Ina is a peculiar small depression ("crater" in IAU nomenclature) on the Moon, in Lacus Felicitatis.

They are the small craters Osama on Ina's southwestern edge and Dag to its northwest (both 400 m in diameter).

The widest hill in the eastern part of Ina (650 m wide) was named Mons Agnes in 1979.

In July 2023, NASA announced the selection of a new scientific payload called Dating an Irregular Mare Patch with a Lunar Explorer (DIMPLE) to establish the age and composition of volcanic activity at Ina.

[14] Ina is located on top of a rounded upland (dome) 300 m high and 15 km in diameter.

In addition, although the sample size is not great, the hills do have an impact crater density intermediate between the fresh lowlands and the ancient neighboring plains of Lacus Felicitatis.

[1][10] Ina's lowlands are much rougher than its hills and show lots of small irregular relief features whose height is no more than several meters.

These features differ from lunar meniscus hollows in having bright halos; they are also more widespread, often bigger and usually located in impact craters.

The Moon's surface darkens over time and multiple meteorite impacts dot it with craters, blur sharp edges of all relief features and make slopes more gentle.

[10] The surface of the hills is much older: its age seems to be roughly equal to the age of the usual surface of Lacus Felicitatis (more than 1 billion years[10]) but the slopes and edges of these hills are young: they couldn't maintain their steepness and sharpness even for 50 million years.

That porous surface, Head and his colleagues say, is created by the nature of the lava erupted in the late stages of events like this.

"Regolith is jostled into holes rather than sitting on the surface, which makes Ina look a lot younger."

Laboratory experiments using a high-speed projectile cannon have shown that impacts into porous targets make much smaller craters.

The researchers estimate that the porous surface would reduce by a factor of three the size of craters on Ina's mounds.

Taking that scaling relationship into account, the team gets a revised age for the Ina mounds of about 3.5 billion years old.

The researchers believe this work offers a plausible explanation for Ina's formation without having to invoke the puzzling billion-year pause in volcanic activity.

"We think the young-looking features in Ina are the natural consequence of magmatic foam eruptions on the Moon," Head said.

[6][7] Another version considers it as a result of powerful ejection of some gases (volcanic or even radiogenic), which removed regolith.

[16] According to one another version, Ina appeared (and continues to form) due to collapse of the regolith into some underground cavities.