Evidence is mounting that a tiny subatomic particle seems to be disobeying the known laws of physics, scientists announced Wednesday, a finding that would open a vast and tantalizing hole in our understanding of the universe. The result, physicists say, suggests that there are forms of matter and energy vital to the nature and evolution of the cosmos that are not yet known to science. “This is our Mars rover landing moment,” said Chris Polly, a physicist at the Fermi National Accelerator Laboratory, or Fermilab, in Batavia, Illinois, who has been working toward this finding for most of his career. The particle célèbre is the muon, which is akin to an electron but far heavier and is an integral element of the cosmos. Polly and his colleagues — an international team of 200 physicists from seven countries — found that muons did not behave as predicted when shot through an intense magnetic field at Fermilab.

The aberrant behavior poses a firm challenge to the Standard Model, the suite of equations that enumerates the fundamental particles in the universe (17, at last count) and how they interact.

“This is strong evidence that the muon is sensitive to something that is not in our best theory,” said Renee Fatemi, a physicist at the University of Kentucky.

The results, the first from an experiment called Muon g-2, agreed with similar experiments at the Brookhaven National Laboratory in 2001 that have teased physicists ever since.

At a virtual seminar and news conference Wednesday, Polly pointed to a graph displaying white space where the Fermilab findings deviated from the theoretical prediction. “We can say with fairly high confidence, there must be something contributing to this white space,” he said. “What monsters might be lurking there?”

“Today is an extraordinary day, long awaited not only by us but by the whole international physics community,” Graziano Venanzoni, a spokesperson for the collaboration and a physicist at the Italian National Institute for Nuclear Physics, said in a statement issued by Fermilab. The results are also being published in a set of papers submitted to several peer-reviewed journals.

The measurements have about one chance in 40,000 of being a fluke, the scientists reported, well short of the gold standard needed to claim an official discovery by physics standards. Promising signals disappear all the time in science, but more data are on the way. Wednesday’s results represent only 6% of the total data the muon experiment is expected to garner in the coming years.