Free Astronomy Magazine January-February 2024

17 JANUARY-FEBRUARY 2024 ASTRO PUBLISHING rate, limiting the time planets have to form. “How did we get here? It really goes back to that big ques- tion, 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,” said astronomer Catherine Espaillat of Boston University, in Massachusetts, who led both the 2008 Spitzer ob- servations and the newly published Webb results. “The raw materials for Earth, and eventually life, were pres- ent in the disk of material that sur- rounded 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.” Scientists use neon as an indicator of how much, and what type, of radia- tion is hitting and eroding the disk around a star. When Spitzer ob- served SZ Cha in 2008, it saw an out- lier, with neon readings unlike any other young T-Tauri disk. The differ- ence was the detection of neon III, which is typically scarce in proto- planetary disks that are being pum- meled by high-energy X-rays. This meant that the high-energy radia- tion in the SZ Cha disk was coming from ultraviolet (UV) light instead of X-rays. Besides being the lone odd- ball result in a sample of 50-60 young stellar disks, the UV vs. X-ray difference is significant for the life- time of the disk and its potential planets. “Planets are essentially in a race against time to form up in the disk before it evaporates,” ex- plained Thanawuth Thanathibodee of Boston University, another as- tronomer on the research team. “In computer models of developing sys- tems, extreme ultraviolet radiation allows for 1 million more years of planet formation than if the evapo- ration is predominately caused by X- rays.” So, SZ Cha was already quite the puzzle when Espaillat’s team re- turned to study it with Webb, only to find a new surprise: The unusual neon III signature had all but disap- peared, indicating the typical domi- nance of X-ray radiation. The research team thinks that the differences in neon signatures in the SZ Cha system are the result of a variable wind that, when present, absorbs UV light and leaves X-rays to pummel the disk. Winds are common in a system with a newly formed, energetic star, the team says, but it is possible to catch the system during a quiet, wind-free pe- riod, which is what Spitzer hap- pened to do. “Both the Spitzer and Webb data are excellent, so we knew this had to be something new we were ob- serving in the SZ Cha system – a sig- nificant change in conditions in just 15 years,” added co-author Ardjan Sturm of Leiden University, Leiden, Netherlands. Espaillat’s team is already planning more observations of SZ Cha with Webb, as well as other telescopes, to get to the bottom of its mysteries. “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,” said co-author Caeley Pittman of Boston University. “It’s possible that brief, quiet periods dominated by extreme UV radiation are common in many young plane- tary systems, but we just have not been able to catch them.” “Once again, the universe is show- ing us that none of its methods are as simple as we might like to make them. We need to rethink, re-ob- serve, and gather more information. We’ll be following the neon signs,” said Espaillat. I n this artist concept, the young star SZ Chamaeleontis (SZ Cha) is surrounded by a disk of dust and gas with the potential to form a planetary system. Once our solar system looked something like this, before planets, moons, and aster- oids formed. The raw ingredients, including those for life on Earth, were present in the Sun’s protoplanetary disk. [NASA, ESA, CSA, Ralf Crawford (STScI)] !