A pair of astronomers from Yale University believes that they have found the answer to the decades-old mystery surrounding a number of planets that lie outside the solar system.

NASA's Kepler Space Telescope discovered thousands of exoplanets throughout its nine-year observation of the night sky. The mission also revealed a phenomenon that has been making scientists scratch their head in wonder.

About 30 percent of stars similar to the sun has "super-Earths," exoplanets bigger than Earth but smaller than Uranus or Neptune, that have nearly circular and coplanar orbits and take fewer than 100 days to complete a revolution. What baffles scientists is the discovery that a great number of these exoplanets exist in pairs with orbits that seem to have been pushed apart by a great but unknown force.

Link Between A Planet's Tilt And Orbit

Sarah Millholland and Gregory Laughlin, astronomers from Yale and the authors of a recent study published in Nature Astronomy, have a theory and it implies that these planets are extremely tilted like Uranus. They proposed that an exoplanet's obliquity, the measure of tilting between the planet's axis and orbit around the star, play a major role in the planet pairs' odd configuration.

"When planets such as these have large axial tilts, as opposed to little or no tilt, their tides are exceedingly more efficient at draining orbital energy into heat in the planets," explained Millholland. "This vigorous tidal dissipation pries the orbits apart."

Planets orbiting the sun do not have the same pattern, but it is fairly common within the solar system. A close example is the Earth's relationship with the Moon.

The moon, as previous observations have revealed, is drifting away from the Earth at a rate of about 1.5 inches per year due to the tidal forces. As a result, Earth's rotation on its axis slows down, causing days on Earth to grow longer.

What Tilting Can Say About The Planet

Laughlin added that their discovery has a major impact in the future for astronomers who want to observe exoplanets.

"It impacts several of their physical features, such as their climate, weather, and global circulations," he said. "The seasons on a planet with a large axial tilt are much more extreme than those on a well-aligned planet, and their weather patterns are probably non-trivial."