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.

5 Fast Facts About the Spring Equinox

iStock.com/AHPhotoswpg
iStock.com/AHPhotoswpg

The northern hemisphere has officially survived a long winter of Arctic temperatures, bomb cyclones, and ice tsunamis. Spring starts March 20, which means warmer weather and longer days are around the corner. To celebrate the spring equinox, hear are some facts about the event.

1. The spring equinox arrives at 5:58 p.m.

The first day of spring is today, but the spring equinox will only be here for a brief time. At 5:58 p.m. Eastern Time, the Sun will be perfectly in line with the equator, which results in both the northern and southern hemispheres receiving equal amounts of sunlight throughout the day. After the vernal equinox has passed, days will start to become shorter for the Southern Hemisphere and longer up north.

2. The Equinox isn't the only time you can balance an egg.

You may have heard the myth that you can balance on egg on its end during the vernal equinox, and you may have even tried the experiment in school. The idea is that the extra gravitational pull from the Sun when it's over the equator helps the egg stand up straight. While it is possible to balance an egg, the trick has nothing to do with the equinox: You can make an egg stand on its end by setting it on a rough surface any day of the year.

3. Not every place gets equal night and day.

The equal night and day split between the northern and southern hemispheres isn't distributed evenly across all parts of the world. Though every region gets approximately 12 hours of sunlight the day of the vernal equinox, some places get a little more (the day is 12 hours and 15 minute in Fairbanks, Alaska), and some get less (it's 12 hours and 6 minutes in Miami).

4. The name means Equal Night.

The word equinox literally translates to equal ("equi") and night ("nox") in Latin. The term vernal means "new and fresh," and comes from the Latin word vernus for "of spring."

5. The 2019 spring equinox coincides with a supermoon.

On March 20, the day the Sun lines up with equator, the Moon will reach the closest point to Earth in its orbit. The Moon will also be full, making it the third supermoon of 2019. A full moon last coincided with the first day of spring on March 20, 1981, and it the two events won't occur within 24 hours of each other again until 2030.

A Full Pink Moon Is Coming in April

Ana Luisa Santo, Flickr // CC BY-ND 2.0
Ana Luisa Santo, Flickr // CC BY-ND 2.0

Mark your calendars for Friday, April 19 and get ready to snap some blurry pictures of the sky on your way to work. A full pink moon will appear early that morning, according to a calendar published by The Old Farmer's Almanac.

Considering that the full moon cycle is completed every 29.5 days, the April full moon will be the fourth full moon of 2019. Despite its name, the surface of the moon doesn't actually appear rosy. The name refers to the wild ground phlox, a type of pink wildflower, that tends to sprout in the U.S. and Canada around this time of year. It's also sometimes called an egg moon, fish moon, or sprouting grass moon.

What does the Full Pink Moon mean?

The April full moon might be a bit of a misnomer, but it still plays a pretty important role in the Christian tradition. The date on which the full pink moon appears has historically been used to determine when Easter will be observed. The holiday always falls on the Sunday following the first full moon that appears after the spring equinox. However, if the full moon falls on a Sunday, Easter will be held the following Sunday.

This rule dates back to 325 C.E., when a group of Christian churches called the First Council of Nicaea decided that the light of the full moon would help guide religious pilgrims as they traveled ahead of the holiday. Since the full moon will be visible on April 19 this year, Easter will be held on April 21.

When to see the full pink moon

The best time to view this April full moon is around 4:12 a.m. on the West Coast and 7:12 a.m. on the East Coast. The exact time will vary depending on your location. For a more specific estimate, head to the Almanac's website and type in your city and state or ZIP code.

If you happen to miss this spectacle because you're enjoying a full night’s sleep, don't fret too much. A full flower moon will be arriving in May.

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