Tilted planets in Earth’s solar system aren’t so weird after all

The discovery is "reassuring," says Malena Rice says. "It tells us that we're not a super-weird solar system. This is really like looking at ourselves in a funhouse mirror and seeing how we fit into the bigger picture of the universe." (Credit: Getty Images)

A new discovery finds that, even in “pristine” solar systems, planets exhibit a bit of a tilt.

Scientists have long puzzled over why all of the planets in Earth’s solar system have slightly slanted orbits around the sun. The new study, published in the Astronomical Journal, suggests this phenomenon may not be so unusual after all.

Astronomers had long assumed that planets with pitchy, angled orbits—orbits that don’t align with the spin axis of their host sun—are the result of some high-level cosmic hubbub, such as nearby stars and planets pushing around their neighbors.

For the study, the researchers conducted a comprehensive analysis of pristine, multi-planet solar systems, where the orbits of planets have remained relatively undisturbed since their formation.

“This type of configuration, where one planet’s orbit is precisely ordered with another in an exact integer ratio of orbital periods, is likely common to find in a solar system early in its development,” says lead author Malena Rice, an assistant professor of astronomy at Yale University. “It’s a gorgeous configuration—but only a small percentage of systems retain it.”

And even in these solar systems, Rice and her coauthors found, planets can have an orbital tilt of up to 20 degrees.

The researchers began their work by measuring the slanty orbit of TOI-2202 b, a “warm Jupiter” planet in a pristine solar system. A warm Jupiter is a planet much larger than Earth with a significantly shorter orbital period than Earth’s 365 days.

The researchers compared TOI-2202 b’s orbit with orbit data from the full census of similar planets found in the NASA Exoplanet Archive. Put in this larger context, there was a typical tilt of as much as 20 degrees for such planets, with TOI-2202 b’s system being one of the most strongly tilted such systems.

Rice says the discovery provides valuable information about early solar system development—and says something important about Earth’s system: that a little bit of tilting is par for the cosmic course.

“It’s reassuring,” Rice says. “It tells us that we’re not a super-weird solar system. This is really like looking at ourselves in a funhouse mirror and seeing how we fit into the bigger picture of the universe.”

The new study also aids Rice in her research quest to understand “hot” Jupiter solar systems, which are systems that contain gas giant planets that may be similar to Jupiter, but with very short orbital periods.

“I’m trying to figure out why systems with hot Jupiters have such extremely tilted orbits,” Rice says. “When did they get tilted? Can they just be born that way? To find that out, I first need to find out what types of systems are not so dramatically tilted.”

Support for the research came, in part, from the Heising-Simons Foundation and the 51 Pegasi b Fellowship Program.

Source: Yale University