Exoasteroid

An exoasteroid, exo-asteroid or extrasolar asteroid, is an asteroid located outside the Solar System. While exoasteroids and exoasteroid belts were once considered hypothetical, recent scientific studies and thorough analyses have provided evidence for their existence.

Evidence
Scientists propose that the formation of exoasteroids often results from the fragmentation of exoplanets by gas giants. These exoasteroids are presumed to be the remnants of smaller celestial bodies that endured the demise of their parent exoplanet. Analogous processes are hypothesized to have occurred during the formation of our Solar System.

NASA has conducted studies affirming that the presence of asteroid belts around stars is a common phenomenon in nearly any solar system hosting planets comparable in size to the outer and inner planets of our Solar System.

History
In December 1988, American astrophysicists Benjamin Zuckerman and Eric Becklin detected a substantial circumstellar disc encircling the white dwarf star G 29-38, stemming from a near-infrared survey of 200 white dwarfs. Zuckerman and Becklin conducted further investigations on the white dwarf star, uncovering that the circumstellar disc emits notable radiation within the 2 to 5 micrometer range. This discovery suggests potential interactions between exoasteroids and radiant matter, possibly leading to their ejection into space. Subsequent observations in 2004 by the Spitzer Space Telescope revealed the presence of a dust cloud surrounding G 29-38. This phenomenon is believed to have originated from the disintegration of an exocomet or exoasteroid as it interacted with the white dwarf over time. Spitzers observations further proved that exoasteroids could exist.

In May 2023, the James Webb Space Telescope provided images of Fomalhaut, a young star positioned 25 light-years (ly) away from Earth. Scientists analyzed these images and conducted simulations and tests on Fomalhaut's asteroid belt, proposing that it likely formed due to collisions involving larger celestial bodies.

Another notable star hosting an asteroid belt is the white dwarf star WD 0145+234. It is hypothesized that WD 0145+234 once hosted an exoasteroid or exoplanet in orbit around it, which was subsequently disrupted, leading to the formation of a substantial exoasteroid belt. Due to the star's dimensions, scientists infer that the accretion disk surrounding WD 0145+234 is highly active, resulting in the regular disruption of exoasteroids by the star's gravitational pull. In 2018, astronomers observed a 10% increase in the star's mid-infrared light, indicative of the recent destruction of an exoasteroid, which led to the formation of a cloud of metallic dust partially obscuring WD 0145+234 from Earth's view.

Detection
In 2013, astronomers discovered fragmented remnants of an exoasteroid orbiting the star GD 61. Upon detailed examination, scientists determined that the asteroid possessed a surface rich in water, comprising approximately 26% water by mass, a composition akin to the surface water, primarily in the form of ice, found on the dwarf planet Ceres. It suggests the potential existence of an exoplanet with liquid water around the star at some point in its history. It is postulated that the asteroid met its demise due to interactions with its star, leading to its fragmentation and subsequent formation of an asteroid belt around the star.

Following this discovery, scientists used the Cosmic Origins Spectrograph aboard the Hubble Space Telescope to analyze the chemical composition of the asteroid; it showed the presence of magnesium, silicon, iron, and oxygen within the asteroid's water.

Proposed observational methods
Exoasteroids can be detected through various methodical processes. The transit method is a common technique used to discover extrasolar objects as they pass in front of their host star, providing scientists with the opportunity to observe their shape. Spectroscopy can be used to identify distinctive characteristics of exoasteroids, and allows to detect surface features. Other techniques include remote sensing and data from past missions to minor planets.