Category Archives: planetary science

planetary history, planetary science, planets

It Looks So Familiar

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Where in the Solar System is It?

What planet do we know of that has deserts and crater fields and looks rather reddish?  Where the sands of time have covered up any traces of water that may have flowed across the surface? That has scenes like this one?

Where is this?
Where is this?

One of the most intriguing things about studying the surfaces of other worlds is figuring out just how they came to be the way they are. Planetary scientists know of several processes that shape solid surfaces: cratering (made by incoming projectiles), weathering (caused by liquid or wind erosion (which is itself often termed “aeolian”)), volcanism (molten materials from deep beneath the surface that flow across terrains and cover over what was there before, or disrupt the landscapes with calderas and pits), and tectonism (the processes that fault and fold the surface of a planet or moon (such as earthquakes, mountain-building)).

So, if you look at a surface like the one shown above, you see no water, but you do see dunes and fields of sand and  dust. This tells you that at least wind-blown erosion and deposition are taking place.  You can also see some circular impressions that turn out to be the ancient, eroded remains of impact craters. Erosion takes time, which means that this surface is not  young and fresh. Weathering and deposition are covering up what’s left of these craters and various surface measurements give an estimated age of the craters themselves at about 140 million years old. And so we ask again: what planets in the solar system have evidence of aeolian (wind-blown) weathering and ancient impact cratering?  And, whose sands look some what reddish?

What does scene this tell you about the planet where this terrain lies? What assumptions can you make to help you guess where this scene is?  Think about it before dragging your pointer across the blank-looking area between the ( ) for the answer.

(It’s on Earth — in a desert area in Libya (northern Africa), that sports a pair of ancient impact sites called the Arkenu craters. This image was provided by astronauts aboard the International Space Station.)

book reviews, national geographic, planetary science

Planetology

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More than Just a Surface Study

Due out on November 18, 2009
Due out on November 18, 2009

I got a nice surprise in the mail a week or so back — a beautiful  review copy of a magnificent book called Planetology: Unlocking the Secrets of the Solar System. It’s from the friendly folks at National Geographic and is written by planetary scientists Tom Jones and Ellen Stofan.  Somebody at NatGeo must have known what a fan I am of planetary science because this is the book I would have written if I were tasked to bring the beauty and excitement about planetary studies to a broad audience. (And, hey, just in case anybody from NatGeo sees this, I’m available to write books and documentaries!)

Planetology really is a nice collection of images coupled with very clear science writing. I’m in awe at the work that Jones and Stofan put in on it.

I paged through the book first, just drinking in the great images. Then, I went back and started reading. Now mind you, I took a few semesters of geology back in college and in graduate school I studied some planetary science. And, as most of my readers know, I’ve written about planetary science in my own books (Hubble Vision, and Visions of the Cosmos) and was co-editor of a well-known (and widely used) planetary science book, The New Solar System. So, I wasn’t coming to this book without some background.  In planetary science and geology classes we learned about the processes that shape worlds: volcanism, tectonism, impacts, and weathering.  Volcanism I’ll discuss below; tectonism is the faulting or folding (the deformation) of the top layers of a planet; impacts are just what they sound like — the craters gouged out when debris slams into a surface; and weathering is another term for erosion (which can happen when water runs across a surface, wind scours a surface, or in some severe cases, when acid rain erodes a surface).

I’m happy to see that this book takes a really inviting approach to presenting those processes and what they do to planetary surfaces. It does this by comparing and contrasting Earth’s scenes with how the same processes work elsewhere in the solar system. And sometimes, what we learn “out there” teaches us a valuable lesson about how it works right here at home on Earth. Planetary science is funny that way…

A lava flow on the Big Island of Hawaii (Copyright 2007, Mark and Carolyn Collins Petersen)
A lava flow on the Big Island of Hawai'i (Copyright 2007, Mark and Carolyn Collins Petersen)

Let’s take volcanism as an example. The book steps through how volcanism works on Earth, complete with some really cool pix of volcanos and the obligatory, but (to me) chilling images of what volcanism did to humans in Pompeii in 79 A.D.

Since I’m a volcano junkie, that section really spoke to me. But, the authors take the reader one step further and show how volcanism works on other worlds — the heart of comparative planetology.

This is where it gets really interesting, because volcanism doesn’t just heat up rocks on other worlds. It also heats up ice!  Which means that we get a great look at volcanism on Earth, Mars, Venus and Io, but we also get to see the cryovolcanoes of Europa and Triton and Enceladus and other frozen worlds of the outer solar system.

Ice volcanoes spew out material from Enceladus (as seen by the Cassini spacecraft).
Ice volcanoes spew out material from Enceladus (as seen by the Cassini spacecraft).

For people who thought that volcanoes only spewed out lava, finding out that they can spew molten, sluggish ice or blast out ice geysers is quite a wake-up call!

Volcanism is just one part of the very intricate story told in this book about the processes that shape Earth and the other planets and moons of the solar system.

I’ve been through this book twice, and I’m about to head through it again. While it’s not a textbook (and it doesn’t need to be) it is a leisurely look at comparative planetology told in terms that we can all enjoy — no matter what our level of science education. Planetology is coming onto bookshelves starting November 18 (I have a link to it in my online store if you want to pre-order it) and I think it would make a great gift for somebody (or even yourself).

Check it out!  (And a tip of the hat to National Geographic for sharing a pre-release copy!)