Amazing Mega-Impacts That Shaped Earth, the Moon, and Mars

Biggest Impact Crater Ever?

In the last decade, scientists may have uncovered the secret of Mars' split personality.
In the last decade, scientists may have uncovered the secret of Mars' split personality. | Source

When Worlds Collide

I once thought the dinosaurs had it rough.

In recent years, science has uncovered signs of spectacular, world-reshaping collisions that changed the fates of the Earth, the Moon, Mars, and perhaps Mercury.

Now, powerful telescopes are discovering the debris of planetary collisions around other stars!

I've been aware of the prevailing theory of the Moon's formation, but NASA's recent discovery of the biggest impact crater in the solar system has humbled me anew.

Let's take a look at the scars of these colossal planetary collisions. They're a fascinating glimpse into the crazy, reckless teenaged years of our own solar system.

Isotopes: Molecular Fingerprints

Every atom has variants called isotopes. These have a few extra (or a few missing) neutrons in their core. Each planet has a unique mix of isotopes, just like every soup is salted differently. Scientists use isotopes as a planetary fingerprint!
Every atom has variants called isotopes. These have a few extra (or a few missing) neutrons in their core. Each planet has a unique mix of isotopes, just like every soup is salted differently. Scientists use isotopes as a planetary fingerprint! | Source

The Moon's Formation

The moon is not made of green cheese. When astronauts took rock samples from the moon's surface and brought them home, geologists discovered something odd: the moon seems to be made (mostly) of the Earth's own crust!

The moon has an extremely small metal core, unique among bodies of that size. Moreover, the isotopes found in moon rocks are a close match to Earth's.

Scientists have gradually come to accept one theory which explains this: the "Impact Trigger Theory" first proposed by Dr. William K. Hartman and Dr. Donald R. Davis in 1975. A Mars-sized ancient protoplanet, usually called Theia, had a fatal encounter with Earth very early in its history. The Earth's splattered crust plus a few remnants of Theia coalesced into the Moon.

A good thing, too. The Moon has had a positive influence on the Earth, slowing it down from a 5 hour day, keeping its tilt relatively steady like a gyro, and favoring us with tides, which helped life get going.

And the Hits Keep on Coming (NASA video with added narration)

Elevation Maps of Mars

No, the blue parts aren't water, that's just low elevation. The Borealis Basin (light blue) is probably the largest impact crater in the solar system. The dark blue Hellas Basin in the south is another big impact crater.
No, the blue parts aren't water, that's just low elevation. The Borealis Basin (light blue) is probably the largest impact crater in the solar system. The dark blue Hellas Basin in the south is another big impact crater. | Source
Ouch. The Mars Orbiter's topographical relief maps reveal the ancient scars of the Borealis (north, light blue) and Hellas (south) Basins.
Ouch. The Mars Orbiter's topographical relief maps reveal the ancient scars of the Borealis (north, light blue) and Hellas (south) Basins. | Source

A Martian Crime Scene: The Borealis Basin

Most scientists now accept the Theia-impact as the best explanation for the moon's origin.

The Mars impact theory is newer, but it explains two extremely puzzling things about Mars. There is a mysterious dichotomy (difference, from Greek for "double+cut" or "cut in two") between its northern and southern hemispheres. Its northern half is smoother, with lower elevations and a significantly thinner crust than the southern half. It's as if Earth had all its continents and mountain ranges piled up south of the equator. This means that back when Mars had liquid water on the surface, all the rivers tended to flow north (downhill)!

Furthermore, probes to Mars have discovered there's no magnetic field for most of the northern hemisphere, although it's got a magnetic field over much of the south. This has made Mars a far less habitable place. A planet's magnetic field protects its atmosphere from the eroding effects of the solar wind. Lacking a magnetic "hat," Mars has had most of its atmosphere stripped away, and some of its water, too.

How did it happen? Various theories have been put forward, including odd plate tectonics. But recent surveys of the ancient Mars crust have revealed a giant, ellipse-shaped scar wrapping the top half of the planet. It looks like a divot gouged out by an intergalactic golf club.

Dr. Margarita Marinova's 2008 dissertation demonstrated that a glancing mega-impact by a very large body could have carved out this huge impact crater known as the Borealis Basin. Recent evidence from Phobos, one of the moons of Mars, bolsters this theory: like the Earth's moon, it appears to be composed of crust from the planet it orbits.

