As one of our nearest neighbors, Mars gets a lot of attention. It's the only planet we've visited with rovers, combing over its surface, snapping pictures and taking detailed measurements.
Yet we still know little about what lurks beneath that dusty red surface, which may be why a simple hole on the red planet has grabbed our attention.
What's striking about this hole may be its sheer simplicity. It was discovered back in 2011 by the HiRISE camera aboard the robotic Mars Reconnaissance Orbiter, an instrument so precise it could spot a kitchen table on the planet's surface from 250 miles away.
(You can see some of the mesmerizing images taken by HiRISE here.)
But an image of the hole is making the rounds again after being posted this week on NASA's science blog. While the Martian landscape boasts some dramatic geological features — deep canyons, dead volcanoes, dizzying mountain ranges — what's fascinating about this perfectly round hole is what it may lead to.
As the space agency notes, the image suggests this hole, near the slopes of the Pavonis Mons volcano, is an opening to an underground cavern. While it's just 115 feet wide and 66 feet deep, the partial illumination on the right side of the image suggests some kind of subterranean network.
"Why there is a circular crater surrounding this hole remains a topic of speculation, as is the full extent of the underlying cavern," NASA notes. "Holes such as this are of particular interest because their interior caves are relatively protected from the harsh surface of Mars, making them relatively good candidates to contain Martian life."
Indeed, if there is life on Mars — and we haven't already found it, as one former NASA scientist suggests — we're going to have to dig for it. Or explore some holes that appear to have already been dug.
"These pits are therefore prime targets for possible future spacecraft, robots, and even human interplanetary explorers," NASA explains.
Following just one of these gateways may finally answer the question we've asked since the first Viking landers stirred the Martian dust in the 1970s: Is there anything alive here?
Some scientists think it's possible. Indeed, there may be briny lakes flowing below, with just enough oxygen to support sponge-like lifeforms.
The next question: Who's going down there first?