Interstellar object ‘Oumuamua believed to be ‘active asteroid’

Scientists believe cigar-shaped visitor to our solar system is fragment of a larger body

The cigar-shaped interstellar visitor to our solar system known as ‘Oumuamua could be the remnants of a larger body that was torn apart by its host star, according to researchers.

The dark, reddish object that hurtled into our solar system in 2017 and was named after the Hawaiian word for messenger or scout has long puzzled scientists.

Among its peculiarities is the lack of an envelope of gas and dust that comets typically give off as they heat up. Further work by experts suggested the body was accelerated by the loss of water vapour and other gases – as seen with comets but not asteroids. The upshot was that ‘Oumuamua was labelled a “comet in disguise”.

Now scientists say they have shed light on the mystery and addressed the myriad pieces of the ‘Oumuamua puzzle.

They say ‘Oumuamua is an “active asteroid” formed from a body that was torn apart by its parent star and then ejected into interstellar space.

“Most planetary bodies … consist of numerous pieces of rock that have coalesced under the influence of gravity. You could imagine them as sandcastles floating in space,” said Dr Yun Zhang, a co-author of the new study from the Observatoire de la Côte d’Azur in France.

These bodies experience a number of forces as they pass their star.

“A tidal encounter between a planet or small body and a star is a tug-of-war game between the gravitational pull of the star and the self-gravity of the flyby body,” said Zhang, noting that when the body passes too close to the star and enters the tidal disruption region, it can stretch and be torn apart giving rise to fragments.

Writing in the journal Nature Astronomy, Zhang and Prof Doug Lin of the University of California’s Lick Observatory, report how they used computer models to reveal that such a process could have produced ‘Oumuamua and explain features including its tumbling motion, colour and unusual shape.

Zhang said near and far parts of ‘Oumuamua’s parent body would have been pulled apart from each other in the tidal disruption region, resulting in the formation of elongated fragments, such as ‘Oumuamua, which would be glued together by surface material that melted near the star and froze as it flew on.

Zhang said most of the volatile substances on ‘Oumuamua’s surface would have been lost from heating by the star around which it formed, but some residual water ice could have been preserved below its surface and subsequently heated by our, hotter, sun – explaining its unusual acceleration. “We may call ‘Oumuamua an active asteroid,” said Zhang.

The team say ‘Oumuamua could have formed from either a comet or a planet several times the size of Earth, but the former better explains ‘Oumuamua’s apparent subsurface water ice. The star around which ‘Oumuamua formed, they add, would probably have been similar to our sun but smaller and denser – or possibly a white dwarf.

Zhang says the findings not only scotch again the much-publicised notion that ‘Oumuamua is an alien spacecraft, but offer an efficient way in which asteroidal interstellar objects, previously thought to be rare, can be formed.

What’s more, she says, with objects such as ‘Oumuamua passing through “habitable zones”, such as our own solar system, they may even carry seeds of life.

Dr Alan Jackson, of Arizona State University, who was not involved in the study but has previously carried out research into ‘Oumuamua, welcomed the work.

“The idea of ‘Oumuamua being a fragment of a larger body that was tidally disrupted by passing close to its parent star was suggested by Matija Ćuk in 2018,” he said. “But this is the first work that I have seen that really explores that idea in detail and shows that it might explain how ‘Oumuamua was produced and a lot of its unusual features.”

Contributor

Nicola Davis

The GuardianTramp

Related Content

Article image
Scientists solve mystery of interstellar object 'Oumuamua
Visitor from another solar system is acutally a comet in disguise, say researchers

Nicola Davis

27, Jun, 2018 @5:00 PM

Article image
Interstellar object ‘Oumuamua covered in 'thick crust of carbon-rich gunk'
Cigar-shaped body has a deep surface layer made of organic ices baked in interstellar radiation – and potentially has ice in its heart, say astronomers

Ian Sample Science editor

18, Dec, 2017 @4:00 PM

Article image
Mysterious object seen speeding past sun could be 'visitor from another star system'
If its origins are confirmed, the asteroid or comet, named A/2017 U1, will be the first object known to come from elsewhere in the galaxy, say astronomers

Nicola Davis

27, Oct, 2017 @2:27 PM

Article image
Starwatch: First interstellar visitor's name is nod to Hawaiian sighting
Astronomers using the Pan-STARRS 1 telescope on Maui identified 1I/‘Oumuamua as it passed 24m km from Earth

Alan Pickup

12, Nov, 2017 @9:30 PM

Article image
Water inside moon mostly from asteroids, study suggests
Hydrogen in lunar samples reveals water could have been delivered by asteroids crashing into the moon’s vast magma ocean billions of years ago

Nicola Davis

31, May, 2016 @3:00 PM

Article image
Why don’t we see more meteorites after big asteroid belt collisions?
Amount of cosmic debris reaching Earth has stayed surprisingly constant in last 500m years, say scientists

Kate Ravilious

03, Aug, 2021 @5:00 AM

Article image
Armageddon: scientists calculate how stars can nudge comets to strike Earth
Plotting how often stars stray into the Oort cloud allows astronomers to assess the risk of all life being wiped out by a cosmic cataclysm

Hannah Devlin Science correspondent

31, Aug, 2017 @5:16 PM

Article image
British engineers to start work on 'comet chaser' probe
Mission will record details about the composition of the astral bodies and could be launched in 2028

Ian Sample Science editor

14, Dec, 2020 @12:01 AM

Article image
Nasa to slam spacecraft into asteroid in mission to avoid future Armageddon
Test drive of planetary defence system aims to provide data on how to deflect asteroids away from Earth

Linda Geddes

22, Nov, 2021 @4:04 PM

Article image
‘Don’t Look Up’: humanity could avert asteroid Armageddon, say scientists
Planet likely to be spared from catastrophic end if 10km-wide Earthbound asteroid was spotted, analysis finds

Hannah Devlin Science correspondent

27, Jan, 2022 @6:28 PM