Mercury's 'dynamic and complex world' revealed by Nasa's Messenger

First time planet has high-resolution maps after Nasa spacecraft orbited planet over course of a year

Mercury is the smallest of the solar system's eight planets and, for decades, also its most neglected by humans. While Mars, Venus, Jupiter and Saturn have been probed and photographed in exquisite detail during the space age, the closest planet to the Sun has had to make do with a few flybys from the Mariner 10 spacecraft in the early 1970s.

Now Mercury has its own high-resolution maps, down to the scale of kilometres, made from thousands of images taken by Nasa's Messenger spacecraft as it orbited the planet over the course of a year.

"Messenger has revealed Mercury to be a fascinating, dynamic and complex world," said David Blewett at the Applied Physics Laboratory at Johns Hopkins University and a scientist for the Messenger mission. Part of the reason, he said, that it had taken more than 30 years to revisit the planet since the Mariner 10 flybys was that most people thought Mercury was probably like the moon and largely inert and boring.

"We know now that it is an oddball planet," said Blewett, speaking ahead of a briefing on Friday at the annual meeting of the American Association for the Advancement of Science in Boston. "It's the smallest of the eight planets but has the highest density. The interior structure is different than the other planets. The geologic surface is different to the moon and Mars. The surface composition is enigmatic because ... it consists of rock types that we don't have much experience with. It has a global, Earth-like magnetic field, Venus and Mars do not."

The new global colour map is an enhanced image that shows the different compositions of rocks on the surface of Mercury. The more orange areas are volcanic plains while the make-up of the rocks in the deep blue areas is unknown. Though Messenger was able to detect the abundance of individual elements on Mercury's surface - including iron, titanium, sulphur and potassium - without rock samples to study, scientists cannot determine the exact compounds or minerals in which those elements are arranged.

Mercury orbits the sun in an eccentric orbit that gets as close as 46m kilometres and never goes further than 70m kilometres from our star (earth, for comparison, stays about 150m kilometres away). This means the surface of the planet can reach more than 400C.

Nasa's Messenger spacecraft made its first flyby of the planet in 2008 and began to orbit in early 2011, since when it has been mapping and measuring the surface of the planet. In November 2012, Nasa announced there was water ice and tar-like organic molecules at Mercury's poles. Because the planet's axis of rotation around the sun barely tilts from the vertical, the deepest parts of craters at the polar regions never get sunlight and the temperatures there are about -200C. The presence of ice and organic compounds lends weight to the idea that the planet was pummeled by icy comets during the early years of the solar system.

The biggest surprise for researchers is that, on the surface, the abundance of relatively volatile elements such as potassium and sulphur is so high. Most of the models for the formation of Mercury predict that these elements should have evaporated away during the planet's formation.

"The big problem in making Mercury is how do you get a planet that has such a huge iron core and such a small proportion of rock? One of the ideas was that maybe there was a giant impact that stripped off much of the rocky outer layers and left you with unusually high proportion of iron in the core," said Blewett. But Messenger's data, he said, meant planetary scientists would have to come up with new ideas.

One alternative candidate is that the chemical conditions in the inner part of the nebula where Mercury was forming were different than scientists had expected, and this probably allowed iron to condense first, while the rockier parts of the planet were swept away. "That model seems to predict the correct sulphur and potassium abundance for the surface and that's probably the leading contender right now," said Blewett.

Asteroid to pass closer to Earth than TV satellites

Rock measuring 46 metres across is expected to come within 17,100 miles but will not hit Earth, says Nasa

A small asteroid will pass closer to Earth next week than the TV satellites that ring the planet, but there is no chance of an impact, Nasa has said.

The celestial visitor, known as 2012 DA14, was discovered last year by a group of amateur astronomers in Spain. The asteroid is about the size of an Olympic swimming pool at 46 metres (150ft) in diameter and is projected to come as close as 17,100 miles (27,520km) from Earth during its approach on 15 February.

That would make it the closest encounter since scientists began routinely monitoring asteroids about 15 years ago.

Television, weather and communications satellites fly about 500 miles (800km) higher. The moon is 14 times farther away.

Even so, "no Earth impact is possible", the astronomer Donald Yeomans, with Nasa's Jet Propulsion Laboratory in Pasadena, California, told reporters during a conference call.

