musique musiqueThis map puts Mars Valles Marineris into perspective in terms of its size.
Valles Marineris on Mars is the longest and deepest canyon in the Solar System. The deep gash in the side of Mars is a pretty good companion for the tallest mountain in the Solar System, Olympus Mons, which also on Mars. The pair demonstrate the world of extremes that is the Red Planet. Valles Marineris is 4,000 km long, 200 km wide at points, and up to 7 km deep. It runs along the Martian equator and covers nearly a quarter of the planet’s circumference and 59% of its diameter. The Valles Marineris system is a network of interconnected valleys that begin in the west. Noctis Labyrinthus is considered the starting point of the system, then it moves east to include the Tithonium chasmata and Ius chasmata. In the mid region are the Melas, Ophir, Coprates, Ganges, Capri, and Eos chasmata. The canyon moves through an area of chaotic terrain(ridges, cracks, and plains jumbled together)before it ends in the basin region of Chryse Planitia. One of the largest debates surrounding the area is about how it formed. In the 1970s, erosion by water and/or melting permafrost were popular theories. Liquid water can not exist in current Martian conditions, but has in the past, making the feature billions of years old. Another theory from the 1970s was that the feature formed when subsurface magma withdrew from the area. At the end of 1989, a theory emerged that it was formed by tensional fracturing. The theory most widely shared today is that it formed by rift faults and was made bigger by erosion and the collapsing of the rift walls. A rift valley is usually formed between two mountain ranges and is caused by the formation of the mountains. In this case, the formation is tied to the Tharsis Bulge. Valles Marineris is named after NASA’s Mariner 9 spacecraft, which first photographed it up close in 1971-1972. Mariner 9 was the first spacecraft to orbit another planet, just ahead of the Soviet space program’s twin missions Mars 2 and Mars 3. Valles Marineris on Mars is the focus of many astrogeologists because of its tantalizing view into the Martian geologic past. Evidence within the valley also points to a much wetter and warmer climate on Mars millenia ago. You can be sure that scientists will be looking for more clues in every set of data from the area.
This image is a composite of 25 separate images spanning the period of April 16, 2012, to April 15, 2013.
It uses the SDO AIA wavelength of 171 angstroms and reveals the zones on the sun where active regions are most common during this part of the solar cycle.
Credit: NASA/GSFC/SDO/AIA/S. Wiessinger
Jupiter’s moon Io, photographed by Voyager 2, 10 July 1979.
The end of this blog’s Io-thon follows on from yesterday’s post. The photos used in this gif were taken with longer exposures than yesterday’s, so there is a better contrast between Io and the background. Two volcanic eruptions are clearly visible in the top-left: I think that they are from Amirani and Maui. There’s also an eruption on the right-hand side, but as its only lit by reflected light from Jupiter, it requires a lot of brightening to see (NASA’s photojournal shows it here).
You can also see a volcano in the south, tall enough to stay in sunlight even as the surrounding areas fall into darkness.
Yesterday I mentioned the bright spot glinting near the equator. I asked Jason Perry (who used to write an Io blog) about it on Twitter and he said that it “looks like specular reflection off of glassy, cooled lava near Hi’iaka Patera.” So there you go.
Iconic images of Earth from space. Click them for the description.
When is the next Blue Moon?
There are different definitions for Blue Moon. By popular acclaim, the Blue Moon refers to the second of two full moons to occur in the same calendar month. A Blue Moon is also regarded as the third of four full moons in a single season – a season being defined as the time period between a solstice and an equinox, or vice versa. Or, someday, you might see an actual blue-colored moon. The next Blue Moon will fall on August 20-21, 2013. It’ll be a Blue Moon by the seasonal definition, that is, the third of four full moons to take place in a season, in this case between the June 2013 solstice and September equinox. The last Blue Moon by this definition happened on November 21, 2010.
The next Blue Moon by the second-full-moon-in-a-calendar-month definition will be on July 31, 2015. The first full moon of July 2015 will be on July 1, 2015. Previously, the last monthly Blue Moon happened on August 31, 2012.
The term once in a blue moon used to mean something rare. As you can see, now that the rules for naming Blue Moons include so many different possibilities, they’re really pretty common!
Image 1 | The August 20-21, 2013 will not be blue in color. This photo was created using special filters. Image via EarthSky Facebook friend Jv Noriega.
Image 2 | Another beautiful image by our friend Jv Noriega – the moon among fast-moving clouds. Will the August 20-21, 2013 be blue in color like this? No. This image was made using blue filters, too.
Image 3 | What most call a Blue Moon isn’t blue in color. It’s only Blue in name. This great moon photo from EarthSky Facebook friend Rebecca Lacey in Cambridge, Idaho.
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
