NEW ORLEANS — How is a little Pacific island like the planet Mars?
Let James Garvin count the ways.
In December 2014, an underwater volcano amid the islands of Tonga in the South Pacific erupted. When the eruption ended and ashes settled a month later, a new island had emerged, rising 400 feet above the ocean’s surface.
Scientists unofficially named the island Hunga Tonga-Hunga Ha’apai, a concatenation of two older, uninhabited islands it nestles between.
Since then, scientists have been tracking how the new land mass has eroded and shifted. What they have found could make the island a Rosetta Stone to understanding volcanic features on Mars that also appear to have erupted underwater, providing clues about when the red planet was wet several billion years ago.
“We see things that remind us of this kind of volcano at similar scales on Mars,” said Dr. Garvin, the chief scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “And literally, there are thousands of them, in multiple regions.”
He and colleagues presented the findings on Monday at a news conference at a meeting of the American Geophysical Union here.
Networks of river channels chiseled into Mars persuasively argue that liquid water once flowed across the red planet, but the current thinking of many planetary scientists is that Mars remained frozen through much of its history, punctuated with episodes of melting and flowing water.
Some Martian volcanoes that look as if they erupted underwater could offer clues. By analyzing these leftover structures, scientists may be able to tease out information like how deep the water was when the volcanoes erupted and how long water persisted.
But to fully understand the terrain on Mars, researchers need a model to compare it against, and that’s where the new island comes in.
While Tonga is in the middle of the ocean, Hunga Tonga-Hunga Ha’apai and its neighbors sit on the rim of a large volcano that rises about a mile above the deep ocean floor. Thus the water around the island is shallow, perhaps similar to what existed around the Martian volcanoes.
Since the eruption, satellites have repeatedly viewed the new Tongan island, not much more than a square mile in size, allowing scientists to generate detailed maps of the shifting topography.
Scientists have also made visits to map the surrounding seafloor and walk around for up-close examination. That’s an advantage that Earth scientists have over Mars researchers — they can directly compare what satellites see from orbit with samples they pick up.
Islands formed by explosive underwater eruptions are usually short-lived, the ash washed away by crashing waves. In the initial months of its existence, Hunga Tonga-Hunga Ha’apai shifted in shape quickly. Initially oval, the island’s southern shore eroded rapidly, allowing the Pacific Ocean to break through into the lake at the center of the island. Steep walls around the lake appeared in danger of collapse, and it looked as if the island might have been about to vanish.
But then a sandbar formed, sealing off the lake again, and the landscape stabilized.
When conditions are right, chemical reactions with warm water cement volcanic ash into resilient rock, and the scientists speculate that similar reactions may have occurred on Hunga Tonga-Hunga Ha’apai. It is only the third such island in the last 150 years to survive more than a few months. They estimate that the island could now last for decades.
The evolving island can be compared with erosion patterns around Martian volcanoes. If some of the volcanic shapes on Mars matched an intermediate state of Hunga Tonga-Hunga Ha’apai, that could suggest that the water disappeared and the erosion stopped.
“That will give us a window into some of those murkier times of Mars, when we think there were standing bodies of water,” Dr. Garvin said.