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7 Spacecraft NASA Has Landed on Mars

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A portion of a poster titled "Mars Explorers Wanted," one of a series NASA originally commissioned for an exhibit at the Kennedy Space Center Visitor's Complex in 2009. They're all available online for download. Image credit: NASA/KSC

Imagine the surface of Mars on July 20, 1976. It's cold and breezy on the golden plains and sunset is fast approaching. Above, a meteor streaks across the sky, 250 meters per second, a zip of light. Uncommon for a meteor, however, is the parachute that deploys, slowing it in an instant by three-quarters of its speed.

About a mile above the surface, the object resolves into view. It's not smooth like a flying saucer, but rather looks like a machine of some sort, all cylinders, boxes, and cabling. Retrorockets beneath begin to fire, and the whole thing eases to the ground at a few feet per second. It lands, and Mars is again quiet.

As dust begins to settle, the alien spacecraft switches on. An antenna dish rises and orients. It's looking for something. Home. Arms begin to extend, one toward the sky. Viking I, the first scientist to survive the trip to the Martian surface, gets to work.

As NASA celebrates the 40th anniversary of the historic mission, here is a list of every NASA spacecraft to operate successfully on the Martian surface. 


Viking 1's view of Mars. Image credit: NASA

The Viking I lander was looking for life. How little did we know? Carl Sagan lobbied to have a small light installed on the lander's exterior, hoping Martian animals might investigate it during nighttime hours. The lander's feet are lily pad–shaped because scientists thought the surface of Mars might have the consistency of shaving cream. Just to land successfully was an achievement, and everything Viking I and its twin Viking II (which landed two months later) found and didn't find added immeasurably to our then relatively meager understanding of Mars.

The spacecraft collected and analyzed soil samples, returned 360-degree images of the surface, and monitored the weather. Viking I operated for six years—a record unbroken until 2010, by the rover Opportunity. (Viking II operated just over 3.5 years.) Engineers at JPL think the Viking orbiters are still circling Mars, lifeless but speeding along. They've earned their rest, having imaged the entire planet in high resolution, mapped Mars's thermal activity, and studied its atmosphere.


The Sojourner rover checks out (or perhaps bumps into) a boulder. Image credit: NASA

After the Viking landers found no animals, planetary scientists moved on for a while. They explored Venus, and the Voyager probes checked the boxes for the outer planets—those worlds beyond the asteroid belt. Pathfinder was the ultimate test of NASA's "cheaper, faster, better" initiative in the 1990s—and a grand return to the red planet.

Pathfinder was comprised of two elements: the rover Sojourner and a base station, later named the Carl Sagan Memorial Station. The duo neared the surface on July 4, 1997 in a capsule and parachute similar to the Viking lander. When 355 meters above the ground, Pathfinder seemed to burst like a kernel of popcorn, surrounded in a fraction of a second by an inflated shell of giant airbags. Completely encased, when Pathfinder hit the ground, it violently bounced across the Martian surface, the airbags only deflating after the package lulled to a stop.

The rover would have been an astounding success if it operated for a week. It ended up operating for nearly three months. By the numbers, according to NASA, Pathfinder returned: 2.3 billion bits of data; 16,500 images from the base station; 550 images from Sojourner; and data from "15 chemical analyses of rocks and soil and extensive data on winds and other weather factors." Pathfinder data revealed something amazing: Mars was once a warm and wet world.


The Mars rovers Spirit and Opportunity landed in fashions very similar to Pathfinder—airbags, bounces, and all. Spirit first touched Martian soil on January 4, 2004; 24 days and half a planet later, Opportunity landed. The rovers were designed for greater mobility and range than Pathfinder, though they largely studied the same things: rocks, soil, and air. Spectrometers scanned the planet's mineral and chemistry composition. Cameras captured and returned more than 100,000 high-resolution images of terrain and sky (including the first-ever photo of Earth from the ground on another world).

Another similarity to Pathfinder: bang for your buck. Spirit was designed to last 90 days. It ran for six years. In the end, it became stuck in patch of iron sulfate that was concealed by a thin layer of soil. Because of the low cohesion, the rover lost traction. The rover was declared a stationary science platform, and continued to do science for another two months, until low sunlight left its batteries drained. Eventually contact was lost.

Opportunity, meanwhile, refuses to stop working. The closest it came to a demise was in 2005, when the rover drove through a punishing sand trap and was nearly halted. In 2014 (year 10 of its 90-day mission), its flash memory became unreliable to the point that scientists discontinued its use, opting to store data in RAM instead. Last year, it even completed a marathon on Mars, crossing the 26.2-mile mark. Among the findings of the two rovers is a bonanza of water interactions from the Martian past—groundwater, water and magma, frost shaping rock, you name it. Opportunity most notably found evidence that Mars might have been habitable for hundreds of millions of years.


