Hot Jupiters Form in All Sorts of Ways

Jun 13, 2022 | AAS, Daily Space, Exoplanets

Hot Jupiters Form in All Sorts of Ways
IMAGE: An arrow at the bottom of the image indicates the age of the system increasing toward the right of the image from 1-10 Million years, to 10-100 Million years, to greater than 100 Million years. In the middle of the image, at left (1-10 Million years) there is a star surrounded by a disk of gas and dust. A planet is forming in it and migrating closer to the star. At 10-100 Million years the disk is gone and hot Jupiter has already arrived, and is on an aligned orbit. At the top of the figure, there is a planet forming in the disk at 1-10 Million years, but it forms further out than in the bottom panel. There is an arrow spanning the entire 10-100 Million years section. At more than 100 Million years, the planet is on an eccentric, misaligned orbit. A small amount of time later, the planet’s orbit is circular and misaligned. CREDIT: Jacob Hamer

Next week is this year’s American Astronomical Society conference, and we’ve been struggling to find press releases as universities and research groups hold onto their stories until then. Luckily, some previews are trickling out, so we’re not completely without news.

In new research to be presented fully at the conference on June 13 and published in The Astronomical Journal, astronomers from Johns Hopkins University have measured the relative ages of hot Jupiters using Gaia data. I love that mission. I really do.

Hot Jupiters, of course, are Jupiter and larger-sized planets that orbit close in to their stars, reaching surface temperatures of thousands of degrees Celsius. Planetary formation theories have been trying to understand just how these planets came to exist, and their mere existence has really forced us to change those theories. That’s how science is supposed to work, so this is a good – albeit frustrating – problem to have.

When these planets were first discovered over twenty years ago, the prevailing theory of their formation said they formed that close in and then migrated farther out over time to reach positions like that of our own Jupiter. Or vice versa – forming farther out and migrating inward – and causing violent changes to the inner regions of stellar systems. And now, using all that precision Gaia data, astronomers have found that the answer is both. And then some.

Gaia’s data was used to determine the velocities – that is speed and direction – of the parent stars in several systems. From there, the age of the star can be determined, as stars born together move similarly to one another at the beginning of their lives. Over time, the velocities changes, and the planets in the system shift accordingly but not necessarily as quickly. And that helped us understand just how hot Jupiters evolve… sort of. Lead researcher and graduate student Jacob Hamer explains: One [formation process] occurs quickly and produces aligned systems, and [the other] occurs over longer timescales and produces misaligned systems. My results also suggest that in some systems with less massive host stars, tidal interactions allow the hot Jupiters to realign the axis of their host star’s rotation to be aligned with their orbit.

We look forward to hearing more about this groundbreaking research next week during the conference, and we’ll be bringing you more stories as they are announced.

More Information

JHU press release

“Evidence for the Late Arrival of Hot Jupiters in Systems with High Host-star Obliquities,” Jacob H. Hamer and Kevin C. Schlaufman, to be published in The Astronomical Journal (preprint on


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