Tonight the returning young crescent Moon puts down stakes near the planet Mars in Sagittarius. Look for the pair low in the southwestern sky at dusk.
We’re used to hearing how ancient the Moon is. Its origin goes back to 4.48 billion years ago when a Mars-sized planet sideswiped the Earth, blasting debris into space that quickly coalesced into our satellite. While it’s true that most of the Moon’s crust and craters date from then, recent close-up photos from NASA’s Lunar Reconnaissance Orbiter (LRO) suggest the Moon remained volcanically active until not that very long ago. At least on geological time scales.
100 million years ago, when dinosaurs cracked jokes about the early mammals, lava oozed from cracks in the Moon’s crust to create what astronomers nowadays call IMPs or Irregular Mare Patches. They’re characterized by a mixture of smooth, shallow mounds next to patches of rough, blocky terrain. Only one, called Ina, is large enough to see in amateur telescopes. The others, liberally sprinkled across the lunar nearside, are generally less than 1/3 mile (500 m) across. Using the LRO, a team of researchers led by Sarah Braden of Arizona State University has found 70 landscapes similar to Ina.
Maria (plural of “mare”) are those big dark spots the make up the face of the man in the moon. They’re actually huge expanses of lava that welled up from cracks in the Moon’s crust several billion years ago after asteroid impacts. IMPs are much more recent. Some may be as “young” as 50 million years old. This was well after the dinosaurs succumbed to major climate changes induced by the impact of a 6-mile-wide asteroid hit here on Earth. Now the mammals are cracking jokes about the dinos.
“Discovering new features on the lunar surface was thrilling!” says Braden. “We looked at hundreds of high-resolution images, and when I found a new IMP it was always the highlight of my day.”
Astronomers determine ages of lunar features by doing crater counts. The more lightly cratered an area is, the younger.
Some of you may be early morning observers. Well, I’ve got a special event to share with you. Tomorrow morning November 26th, Jupiter’s bright moon Callisto will be eclipsed by Jupiter’s shadow starting at 4:50 a.m. (CST) and disappear for nearly five hours.
Just 15 minutes after Callisto disappears, Ganymede emerges from eclipse at 5:05 a.m. (CST). One disappears, the other reappears. Pretty cool! Jupiter will be the brightest thing in the sky high in the south in Leo at the time. You can always find out what Jupiter’s moons anytime of day or night by visiting Sky and Telescope’s Jupiter’s Moons site.