Panspermia is the term for the most scientifically plausible version of this concept, but it isn't necessarily what science fiction usually presents. The panspermia hypothesis holds that the building blocks of life are not found exclusively on planetary bodies but are instead found scattered throughout the cosmos, and it is these spaceborne particles that are at least partly responsible for life on Earth. There's a little circumstantial evidence for the theory (although far, far more to support the reliable old "Life comes from Earth" hypothesis), and there is something undeniably fascinating about the subtext – the aliens are already here, and we are they. But science fiction barely ever depicts the actual theory of panspermia, mostly because it's just a physical process that takes billions of years to play out and is pretty boring unless you're willing to get really mystical.

What science fiction more properly deals with is exogenesis, which simply states that humanity or its genetic ancestors didn't always live on Earth. That generally means one of two things – either an ancient alien race introduced life to a previously dead Earth (sometimes as part of a larger directed panspermia project) or a bunch of humans from some other civilization colonized Earth, a fact that somehow slipped the minds of their descendants (you know…us). Plenty of science fiction deals with both, including two of the big science fictions works currently in the news. (The occasional spoiler may lie ahead.)

Outlander
One of the most satisfying little details of everybody's favorite Vikings vs. aliens epic is its answer to why Jim Caviezel's character, the alien Kainan, looks exactly like the Norsemen and how he can possibly speak their language.Outlander solves both of these problems by revealing Earth is an "abandoned seed colony" of Kainan's spacefaring civilization. Unfortunately, the whole notion that Earth was colonized by an interstellar race really opens up a far bigger plot hole than the one it was meant to fill. After all, Kainan's people would have had to have "seeded" Earth eons ago. If they could pull off planetary engineering on that sort of scale way back then, you'd think they wouldn't have so much trouble with a bunch of bioluminescent dragons. In the end, it's probably best not to think too much about the logistics of the whole abandoned seed colony concept. Because, ultimately, the very inclusion of the idea in the first place is, like so much of Outlander, awesome.

Battlestar Galactica
In both the original and new versions of the series, humans originally came from Kobol, the legendary planet of the gods, and Earth is just the fabled lost colony. The new series is busy dealing with Earth, so it's entirely possible a couple "What the frak?" moments still lie ahead that will reveal humanity actually did come from Earth. The original series, however, left no doubt that Kobol was where we all came from, as the no-budget god-awfulness that is Galactica 1980 established contact between the Galactica and contemporary Earth. Flying motorcycle chases ensued.

Star Trek
The Next Generation episode "The Chase" sought to acknowledge and explain the genetic improbability of a galaxy full of nothing but humanoid aliens with rubber foreheads. The solution – ancient aliens who, upon finding themselves all alone in the galaxy, seeded various planets with their genetic codes – is surprisingly deft, and actually turns a three-decade failure of imaginations and budgets into something almost elegaic. As one would expect, Picard takes this existence-altering revelation in his usual stride, while the Cardassians look a bit grumpy.

Stargate
Honestly, between all the genetic engineering, forced relocations of ancient humans, and universe-altering civil wars between godlike aliens it all gets a bit difficult to keep track of which species actually came from where. In short, a bunch of plague-decimated demigods maybe used this thing called the Dakara superweapon millions of year ago to shoot their genetic information throughout the Milky Way, which maybe had something to do with humanity's evolution. Or maybe not.

Babylon 5
Since we might as well finish off the sweep of nineties science fiction, the Centauri initially tried to dismiss Earth as one of their lost colonies. Sure, this probably wasn't true, but how else are you going to haze the new interstellar species?

Isaac Asimov
Most aliens seem to create life on Earth for slightly more practical (well, relatively speaking) reasons than the Star Trek aliens' "monument to our existence." Asimov imagined Earth as an eons-old alien experiment not once but twice – in "Jokester", the aliens did it to explore the concept of humor, while in "Breeds there a Man…?" the aliens are engaged in a more vague exercise in genetics. There’s also "Death Sentence", where an anthropologist for the Galactic Federation discovers that a previous civilization created a planet of robots as part of a larger psychological experiment. Realizing the Federation will surely have to destroy the planet as a potential threat, he decides to take his dire warning to one of the robots' biggest cities: New York.

Wildstorm Comics
The Kherubim people sent their genetic seed throughout the universe in a bid to conquer the universe without their genetic descendants even knowing it, which they then followed up by actually conquering much of the universe.

