An exoasteroid, exo-asteroid or extrasolar asteroid, is an asteroid outside the Solar System. Exoasteroids (and related exoasteroid belts) were considered to be hypothetical, but scientific study and thorough analysis has provided evidence for their existence.^[1]

Evidence

On how exoasteroids would form, scientists concluded that gas giants would have to break apart exoplanets. The leftover smaller celestial bodies that survived during the destruction of the planet are the exoasteroids. The same processes happened during the formation of the Solar system. ^[2][3]

NASA once conducted studies, confirming that almost any solar system with planets as large as the outer gas giants and inner planets as large as the inner terrestrial planets could form an asteroid belt around its star.^[3]

History

In December 1988, a study conducted by Benjamin Zuckerman and Eric Becklin found evidence of a large circumstellar disc around white dwarf star G 29-38 after a near-infrared survey of 200 white dwarfs. ^[4] Both scientists conducted studies on the white dwarf star, eventually discovering the circumstellar disc radiate a substantial emission between 2 and 5 micrometres. This could prove the existence of asteroids, and them bouncing of radiant matter into space. ^[5] Later observations made in 2004 by the Spitzer Space Telescope indicated the presence of a dust cloud around G 29-38, which may have been created by an exocomet or exoasteroid being ripped apart by the white dwarf during its history. ^[6] Spitzers observations further proved that exoasteroid belts and exoasteroids could exist.

In May 2023, the James Webb Space Telescope captured images of Fomalhaut,^[7] a young star located 25 light-years (ly) from Earth. Scientists conducted simulations and tests of Fomalhaut's asteroid belt, and concluded that the asteroid belt may have formed due to larger body collisions.^{[7][clarification needed]}

Another star that has been detected to have an asteroid belt around it is white dwarf star WD 0145+234. It is thought that WD 0145+234 had a previous exoasteroid or exoplanet orbiting it, which was later destroyed, subsequently forming a massive exoasteroid belt. Due to the star's radius, scientists have concluded that the accretion disk orbiting WD 0145+234 is very active, with exoasteroids being ripped apart by the star's gravitational pull relatively normally. In 2018, astronomers detected that the star's light was 10% more intense in the mid-infrared spectrum, and concluded that a recent exoasteroid was pulled apart, creating a cloud of metallic dust that blocks WD 0145+234‘s view from Earth, albeit the gas cloud doesn't block much light from Earths view.^[8]

Detection

In 2013, astronomers discovered shattered remains of an exoasteroid around star GD 61. On closer analysis, scientists concluded that the asteroid previously had a water-rich surface: originally some 26% water by mass on its surface, almost close to the surface water (in the form of ice) on the dwarf planet Ceres. This evidence suggests that an exoplanet that carried liquids could have existed around the star at some point in its history. It is thought the asteroid was destroyed by its star, leaving tiny fragments behind; also creating an asteroid belt around the star.

Subsequently, scientists used the Cosmic Origins Spectrograph aboard the Hubble Space Telescope to determine the chemical elements contained in the asteroid: magnesium, silicon, iron, and oxygen were detected in the asteroid's water.^[9]

As of December 2023, GD 61 is the only star known to have had an asteroid orbiting it.^{[citation needed]}

Observation methods

Exoasteroids can be detected as they transit their star, which could also allow for scientists to see the shape of the asteroid. Spectroscopy can also be a useful resource in finding interesting characteristics of an exoasteroid, as scientists could detect surface features on the asteroid, giving a better understanding of the asteroid.

Using information from our Solar System

Remote sensing of the object ʻOumuamua found it was primordially covered with rocks and metals.^[10] As ʻOumuamua is an extrasolar object, using this information could be reliable information, and scientists could discover that most exoasteroids could be covered with the same materials ʻOumuamua carries. Scientists could also use data from past missions that studied asteroids or comets as well, although they would not be as reliable.