The Mars Reconnaissance Orbiter captured this image of Phoenix descending by parachute to Mars, with a crater in the background. Image credit: NASA/Jet Propulsion Lab-Caltech/University of Arizona

The Mars Polar Lander was intended to be the first spacecraft to set down on a Martian pole. Sadly, a likely crash landing left the spacecraft unresponsive. No one knows for sure what happened, and the Mars Reconnaissance Orbiter has been unable to find its remains.

Out of the missing ashes of MPL rose Phoenix, which carried improved versions of several instruments of its ill-fated progenitor, as well as a lander that had been intended originally for the Mars Surveyor, a canceled mission. Phoenix's landing on May 25, 2008 was notable in that the Mars Reconnaissance Orbiter was able to capture an image (above) of its parachute descent—the first time we've ever seen such a thing. Like Viking I, its final descent used rockets. The mission was a great success, proving the evidence of water ice on Mars just below the surface. It observed falling snow on Mars and, most notably for NASA's "Journey to Mars," found perchlorate, which can be used in the production of both rocket fuel and oxygen—useful items indeed for future Martian colonists. The mission, intended to last three months, went on for five. Poor sunlight and a dust storm interfered with its solar collection, and its batteries were eventually depleted.


Curiosity took this composite image of the higher regions of Mount Sharp on September 9, 2015. Image credit: NASA/JPL-Caltech/MSSS

The rover Curiosity's Rube Goldberg–like landing—which involved rockets, parachutes, sky cranes, tethers and perfect timing—was unlike anything NASA had ever previously attempted. (This landing system will not be a one-off, though. It will be used for the Mars 2020 rover, which launches that year and arrives in 2021.) Curiosity is a habitability study. It is, perhaps, an echo of Viking I, and a reflection of all we've learned. Where scientists in those heady days longed to catch images of Martian animals scurrying up to the spacecraft's nightlight, Curiosity steps back and asks, "Was Mars ever habitable?"

The answer: yes. As it relates to human life on Mars, Curiosity also found radiation levels similar to those on the International Space Station, meaning that colonists might not risk certain death by cancer when they arrive. The mission, now in its fourth year of a two-year mission, could survive well over a decade. Unlike previous Mars rovers, it is nuclear powered and impervious to the whims of dense Martian sandstorms or punishing winters. On the other hand, its wheels have sustained damage, leaving scientists uncertain as to how long the rover can keep moving. 

We'll take a deeper look at the Mars 2020 mission later this week. Until then, check out this awesome clip from the 2006 IMAX documentary Roving Mars

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Big Questions
Who Owns the Land on Mars?
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Nicolas Nelson:

“Who owns the land on Mars? Suppose I go there and [claim the planet by right of conquest or first discovery] and say ‘Hey, I’m selling the whole planet...'"

Sorry, friend, can’t do that.

The Outer Space Treaty of 1967 clearly states that all extraterrestrial real estate “belongs to all mankind” and cannot be claimed as sovereign territory by any nation-state. That kind of sovereign ownership used to be fundamental to any subsequent private ownership claims: the “crown” (or whatever government) had to deed it to you somehow. Nowadays, land ownership can derive from a legal regime, either a nation’s constitution (which inherited “sovereignty” from the old monarchies) or by an international treaty that establishes such a regime … which in this case is exactly what the Outer Space Treaty does.

On the other hand, the OST-1967 does not make private ownership illegal in space or on other planets. Like any good legal regime, the OST-1967 laid a foundation, and later laws passed in nations that are signatories to that treaty have been building upon it. For instance, both Luxembourg and the United States of America have passed laws that clarify property ownership of “space resources,” whether acquired in free-fall (like asteroids, comets, or even the solar flux that photovoltaic panels turn into electricity) or on a planetary surface, or beneath it (like any resources you collect on Mars … or Venus or whatever).

So, as I understand it currently, you can land on Mars and set up your settlement: you own all the stuff you brought with you, but not the land you plopped it onto.

But as your construction bots bulldoze regolith up onto your inflatable dormitory to protect it from radiation, that regolith is now a “resource” that you’ve collected and are using. Now you own that, too.

Your Sabatier-reactors (no radiation, don’t freak out) and your RWGS plant begin sucking in the thin Martian atmosphere and making oxygen, methane, and water out of it. You drill a well down to a geothermally-heated aquifer deep beneath your settlement and use that well to generate electrical power, heat your settlement, do cool science with it (look for microbial life!), and very carefully filter it so you can add it to your water supply: all those “resources” now belong to you.

