It’s a thrilling prospect given that volatiles — particularly water — are needed to kick-start life. Though the team cannot say which volatiles were present, there is reason to hope that water might be one of them, Dr. Domingue said.

The finding runs against the notion that Mercury is inhospitable. At such a close distance to the sun, its surface reaches a scorching 800 degrees Fahrenheit during its day. Then, because the planet has no atmosphere to retain the heat, its surface plummets to minus 290 degrees Fahrenheit during its night.

But a short distance below the surface, the temperatures are much cooler, even pleasant — at least for some life-forms, said Jeffrey Kargel, a co-author of the study who is also from the Planetary Science Institute.

“It is possible that as long as there was water, the temperatures would be appropriate for the survival and possibly the origin of life,” Dr. Kargel said. But at first, even he was not convinced.

“I thought Alexis had lost it at some point,” he said, referring to Dr. Rodriguez. “But the more I dug into the geologic evidence and the more I thought about the chemistry and physical conditions there, the more I realized that this idea — well it might be nuts, but it’s not completely nuts.”

Dr. Hayne, however, thinks that water is an unlikely culprit. The only scenario in which it might be possible is one where water is bound to the rocks.

“So you could have transient pockets of high water activity, but I don’t think this is a case where we’d see massive pools of water and subsurface lakes and that sort of thing,” Dr. Hayne said.