NEW YORK — A Mars-orbiting satellite recently spotted seven dark spots near the planet’s equator that scientists think could be entrances to underground caves.

The football-field-sized holes were observed by Mars Odyssey’s Thermal Emission Imaging System (THEMIS) and have been dubbed the seven sisters — Dena, Chloe, Wendy, Annie, Abbey, Nikki and Jeanne — after loved ones of the researchers who found them. The potential caves were spotted near a massive martian volcano, Arisa Mons. Their openings range from about 100 meters to 250 meters wide, and one of them, Dena, is thought to extend nearly 130 meters beneath the planet’s surface.

The researchers hope the discovery will lead to more focused spelunking on Mars.

“Caves on Mars could become habitats for future explorers or could be the only structures that preserve evidence of past or present microbial life ,” said Glenn Cushing of Northern Arizona University, who first spotted the black areas in the photographs.

Now, researchers from NASA, Northern Arizona University and the U.S. Geological Survey aim to refine the visual and infrared techniques THEMIS used to find the martian caves and to develop robots that can one day explore them.

The Earth-Mars Cave Detection Program will test their approach in “Mars analogue” sites, terrestrial environments with similarities to martian landscapes such as the Mojave Desert in California and the Atacama Desert in Chile, as well as frigid environments like Iceland and Antarctica.

The researchers already have acquired the thermal signatures of a dozen caves in Arizona and New Mexico using an experimental infrared detector flown aboard an airplane, dubbed the Quantum Well Infrared Photodetector (QWIP), as well using a hand-held thermal camera on the ground.

Scientists used QWIP to spot regions in the landscape where temperatures are different from the surroundings. Inside a cave, temperatures are nearly constant due to lack of sunlight, while outside temperatures fluctuate with the rising and setting of the sun. At a cave entrance, these two temperature regimes mix together to create a unique thermal signature.

“The caves show up as hotspots in a sea of cold, or as cold spots in a sea of warmth,” said study team member Murzy Jhabvala, chief engineer of the Instrument Systems and Technology Center at NASA’s Goddard Space Flight Center.

“It jumps out at you,” said Jut Wynne, a biospeleologist, or cave biologist, with the U.S. Geological Survey and Northern Arizona University.

Next, the researchers will tweak their technique to figure out the best wavelengths to use and optimal times during the day for cave hunting, and then apply their findings to Mars, according to Wynne, who is also the Earth-Mars Cave Detection Program project leader.

The project team also aims to design robots that can explore newly spotted martian caves. But the researchers may have to design multiple robots, according to Natalie Cabrol, a planetary geologist with NASA Ames Research Center and the SETI Institute.

“There are many types of caves,” Cabrol, a Mars robot veteran who helped engineers field-test the Spirit and Opportunity robotic rovers , said in a telephone interview. “It may be that we come up with one very versatile design … or we might end up with several designs.”

If the caves have a relatively simple structure — like the straight and simple lava tubes carved by flowing magma — a rover-type robot might work, Cabrol said. “I would doubt that a rover, equipped as they are now, would do a good job in a cave” with a more complicated geometry, she said.

The researchers also are considering deploying several miniature robots together into a cave.

“You could throw out an array of microbots in a birdshot approach over an area where you think there is a cave,” Wynne said . The microbots could then use sonar to confirm the presence of a cave and pinpoint its location.

Regardless, these robotic explorers will have to be agile, have some basic sense of self-awareness, sport excellent night vision and have the ability to communicate in some innovative way, since conventional radio communication might not work well in caves, Cabrol said.

“We are very much on the starting line on this,” she added. “This is very exciting.”