NASA scientists announced Monday that the James Webb Space Telescope has detected complex organic compounds in the surface ice of Europa, Jupiter's fourth-largest moon — a discovery that dramatically raises the probability of microbial life in the moon's vast subsurface ocean.

The compounds, which include carbon-bearing molecules similar to those associated with biological processes on Earth, were identified in infrared spectra captured during a series of targeted observations conducted over the past six months.

"This is the most significant astrobiology finding since the confirmation of liquid water beneath Europa's ice shell," said Dr. Samantha Croft, lead author of the study published in Nature Astronomy. "We are not claiming we have found life. We are saying the ingredients and conditions are there."

Europa's subsurface ocean is believed to contain twice the volume of all Earth's oceans combined. It is kept liquid by tidal heating — the gravitational squeezing caused by Jupiter's immense pull — and is thought to be in contact with a rocky seafloor, providing the mineral nutrients that life requires.

The discovery has accelerated planning for Europa Clipper, the NASA spacecraft currently en route to Jupiter for arrival in 2030. Scientists are now discussing whether the mission's instruments can be reconfigured to search more specifically for biosignatures.

The European Space Agency's JUICE mission, also currently in transit to the Jovian system, will make three close Europa flybys in 2034, providing additional opportunities to examine the moon's composition.

Not all scientists are convinced that the organic compounds point to biological processes. Several astrochemists pointed out that organic molecules can be produced through purely geological and chemical reactions that do not involve life.

"The exciting thing is not what we found, but what it tells us about where to look next," said Professor Jonah Wheeler of Caltech. "Europa just moved to the very top of the priority list for astrobiology."