moons of saturn Archives ⋆ Dimensional Bliss

Mercury's extreme temperatures and lack of an atmosphere would make it very difficult, if not impossible, for people to live on the planet. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Excerpt from space.com

By Joseph Castro, Space.com Contributor

Have you ever wondered what it might be like to homestead on Mars or walk on the moons of Saturn? So did we. This is the first in Space.com's 12-part series on what it might be like to live on or near planets in our solar system, and beyond. Check back each week for the next space destination.

With its extreme temperature fluctuations, Mercury is not likely a planet that humans would ever want to colonize. But if we had the technology to survive on the planet closest to the sun, what would it be like to live there?

To date, only two spacecraft have visited Mercury. The first, Mariner 10, conducted a series of Mercury flybys in 1974, but the spacecraft only saw the lit half of the planet. NASA's MESSENGER spacecraft, on the other hand, conducted flybys and then entered Mercury's orbit — in March of 2013, images from the spacecraft allowed scientists to completely map the planet for the first time.

MESSENGER photos of Mercury show that the planet has water ice at its poles, which sit in permanent darkness. Mining this ice would be a good way to live off the land, but setting up bases at the poles might not be a good idea, said David Blewett, a participating scientist with the Messenger program.

"The polar regions would give you some respite from the strength of the sun on Mercury," Blewett told Space.com. "But, of course, it's really cold in those permanently shadowed areas where the ice is, and that presents its own challenge."

A better option, he said, would probably be to set up a home base not far from one of the ice caps, perhaps on a crater rim, and have a water mining operation at the pole.

Still, dealing with extreme temperatures on Mercury would likely be unavoidable: Daytime temperatures on the planet can reach 800 degrees Fahrenheit (430 degrees Celsius), while nighttime temperatures can drop down to minus 290 degrees Fahrenheit (minus 180 degrees Celsius).

Scientists once believed Mercury was tidally locked with the sun, meaning that one side of the planet always faces the sun because it takes the same amount of time to rotate around its axis as it does to revolve around the star. But we now know that Mercury's day lasts almost 59 Earth days and its year stretches for about 88 Earth days.

Interestingly, the sun has an odd path through the planet's sky over the course of Mercury's long day, because of the interaction between Mercury's spin rate and its highly elliptical orbit around the sun.

"It [the sun] rises in the east and moves across the sky, and then it pauses and moves backwards just a tad. It then resumes its motion towards the west and sunset," said Blewett, adding that the sun appears 2.5 times larger in Mercury's sky than it does in Earth's sky.

And during the day, Mercury's sky would appear black, not blue, because the planet has virtually no atmosphere to scatter the sun's light. "Here on Earth at sea level, the molecules of air are colliding billions of times per second," Blewett said. "But on Mercury, the atmosphere, or 'exosphere,' is so very rarefied that the atoms essentially never collide with other exosphere atoms." This lack of atmosphere also means that the stars wouldn't twinkle at night.

Without an atmosphere, Mercury doesn't have any weather; so while living on the planet, you wouldn't have to worry about devastating storms. And since the planet has no bodies of liquid water or active volcanoes, you'd be safe from tsunamis and eruptions.

But Mercury isn't devoid of natural disasters. "The surface is exposed to impacts of all sizes," Blewett said. It also may suffer from earthquakes due to compressive forces that are shrinking the planet (unlike Earth, Mercury doesn't have tectonic activity).

Mercury is about two-fifths the size of Earth, with a similar gravity to Mars, or about 38 percent of Earth's gravity. This means that you could jump three times as high on Mercury, and heavy objects would be easier to pick up, Blewett said. However, everything would still have the same mass and inertia, so you could be knocked over if someone threw a heavy object at you, he added.

Finally, you can forget about a smooth Skype call home: It takes at least 5 minutes for signals from Mercury to reach Earth, and vice versa.

