spaceplasma:

Meteorites on Mars

The sky falls on Mars, too, just as it does sometimes on Earth. In its long crosscountry drive over the pool table expanse of Meridiani Planum, Mars Exploration Rover Opportunity has encountered more than a dozen meteorites, all of them iron or stony-iron in composition.

Meteorites found on Mars are curiosities, but they can be something more than that, as a  paper in the Journal of Geophysical Research points out. A team of scientists led by James Ashley (Arizona State University) notes that because we have samples on Earth of the same kinds of meteorites found there, scientists can use the weathering seen on the Martian examples to probe bygone Martian climates.

The paper details three of Opportunity’s Mars meteorites, dubbed Block Island, Shelter Island, and Mackinac Island. Block Island was found by Opportunity on sol (Mars day) 1961 (July 31, 2009), Shelter Island on sol 2022 (October 1, 2009), and Mackinac Island on sol 2034 (October 14, 2009).Scientists are naming rocks of scientific interest after islands on earth.

 What’s most distinctive about these meteorites is that they show evidence for repeated episodes of weathering. For example, Block Island (an iron meteorite) shows two dramatically different faces: one smoothed, probably by sandblasting, and the other deeply pitted, probably by acidic corrosion. The corrosion likely occurred as thin films of water encountered iron sulfide minerals commonly found in iron meteorites.

Both Block Island and Shelter Island show evidence for multi-stage weathering. Close examination of their surfaces show that both have lost through weathering the fusion crusts that meteorites commonly develop as they speed through the atmosphere. Then exposure to water (or probably ice) created an oxydized (rusted) outer layer. This in turn has been largely scoured away by wind erosion.

There’s no way at present to determine how long those meteorites rested on the surface before Opportunity rolled by. But the weathering is unlikely to have happened recently, given Mars’ current arid, cold climate. Yet scientists know that over the last half million years at least, the planet’s spin axis has changed its tilt with respect to the Martian orbit. This has produced periods when snow and ice have come down from the polar regions and accumulated near the equator, probably including Meridiani Planum.

Credit: NASA/JPL

(via itsfullofstars)

spaceplasma:

Io

Looking like a giant pizza covered with melted cheese and splotches of tomato and ripe olives, Io is the most volcanically active body in the solar system. Volcanic plumes rise 300 km (190 miles) above the surface, with material spewing out at nearly half the required escape velocity.

A bit larger than Earth’s Moon, Io is the third largest of Jupiter’s moons, and the fifth one in distance from the planet.

Although Io always points the same side toward Jupiter in its orbit around the giant planet, the large moons Europa and Ganymede perturb Io’s orbit into an irregularly elliptical one. Thus, in its widely varying distances from Jupiter, Io is subjected to tremendous tidal forces. These forces cause Io’s surface to bulge up and down (or in and out) by as much as 100 m (330 feet)! Compare these tides on Io’s solid surface to the tides on Earth’s oceans. On Earth, in the place where tides are highest, the difference between low and high tides is only 18 m (60 feet), and this is for water, not solid ground!

This tidal pumping generates a tremendous amount of heat within Io, keeping much of its subsurface crust in liquid form seeking any available escape route to the surface to relieve the pressure. Thus, the surface of Io is constantly renewing itself, filling in any impact craters with molten lava lakes and spreading smooth new floodplains of liquid rock. The composition of this material is not yet entirely clear, but theories suggest that it is largely molten sulfur and its compounds (which would account for the varigated coloring) or silicate rock (which would better account for the apparent temperatures, which may be too hot to be sulfur). Sulfur dioxide is the primary constituent of a thin atmosphere on Io. It has no water to speak of, unlike the other, colder Galilean moons. Data from the Galileo spacecraft indicates that an iron core may form Io’s center, thus giving Io its own magnetic field.

Io’s orbit, keeping it at more or less a cozy 422,000 km (262,000 miles) from Jupiter, cuts across the planet’s powerful magnetic lines of force, thus turning Io into a electric generator. Io can develop 400,000 volts across itself and create an electric current of 3 million amperes. This current takes the path of least resistance along Jupiter’s magnetic field lines to the planet’s surface, creating lightning in Jupiter’s upper atmosphere.

As Jupiter rotates, it takes its magnetic field around with it, sweeping past Io and stripping off about 1,000 kg (1 ton) of Io’s material every second! This material becomes ionized in the magnetic field and forms a doughnut-shaped cloud of intense radiation referred to as a plasma torus. Some of the ions are pulled into Jupiter’s atmosphere along the magnetic lines of force and create auroras in the planet’s upper atmosphere. It is the ions escaping from this torus that inflate Jupiter’s magnetosphere to over twice the size we would expect.

Discovery:
Io was discovered on 8 January 1610 by Galileo Galilei. The discovery, along with three other Jovian moons, was the first time a moon was discovered orbiting a planet other than Earth. The discovery of the four Galilean satellites eventually led to the understanding that planets in our solar system orbit the sun, instead of our solar system revolving around Earth. Galileo apparently had observed Io on 7 January 1610, but had been unable to differentiate between Io and Europa until the next night.

How Io Got its Name:
Galileo originally called Jupiter’s moons the Medicean planets, after the Medici family and referred to the individual moons numerically as I, II, III, and IV. Galileo’s naming system would be used for a couple of centuries.

It wouldn’t be until the mid-1800s that the names of the Galilean moons, Io, Europa, Ganymede, and Callisto, would be officially adopted, and only after it became apparent that naming moons by number would be very confusing as new additional moons were being discovered.

Io was originally designated Jupiter I by Galileo because it is the first satellite of Jupiter. Io is named for the daughter of Inachus, who was raped by Jupiter. Jupiter, in an effort to hide his crime from his wife, Juno, transformed Io into a heifer.

Credit: NASA/JPL

(via itsfullofstars)

unknownskywalker:

The fractured features of Ladon basin

ESA’s Mars Express has observed the southern part of a partially buried approx. 440-km wide crater, informally named Ladon basin. The images, near to where Ladon Valles enters this large impact region reveal a variety of features, most notably the double interconnected impact craters Sigli and Shambe, the basins of which are criss-crossed by extensive fracturing.

This region, imaged on 27 April by the high-resolution stereo camera on Mars Express is of great interest to scientists since it shows significant signs of ancient lakes and rivers. Large-scale overview maps show clear evidence that vast volumes of water once flowed from the southern highlands. This water carved Ladon Valles, eventually flowing into Ladon basin, an ancient large impact region.

The interconnected craters Sigli and Shambe are thought to have formed later when an incoming projectile split into two pieces just before impact. The joined craters were then partly filled with sediments at some later epoch. Scientists have suggested that a fluidised ejecta pattern indicates the presence of subsurface ice which melted during the impact.

Images: (1) High-Resolution Stereo Camera (HRSC) nadir and colour channel data taken during revolution 10602 on 27 April 2012 by ESA’s Mars Express have been combined to form a natural-colour view of the Ladon Valles region. (2, 3) Computer-generated perspective view created using data obtained from the High-Resolution Stereo Camera (HRSC) on ESA’s Mars Express.

learn-a-little:

Petrified Lightning: Natural glass formed by lightning strikes is called fulgurite. It is created when a lightning strike hits a sandbank, blowing a super-heated hole right through it. This quickly cools into a beautiful glass. The name comes from Latin fulgur, or lightning.

(Image credit to flickr, Carion Mineraux, and Nature. Thanks Grandma.)

By the beard of Zeus!!

(via mothernaturenetwork)

expose-the-light:

Patterns in Nature: Rocks and Lava

expose-the-light:

Patterns in Sand

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