Webb detects neon in young star system, provides insight into planet formation

by Haygen Warren

In 2008, observations from NASA’s now-retired Spitzer infrared space telescope hinted at the presence of neon within the protoplanetary disk of Sun-like star SZ Chamaeleontis (SZ Cha). However, Spitzer’s instruments could not confirm whether this reading was correct. Over a decade after Spitzer’s results were published, the joint NASA, European Space Agency, and Canadian Space Agency James Webb Space Telescope observed SZ Cha and directly detected distinct amounts of neon in the protoplanetary disk of SZ Cha — confirming Spitzer’s observations from 2008.

Webb’s observations, coupled with Spitzer’s data from 2008, are allowing scientists to better understand SZ Cha and its future as a star system while also providing scientists with insight into what our own solar system may have looked like during its formation.

“How did we get here? It really goes back to that big question, and SZ Cha is the same type of young star, a T-Tauri star, as our Sun was 4.5 billion years ago at the dawn of the solar system. The raw materials for Earth, and eventually life, were present in the disk of material that surrounded the Sun after it formed, and so studying these other young systems is as close as we can get to going back in time to see how our own story began,” said lead author Catherine Espaillat of Boston University in Massachusetts, who also led the 2008 Spitzer observations.

Small differences in the specific types of neon detected by Spitzer and Webb have revealed a change in high-energy radiation within the disk — a never-before-observed phenomenon. This change in high-energy radiation is predicted to eventually cause the protoplanetary disk around SZ Cha to evaporate, limiting the total amount of time planets have to form within the disk. Neon is a great indicator of how much radiation is hitting and eroding the protoplanetary disk around a star, which is why many scientists search for neon around young stars.

Spitzer’s observations hinted at the presence of neon III within SZ Cha’s protoplanetary disk — an extremely rare neon reading that is uncommon in other young T-Tauri star disks, specifically protoplanetary disks that are continuously exposed to high-energy X-rays. The presence of neon III means that the aforementioned high-energy radiation within SZ Cha’s disk was being produced by ultraviolet (UV) light rather than the more common X-ray light. It was the only detection of neon III in a sample of 50 to 60 stellar protoplanetary disks, making the difference in UV light and X-rays even more significant for the planets within SZ Cha’s disk and the lifetime of the disk as a whole.

“Planets are essentially in a race against time to form up in the disk before it evaporates. In computer models of developing systems, extreme ultraviolet radiation allows for 1 million more years of planet formation than if the evaporation is predominately caused by X-rays,” said co-author Thanawuth Thanathibodee of Boston University.

However, when Espaillat et al. returned to SZ Cha and its protoplanetary disk with Webb, they found that the neon III signature detected by Spitzer wasn’t there — likely meaning that the neon III within SZ Cha’s protoplanetary disk had entirely disappeared. The disappearance of the neon III from the disk was probably due to the dominance of X-ray radiation within the disk — a typical occurrence within these types of protoplanetary disks.

More specifically, the team believes that different neon signatures within SZ Cha’s disk create a variable wind that, when present within the disk, causes UV light to be absorbed — meaning only X-rays are left behind to pummel the disk when the UV light is absorbed. These types of winds are not uncommon in newly forming star systems with energetic stars at their core, but occasionally, there is a quiet period where the winds don’t exist in the disk. This quiet period is what allowed for the presence of neon III in the disk when Spitzer observed SZ Cha in 2008.

Data from Webb and Spitzer’s observations of SZ Cha. Note the absence of neon III in Webb’s observations. (Credit: NASA, ESA, CSA, Ralf Crawford (STScI))

“Both the Spitzer and Webb data are excellent, so we knew this had to be something new we were observing in the SZ Cha system – a significant change in conditions in just 15 years,” explained co-author Ardjan Sturm of Leiden University, Leiden, Netherlands.

Discovering the variable wind and the disappearance of neon III from the system were just two of the many mysteries of SZ Cha, and even following their discoveries Espsillat et al. still have many questions. The team is already planning to use Webb to observe SZ Cha again, as well as with other telescopes.

“It will be important to study SZ Cha, and other young systems, in multiple wavelengths of light, like X-ray and visible light, to discover the true nature of this variability we’ve found. It’s possible that brief, quiet periods dominated by extreme UV radiation are common in many young planetary systems, but we just have not been able to catch them,” said co-author Caeley Pittman of Boston University.

Webb and Spitzer’s observations continue to show how useful infrared telescopes are for discovering and investigating various objects and phenomena in the universe. Without observations like the SZ Cha observations, scientists wouldn’t have known about the variable wind and how it affects neon and other elements within a young T-Tauri star’s protoplanetary disk.

“Once again, the universe is showing us that none of its methods are as simple as we might like to make them. We need to rethink, re-observe, and gather more information. We’ll be following the neon signs,” Espaillat explained.

Espaillat et al.’s research was published in The Astrophysical Journal Letters journal on Nov. 15.

(Lead image: Artist’s concept of SZ Cha and its protoplanetary disk. Credit: NASA, ESA, CSA, Ralf Crawford (STScI))

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