Ringworld, by Larry Niven
It turns out we're all part of a larger plan by the Pak race to create a galaxy full of ultra-lethal, ultra-intelligent superhumans. Apparently, the plan failed because there wasn't enough of the right kind of fruit.

Mission to Mars
In this Brian de Palma stinker, a bunch of Martians that didn't flee their dying planet shot the neighboring Earth – then a barren chunk of rock – full of the building blocks of life because…um, because they wanted to take Gary Sinise on a tour of the universe? (And that was probably the least nonsensical part of that movie.)

Salvage Rites, by Eric Brown
One of the very few times when a race made from directed panspermia confronts their creators, this short story finds a group of Benedictine monks in a cathedral-shaped starship seeking out what is, for all intents and purposes, God.

South Park
In easily the most awesome use of the concept, the anniversary episode “Canceled” revealed Earth for what it really is – one giant reality show. At least in South Park, someone is actually bothering to watch.

Starliner, by David Drake
In this 1992 novel, the narrator explains that no one bats an eyelid at botanists cross-breeding plants from different worlds because panspermia is "no longer a hypothesis but simple observation." Not the most earth-shattering application of panspermia, but still.

Ej-es by Nancy Kress
A rather less mundane spin on that same idea, as members of an interstellar marine corps realize a deadly plague on one planet threatens all the intelligent species in the universe – because panspermia makes them all genetically related.

Doctor Who
The classic "City of Death" features a more accidental case of aliens creating life on Earth. In the midst of all the ridiculously complex art forgery, random acts of violence, Monty Python cameos, and endless location shots that prove the thing really was shot in Paris, writer Douglas Adams somehow squeezes in the origin of all life on Earth. As it turns out, an exploding Jaggaroth ship kickstarted the whole "life" thing. That was nice of them.

The Hitchhiker’s Guide to the Galaxy, by Douglas Adams
Speaking of Douglas Adams, his most famous work envisions the noblest version of the alien-built Earth. Indeed, the emphasis here is on "built", as Earth is not a planet at all but instead a ten million year old computer program supervised by hyper-dimensional mice designed to determine the question to life, the universe, and everything. Of course, as is so often the case, this wondrous philosophical pursuit was interrupted by a bunch of hairdressers, TV producers, and telephone sanitizers from the planet Golgafrincham, who obliviously managed to replace the native humans and almost wreck the entire program. All of which rather neatly leads us back to wandering, forgetful colonists.

The Hainish Cycle, by Ursula K. Le Guin
In ancient times, colonizers from the planet Hain came to Earth and, for a time, coexisted with its native hominids. Whether the settlers ultimately killed the native Earthlings or simply bred them out of existence is anybody's guess, but the Hainish now consider modern humans their descendants.

Women of the Prehistoric Planet
This MST3K entry builds a whole parable of post-War American-Japanese relations around two rival alien races, time dilation, and giant iguanas, with plenty of sixties-era chauvinism left to go around. After a whole lot of silliness (as that previous sentence probably suggested) the marooned lovers Tang and Linda settle down on the titular prehistoric planet, which they decide to call…well, I think you can guess, but it rhymes with "Mirth."

Earthsearch
The classic BBC radio series had one of the best twists on this idea, as the four teenaged survivors of the massive starship Challenger search for Earth-like planets to colonize. It's slowly revealed that the planet they call Earth has some rather unrecognizable geography, but that the Earth-like planet they finally do discover, with its saltwater oceans covering two-thirds of the planet, sounds very familiar.

The Twilight Zone
But stories don't get much more familiar than the 1963 episode "Probe 7, Over and Out." Astronaut Adam Cook finds himself stranded on a faraway planet just as nuclear war is breaking out back home. He encounters Eve Norda, an alien who cannot understand his language. The pair ultimately agrees to start a new life together on the planet that Eve keeps calling "Irth." Judging by their first names, I’m guessing they'll do just fine.

12) Searle in Sunshine.