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scientificamerican.com

A massive feature on the moon formed due to lunar rifts, in a surprise revision to earlier theories, research shows. Previously, scientists thought the moon's Ocean of Storms was a round crater left after a giant impact, but now researchers have found it is underlain by a giant rectangle created by cooling lunar lava as the moon formed.
This finding reveals the early moon was far more dynamic than previously thought, scientists added.
The Ocean of Storms, or Oceanus Procellarum, is the largest of the moon's maria, giant dark spots visible on the near side of the moon. Early astronomers, mistaking these features for oceans, named them maria, Latin for seas. However, they are actually giant plains of the dark rock basalt.
Stormy history for Ocean of Storms
Scientists had previously thought the Ocean of Storms was created by a giant cosmic impact that left a crater about 2,000 miles wide (3,200 kilometers) that filled with lava. Now, data from NASA's GRAIL mission reveals that Procellarum is not round, but instead is surrounded by a strange giant rectangle underneath the moon's surface. This suggests the Ocean of Storms was not caused by a meteor strike on the moon. Instead, researchers suggest, it formed as the moon's surface rifted apart.
"GRAIL has revealed features on the moon that no one anticipated before we had this data in hand," said lead study author Jeffrey Andrews-Hanna, a planetary scientist at the Colorado School of Mines in Golden. "One can only wonder what might lie hidden beneath the surfaces of all of the other planets in the solar system."
NASA's twin GRAIL spacecraft, named Ebb and Flow, orbited the moon and measured how the strength of the moon's gravitational pull varied over its surface. Anything that has mass has a gravitational field that pulls objects toward it, and the strength of this field depends on the amount of mass in the object. Variations in the strength of the moon's gravitational pull can therefore help reveal how mass is concentrated there below the surface. NASA launched the GRAIL moon gravity probes (the name is short for Gravity Recovery and Interior Laboratory) in September 2011. The mission ended in December 2012 when the two spacecraft were intentionally crashed into the moon's surface.
The ultra-precise gravity map of the moon from the GRAIL mission unexpectedly revealed a set of linear structures arranged in a rectangular shape about 1,600 miles (2,600 km) wide around Procellarum. The angular shape of the Ocean of Storm's borders reveal it was not created by a cosmic impact, which would have left a crater with a circular rim.
"The observed pattern of gravity anomalies on the moon is so strikingly geometric and in such an unexpected shape that it is forcing us to think in new and different ways about the processes operating on the moon and planets in general," Andrews-Hanna told Space.com.
Lunar lava and moon geometry
The researchers suggest these newfound structures are the remnants of valleys filled in with frozen lava. These valleys arose as the surface of the moon rifted open.
"As a solid cools and contracts, fractures and faults can form, and these fractures will commonly take on a polygonal pattern," Andrews-Hanna explained. "An excellent example of this is found in cooling lava flows on Earth where the lava breaks up into hexagonal columns, as can be seen at Devil's Postpile National Monument in California. These hexagons form because when three cracks intersect, they do so at 120-degree angles, and the only polygon on a flat surface that you can make with all 120-degree angles is a hexagon. These 120-degree intersections are seen at all scales, from the intersections of centimeter-scale cracks in drying mud to the intersections of giant rift valleys in eastern Africa."
On the moon, these ancient rift zones took on a rectangular order.
"Geometry on a sphere is different than geometry on a flat surface — this is why airplanes appear to follow curved paths when you look at their flight trajectories on a map," Andrews-Hanna said. "For a feature of the size of the Procellarum region, a polygon with 120-degree corner angles has four sides instead of six — or, stated another way, a square the size of Procellarum on the surface of a sphere the size of the moon has 120 degree angles instead of the 90 degree angles you expect on a flat surface."
The rift valleys filled in with lava until 3.5 billion years ago. This lava likely came from sources within the rift valleys themselves, Andrews-Hanna said. It remains uncertain whether the rift valleys formed before or during the volcanism that filled Procellarum with the lava that cooled to form the black rock that currently dominates the area, he added.
Rift zones are well known on Earth, Venus and Mars, but previously unknown on the moon. "This reveals a much more dynamic early moon than we had previously envisioned," Andrews-Hanna said. "I think we are only just beginning to understand the earliest history of the moon."
The newfound pattern of structures on the moon is quite similar to the structures seen on Saturn's icy moon Enceladus, which may have experienced a similar geological history, the researchers noted. Prior research had not predicted these structures on either the moon or Enceladus, "which tells us that we have much left to learn in order to understand the full spectrum of planetary evolution," Andrews-Hanna said.
The research is detailed in the Oct. 2 edition of the journal Nature.

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