The time of the asteroid's closest approach will be 7.24pm GMT (2.24pm EST) - daylight in the US but dark in Europe, Asia and Australia, where professional and amateur astronomers will be standing by with telescopes and binoculars to catch a glimpse.

DA14 will soar through the sky at about 8 miles (13km) a second. At that speed, an object of similar size on a collision course with Earth would strike with the force of about 2.4m tonnes of dynamite. The last time that happened was in 1908 when an asteroid or comet exploded over Siberia, levelling 80m trees over 830 square miles (2,150 sq km).

"Although they wouldn't [cause] a global catastrophe if they impact the Earth, they still do a lot of regional destruction," said Lindley Johnson, who oversees the Near-Earth Object Observations Programme at Nasa's headquarters in Washington DC.

Nasa has been on a mission to find and track all near-Earth objects that are 0.62 miles (1km) in diameter or larger. The effort is intended to give scientists and engineers as much time as possible to learn if an asteroid or comet is on a collision course with Earth, in the hope of sending up a spacecraft or taking other measures to avert catastrophe.

About 66m years ago, a six-mile (10km) diameter object smashed into what is now the Yucatan peninsula in Mexico, leading to the demise of the dinosaurs as well as most plant and animal life on Earth.

The planet is regularly pelted with objects from space, adding up to about 100 tonnes of material a day, Yeomans said.

"Basketball-sized objects come in daily. Volkswagen-sized objects come in every couple of weeks. As you get to larger and larger sizes the number of objects out there is less and less, so the frequency of hits goes down," Yeomans said.

Something the size of DA14 can be expected to strike Earth about every 1,200 years.

"For objects of this size, this is the closest predicted encounter that we're aware of," Yeomans said.

Elon Musk wants to send 80,000 people to live on Mars

SpaceX founder Elon Musk has big plans for the human race. He wants to create a colony on Mars consisting of a population of 80,000 humans. The citizens would be ferried to the planet in a reusable rocket that runs on liquid oxygen and methane. For the initial trip, the rocket would contain less than 10 humans, who would be sharing their space with enough equipment to found a colony ready for the other 79,990.

The colony would be founded in transparent domes, and would be pressurized with CO² from the Martian atmosphere so colonists could grow Earth crops in Martian soil. In order to develop an atmosphere that would provide the tools for colonists to sustain themselves, the rocket would carry machines that can create fertilizer, oxygen, and methane out of subsurface water, nitrogen, and carbon dioxide found on Mars.

Musk did not disclose the details of the rocket he envisions being able to transport the machinery and colonists to Mars, though left curious folk with a hint. Musk was asked if the rocket would be a SpaceX reusable rocket that is rumored to be in development — the MCT — which is said to either stand for Mars Colony Transport or Mass Cargo Transport. He simply replied, “Maybe.”

Though Musk has yet to reveal details of the craft capable of delivering the payloads of humans and machines, a recent trip SpaceX made to the International Space Station using Dragon cost $91,000 per pound. However, Dragon only carried 1,455 pounds of cargo to the ISS, and the total carrying capacity of the ship is 13,000 pounds, so the more cargo the ship carries, the cheaper the cost per pound. There are currently no disclosed details regarding what kind of carrying capacity the theorized Mars ship would require.

Unfortunately for would-be space explorers, Musk estimated a ticket price of $500,000 per person could conceivably cover the cost of the trip. He feels half a million bucks is an amount of money that people in “advanced countries” could eventually scrounge together. This isn’t actually as crazy as it might initially sound. If you’re giving up life on Earth to help found a colony on Mars, you could probably sell the majority of your possessions — like your house — to help reach that target.

Musk also feels the entire project would end up costing around $36 billion, stating that a colony that costs around 0.25 or 0.5 percent of a nation’s GDP would be seen as acceptable. In 2010, the United States’ GDP was $14.5 trillion, and 0.25 percent of that is the estimated $36 billion. That $36 billion would be reached if all of the projected 80,000 colonists paid Musk’s ticket price of $500,000.

As exciting as Musk’s vision is, there just isn’t enough detail yet to get too hopeful about this endeavor.

via Discovery News

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