Okay, I may be the only person who really loved Danny Boyle's blazing space opera about a doomed crew trying to reignite the sun. That's okay, I can be right all on my own. I especially love the way the character of Searle, the ship's psychiatrist, surprises you in his final moments. He's kind of a prurient asshole for most of the movie, obsessed with looking into the sun with as little filter as possible. He's a pretty terrible therapist. But when the chips are down, he knows he's the most expendable crewmember. When four crewmembers from the Icarus II get trapped on the wrecked ship Icarus I, with the airlock damaged, Searle agrees to stay behind so the rest of the away team can get back to the Icarus II. He helps blast the others out the airlock, then exposes himself to the sun, dying the same way as the Icarus I's crew.
If you're going to be a creepy therapist, the least you can do is self-immolate to save the rest of us.

11) Woody in Mission To Mars.

This is a pretty terrible movie overall, but a fantastic death scene. Our heroes have to abandon their vessel. And then Woody, played by Tim Robbins, leaves the others and launches himself at the Resupply Module (REMO), but after he attaches the line from the other astronauts at the REMO, he keeps moving towards the planet. His wife, Terri, wants to go after him, but Woody knows she'll die in the rescue attempt. So he takes off his own helmet and dies of depressurization rather than let her die for him. (Thanks to Meredith for the suggestion!)

Runner up: Speaking of depressurization deaths, Graeme really wanted me to include Cally's death from Battlestar Galactica. But I didn't really think her death was awesome. Sorry, G.

10) Graham in "The Sleeper Wakes" by H.G. Wells.

One of Wells' weirdest stories involves a man known only as Graham, who sleeps for over 200 years and wakes to find that he's not just the richest man in the world, but actually the owner of the entire world. He eventually discovers that the White Council, which governs in his name, is oppressing everyone, and he helps a revolutionary named Ostrog to mount a revolution. But afterwards, Ostrog starts oppressing people just as badly as the White Council had. So finally Graham gets mad. This time, it's personal — he gets into an airplane and rams a whole bunch of Ostrog's air fleet. (Remember, this was written in 1910.) Finally, he rams his plane into Ostrog's, then spirals to Earth, knowing that the revolution will prevail at last.

Runner up: Someone suggested Hari Seldon from Forward The Foundation, but I haven't read that book and couldn't find much about it or track down a copy. Was his death truly awesome? Let me know.

9) The Controller in Doctor Who, "Day Of The Daleks"

"Day Of The Daleks" is probably not on my list of the 100 greatest Doctor Who stories of all time, but it has a few really amazing moments. The greatest of these is where the Controller finally stands up to his Dalek masters. All along, the 22nd century bureaucrat has been fooling himself that he can help the Daleks govern the human race and actually do some good along the way, helping people when the Daleks aren't looking. But after a few chats with the Doctor, he finally realizes you can't work within the Dalek system. He helps the Doctor escape, and when his coverup fails, the Daleks decide to exterminate him. "Who knows?" he says. "I may have helped to exterminate you." Awesome.

Runners up: Various people suggested the deaths of various Doctors, but none of them really jumped out at me as especially cool. One person suggested Adric, and I'll protect his/her identity, to save him/her from the inevitable scorn of the masses.

8) Lt. Paul Wang from Space: Above And Beyond.

"Everybody's favorite tortured bipolar guy," Lt. Wang, callsign "Joker," gives his life to hold off the aliens while everyone else gets away. "This is for you!" he shouts as he pours ammo into the enemy. Commenter oconnellmd suggested this scene, and I can see why.

7) Certain people in Blake's 7, "Blake"

I'm going to show an unusual degree of restraint and not say who dies in this episode. Let's just say it's an incredibly fitting end for the saga, one which makes all of the stuff that comes before seem cooler because it leads up to this. In my write-up on how to discover Blake's 7, I actually advocate watching the last episode first. At the very least, I think this is one spoiler that makes you appreciate the rest of the show more. But don't take my word for it: watch for yourself.

6) Pham Nuwen from A Fire Upon The Deep by Vernor Vinge.

Pham Nuwen is animated by the Old One, a super-powerful artificial intelligence, and he dies fighting the Blight, another super-A.I. First Pham downloads as much of the Old One into his brain as possible, overclocking his human brain by containing this massive superhuman intelligence, which will inevitably destroy him. And then he launches the Countermeasure, an advanced weapon which moves the boundaries of the Slow Zone far enough to enclose and destory the Blight. But the Countermeasure also has the effect of terminating Pham at the same time:

The Countermeasure's writhing had slowed. Its light flickered bright and then out. Bright and then out. She heard Pham's breath gasp with every darkness. Countermeasure, a savior that was going to kill a million civilizations. And was going to kill the man who triggered it.

