Free Astronomy Magazine September-October 2025

36 SEPTEMBER-OCTOBER 2025 T hese images illustrate how hot gas condenses into solid minerals around the baby star HOPS-315. The image to the left was taken with the Atacama Large Millimeter/submil- limeter Array (ALMA), in which ESO is a partner. Two insets show artist’s impressions of mole- cules of silicon monoxide condensing into solid silicates. [ESO/L. Calçada/ALMA(ESO/NAOJ/ NRAO)/M. McClure et al.] T his image shows jets of silicon monoxide (SiO) blowing away from the baby star HOPS-315. The image was obtained with the with the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner. The blue jet is moving towards us, and the red one is moving away. Observations taken with the James Webb Space Telescope (JWST) show signatures of SiO moving at about 10 km/s. The SiO jets seen in this ALMA image move about 10 times faster though. This means that the slow-moving SiO must be located in a small area around the star, about the size of the asteroid belt around our Sun, too small to be seen in this image. Also, the abundance of gaseous SiO measured in the jet seen with ALMA is lower than expected. Since the composition of the jet should be similar to that of the disc from where the jet emerges, this means that some of the gaseous SiO in the disc is condensing into solid material. [ALMA(ESO/NAOJ/NRAO)/M. McClure et al.] European and Canadian space agen- cies. To find out where exactly the signals were coming from, the team observed the system with ALMA, the Atacama Large Millimeter/submil- of these crystalline minerals. With their new discovery, astronomers have found evidence of these hot minerals beginning to condense in the disc around HOPS-315. Their results show that SiO is present around the baby star in its gaseous state, as well as within these crys- talline minerals, suggesting it is on- ly just beginning to solidify. “This process has never been seen before in a protoplanetary disc — or any- where outside our Solar System,” says co-author Edwin Bergin, a pro- fessor at the University of Michigan, USA. These minerals were first iden- tified using the James Webb Space Telescope, a joint project of the US, limeter Array, which is operated by ESO together with international partners in Chile’s Atacama Desert. With these data, the team deter- mined that the chemical signals were coming from a small region of the disc around the star equivalent to the orbit of the asteroid belt around the Sun. “We’re really see- ing these minerals at the same loca- tion in this extrasolar system as where we see them in asteroids in the Solar System, ” says co-author Logan Francis, a postdoctoral re- searcher at Leiden University. Because of this, the disc of HOPS-315 provides a wonderful analogue for studying our own cosmic history. As van ‘t Hoff says, “this system is one of the best that we know to actually probe some of the processes that happened in our Solar System.” It also provides astronomers with a new opportunity to study early planet formation, by standing in as a substitute for newborn solar sys- tems across the galaxy. ESO astronomer and European AL- MA Programme Manager Elizabeth Humphreys, who did not take part in the study, says: “I was really im- pressed by this study, which reveals a very early stage of planet forma- tion. It suggests that HOPS-315 can be used to understand how our own Solar System formed. This result highlights the combined strength of JWST and ALMA for exploring pro- toplanetary discs.” !