TORONTO -- Three years after a mysterious cigar-shaped interstellar object was spotted hurtling through our solar system, sparking questions of alien spaceships and solar sails, a new study suggests this visitor may actually have been the cosmic version of a massive iceberg, formed in the birthplace of stars out of frozen hydrogen gas.
And it could be one of many.
Since it was first spotted by the Pan-STARRS 1 telescope in Hawaii in October 2017, the 400 metre-long 鈥極umuamua -- which means 鈥渕essenger from afar arriving first鈥� or 鈥渟cout鈥� in Hawaiian -- has sparked numerous studies and research trying to unravel its mysteries.
鈥極umuamua was our first visitor from a different solar system, discovered while already on its way out of our system, and it defied the known rules for asteroids and comets. Its oblong shape was interesting, but most baffling was its speed, which was faster than should鈥檝e been possible if it was being propelled through space purely by gravitational force.
It was observed moving at an estimated 26 kilometres per second, and was accelerating -- with no visible reason for the acceleration. Harvard researchers speculated that this could mean it was an alien probe, sent from deep space to investigate us, but further studies debunked this tantalizing prospect.
One space object that can accelerate is comets, but researchers didn鈥檛 think 鈥極umuamua could be a comet at first due to the fact that it didn鈥檛 seem to have a gas tail or a coma, which is the term for the fuzzy atmosphere of gas and dust surrounding the icy centre of a comet.
Still, several studies posited that 鈥極umuamua could feasibly be a type of comet -- if the gas it was expelling simply wasn鈥檛 visible through our telescopes.
That still left the important question of what exactly it was made of.
, written by researchers from the University of Chicago and Yale and accepted for publication in the Astrophysical Journal Letters, suggests an answer.
Most comets are composed of dust, rock, and ice made largely from frozen water, but also some other frozen substances, including ammonia, carbon dioxide and methane.
Researchers knew how fast 鈥極umuamua had been seen moving, so they worked backwards to see which elements could account for that acceleration once burned up. Frozen hydrogen gas explained 鈥極umuamua鈥檚 movement better than any other type, and would need to 鈥渃over only a fraction鈥� of the object鈥檚 surface, the paper said.
To solidify the theory, hydrogen gas is 鈥渄ifficult to observe,鈥� according to the paper, and the outgassed H2 would not have been picked up by the telescopes observing 鈥極umuamua.
鈥淚t鈥檚 a frozen iceberg of molecular hydrogen,鈥� Darryl Seligman, one of the paper鈥檚 authors, 鈥淭his explains every mysterious property about it.
Hydrogen gas is 鈥渢he dominant constituent of Giant Molecular Clouds,鈥� which are enormous clusters of gases spanning hundreds of light years in size.
The densest parts of these clouds are where stars are born. The temperatures within these dense cores can also be some of the coldest in the universe. The paper suggests that 鈥渕acroscopic bodies composed of frozen molecular hydrogen gas that are not incorporated into stellar systems,鈥� are then 鈥渞eleased into low-velocity dispersion galactic orbits,鈥� meaning that objects such as 鈥極umuamua are some of the leftovers from the process of creating stars.
The paper estimates that 鈥極umuamua could be 100 million years old.
The paper also explained that 鈥極umuamua鈥檚 unusual shape could be a byproduct of its travel through our solar system, and that it likely was much larger before it got close to our Sun -- and before we ever laid eyes on it.
If 鈥極umuamua had never encountered our solar system, the paper said, it may have survived for around 37 million more years before a significant reduction in size.
The researchers wrote in their conclusions that if they are right about the origins and makeup of 鈥極umuamua, 鈥渋t is likely that a large population of similar objects exist.鈥�
If space truly is an ocean filled with these icebergs, it could open up new avenues of research and allow scientists to pry further into the intricate workings of space.
鈥淎 galactic sea of unbound planetesimal-sized objects has potential consequences for star and planet formation,鈥� the paper states.
Considering the outflow of these objects isn鈥檛 even visible, Seligman told UChicago News that us seeing one at all 鈥渋mplies that there鈥檚 a ton of these things out there.
鈥淭he galaxy must be filled with these dark hydrogen icebergs. That鈥檚 incredibly cool.鈥�
