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Astronomers document eccentricities in nearby planet systems

An unexpected eccentricity in the debris disk of a nearby star may help us understand the formation of planetary systems like our own.

(CN) — In a presentation made at the American Astronomical Society on Tuesday, astronomers presented our clearest and most detailed image yet of the debris disk of a nearby, Sun-like star. The debris disk is part of a solar system analogue that can act as a ‘fossil record’ for what our solar system looked like in the past.

The image of star HD 53144's debris disk, generated using the Atacama Large Millimeter/ Submillimeter Array (ALMA) in Chile, also revealed some unexpected eccentricities that complicate our understanding of how planets form and evolve.

It is generally understood that planets form out of gases and dust that cluster together around stars. This disk of gas and dust provide the material for planets to form. Much of this material is cleared away after planet formation, and the leftovers of this process become debris disks. In our own solar system, they are more commonly known as the asteroid belt, found between Mars and Jupiter, and the Kuiper Belt in the outer solar system beyond Neptune.

Astronomers look toward debris disks in particular as a way to understand a bigger picture of planetary formations, in hopes of gaining a deeper understanding of our own solar system.

Meredith MacGregor, an associate professor at the Center for Astrophysics and Space Astronomy and the department of Astrophysical and Planetary Sciences at the University of Colorado Boulder, and the study’s lead author clarifies, “Without a debris disk, we might be able to detect large inner planets, but we would have no way to know what’s going on in the entire planetary system, out to the larger Neptune analogues. By targeting these stars that have these disks, that gives us the outer information, it’s letting us get a peek at the entire planetary system.”

Although there have been other debris disks imaged by ALMA, the debris disk of HD 53143 stands out, not only for its eccentricities, but also because of the star itself, which is of similar mass and spectral type to our Sun.

“For this particular system, it’s a younger analogue of our solar system, which is especially exciting, because we can’t see how our solar system was formed,” Macgregor explains. “We try to understand that through models but if we can see it happening in other systems, that gives us a glimpse of the early history of our solar system.”

Although initially targeted for research for these similarities to our Sun and solar system, the astronomers soon discovered that the debris disk had some surprises in store. Most debris disks are symmetric circles, with the star centering the system. When the debris disk of HD 53143 was first imaged with the Hubble Space Telescope in 2006, it appeared to be a fairly standard debris disk, and and the image didn't indicate any particular oddities.   

This new debris disk is twice as eccentric as the Fomalhaut disk, imaged with ALMA by MacGregor in 2017, which was the most eccentric system studied up to this point. The disk is elliptically shaped, with a star at one focus, rather than the center. Further investigation revealed that the system also has inner disk, closer to the star.

This second disk does not line up with the rest of the system, and falls along a different plane than the first, outer disk. Authors of the paper posit a potential interruption caused by an unseen planet as an explanation for the eccentricity. The study attributed these differences to possible planetary formation and movement in the gap between the two disks.

“We’re seeing this really complicated looking disk but actually around a star that’s like our own sun, so it’s much more interesting to look at,” MacGregor said.

In order to resolve an image of this debris disk, astronomers required a telescope that could look in the millimeter wavelength. With an array of 66 individual telescopes spread over a great distance in the Atacama Desert in northern Chile, ALMA was able to provide the image clarity and resolution needed to discover these eccentricities. Although the image of the debris disk of HD 35143 has a higher resolution than astronomers were able to gain before, MacGregor wants to go even further. Her next goal is to use ALMA to push even deeper into the structure of the inner disk, and to expand to other debris disks.

“The more of these disks that we look at, the more interesting structures we’re going to see, and it’s really complicating our picture of planet formation to see all these really interesting structures, and every star we look at we learn something new and see all these detailed things. There’s a lot of space to do that,” she says.

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