The Borealis Basin is the largest known impact crater in the solar system.

The Mars Mega-Impact (Including Simulation by Dr. Marinova)

Near Side and Far Side of Moon

The near and far faces of the Moon. The Moon's face turns as it orbits, so that we always see the same side. That's one of the things that makes our Moon special!
The near and far faces of the Moon. The Moon's face turns as it orbits, so that we always see the same side. That's one of the things that makes our Moon special! | Source

Did the Moon Get Clobbered?

The Moon also has two faces. The far side of the moon looks very different: it's covered in piled-up mountains and solidified rocky goop. Is this simply because one of the Moon's faces is locked towards Earth, so that the far side serves as a sort of windscreen? Or did it take a big hit as well?

Recent research by Martin Jutzi and Erik Asphaug at UC Santa Cruz suggests that for a while, Earth may have had two moons, but the smaller one eventually plowed into the larger and produced a "Big Splat" (not to be confused with the book of the same name, which explains the science behind the Theia impact theory).

Cores of Earth & Mercury

Mercury's core takes up 42% of the planet, in contrast to Earth's core, which is only 17%.
Mercury's core takes up 42% of the planet, in contrast to Earth's core, which is only 17%. | Source

Mercury: Another Mega-Impact?

The fantastic NASA spacecraft you've never heard of, Mercury MESSENGER, has been orbiting, photographing, and mapping the planet for ten years.

Here's one of the burning questions that MESSENGER is trying to answer: why is Mercury so dense? No, that's not an insult. The planet is only a little larger than our Moon. But it's almost half core, with a surprisingly thin rocky crust.

Where's the rest of it?

One leading theory is that Mercury, too, suffered a cosmic collision that threw most of its outer material into space. What's left is the metal core of a planet that may once have been closer to Earth-sized.

And if that weren't bad enough, it looks like the enormous Caloris Basin may be the scar of a giant impact that slowed Mercury's rotation almost to a standstill. Its days last over 58 Earth days. If you want your hamburger really, really well-done, leave it on Mercury.

Amazing Discovery: A Planetary Collision Around Another Star!

The Impact Trigger Theory

The Big Splat, or How Our Moon Came to Be
The Big Splat, or How Our Moon Came to Be

Fantastic, readable account of how the moon's origins were discovered, from Gallileo and medieval astronomers to the Apollo program. Missing some of the lastest lunar survey info, but this is a great book nonetheless.

 

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Comments 12 comments

Cyndi10 profile image

Cyndi10 4 years ago from Georgia

This was a very informative article with good videos to provide further information. Mars is always a fascinating planet to learn about and it seems there is more information all the time, especially since the probes landed. Well written.


sandrabusby profile image

sandrabusby 4 years ago from Tuscaloosa, Alabama, USA

I read this to get an idea of how you link to other sites, and what a good learning experience it was, too. Although my own mind is not as scientific as yours, I got an appreciation for a highly scientific topic by reading your hub which was the result of your research on this topic. This technique is similar to what I do in another area -- read material other people don't want to take the time to read and make a composite that the "average" person can understand and enjoy. I'm off to do more hubbing. Thanks, again.


Greekgeek profile image

Greekgeek 4 years ago from California Author

Absolutely! We're Content Concierges -- we do the research, find and link to the good sites, and explain topics we know for people who don't have time to do that but want to know more. :)


kiwi91 profile image

kiwi91 4 years ago from USA

My daughter is really interested in astronomy, a subject I was really interested in as a kid, but got sidetracked by later in life. I find this stuff fascinating, and to think that we had two moons at one point, or how the earth's surface must have looked after a major collision is unreal.

The other day I came across a page on Tyche, the proposed name for the possible 9th planet. It would be cool to see if they discovered this in our lifetime if it exists. Great hub, very understandable and interesting!


Greekgeek profile image

Greekgeek 4 years ago from California Author

Good for your daughter!

I'm like you: I was completely hooked on astronomy when I was a kid, collecting William K. Hartman books while my peers were reading Sweet Valley High...but then I went off into the humanities. Lately I've been indulging the astro-bug again.

Astronomers keep finding Pluto-sized "dwarf planets" out in Pluto's neighborhood and beyond, but I'd be surprised (and pleased!) if they discovered something bigger. They might have a hard time determining it, though. The new definition for a full-fledged planet -- which demoted Pluto to "Dwarf Planet" along with Eris and some of the other half pints -- is that it has to clear the area of its orbit of debris. It's hard to see small stuff out past Pluto!

