As NASA says, comets are “cosmic snowballs” of frozen gases, rock, and dust that include a good amount of organic materials. Accordingly, scientists have long suggested that a comet brought these molecules to Earth and that they became the building blocks for life here. But a new study explains how that scenario might actually be impossible.

It’s very likely that comets carrying organic materials have crashed into Earth at some points in our distant past. The issue, however, has to do with whether these fragile molecules survived its vessel’s violent entry—and the odds are very slim, as researchers explained in a study published today in Scientific Reports. According to the paper, modeling simulations strongly suggest that comets travel too fast and at too sharp an angle to Earth’s atmosphere for the molecules to escape vaporization.

“Historically, scientists thought that comets were important for the origin of life on Earth, because they carried carbon- and nitrogen-bearing molecules,” Richard Anslow, the study’s lead author and an astronomer at Cambridge University in the U.K., said in a statement. “So these giant space snowballs were almost like a ‘get out of jail free card’ that brought all the molecules a planet would need to seed life. It’s kind of a romantic idea, but our results suggest it’s highly unlikely.”

In 2023, Anslow and colleagues explored an idea that was arguably favorable to this “get out of jail free card,” as he puts it. Specifically, they explored whether comets could deposit similar organic materials on other planets in the galaxy, with the understanding that such systems would be promising candidates in the search for extraterrestrial life.

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