Almost unthinking, she dodged past the thing, reaching for Pham. But razors upon razors blocked her, raking her arms.

Pham was looking up at her. He was trying to say something more.

Then the light went out for a final time. From the darkness all around came a hissing sound and a growling, bitter smell that Ravna would never forget.

(Thanks Annalee!)

5) The T-800 in Terminator II.

After Arnold Schwartzenegger's T-800 helps Sarah and John Connor defeat Robert Patrick's mean T-1000 by blowing it up and knocking it into molten metal, Arnie knows he has to go too. If there's anything left of the T-800, the technology could be used to reconstitute Skynet and bring the badness down on our heads. So Arnie gets Sarah Connor to lower him — slowly — into the molten metal. He gives a thumbs up as he descends to his robo-fondue doom. (Thanks, Annalee!)

4) Biggs from Star Wars.

I was seriously considering making Obi-Wan the coolest death from Star Wars, but really, screw that guy. First of all, as he points out himself, he comes back a thousand times more powerful afterwards. And secondly and more importantly, he's kind of a big martyr, as everyone points out in the awesome parody Hardware Wars. And Biggs doesn't have any super Force powers, or the ability to come back a thousand times more anything. All Biggs has is a X-ing, a can-do attitude, and an awesome porn-stache. And he's the greatest wingman ever, taking enemy fire and blowing up so that Luke can nuke the death star and get all the glory afterwards. And look how stoic Biggs is in this deleted scene from Episode IV, telling Luke he may never come home again because he's off to join the rebels:

When does baby Biggs get his own episode of the Clone Wars cartoon? Preferably with a little baby mustache?

3) Spike from Cowboy Bebop.

Martian bounty hunter Spike Spiegel gets into a duel with his former best friend, Vicious after Vicious' Red Dragon gang has killed Spike's girlfriend Julia. Spike finally decides to face the past with Vicious that he ran away from three years earlier, and he storms the Red Dragon headquarters, killing a bunch of its members as he climbs. Vicious manages to slash Spike with his katana, but then Spike shoots Vicious dead. Spike comes down the stairs, wounded and weakened, to face all the remaining members of the Red Dragon. Spike makes a gun with his fingers and says "Bang"... then collapses. Most people seem to assume Spike dies of his wounds, and it's not hard to find tons of people online listing this as one of the coolest death scenes in all anime, or all Asian films, let alone science fiction.

2) Someone from Anathem by Neal Stephenson.

Since this book just came out and it's a bit of a major spoiler, I won't say who dies and how — click here if you've already read the book and/or don't care about spoilers.

1) Spock from Star Trek II: The Wrath Of Khan.

I'm not putting the pointy-eared green blooded Vulcan first just because I know I'd get lynched otherwise. I'm not even including the death of Spock because I pretty much memorized all the dialog from that scene as a little kid. I'm including it because it's the template of how to do a memorable, important death in a science fiction epic. The movie isn't ABOUT Spock at all, but it still feels as though the whole film has been leading up to his death. A lesser film would have been more clumsy and obvious about giving Spock a bunch of cool moments leading up to his death, and trying to manipulate us into feeling the Spock love before he snuffs it. Instead, we do get plenty of cool Spock moments, including giving Kirk his present and mentoring Lt. Saavik. But it's woven into the rest of the movie, and the film's running theme of the "no-win situation" and the impossibility of cheating death every single time help to set up the death of Kirk's best friend way better than a scene where Spock talks about what he's going to do when he retires and goes back to Vulcan. The result is one of the most amazing moments in Trek history, one of those moments where you can really beleive Trek is a sweeping saga instead of just a zany adventure with green women and Saurian brandy.

Runner up: I can't believe I left out Roy Batty in Blade Runner, as various commenters have pointed out. Especially since I went on a whole tangent about Roy's amazing death scene in my rant about why there shouldn't be a BR sequel earlier in the day. Suffice to say the Roy Batty death scene is definitely one of the all-time classic, and easily up there with Spock's.

