How are mares and highlands different?

Unveiling the Moon’s Secrets: Maria vs. Highlands – It’s Not Just About Light and Dark

Ever gazed up at the Moon and noticed those contrasting light and dark patches? Those aren’t just random blotches; they’re distinct geological regions called the lunar highlands and maria (mare for singular), and they tell a fascinating story about the Moon’s past. Think of them as two different chapters in the Moon’s long and eventful life. Understanding what makes them different is like cracking a code to unlock the secrets of our celestial neighbor.

Why “Seas” on a Bone-Dry Moon?

Let’s start with the names. “Maria” is Latin for “seas,” which is a bit of a head-scratcher considering the Moon is drier than the Sahara. Early astronomers, bless their optimistic hearts, thought these dark areas were vast oceans. We know better now, but the name stuck. The lighter areas, being higher in elevation, are simply called “highlands” – pretty straightforward, right?

Rock Talk: What They’re Made Of

The real differences start at the molecular level. The highlands and maria are made of fundamentally different stuff.

• Highlands: Imagine the highlands as the Moon’s ancient backbone. They’re primarily made of anorthosite, a rock loaded with calcium and aluminum. This stuff is relatively light and solidified way back when the Moon was just a baby, forming its original crust. It’s like the Moon’s first skin! And get this: in the central peaks of younger craters, you can find pure, unadulterated anorthosite. Talk about a geological treasure!

• Maria: Now, picture the maria as dark, hardened lava flows. They’re mostly basalt, a volcanic rock rich in iron and magnesium. This gives them that characteristic dark color. Lunar basalts are fine-grained, almost like a smooth paste that cooled quickly, and they’re bone-dry – no water or volatile elements to speak of. Interestingly, they come in different flavors: high-Ti, low-Ti, and even very-low-Ti (VLT) basalts. It’s like the Moon has its own volcanic rock menu!

These contrasting compositions tell us that the highlands and maria were born from different processes and different parts of the Moon’s interior.

Time Travel: How Old Are They, Really?

The highlands and maria also have vastly different ages and formation stories.

• Highlands: The highlands are the Moon’s senior citizens, dating back a whopping 4.1 to 4.5 billion years! They’re believed to have formed as a global magma ocean—yes, the entire Moon was once molten!—cooled and solidified. Think of it like a planet-sized lava lamp. The highlands’ rugged, cratered surface is a testament to billions of years of asteroid and comet impacts. They’ve taken a beating over the eons!

• Maria: The maria are the youngsters of the lunar family, though still ancient by human standards. Most formed between 3.16 and 4.2 billion years ago. These smooth plains are essentially ancient lava floods, where basaltic lava filled in giant impact basins. Because they formed later, they have fewer craters, giving them a smoother appearance.

Seeing is Believing: Surface Differences

The differences in composition and age translate into noticeable differences in how they look.

• Highlands: The highlands are bright, mountainous, and riddled with craters. It’s a rough-and-tumble landscape, a cosmic shooting gallery. All those craters are proof of their age; they’ve been bombarded by space rocks for billions of years. And because there’s no atmosphere, water, or wind to erode them, the highlands have low, rounded profiles.

• Maria: The maria are the opposite: dark, smooth, and relatively crater-free. The dark color comes from the iron-rich basalt. While they’re not completely devoid of craters, they have far fewer than the highlands. It’s like comparing a freshly paved road to a war zone.

The Near Side vs. The Far Side: A Lunar Mystery

Here’s a fun fact: the distribution of maria and highlands isn’t even. The near side of the Moon, the one we always see from Earth, is covered in maria. The far side? Not so much. This asymmetry is a puzzle that scientists are still trying to solve. Maybe it has something to do with Earth’s gravity, differences in the Moon’s crust, or even the way heat is distributed inside the Moon.

Why Should We Care?

So, why bother learning about lunar maria and highlands? Well, studying them is like reading the Moon’s autobiography. Samples brought back by the Apollo missions have given us invaluable information about their composition, age, and formation. By studying the highlands, we can learn about the Moon’s early crust. The maria give us clues about the Moon’s volcanic past and what’s going on deep inside. It’s all part of understanding how our solar system formed and evolved.

In short, the lunar maria and highlands are two distinct worlds on the Moon, each with its own unique story to tell. By unraveling their secrets, we’re not just learning about the Moon; we’re learning about ourselves and our place in the cosmos. And that, my friends, is pretty cool.