7 Hot Facts About Mercury

Mercury, the diminutive planet closest to the Sun, was notoriously mysterious due to its difficulty to explore. That changed on March 18, 2011, when the MESSENGER spacecraft from Johns Hopkins' Applied Physics Laboratory achieved orbit around Mercury. The mission spent the next four years transforming scientists' understanding of how Mercury works and what it is made of. Mental Floss spoke to Sean Solomon, the principal investigator of MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging), to learn what's most interesting about the first rock from the Sun.

1. MEET MERCURY BY THE NUMBERS.

Mercury is the smallest terrestrial planet of the solar system. Comparatively, Mercury is about midway in size between Earth's moon and the planet Mars. (Mars is a lot smaller than you might think, and our moon a lot larger.) Mercury is 3032 miles in diameter, which is, as the crow flies, just a little less than the distance from Anchorage to Dallas. Its gravity is 38 percent of Earth's, which means if you weigh 150 pounds here, you'd weigh 57 pounds on Mercury (the same as you would on Mars).

One day on Mercury lasts 59 Earth days, and one year lasts 88, which would make figuring out your age a thorny algebra problem. As you might imagine, days on Mercury can get pretty hot—around 800°F. On Earth a brick of coal at that temperature would burst into flames. (This is not a problem on Mercury, as the planet lacks an atmosphere.) Its nights, meanwhile, are a brisk -280°F. This is the widest day-to-night temperature variation of any planet in the solar system, and would make packing for a trip there very difficult indeed.

2. DESPITE BEING CLOSEST TO THE SUN, IT ISN'T THE HOTTEST PLANET.

Logic would suggest that Mercury is the hottest planet, considering its proximity to the giant fusion reactor at the center of our solar system that is 1,400,000,000,000,000,000,000,000,000,000 cubic meters in volume. The hottest planet honor, however, belongs to its neighbor Venus, one planet away, where the average surface temperature is 864°F. On Venus, lead would melt the way an ice cube melts on Earth.

3. MERCURY HAS SURPRISING CHEMISTRY.

Pretty much everything about Mercury should astound the casual observer, but what most surprises the principal investigator of MESSENGER, the first orbiter mission there? "The chemistry—that was the biggest surprise," says Solomon, who is also director of the Lamont-Doherty Earth Observatory at Columbia University. "We still don't have a good physical and chemical model for planet formation, and so the result that Mercury is this iron-rich planet, in which the silicate fraction is not only not depleted in elements easily removed by high temperatures, but is more abundant in some of those elements than Earth." The big takeaway from Mercury's chemical profile, Solomon says, is that "we don't really understand how the planets were assembled."

4. UNDERSTANDING ITS FORMATION WILL HELP US UNDERSTAND THE TERRESTRIAL PLANETS.

"How did we end up with four bodies of rock and metal that are quite different?" asks Solomon. "Venus and Earth are different because of their different atmospheres. The different evolution of the climate, and the feedback between climate and interior, led to very different tectonic evolution."

Mars and Earth are different because Mars is so much smaller than Earth, only 10 percent of Earth's mass, he explains. As for Mars and Venus: "A lot of Mars's atmosphere was stripped away by the solar wind, so it turned into this cold, barren desert world, whereas Venus has this dense CO2 atmosphere. Runaway greenhouse [effect] turned it into a hothouse world." Earth is in between.

Mercury suggests that the process of planet forming depends on more than simply planet size, solar distance, and differences in atmosphere. The original building blocks of planets also varied across the inner solar system in important ways. "The chemistry varied, volatile abundances varied, and some conditions must have helped during planet formation that can't be ascribed to late-stage processes like a collision," Solomon says.

Now that we've performed one comprehensive study of Mercury, scientists can endeavor to explain the diversity of the terrestrial planets. "We now have filled in the last missing piece in describing the four siblings of that process [of planetary formation]. They're all different, and yet the parental processes, if you will, must have been in common, so it's a kind of planetary genome expression," Solomon says. "How the heck can gene expression be so different among these four siblings, given that they all started out at the same time by the same processes, in just slightly different places in the inner solar system?"

5. MERCURY IS SHRINKING.

"There are faults all over the surface, and most of those faults involve horizontal shortening," or shrinking. The idea goes all the way back to Mariner 10, a robotic space probe launched by NASA in 1973, says Solomon. "The faults that accommodate horizontal shortening are seen on top of every kind of terrain, and they have a wide range of orientations. The Mariner 10 proposed—and the MESSENGER team confirmed—that contraction has dominated the history of the planet, and is consistent with the planet shrinking over time as the result of interior cooling and contraction of the interior." This tectonic activity has been active over most of the history of the planet, as the planet continues to cool.

But were you to stand on Mercury's surface, you couldn't expect Seti Alpha VI-like cataclysms as the planet suddenly contracts. "Were we to send a seismic experiment to Mercury, we would probably see mercury-quakes not anywhere near the frequency or size of earthquakes, but something more akin to moonquakes," Solomon says.

