The discovery of the first interstellar visitor , a blank stone called‘Oumuamua , sent wafture of upheaval across the scientific community . It also started a mystery . The object had all the characteristics of an asteroid , smallish sizing and no visible tail approaching the Sun ; and yet as it approach our star , it mysteriously accelerated , behaving more like a comet but without any evidence it was ejecting throttle . Now , we may know why .

scientist suspected some variety of outgassing . And although there has been the odd claim that the object was analien probe of some kind , researchers adjust out to find how the interstellar object come to move in that unearthly fashion .

Now they think they have the resolution . It was indeed down to outgassing fromthis cometary object . Specifically , atomic number 1 escaping the comet would have given it the push it want to explain its uncanny apparent movement . The research worker needed a way for atomic number 1 to form , and it turns out that cosmic radiation between the stars is more than capable of exempt the H from weewee frappe .

" A comet traveling through the interstellar metier basically is getting cooked by cosmic irradiation , forming hydrogen as a result . Our thought was : If this was go on , could you really immobilise it in the body , so that when it come in the Solar System and it was warmed up , it would outgas that hydrogen ? " lead source Dr Jennifer Bergner , a UC Berkeley help professor of chemistry , enunciate in astatement . " Could that quantitatively produce the power that you require to explicate the non - gravitational acceleration ? "

There are actually decades ' worth of research on what high - energy corpuscle can do to ice , going all the means back to the 1970s . The team expects cosmic irradiation to penetrate X of meters into the ice and turn a quartern or more of it into atomic number 1 gas , as some psychoanalysis hassuggested . This might not be much for a big comet but ‘ Oumuamua was estimated to be around just 115 by 111 meter ( 377 by 364 feet ) in size , and about 19 meters ( 62 feet ) thick .

" For a comet several kilometers across , the outgassing would be from a really thin casing comparative to the bulk of the target , so both compositionally and in term of any acceleration , you would n’t necessarily expect that to be a detectable effect , " Bergner explained . " But because ' Oumuamua was so little , we remember that it actually produced sufficient force play to power this speedup . "

The model developed by Bergner with Darryl Seligman , now at Cornell University , explains the unusual properties of ‘ Oumuamua without hold to contribute additional parameter to make it fit the watching . And this work once again supports the thought that this body was a fragment of a planetesimal , maybe aPluto - similar objectat the edge of another solar system .

" We had never seen a comet in the Solar System that did n’t have a dust comatoseness . So , the non - gravitative acceleration really was weird , " Seligman said .

" The main takeout food is that ' Oumuamua is ordered with being a stock interstellar comet that just experienced heavy processing , " Bergner added . " The example we ran are reproducible with what we see in the Solar System from comets and asteroids . So , you could essentially start with something that looks like a comet and have this scenario run . "

The subject is published in the journalNature .