I love the idea that Earth may once have had two moons, too.

Lately I've been chewing through all the National Geographic and Discovery Channel astronomy specials on NetFlix. (Then I have to double-check NASA and reputable sites online, because there's a lot of pseudoscience mixed into some documentaries.) It's fun learning about all the stuff that's been figured out in the last 10 years or so!


kiwi91 profile image

kiwi91 4 years ago from USA

I should say that my daughter is two and enjoys star gazing and loves to find the moon (even during the day she finds it). She even can identify Saturn on the solar system, but I'm gushing a little here. She has got me further interested in astronomy though, so she's rekindled my interest without even knowing it. In the next few years, I'm going to have to invest in a telescope of some type.

It might be wishful thinking that they find anything large beyond Pluto, but I'll settle for a abnormally large Dwarf Planet even!

Have any recommendations on Discovery Channel astronomy specials? I'd like to see a couple. Thanks!


Greekgeek profile image

Greekgeek 4 years ago from California Author

Kiwi: I just had a chance to review my recent Netflix watchlist so I can give you the names of some of the astronomy specials I've been enjoying lately. Unfortunately, I have an unhealthy fondness for "things that go boom!" specials, so my watchlist reads like a bunch of Bruce Willis films. Depending on your two-year-old's imagination, I would pre-screen these to make sure they're not too scary:

-- Asteroids: Deadly Impact (with Eugene Shoemaker, GREAT documentary)

-- Into the Universe with Stephen Hawking (a bit silly/speculative at times, but come on, it's Stephen fricking Hawking)

-- Prehistoric Disasters (there I go again, but honestly, this is a FASCINATING series of four episodes; well worth watching)

-- How the Earth Was Made: I love a lot of the episodes in this series (my interest extends to geology)

-- How the Universe Works series (which is a lot of whiz-bang CGI, but if you look closely a good number of the animations are taking REAL photos from the Hubble, then zooming into them as 3D spacescapes... like flying into them!) which I've been watching for the past week

-- 400 Years of the Telescope

-- National Geographic: Amazing Planet miniseries

-- The Pluto Files: Nova (I want to stick a PIE in the face of Dr. Tyson, who is too full of himself, but the story of "why did Pluto get demoted?" is kind of interesting)

Carl Sagan's old "Cosmos" series is also on Netflix. Somewhat dated, but I remember being utterly entranced by it as a child, looking forward eagerly to new episodes every week, and I keep meaning to watch it again. Sagan had a gift for firing the imagination and making cold space come alive with his words, even if we laugh at his "billions and billions of stars" and "we are star stuff" and "pale blue dot" sayings now.

Also, of course, I recommend the "If We Had No Moon" special I linked to at the end of this hub. It was uploaded to YouTube by Kurdistan planetarium, and is excellent.

And I would just like to note that I've moved to the right place for things that go boom; we had another earthquake today. (But it was the "fun" kind: no damage, just a good loud rumble and brief shaking; once we have the Big One I probably wouldn't be able to enjoy them anymore.)


SidKemp profile image

SidKemp 4 years ago from Boca Raton, Florida (near Miami and Palm Beach)

Very clear explanation, and great selection of videos. Thanks for bringing my history of the solar system up to date! Voted up and awesome


Paula Atwell profile image

Paula Atwell 2 years ago from Cleveland, OH

@GG you sound just like my family, especially my husband and one daughter who love watching shows with explosions.


Greekgeek profile image

Greekgeek 2 years ago from California Author

Yes, I'm afraid I have an unhealthy fondness for exciting geology. At least I'm living in the right place for it. ("I feel the Earth... move... under my feet...")


Cari Kay 11 profile image

Cari Kay 11 2 years ago

My under- and post- graduate studies were in the geosciences. Love it. Love it so much that as a homeschooling mama, I spent an entire schoolyear teaching astronomy. A local teacher liked my plan so much she adopted it for her classroom as well. The earth and the stars are just so fascinating.


Greekgeek profile image

Greekgeek 2 years ago from California Author

Wow, congratulations, Cari! I hope your kids enjoyed the chance to look up and out. My memories of the Voyager missions and my love of the space shuttle program shaped my whole life, even though I'm the only non-scientist in my family. (Dad is a rocket scientist, and my grandma was a planetarium director.)

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