6. IT HAS WATER ICE.

The orientation of craters found on the poles of Mercury allows for permanently shadowed regions—that is, areas that never receive sunlight, no matter the planet's rotational position or place in its revolution. The conditions in those craters are amenable to stable water ice, on or mere centimeters below the planet's surface. MESSENGER's nuclear spectrometer yielded measurements consistent with water ice on the north pole, and its camera later captured optical-light images of that ice.

7. IT'S HARD TO GET NEAR—BUT WE'RE GOING BACK.

Only two missions have thus far explored Mercury: the Mariner 10 space probe in 1974, and the MESSENGER orbiter in 2011. This is in part because of the tremendous challenges associated with visiting the planet. "Mercury is in a challenging environment," says Solomon. "The Sun is 11 times brighter than it is at Earth. The surface temperature of the day-side is very hot. The night-side temperature, however, is quite cold, so the swings in temperature are large. The radiation environment that close to the Sun is challenging, as we anticipated going into the mission. We were hit directly by streams of energized particles from the Sun."

Mariner 10 performed three fast flybys of Mercury, and scientists spent the next three decades working largely from the close-up science it performed. Mariner's findings and the questions they raised would further contribute to the scientific rationale of an orbiter—what would be the eventual MESSENGER spacecraft.

A Mercury orbiter, of course, is no small order, and placing a spacecraft in orbit around that planet is one of the great achievements of the American space program. You can't just fly to Mercury and enter orbit. A spacecraft would be moving at a velocity far too great for that, as Mercury lacks the atmosphere to allow aerobreaking. Instead, a trajectory had to be calculated in which MESSENGER bounced around the solar system, from Earth, around the Sun and back to Earth; around the Sun and to Venus; around the Sun and back to Venus; and around the Sun four more times, flying closer and closer to Mercury each time, until at last it could enter Mercury's orbit. In essence, MESSENGER borrowed the gravity of other planets to compensate for what Mercury could not provide on a direct flight.

Due to this circuitous route, MESSENGER had to travel 5 billion miles over six-and-a-half years to reach a planet 100 million miles away. Once there, the challenge continued. The spacecraft had to maintain an orientation that kept between its scientific payload and the Sun a giant sunshade, lest the Sun fry the instruments. But extreme heat wasn't the only problem. So was extreme cold. When the spacecraft crossed into Mercury's shadow, an onboard heater had to warm the spacecraft lest the instruments freeze.

Despite the challenges, we're going back. The next mission bound for Mercury will launch in 2018. BepiColombo, a joint mission between the European and Japanese Space Agencies, will place two satellites in orbit around Mercury, where they will study its composition, tenuous atmosphere, and magnetosphere. Like MESSENGER, the spacecraft will require a complex trajectory—and a very long time to reach its target. It will achieve orbit around Mercury in December 2025.

10 Out-of-This-World Facts About Space Camp

U.S. Department of Education, Flickr // CC BY 2.0
U.S. Department of Education, Flickr // CC BY 2.0

Each year, millions of kids fill their summer vacation days with songs, crafts, and outdoor activities at camp. Summer camps across the U.S. share many similarities, but Space Camp in Huntsville, Alabama is unique. Instead of canoeing and archery, young attendees get to ride spacecraft simulators, build robots, and program computers. It’s the closest young civilians can come to working for NASA.

Space Camp welcomed its first aspiring astronauts in 1982, and since then, more than 900,000 campers have attended the program. From its famous alumni to its depiction in film, here are some more facts about Space Camp.

1. The movie SpaceCamp boosted its popularity.

SpaceCamp, the movie inspired by the real camp in Huntsville, Alabama, wasn’t a huge hit when it debuted in theaters in 1986. It grossed just $9,697,739—a little more than half its reported budget. But it didn’t fade into obscurity completely. The film saw success in the home video market and became popular enough to leave a lasting mark on pop culture. Dr. Deborah Barnhart, the real camp’s director for part of the 1980s, told AL.com that attendance doubled following the movie’s release. SpaceCamp shot many of its scenes on location at the Huntsville center. The life-sized space-shuttle flight-deck and mid-deck built for the film were donated to the camp and used as a simulator there from 1986 to 2012.

2. Space Camp was the brainchild of a missile designer.

Some people may be surprised to learn that Space Camp is located in Alabama and not Florida, home to Cape Canaveral and the Kennedy Space Center (the movie SpaceCamp is set in Florida despite being filmed in Alabama). But Huntsville, Alabama, has been a major aeronautics center since the 1950s when Wernher von Braun and his team of rocketeers moved there. The German scientist had designed ballistic missiles for the United States military after World War II, and shortly after relocating to Huntsville, he redirected his attention to space flight. He launched the U.S. Space and Rocket Center as a way to demonstrate the area’s rocket technology to tourists. Von Braun also came up with the idea for a science-focused alternative to traditional summer camps after seeing children touring the rocket center and taking notes. Space Camp opened at the center in 1982, a few years after his death.

