Gaseous and scorching “hot Jupiters” make tilted loops around their parent stars

Gaseous and scorching “hot Jupiters” make tilted loops around their parent stars

Gaseous and scorching “hot Jupiters” make tilted loops around their parent stars

a fiery type from an alien world dubbed a “hot Jupiter” could enter a tilted orbit relative to its parent star, and a new study could help puzzled researchers figure out why.

In March, NASA announced the 5,000th known exoplanet — with the first discovered around a Sun-like star in 1995. But that planet was like nothing we’d seen before. The first discovered planet orbiting a main sequence star, 51 Pegasi b, orbits its parent star in just four days, orbiting less than five percent of the distance between the sun and Earth. But astronomers have never been quite sure how these hot Jupiters form.

NASA explains exoplanets.

But the new study, accepted for publication in The Astrophysical Journallooks at possible scenarios for how they form and why the solar system is not.

Why it matters – Our solar system provides a good measure of the types of planets that can exist in deep space well beyond the influence of the sun. Astronomers use those near Earth, such as Venus, to shape how they interpret data about these distant worlds known as exoplanets.

In fact, scientists also use solar system names to describe exoplanets that don’t have exact proxies in our cosmic environment. You’ll find astronomers using terms like “super-Earth” and “mini-Neptune,” and in this case hot Jupiters.

A curious difference between our home and those distant galaxies is that the Earth and its siblings rotate along the same plane and align with the sun’s equator. The solar system is a flat disk, with all planetary orbits essentially operating as concentric circles. But that is not always the case.

“While we’ve found that some hot Jupiters are aligned just like the Solar System, we’ve also seen that many hot Jupiters are misaligned due to the rotation of their host stars,” Jacob Hamer, an astrophysicist at Johns Hopkins University, said Monday while presentation of the new work at the 240th meeting of the American Astronomical Society (AAS).

These puzzling slopes, called obliquities, could be a big clue as to how hot Jupiters form.

Dive into the details — Before starting to collect some hot Jupiter observations, Hamer’s team thought it was possible that all hot Jupiters would form in shaky orbits. By interacting with their stellar parent, they eventually spin aligned or flat compared to the star’s rotation.

If this is true, aligned systems should be older than unaligned systems, as the disorderly hot Jupiters would take time to get into the aligned groove.

“It was very difficult to answer this question,” says Hamer, “because measuring the age of an individual star very precisely is one of the most difficult problems in astrophysics.”

What’s new – Enter Gaia, the eight-year-old satellite that maps the movements of 1 billion stars in the Milky Way.

Hamer’s team was surprised by what they found. After determining the relative ages for various hot Jupiter systems thanks to Gaia’s Data Release 2 (DR2) and Early Data Release 3 (EDR3) observations, they found that the misaligned orbits were older than the aligned orbits, giving rise to the idea that hot Jupiters with tilted orbits that eventually softened in the plane of their parent star.

“We think there is only one explanation for this observation,” Hamer said. “Misaligned hot Jupiters arrive late in their orbits, and misaligned hot Jupiters arrive early in their orbits.”

A diagram for misaligned versus misaligned orbits of hot Jupiters. Jacob Hamer/AAS

What they discovered – Stars and planets are made of the material that spins in a protoplanetary disk. In these early stages, hot Jupiters form and then migrate to the center of the system to be next to their parent star.

Jupiter, Saturn, Uranus and Neptune are outer planets because they are likely formed further from the sun than rocky worlds like Earth. The same is likely happening in many distant systems. A gaseous exoplanet will form far from its star and become a hot Jupiter by migrating inward.

This trip could be the cause of the obliquities.

If a hot Jupiter crawls into its parent star after the disk disappears, a hot Jupiter could form a cosmic bee line to their final, tight orbit. But suppose a hot Jupiter begins that journey inward while there is still a disk. In that case, the planet will interact with other objects — perhaps another exoplanet or companion star — and arrive in its eccentric orbit later.

Sometimes a misaligned hot Jupiter can correct itself and become misaligned.

What’s next – “This tells us there’s no way hot Jupiters are formed,” Hamer said. “They actually have multiple formation processes.”

There is still plenty to discover. Astronomers can expand the science of hot Jupiters and reveal more about the idiosyncrasies of planetary formation as the sensitive instruments on missions like NASA’s James Webb Space Telescope begin to detect even more alien worlds.