitable Worlds, Penn State University


After more than a decade, the mysterious behaviour of two exoplanets orbiting around binary star 55 Cancri has finally been explained.

The planets orbit closer to the star than Mercury in what should be an impossibly unstable course, but recent computer simulations by researchers at Penn State University have shown how these remarkable objects have managed to survive

55 Cancri was one of the first stars found to harbour exoplanets.

Since the discovery of the system in 2002, the star has been the subject of thousands of observations, making it one of the best-observed exoplanetary systems to date.

This means that scientists have a good knowledge of the planets’ sizes, orbits and behaviours.

But for years the two innermost planets have puzzled scientists.

The planet nearest to the star is eight times the mass of Earth, and so close it completes an orbit every 18 hours.

Finding a planet in this proximity to its host star is not unusual, but what really made 55 Cancri stand out was the discovery of a second planet in a tight trajectory, taking just 14 days to orbit the star.

Since their discovery, scientists have been busy trying to work out how these two planets co-exist without hurtling into their parent star or colliding with one aother.

The new simulations carried out at Penn State University are the first to focus on planet-to-planet interactions.

They found that the two planets were in a delicate balance, keeping each other in stable orbits.

"These two giant planets of 55 Cancri interact so strongly that we can detect changes in their orbits,” says graduate student Benjamin Nelson, who created the new simulation.

“These detections are exciting because they enable us to learn things about the orbits that are normally not observable.”

It’s hoped that this technique could be used to characterise more systems as they are discovered and observed with the next generation of dedicated exoplanet telescopes currently being developed.

"Astronomers are developing state-of-the-art instrumentation for the world's largest telescopes to detect and characterise potentially Earth-like planets,” says Eric Ford, a Professor of Astronomy and Astrophyics at Penn State University.


“We are pairing those efforts with the development of state-of-the-art computational and statistical tools.”


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