Do you remember what it felt like decades ago, when we were visited by a comet from another solar system in 2019? the interstellar comet ‘Oumuamua it captured headlines when its cigar-shaped body was spotted following an unusual orbit through our solar system, and subsequent research suggested it may once have been part of a Pluto-like planet and was possibly pancake-shaped.
However, one thing particularly puzzled astronomers, because the comet was speeding away from the sun in a path that seemed strange. Now, the researchers say they have an explanation for their unusual path, and it’s not aliens, it’s a natural phenomenon called outgassing.
Comets are made mostly of dust, rock, and ice, and as they get closer to the sun they heat up and emit particles of water and dust (which form the distinctive comet tails). We are used to seeing medium-sized comets ejecting gases, giving the comet a little kick and changing its trajectory ever so slightly.
But ‘Oumuamua was much smaller than a typical comet, at just over 100 meters in diameter, and when first observed, it had no tail and did not appear to be spewing water. So how could its trajectory be different from the typical elliptical orbit created by gravity?
The lead investigator, an astrochemist, worked with an astronomer on the idea that hydrogen outgassed by the comet could have been trapped within the comet’s own ice.
“A comet traveling through the interstellar medium is basically being cooked by cosmic radiation, forming hydrogen as a result. Our thinking was: if this was happening, could you really trap it in the body, so that when it went into the solar system and got warmer, it would outgas that hydrogen?” researcher Jennifer Bergner said in a paper. release. “Could that quantitatively produce the force you need to explain non-gravitational acceleration?”
The pair found that the trapping effect did occur, but only in a thin shell around a comet’s outer body. Most of the comets we observe are much larger than ‘Oumuamua, at just a few miles in diameter, so the effect is almost invisible. But in tiny ‘Oumuamua, the researchers found that the effect would be significant enough to alter its orbit.
“The beautiful thing about Jenny’s idea is that it’s exactly what should happen with interstellar comets,” said the other researcher, Darryl Seligman. “We had all these stupid ideas, like hydrogen icebergs and other crazy things, and it’s just the most generic explanation.”
The research is published in the journal Nature.