Composition of extreme debris discs across time

A team of researchers compiled the largest sample of extreme debris discs to date thanks to data from the NASA/ESA/CSA James Webb and NASA’s Spitzer space telescopes. These young stellar systems are a subclass of debris discs, which follows the juvenile protoplanetary disc stage.

Interested in the mineralogical makeup of these young stellar systems, the team separated their sample into silica-rich and silica-poor. Based on their categorisation, they were able to infer the type of collisions that are helping create these chaotic, dusty environments.

Of their sample, eight are silica-rich discs (black dots), suggesting that they are produced by high-energy impacts between Mars-sized bodies where a substantial amount of the material is vaporised. Thirteen discs fall into the silica-poor category (purple dots), indicating that the collisions within these discs are less intense in nature and occur between Moon-sized objects. The team also noted the corresponding age of each disc’s star and spotted an interesting trend: The silica-rich discs in their sample are found only around stars younger than 300 million years. The stars with silica-poor discs span a broad range of ages.

The study’s findings are shaping scientists’ understanding of our own Solar System, which may have experienced more than one extreme debris disc phase. Simulations suggest that terrestrial planets should form within the first few hundred million years. This period aligns with the distribution of the silica-rich extreme debris discs and with astronomers’ estimation that Earth and the Moon formed around 100 million years after the Sun formed, with the Moon likely being the result of a collision between Earth and a Mars-sized object.

The distribution of the silica-poor discs is broadly consistent with the Late Heavy Bombardment hypothesis for our Solar System, which proposes that the gas giant planets migrated significant distances and gravitationally disrupted the orbits of smaller bodies. Due to their movements, catastrophic collisions occurred and generated the short-lived, dust-rich phases observed in extreme debris discs.

[Image description: Graphic titled Extreme Debris Discs, Composition Across Time showing a plot and corresponding timeline of the Solar System. The plot’s y-axis is labeled Silica with an up arrow labeled rich and a down arrow labeled poor. The x-axis is labeled Age (millions of years) and starts with 1 at the left and increases by factors of ten, ending with 1000 at right. A key at right has 3 symbols: black dot is Silica-rich disc, purple is Silica-poor disc, and orange is Protoplanetary disc. All 27 orange dots are within the first 10 million years and range in silica composition. The 8 black and 13 purple dots begin to appear around 10 million. The black dots stop around 100 million. The purple dots continue right. The timeline below has the same labels as the plot’s x-axis. A gray band before 100 marks the Moon-forming impact. A gray band before 1000 marks the Late heavy bombardment. 3 blue bands stretch from left to right: Giant planet formation, Terrestrial planet formation, and Giant planet migration/orbital instability.]