Tonight is the season finale of Kyle XY on ABC Family at 8. It's all about the senior prom, which looks chock full of heartwarming, judging from the trailers I've seen. At the same time, this show about a superpowered teen mutant has done a really great job of keeping a sinister undercurrent lately, and Kyle's female counterpart Jessi just gets more and more entertainingly psycho. So if you haven't checked it out yet, you may want to grab your last chance tonight. After all, the episode will also teach us that looking forward to your prom too much will turn you gay:

Also, the History Channel has a new Modern Marvels, about whiskey, at 8 PM. (Not really very science fictional, but maybe the whiskey is sentient?) And then a new Cities of the Underworld at 9 PM.

And Encore is showing Mission To Mars at 9:45, just in case you want to relive Gary Sinise's life-changing encounter with a cheesy CGI alien.

Tuesday night has the next-to-last episode of Jericho season two, on ABC at 10 PM. Sadly, this is looking more and more like the next-to-last episode of Jericho, period, unless the Sci Fi Channel decides Jericho is a better investment than another season of Ghost Hunters. As you'd expect, Major Beck is not terribly happy about the drastic actions that Stanley took at the end of the previous episode, and he's not willing to blame everything on New Bern. Here are the first five minutes of the episode. (I apologize for the streaky video, this is the best source I could find.)

Also, the History Channel has a rerun of The Universe, all about the possibility of life on Mars.

And Encore has back-to-back Aliens and Waterworld, starting at 11:40 AM.

And at 2:10 AM Wednesday morning, Encore has Ultraviolet, the second-best movie featuring Gun-Kata. (The first being director Kurt Wimmer's Equilibrium, of course.)

Wednesday, the Discovery Channel has a new Futureweapons, "Hard Target." Subjects include new inflatable armor, shoulder-fired grenades, and the A-10 Thunderbolt II attack plane. Good times! And at 10, the History Channel has a new UFO Hunters, "UFO Gateways." The Hudson Valley in New York has hosted more than its fair share of UFO sightings — could this area be an interstellar gateway, used to travel across time and space, or even between dimensions? Another possible gateway area is Sedona, Arizona.

And at 10:10, Encore has Alien 3, while FX shows Batman Begins at 5, followed by The Core at 8 and 11.

Thursday there's a new Smallville on The CW at 8. Lionel Luthor has Clark abducted, and there's some crazy prophecy about how The Traveler will change the Earth for ever. But the main reason to watch this episode is to see just how crazy Chief Tyrol has gone since a certain revelation at the end of Battlestar Galactica season three. Here's a clip:

And then there's a new Lost, on ABC at 9, where we find out what Michael's been up to all this time. And Ben tries to convince Alex to flee the Others' camp before a coming assault. We posted a couple of preview clips the other day, and here's the episode's promo:

As for movies, at 12:15 Friday morning, AMC has The Thing

Friday is pretty slow, except for a bunch of Stargate reruns on Sci Fi. Also, at 1 PM, USA has Timecop, the greatest time-traveling Jean Claude Van Damme movie ever.

And at midnight, A&E has The Matrix, while Encore has 12 Monkeys. Try flipping back and forth between the two movies to create a single, crazy-paranoid narrative where nothing is real. And at 1:30 Saturday morning, TBS has Mars Attacks!, followed by Eight-Legged Freaks at 3:45.

Saturday morning, The CW has Legion of Superheroes followed by Spectacular Spider-man (featuring the debut of the Lizard), starting at 9:30.

And then at 9 PM, there's a new Torchwood on BBC America. It's Gwen's wedding day, but unfortunately, she's got a little surprise on the way. Zany wedding-pregnancy action, plus creepy monsters. You can read our recap of the episode here.

Sunday has the first hour of the broadcast premiere of Futurama: Bender's Big Score, in case you didn't already get the DVD. That's on Comedy Central at 8.

To some extent, it's understandable that space adventures play fast and loose with physics. After all, who wants to watch Han Solo spend years on the journey to Alderaan, only to find that the planet has twice Earth gravity and he can barely stand up, much less swagger?

The categories of mistakes in our report card should be pretty self-explanatory, but just in case, I'll expand on them a little bit:

• There's no sound in space
• Not all planets have Earth gravity
• Planets should have diverse climates, instead of one unified climate across a "desert planet" or "forest planet."
• It shouldn't be too easy to communicate with alien creatures, without some kind of high-technology "translator" explanation.
• And it definitely shouldn't be too easy for humans to interbreed with aliens.
• Humans exposed to vacuum without a spacesuit shouldn't explode or shatter. And a "hull breach" where the ship's crew is exposed to vacuum should kill everyone instantly.
• You can't have fires in space, unless there's oxygen leaking out somehow.
• Asteroids or other objects shouldn't be able to float close together without falling into each other's gravity
• People shouldn't be able to dodge lasers and other speed-of-light weapons
• And there's no reason why someone would move in slow-motion in zero gravity.
• Faster-than-light travel is probably not ever going to be possible.

