A new explanation for the rocky world’s jumbled landscape opens a possibility that it could have had ingredients for habitability.
Mercury — a planet with a surface hot enough to melt lead — might once have contained ingredients needed for life. Though that’s a pretty big might.
The new theory, published last week in the journal Scientific Reports, is based on a particularly muddled feature on the planet orbiting closest to the sun, known as “chaotic terrain.” Here, the cracked, uneven and jumbled landscape consists of fractured rock, mismatched peaks and collapsed craters.
“Think of a kid throwing up a bunch of building blocks and how they land,” said Deborah Domingue, a co-author of the study from the Planetary Science Institute, headquartered in Tucson, Ariz. “Some are up, some are down, some are tilted — that’s chaotic terrain.”
For nearly 50 years, scientists have thought the chaos on Mercury was caused by earthquakes that raced throughout the planet when a massive asteroid struck the planet’s far side.
But the new study, led by Dr. Domingue’s colleague Alexis Rodriguez, upends that notion. It suggests the terrain could not possibly have formed in response to the collision because it occurred 2 billion years after the impact crater formed.
In addition, Dr. Rodriguez and his colleagues discovered that areas within the chaotic terrain appear to have dropped. It’s as though the layer of crust just below the surface had simply disappeared.
The easiest explanation is that subsurface volatiles — elements that can easily switch from a solid to a liquid or a gas — heated up as a result of the intrusion of magma below. That caused those elements to transform into a gas, forcing the terrain above them to collapse into a jumbled mess.
“Let’s say I have a house on stilts, and I kick one out,” Dr. Domingue said. “My house is going to tilt right? That’s what’s going on here.”
Paul Hayne, a planetary scientist at the University of Colorado Boulder who was not involved in the study, agrees that the prevailing explanation for Mercury’s mishmash — which has long been unchallenged — is likely wrong. He also notes that the new story is consistent with what scientists have observed on Mars, where similar terrain was likely caused by the release of volatiles.
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.
Nonetheless, the suggestion that water could exist at all on a planet like Mercury provides a compelling clue toward the search for life across the galaxy. Astronomers have discovered thousands of planets orbiting other stars — some of which look similar to Mercury.
“If it’s happening here, it’s happening somewhere else,” Dr. Rodriguez said.