But you’ve made it complicated now. You have drilled a well and have usage rights to that well… does that give you “water rights” to the giant aquifer you tapped? To some degree? You have built so much stuff on a clearly-delineated area: even though you cannot own it like “real estate,” haven't you established a whole blanket of rights to it just as if you’d homesteaded it or staked a mining claim?

You have a launch and landing pad nearby (not too nearby) with radar telemetry around it: you don’t own the rights to the open air above your launch pad because you own the pad, but you can assert those rights because of the way you use that resource: your future neighbor can’t build a bridge right over your launch pad because it would interfere with your ability to use the improved space resource that belongs to you.

Your rude neighbor could be an idiot and set a fragile inflatable dome next to your launch pad, since you can’t point to a property line and say “behind that, fella”, and since it does not physically interfere with your use of your property. You have the right to go on using your preexisting launch facilities and roast his dome. In that way, it isn't a question of property rights but wisdom versus idiocy.

You can see that once people actually begin “harvesting” and “improving” space resources, property laws will mature pretty quickly. They haven't yet … but the fundamental legal regime is clear: Mars “belongs” to everyone—and therefore, in a practical way, to no one.

This post originally appeared on Quora. Click here to view.

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6 Riveting Facts About Mars
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Mars' dust storms can be global. In these images taken a month apart in 2001, the dust storm near the southern polar ice cap (left) soon enveloped the entire planet (right).

August 6 marks the fifth anniversary of the rover Curiosity's landing on Mars. While its predecessors Spirit and Opportunity have been exploring the planet four times as long, Curiosity may be the perfect name for a Mars rover, because few celestial objects have fascinated humankind throughout history more than the Red Planet.

The light of Venus may be brighter in the night sky, but Venus is shrouded in clouds and thus a mystery. Mars hides nothing (except when there are global dust storms, as you can see in the before-and-after image above). Its giant "seas" and landmasses, ice caps, and Martian-made "canals"—for over a century, we've longed to know more about Mars and the beings that we speculated lived there. When NASA dispelled the notion of creatures scurrying along the rusty plains, it raised a more tantalizing prospect: that we might one day be the creatures that call Mars home.

Mental Floss spoke to Kirby Runyon, a researcher at the Johns Hopkins University Applied Physics Laboratory, and Tanya Harrison, the director of research for Arizona State University's NewSpace Initiative, to learn more about the place your kids might live one day.


A Martian year lasts just under two Earth years, taking 687 Earth days for the Red planet make its way around the Sun. A Mars day— called a sol—lasts 24.6 hours, which would be a nuisance for the circadian rhythms of astronauts (but not as bad as a day on Venus, which lasts 5832 hours). Mars looks desert hot—New Mexico with hazy skies, red because of its iron oxide soil—but is actually very cold, with a blistering hot sol being 70°F, and a cold sol a brisk -225°F.

Compared to Earth, Mars is a tiny Styrofoam ball, with a diameter just over half of ours and one-tenth of our mass. Its gravity will be an absolute nightmare for future colonists, at .38 that of their native planet. And you won't want to get a breath of fresh air on Mars unless you are trying to suffocate. Its atmosphere is 95.32 percent carbon dioxide, with a little nitrogen and argon thrown in. When you do try to take that single, hopeless breath, the tears on your eyeballs, saliva in your mouth, and water in your lungs will immediately evaporate. You won't die right away, but you'll probably want to.


Mars has two moons: Phobos and Deimos, which translate to Fear and Dread, respectively, making them the droogs to Mars's Alex. They're shaped like potatoes and don't exactly fill the evening sky. Standing on the Martian surface, Phobos would be about one-third the size of Earth's moon; Deimos would look like a bright star. Future human Martians will have to enjoy Phobos while they can. The tidal forces of Mars are tearing Phobos apart; in 50 million years, the big potato will disintegrate.

In the meantime, Phobos is one of the stepping stones NASA plans to take on its journey to Mars. No part of human exploration of the Red Planet is easy, and before we land on Mars (and then have to figure out how to launch back into space and somehow get back to Earth), it's vastly easier to land on Phobos, do a little reconnaissance, and then take off and return home. As a bonus, on the journey to Phobos, astronauts can bring along hardware necessary for eventual Martian settlement, making the ride a lot easier for the next astronauts.


If you want to climb a really tall mountain, Mars is where you want to be. The tallest mountain on Earth, Mount Everest, is 29,029 feet tall. Olympus Mons on Mars is over 72,000 feet in height, making it the tallest mountain by far on any planet in the solar system. Mountaineers might also want to check out NASA's trail map for hiking the famous Face on Mars. Before you go, be sure to check the latest Martian weather report. If canyons are more your speed, you'll want to visit Valles Marineris. It is the size of North America and, at its bottom, four miles deep. (In the solar system, only Earth's Atlantic Ocean is deeper.) Once Earth's ice caps finish melting, you can always visit the ones on Mars. (If you have a telescope, you can easily see them; they are the planet's most distinctive features visible from your backyard.)


