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
Light and dust in a nearby starburst galaxy
Visible as a small, sparkling hook in the dark sky, this beautiful object is known as J082354.96+280621.6, or J082354.96 for short. It is a starburst galaxy, so named because of the incredibly (and unusually) high rate of star formation occurring within it.
One way in which astronomers probe the nature and structure of galaxies like this is by observing the behaviour of their dust and gas components; in particular, the Lyman-alpha emission. This occurs when electrons within a hydrogen atom fall from a higher energy level to a lower one, emitting light as they do so. This emission is interesting because this light leaves its host galaxy only after extensive scattering in the nearby gas — meaning that this light can be used as a pretty direct probe of what a galaxy is made up of.
The study of this Lyman-alpha emission is common in very distant galaxies, but now a study named LARS (Lyman Alpha Reference Sample) is investigating the same effect in galaxies that are closer by. Astronomers chose fourteen galaxies, including this one, and used spectroscopy and imaging to see what was happening within them. They found that these Lyman-alpha photons can travel much further if a galaxy has less dust — meaning that we can use this emission to infer how dusty the source galaxy is.
The LARS study relies heavily on the high resolving power of Hubble. When Hubble is decommissioned, no telescope will be able to make observations like this in the far ultraviolet part of the spectrum — meaning that small, glittering galaxies imaged and probed by studies like LARS may give us some of the most detailed data we have to work with for some time to come.
Credit: ESA/Hubble & NASA, M. Hayes
blowing up bridges
perfect imagery to describe my last relationship
you can actually see the detcord for a split second
Why is this so mesmerizing?
Hexagonal rocks-WUT: The columns form due to stress as the lava cools. The lava contracts as it cools, forming cracks. Once the crack develops it continues to grow. The growth is perpendicular to the surface of the flow. Entablature is probably the result of cooling caused by fresh lava being covered by water. The flood basalts probably damned rivers. When the rivers returned the water seeped down the cracks in the cooling lava and caused rapid cooling from the surface downward. The division of colonnade and entablature is the result of slow cooling from the base upward and rapid cooling from the top downward. (via Hexagonal rocks)
