Astronomy:Exoasteroid

Short description: Asteroids found outside of the Solar System

Exoasteroid belts around star Fomalhaut
(James Webb Space Telescope; 8 May 2023)

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.

Evidence

In the Solar System’s early history, early gas giants would break apart protoplanets, eventually breaking them up into smaller pieces, and turning into the asteroids we observe today. This goes with other solar systems with asteroid belts surrounding them. Another hypothesis on how exoasteroids, or an exoasteroid belt forms is that early gas giants would fling planets using their gravity, ripping them apart, or flinging them towards the Sun to get ripped apart. Planets are only formed when these asteroids, comets or meteorites form together, eventually creating a planet. Another hypothesis is that when stars form, they form an asteroid belt around them consisting of extra material left over from the star's formation. 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 rocky planets could form an asteroid belt around its star.

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. Both scientists conducted studies on the white dwarf star, eventually finding out the circumstellar disc radiate a substantial emission between 2 and 5 micrometres. 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 in its history. Spitzers observations further proved that exoasteroid belts and exoasteroids in general could exist.

In May 2023, the James Webb Space Telescope captured images of Fomalhaut, 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.

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, more massive exoasteroid or exoplanet orbiting it, which was later destroyed, leaving a massive exoasteroid belt orbiting the star. 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. 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 between the Earth and WD 0145+234.

Detection

Exoasteroid being ripped apart by its star

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 a super-Earth exoplanet 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, eventually creating an asteroid belt around the star. This means that exoplanets orbit GD 61, potentially using their gravity to hold the asteroid belt in place, just as how Jupiter holds its asteroid belt.

Some time later, 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.

As of December 2023, GD 61 is the only star known to have had an asteroid orbiting it; especially orbiting asteroids with water content, leading to a hypothetical planet that might have orbited the star in the past.

Observation

Exoasteroids can be detected as they transit their star. Spectroscopy can be useful in detecting asteroids not visible to telescopes; although coordinates would have to be provided in able to detect such an asteroid. Along with spectroscopy, scientists could detect surface features on the asteroid, giving better understanding of the asteroid; almost how researchers found out water was on the first discovered exoasteroid.

Remote sensing

In 2017, ʻOumuamua passed by our Solar system, marking the first interstellar object to be discovered in our solar system. Scientists used techniques to remotely sense the object, and found out it was primordially covered with rocks and possibly metals. Using this information, 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. Asteroids that closely resemble exoasteroids already discovered are 101955 Bennu, which was found recently to carry phyllosilicates that hold water.

See also

• Accretion disk
• Circumstellar disc
• Debris disk
• Disrupted planet
• List of asteroid close approaches to Earth
• List of exceptional asteroids
• Lost minor planet
• Meanings of minor-planet names
• Protoplanetary disk

External links

• "Alphabetical list of minor planet names". International Astronomical Union. http://www.minorplanetcenter.org/iau/lists/MPNames.html. 
• "Asteroid articles in Planetary Science Research Discoveries". University of Hawaii. http://www.psrd.hawaii.edu/Archive/Archive-Asteroids.html. 
• "JPL Asteroid Watch site". Jet Propulsion Laboratory. http://www.jpl.nasa.gov/asteroidwatch/. 
• NASA Asteroid and Comet Watch site