Astronomers have, for the first time, pinpointed the moment when planets began to form around a star. The observations of the first specks of planet-forming material — hot minerals just beginning to solidify – mark the first time a planetary system has been identified at such an early stage in its formation. The discovery opens a window to the past of our own Solar System.
“This is an important discovery for understanding our origin”, says John H Black, professor emeritus at Chalmers, and part of the team who analysed the data.
This newborn planetary system is emerging around HOPS-315, a ‘proto’ or baby star that sits some 1300 light-years away from us. The star is surrounded by a so-called ‘protoplanetary disc’ of hot gas and dust, the birthplaces of new planets.
What the astronomers have found is evidence of hot minerals that contain silicon monoxide (SiO) beginning to condense in the disc. Their results show that SiO is present around the baby star in its gaseous state, as well as within these crystalline minerals, suggesting it is only just beginning to solidify.
The findings are presented in the article “Refractory solid condensation detected in an embedded protoplanetary disk", in Nature. The study’s lead author is Melissa McClure, professor at Leiden University in the Netherlands. This branch of astronomy is called astrochemistry and focuses on molecules in the universe, their distribution and interaction with radiation.
Teamwork made the discovery possible
John H Black, Professor emeritus at Chalmers, has long-standing collaborations with the astronomers in Leiden, and was part of the team that identified the presence of SiO in HOPS-315, and analyzed its abundance and distribution.
“I was surprised and excited to recognize the infrared signature of silicon monoxide – unexpected things like that often turn out to be important clues. The gaseous SiO points to the earliest stage in the growth of solid silicate minerals, much like those that make up much of the Earth's crust”, says John H Black, whose research has involved developing better methods to analyze how molecular gases respond to the infrared and ultraviolet radiation from disks and stars.
The minerals were first identified using the James Webb Space Telescope (JWST), and to find out exactly where the signals were coming from, the team observed the system with ALMA, the Atacama Large Millimeter/submillimeter Array, in Chile’s Atacama Desert.
Similarities to our Solar system
With the combined data from the telescopes, the team determined that the chemical signals were coming from a small region of the disc around the star equivalent to the orbit of the asteroid belt between Mars and Jupiter, where the same type of minerals can be found in the Solar System today. Because of this, the disc of HOPS-315 provides an analogue for studying our own cosmic history.
“Our own solar system began to take form more than 4.5 billion years ago, yet we can recognize some of the same patterns of structure and composition in a planetary system that is forming now. This is important for understanding our origin. It is also an important part of the story of how chemical changes can continue to affect planets and their atmospheres over time-scales from decades to billions of years, says John H Black, who points out that the crucial factor behind the new discovery is the combination of infrared images and spectra from JWST with the fine detail and sensitivity of mm-wavelength observations from ALMA.
“Both gaseous silicon monoxide and solid crystalline silicate minerals are seen together for the first time. The infrared spectra allow us to identify new chemical components in planet-forming disks while the ALMA data help to trace the assembly of solids from gas in these swirling systems”.
As professor emeritus John H Black still takes active part in the astrochemical community, and he is a part of several research collaborations.
“The study of planet-forming disks is an extremely active field now, with a flood of new developments. Advances are happening on several fronts: observations with JWST and ALMA and other telescopes, laboratory experiments in astrochemistry, and increasingly sophisticated theoretical models. It is very nice for me as a pensioner to stay active in research and to have stimulating interactions with younger colleagues and their students”.
Contact
- Professor Emeritus, Astronomy and Plasma Physics, Space, Earth and Environment