First of all, here's a brief chronology of the Mars movie boom:

1999: Escape From Mars. A made-for-TV movie from UPN. Five astronauts journey to Mars in the second decade of the 21st century. They must deal with corporate greed and inferior computer components, plus their own demons.

2000: Red Planet. Okay, this one isn't quite as serious. Humanity stars seeding Mars with algae that's supposed to create a breathable atmosphere. But then the algae vanishes, and a team led by Carrie-Ann Moss goes to investigate. It turns out Mars now does have a breathable atmosphere, but it also has evil aliens and a killer robot.

2000: Mission To Mars. This may have been the most serious attempt to date at portraying the real conditions on Mars, based on the images that were available at the time. The first crewed mission to Mars gets lost, but there's one survivor. So Gary Sinise and pals rocket off to Mars, only to run into trouble as well. In the end, they enter a giant white mausoleum with breathable air, and the movie falls apart when they meet a cute alien who tells them that Martians seeded Earth with life:

2000: Mars And Beyond. An early Web series, on the Cyber Sci-Fi Network, Mars And Beyond was written by former Star Trek: The Next Generation producer Herbert Wright, also known as the "father of the Ferengi." (Not something I would brag about.) It's 2014, and a team of astronauts is sent to Mars. Officially, their mission is just to explore, but unofficially they're there to answer the question: "Are we alone?"

Ghosts of Mars (2001). I almost left this one out, because in some ways it's a throwback to the old pulpy Martian movies, and it depicts a Mars that's long been settled, like Total Recall and other earlier movies. Mars has been terraformed, and you can breathe the atmosphere without a spacesuit. At the same time, director John Carpenter did make an effort to depict a semi-realistic Mars, using tons and tons of red food dye to make the gypsum-mine location look Martian enough and trying to make the sets look as though the Martian winds had battered them. Plus he had a local holy man bless the set before filming. That has to count for something. Plus it has Reavers, before Joss Whedon put them in Firefly.

2002: Lost On Mars. This sounds pretty horrific, and I'm determined to hunt down a copy now. The first ever astronauts land on Mars, to investigate a strange energy reading. They discover that Mars once held intelligent life, and then they find a device that sends them spiraling back in time THREE BILLION YEARS to a barbarian empire that once ruled Mars. With, like, swords and things. They get captured by the movie's director, wearing a barbarian costume. And then it veers off into matriarchal Martian barbarian politics. Turns out there's a sequel, and they're both coming out on DVD soon.

2002: Stranded aka Náufragos. A Spanish movie, Stranded stars Vincent Gallo as a member of an expedition that crashes on Mars. It's shot in a documentary-like style and tries to depict the Martian landscape realistically. The humans discover the remains of an ancient Martian civilization, complete with an area that has breathable air. And they find out they can eat the ancient lichens on Mars, allowing them to survive until they can be rescued.

Where did the Mars-movie trend come from in the first place? The fact that NASA was prepping a much-publicized push to send orbiters and rovers to Mars may have helped inspire film-makers. (NASA also sent up some craft during the 90s, but they were lost on arrival. Also, as Moria points out, the 1990s was a high-water mark for Mars novels, including Kim Stanley Robinson's Red Mars trilogy and Greg Bear's Moving Mars. The development process for the Mars movies of 2000-2001 probably started in the mid-1990s.

So what ended the Mars movie fad? Well, the fact that it was a fad probably had something to do with it. Just like the asteroid-on-course-for-Earth movie fad, this one had to end. But the fact that more real data, and realistic images, were going to start coming back from Mars may have helped as well. The 9/11 attacks, and the start of the Afghanistan and Iraq wars, may have changed the focus of movies in development, away from exploration and towards war. (But that probably wouldn't have had an impact until a few years later.) There's also the fact that none of these movies did that well: Mission To Mars, grossing around $68 million in the U.S., may have been the biggest, but Red Planet only made $18 million as compared to its $75 million budget.

