In the March 2012 issue of Sky and Telescope magazine there’s a fascinating short article about a possible lunar volcanic landform called Ina Caldera. This 2-mile long D-shaped patch looks like nothing I’ve ever seen on the moon.
Blobs of older, crater-pitted lunar crust (darker blobs) rise some 250 feet above the younger, rubbly surface like melted cheese on pizza. Brighter areas on the moon generally indicate younger surface features. Solar and cosmic radiation darkens airless worlds like the moon and asteroids over the long haul of time. Not only is the bumpy region lighter-toned, but it appears to have far fewer craters, another sign of its relative youth.
Ina was first noticed only as recently as 1971 when photographed by the astronauts aboard Apollo 15. Recent photos taken by the low-flying Lunar Reconnaissance Orbiter (LRO) show a level of detail that reveal how unique this curious feature really is. So what’s going on in Ina?
Theories abound. In a real volcano, calderas are caused by the collapse of material at the volcano’s top after magma from below has drained away following an eruption. Perhaps the top of the low volcanic dome on which Ina sits collapsed unevenly and relatively recently to form the patchwork we see today. Another possibility is that magma from below heated trapped gases like carbon dioxide and water to such high pressures, they violently blasted right through the crust, sending rock and debris flying for miles.
Other researchers with the LRO mission agree that Ina’s two terrains are a contrast of young and old but don’t think the brighter areas are as young as assumed. Additional high resolution photos from the orbiter show a good number of craters there (see photo below). I encourage you to explore Ina yourself by going to the LRO’s ACT-REACT Quick Map and entering its latitude of 18.65 and longitude of 5.31. As you zoom in, you’ll feel as if you’re coming in for a landing.
Whatever happened created an enigmatic moonscape that scientists are still trying to understand. In so many ways, the moon is an undiscovered world. With just six short visits during the Apollo era and 150 lunar meteorites collected on Earth, we’ve barely scraped the lunar regolith.
One of the constant joys of amateur astronomy is seeing with your own eyes what you read or heard about. And trust me, you can see much more than you might think. Even Ina. While most of you will explore via the ACT-REACT map, if you’ve got an 8-inch or larger telescope and you’re generally familiar with the moon, you can start hunting for Ina this evening. This tiny feature is most easily visible when light strikes it from a low angle as it will on tonight’s first quarter moon. If it’s cloudy tonight, try again over the next few nights. Hope for calm air, use high power and you might just be able to spot this enigma.