In the early history of our solar system, scientists theorize that a Mars-sized object called Theia smashed into the infant Earth, vaporizing massive amounts of rock and blasting it into space. Some of that material coalesced into the Moon, where NASA’s Artemis program is returning humans, preparing for Mars, and shaping the future of space exploration.
That long-ago, violent collision
reshaped our home planet. Astronomers have used NASA’s James Webb Space
Telescope to examine a class of young stellar systems that show signs of
similar upheavals, providing clues to the amount of energy in their collisions.
The results offer insights into the composition and evolution of these chaotic
systems.
The team’s findings published
Thursday in The Astrophysical Journal.
Image: Extreme Debris Disk
(Artist’s Concept)
The types of collisions within young stellar systems
known as extreme debris disks are relevant to scientists’ understanding of our
own solar system, which is thought to have undergone similar impact events that
created our Moon and shaped Earth’s initial state.
Artwork: NASA, ESA, CSA, Joseph Olmsted (STScI)
The environment surrounding a star
changes as it ages, beginning with a juvenile, gas-rich protoplanetary disk where forming planets can reside, before evolving to a gas-poor debris disk. During its mission lifetime, NASA’s retired Spitzer
Space Telescope examined the debris disk stage and discovered a subclass termed extreme
debris disks. These systems harbor unusually large amounts of warm dust close
to the star, in the region comparable to where rocky planets orbit in our solar
system. A team of astronomers led by Kate Su of the Space Science Institute in
Boulder, Colorado investigated these intriguing objects with Webb.
Contrary to theoretical
predictions, which suggest we should observe many extreme debris disks,
observations indicate that these environments are rare. Scientists estimate
roughly only 1% of young stars show observable signatures of this phase based
on the data collected so far, including possibly our own solar system during
its formation. Despite their rarity, the team was able to compile a sample of
21 extreme debris disks, including five from Spitzer’s archival data and 16
from Webb, with 12 newly observed disks and follow-up observations on four of
Spitzer’s.
“This is the first time we have
gathered enough systems to truly understand this subclass that we call extreme
debris disks,” said Su, lead author of the paper. “Before Webb, we had limited
information. We knew that they are weird and very different from the typical
cold debris disks that we know, like Vega and Fomalhaut. Now that we have more data, we can pin down what these disks represent
for planet formation and evolution.”
The team confirmed that extreme
debris disks share three key properties: smaller dust grains than those in
protoplanetary or classic debris disks, a high concentration of warm dust, and
irregular brightness variations, all revealed by mid-infrared spectra from Webb and Spitzer.
To determine the driving factor for
these qualities, the team studied the mineralogical makeup of the disks. They
found that their sample could be categorized into silica-rich and silica-poor
disks. Volcanic glass like obsidian is one example of silica-rich material
found on Earth, whereas the silica-poor mineral forsterite appears as green
sand grains on some beaches in Hawaii. An extreme debris disk’s category relays
information on the type of collisions producing the impact debris and may help
account for its variability in infrared brightness.
“To just see their mid-infrared
emission and beautiful spectral features with Webb, which allowed us to
identify their compositions, was the most exciting thing for me,” said Agnes
Kospal of Konkoly Observatory in Budapest, Hungary, and a coauthor of the
study. “We have no other way to study these planetary embryos directly because
they are too small.”
Of their sample, about one-third is
silica-rich, suggesting these disks are produced by high-energy impacts between
Mars-sized bodies where a significant portion of the material is vaporized. The
remaining two-thirds of their sample is silica-poor, indicating that the
collisions are occurring on smaller scales, like grazing, between Moon-sized
objects. Silica-rich disks are found only around stars younger than 300 million
years, while silica-poor disks persist across a broad range of ages and often
show greater brightness variability. The team proposes that this variability is
driven by the rapid evolution of fresh debris through orbital changes and
additional impacts.
Their findings can be applied to
our own solar system, which may have experienced more than one extreme debris
disk phase.
“How rocky planets formed and giant
planets evolved are part of the broader story of the solar system’s formation.
It’s all one story,” said Su. “Our work on extreme debris disks helps us bring
together the big picture of what we currently understand.”
Image: Composition of Extreme
Debris Disks Across Time
By investigating the compositions of extreme debris
disks, scientists inferred that silica-rich disks are produced by high-energy
impacts of Mars-sized objects, while silica-poor disks are created by less
energetic events from Moon-sized bodies.
Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)
Simulations suggest that terrestrial planets, such as Earth, should form within the first few hundred million years of a solar system’s formation. This period fits with the ages of silica-rich extreme debris disks observed so far and aligns with the 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.
As for whether our Sun underwent a silica-poor extreme disk phase, if older silica-poor disks and their random intervals of infrared brightness do reflect orbital instability, this would be broadly consistent with the Late Heavy Bombardment hypothesis for our solar system. In that scenario, the gas giant planets migrated significant distances, gravitationally disrupting the orbits of smaller bodies and triggering catastrophic collisions that generated the short-lived, dust-rich phases observed in extreme debris disks.
“Of course, there’s many things we still don’t know about these disks,” said Attila Moor of Konkoly Observatory, a coauthor of the study. “We expect no silica-rich systems among older extreme debris disks. We only have three disks in our sample that fit that age criteria, so it’ll be nice to observe more of these systems to confirm our hypothesis.”
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
To learn more about Webb, visit: https://science.nasa.gov/webb
Source: NASA’s Webb Provides Crash Course on Planet-Shattering Collisions - NASA Science