The idea of Martians goes back over a century, partially because of popular fiction (War of the Worlds, the 1897 novel by H.G. Wells, sees a Martian invasion force invade England) and partially because of Percival Lowell, the famed astronomer who wrote prolifically on the canals he thought he was observing through his telescope, and why they might be necessary for the survival of the Martian people. (Mars was drying up.)

Though it's easy to dismiss such conclusions today, at the time Lowell not only popularized space science like few others, but left behind the Lowell Observatory in Flagstaff, Arizona—one of the oldest observatories in America and the place where Clyde Tombaugh discovered Pluto.

Today, scientists work tirelessly to unlock the complex geologic history of Mars, to determine whether life exists there today, or did long ago. "We think that Mars was most globally conducive to life around 3.5 to 3.8 billion years ago," Runyon tells Mental Floss. "In the Mars geologic history, that's the end of the Noachian and toward the beginning of the Hesperian epochs." There may once have been a hemispheric ocean on Mars. Later, the world might have alternated between being wet and dry, with an ocean giving way to massive crater lakes. Where there's water, there's a good chance of life.

"If we found life on Mars—either extinct or current—that's really interesting," says Runyon, "but more interesting than that, is whether this life arose independently on Mars, separate from Earth." It is conceivable that meteorite impacts on Earth blasted life-bearing rocks into space and eventually to the Martian surface. "A second life emergence on Mars is not just a geological question. It's a biogeochemical question. We know that Mars is habitable, but we haven't answered the question of whether it had, or has, life."


Mars hasn't hurt for missions in recent years, though scientists now warn of an exploration desert beyond 2020. But that doesn't mean we humans don't have eyes on the planet. Presently in orbit around the planet are the Mars Reconnaissance Orbiter, which images and scans the planet; MAVEN, which studies its atmosphere; Mars Express, the European Space Agency's first Mars mission; MOM, the first Mars mission by the Indian Space Research Organization; the ESA's ExoMars Trace Gas Orbiter, which is searching for methane in the Martian atmosphere; and Odyssey, which studies Mars for water and ice signatures, and acts as a communications relay for vehicles on the ground.

Rolling around on the Martian surface are Curiosity and Opportunity—NASA missions both—which study Martian geology. Though the Russians and Europeans have tried mightily to do so, NASA is the only space agency to successfully land spacecraft on the Martian surface (seven times).

Next year, the delayed InSight mission will launch for Mars, where it will land and study the planet's interior, and in three years, NASA will land the Mars 2020 rover. Where Curiosity studies Mars for signs of habitability, Mars 2020 will look for inhabitants.

"It is going to collect samples that will hopefully be brought back to Earth," says Runyon. "The three landing sites selected for Mars 2020 are Northeast Syrtis, Jezero Crater, and Columbia Hills within Gusev Crater, which is where the dead rover Spirit is currently sitting. Each of these sites is a hydrothermal environment dating from the Noachian-Hesperian boundary. These are some of the most perfect places to look for past signs of Martian life, and can help answer the question of whether life had a second Genesis on Mars."


Most people don't realize how active Mars is," Harrison tells Mental Floss. "Other planets aren't just these dead worlds that are frozen in time outside of our own. There are actually things happening there right now." Imagery from the HiRISE and Context Camera instruments on the Mars Reconnaissance Orbiter have revealed such events as avalanches, sand dune erosion [PDF], and recurring slope lineae (flowing Martian saltwater).

Things are moving, but it's not always clear why. "There's a lot of material that has been eroded away," says Harrison. "We have entire provinces of the planet that look like they've been completely buried and then exhumed. And that's a lot of material. The big question is, where did it all go? And what process eroded it all away?" Curiosity might help answer the question, but to really understand the processes and history of the fourth rock from the Sun, we're going to need to send geologists in spacesuits.

That's because "you can't replace human intuition with a rover," Harrison says. "Looking at a picture on your computer is not the same as standing there and looking around at the context, stratigraphic columns, being able to pick up the rocks and manipulate them, take a hammer to things. So once humans land on the surface, it'll be kind of like the difference between what we knew about Mars from Viking and Mars Global Surveyor and then the revolution between Mars Global Surveyor and Mars Reconnaissance Orbiter. Our view of what we think happened on Mars is going to completely change, and we'll find out that a lot of what we thought we knew was wrong."


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