3. Space Camp activities go beyond space.

The kids at Space Camp do more than ride giant rocket simulators. After enrolling, young campers choose a track to focus on. They can study aviation and learn air navigation and combat techniques, choose robotics and build their own robots, or stick to space-centric subjects and activities. The newest Space Camp experience, cyber camp, teaches kids programming and online security skills.

4. The Space Camp simulators don’t make campers sick.

Space Camp is home to three simulators based on real-life training rigs astronauts use to prepare for space missions. The most intense rig is the multi-axis trainer, and just watching a video of it in action may be enough to make you feel queasy. But according to the camp’s website, campers “should not become sick or dizzy on any of our simulators.” On the multi-axis trainer, this is due to the fact that the rider's stomach remains at the center of the chair throughout the simulation, even as the chair itself is spinning in all directions. Motion sickness is caused when your inner ear fluid and your eyes send your brain conflicting information. Because the rig tumbles so wildly, the rider's inner fluid never has a chance to shift and make them want to vomit.

5. Space Camp boasts some famous alumni.

Space Camp attracts bright young minds from around the world, including a few celebrities. Chelsea Clinton attended the week-long program when her father was in the White House in 1993. Amy Carter, Jimmy Carter’s daughter, and Karenna Gore, daughter of Al Gore, also enrolled in the camp. But not every famous Space Camp graduate came from the world of politics: South African actress Charlize Theron is another notable alumna.

6. Several Space Camp graduates went on to be astronauts.

Many kids who go to Space Camp dream of growing up to be astronauts, and for some of them, that dream becomes a reality. The camp’s alumni includes the “Tremendous 12”—a handful of Space Camp graduates who’ve made it to space. Most members of this elite group were trained by NASA, but a few of them went on to work for other space agencies like the ESA.

7. Most Space Campers end up in STEM professions.

Space Camp in Huntsville, Alabama.
GPA Photo Archive, Flickr // CC BY-SA 2.0

Even if they don’t go on to be astronauts, most Space Camp attendees have bright futures ahead of them. According to the camp, 61 percent of graduates are studying aerospace, defense, energy, education, biotech, or technology, or they’re working in one of those fields already. Of the alumni pursuing careers in STEM, half of them said that Space Camp inspired that decision.

8. There’s a Space Camp for visually impaired kids.

The U.S. Space & Rocket Center in Huntsville, Alabama hosts a second Space Camp that shares a lot in common with its original program. There are space simulators, astronaut-training missions, and even scuba diving—the main difference is that the kids there are blind or visually impaired. Space Camp for Interested Visually Impaired Students, or SCIVIS, offers children in grades 4 to 12 a crash course in various STEM subjects. They use accessible tools, like computers adapted for speech and reading materials printed in braille or large print. Activities for the week-long camp are organized by teachers familiar with the needs of visually impaired students.

9. Double Dare sent winners to Space Camp.

After conquering the obstacle course of the Nickelodeon game show Double Dare, kid contestants were sent home with various prizes. Though no doubt exciting in the 1980s and '90s, many of the prizes—which included encyclopedias, cassette recorders, and AOL subscriptions—haven’t aged well. A trip to Space Camp was one of the biggest awards players could win, and it’s one of the few that would still have value today.

10. Adults can go to Space Camp too.

If you never went to Space Camp as a kid, you haven’t missed your chance. While the regular Space Camp is only open to kids ages 9 to 18, the U.S. Space & Rocket Center also offers camp programs for older space enthusiasts. Family Space Camp is designed for groups that include at least one child and one adult, and if you don’t plan on tagging along with a kid, you can enroll in the three-day Adult Space Camp experience that’s strictly for campers 18 and older.

NASA's First All-Female Spacewalk is Really Happening This Time

NASA astronaut Christina Koch is suited up in a U.S. spacesuit ahead of her history-making spacewalk.
NASA astronaut Christina Koch is suited up in a U.S. spacesuit ahead of her history-making spacewalk.
NASA

After a surprising cancellation in March, plans for NASA's first all-female spacewalk are back on track. Astronauts Christina Koch and Jessica Meir are scheduled to make history on October 21, 2019.

Earlier this year, NASA canceled the first all-female spacewalk because of an issue with spacesuit sizing. Both astronauts originally scheduled for the walk needed medium-sized suits. At the time, the International Space Station had two—but only one was properly configured for a spacewalk. Preparing the other suit in time would have taken hours of crew labor, The New York Times reported, so NASA decided to switch out the astronauts.

“When you have the option of just switching the people, the mission becomes more important than a cool milestone,” NASA spokesperson Stephanie Schierholz told The New York Times.

Still, the milestone is a significant one. Since 1961, nearly 550 people have been sent to space. Of those, only about 11 percent have been female.

“I think it’s important because of the historical nature of what we’re doing and in the past, women haven’t always been at the table,” Koch said on NASA TV. “There are a lot of people that derive motivation from inspiring stories from people who look like them, and I think it’s an important aspect of the story to tell.”

The mission itself is fairly routine—Koch and Meir are scheduled to swap out batteries on the station’s solar panels. Live video of the spacewalk (the 222nd spacewalk in history) will be available on NASA’s website.

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