• Richard Cook, designer of MSL, said that it's three times heavier than Spirit and Opportunity, the two rovers currently on Mars right now. It's powered by nuclear energy, designed to last 20 years, travel 10 km, and comes equipped with a laser for vaporizing rocks so it can do chemical and mineralogical analysis on them. "We call it the death ray," he confessed. Joked NASA Jet Propulsion Lab Director Charles Elachi, "In a few years people will be visiting Mars and see bullet holes all over the place [from the laser]."
• When Cook and his team were designing Spirit and Opportunity, they wanted to do what he called a "built to print," meaning to the specs on paper. They wanted to base it on the model they'd developed for Sojourner, the previous generation Martian rover. But immediately they figured out that wouldn't work, especially with the more-complicated MER rovers, since they still had to fit inside a small lander. "it's hard to take a rover and put it inside a tetrahedron," Cook said with a laugh, referring to the shape of the lander.
• The MSL rover, which will blast off next year, will be able to do experiments that tell us a lot more about Martian water sources. It can do gas chromatography mass spectrometry (GCMS). It has an onboard camera.
• Steve Squyres said he was disappointed when Spirit landed in Gusev Crater, which he hoped would be a lakebed. Instead, it was covered in a layer of lava rocks. "I believe the lakebed is there, but it's covered in lava," he said. Luckily, Spirit was able to make it to the Columbia Hills nearby to study a wide variety of rocks.
• Some of the rocks that Spirit studied show strong evidence of having been saturated by water, probably steam. Most likely, the hit that created the Gusev Crater shot a bunch of superhot rocks out to the Columbia Hills, and these melted ground water into steam.
• "When we talk about water on Mars, what we really mean is sulfuric acid," Squyres explained with a grin.
• There is absolutely no doubt that there has been water on Mars, Squyres said, but the fact is that the ratio of water to rocks has always been very low. One piece of compelling visual evidence he showed us was from a study of the sorts of patterns water leaves in soil over years of flowing on it. He compared images of a characteristic, smile-shaped pattern created by waters from the Colorado River with images from rocks on Mars. The smile shapes and sizes were nearly exactly the same.
• The rover Opportunity is currently at the Victoria Crater, where it is studying layers in the cliffs to learn more about the geological history of Mars. Some layers make it clear that water did at one point saturate the planet's surface. The walls of the crater are so steep that scientists have to pilot the rover based on satellite images taken by a recently-arrived spacecraft. He showed us images from the spacecraft, which are so high-resolution that you can see Opportunity and the shadow of its antenna at the edge of the crater.
• About the Victoria Crater mission, Squyres said, "It takes a lot of guts to drive an 8 hundred million dollar piece of equipment along the edge of a cliff on another planet."
• Andrew Knoll said that the real question isn't whether there has been water on Mars, because surely there has been. The question is whether that water is habitable for life as we know it.
• Unfortunately for people who want to meet alien life, the prognosis is not good. Chemical and mineral evidence suggests that water on the planet is so salty and acidic that it wouln't support any organisms we know. "Water on Mars would be challenging for life as we know it," he said.
• Knoll added that water could have flowed on Mars if it was extremely salty because salt lowers the freezing point of water. Or it could have flowed as a result of asteroid hits that temporarily melted ice.
• MSL will do more definitive mineral analysis to determine what the chemical composition of Martian water might have been (or might be).
• There has been a lot of debate over the Martian "gullies," structures that look like they were cut into the Martian surface with water. Squyres said, "Some were created during the last five years and look like they've been created by water. But all the ones we've looked at have slopes that suggest they were probably caused by avalanche not water."

When the space age ended, the alien age began. In the early 1990s, the Disney Corporation decided to close down its Mission to Mars ride, itself a direct descendant of the Rocket to the Moon attraction Werner von Braun had helped to design. In its place came Alien Encounter, in which an extraterrestrial stows away on a spaceship. This made things easier for Disney, as one executive admitted: "One way for an attraction to remain timeless is for it to be based in fantasy, rather than reality."

After we stopped sending people into space, it was easier to spin elaborate fantasies. We no longer had any narratives about actual space travel, with all its challenges, to compete with our magical interstellar ships, DeGroot argues.

[Dark Side of the Moon: The Magnificent Madness of the American Lunar Quest] NYU Press 2006