Ganymede and Callisto are similar in size and are made of a similar mixture of ice and rock, but data from the Galileo and Voyager spacecraft show that they look different at the surface and on the inside. Just like Earth and Venus, Ganymede and Callisto are twins, and understanding how they were born the same and grew up to be so different is of tremendous interest to planetary scientists.

Ganymede and Callisto’s evolutionary paths diverged about 3.8 billion years ago during the Late Heavy Bombardment, the phase in lunar history dominated by large impact events. Impacts during this period melted Ganymede so thoroughly and deeply that the heat could not be quickly removed. All of Ganymede’s rock sank to its center the same way that all the chocolate chips sink to the bottom of a melted carton of ice cream. Callisto received fewer impacts at lower velocities and avoided complete melting. Ganymede is closer to Jupiter and therefore is hit by twice as many icy impactors as Callisto, and the impactors hitting Ganymede have a higher average velocity.

Image Credit: NOAA/GSD

(Source: swri.org)

The planetary nebula Abell 33 captured using ESO’s Very Large Telescope

Astronomers using ESO’s Very Large Telescope in Chile have captured this eye-catching image of planetary nebula Abell 33. Created when an aging star blew off its outer layers, this beautiful blue bubble is, by chance, aligned with a foreground star, and bears an uncanny resemblance to a diamond engagement ring. This cosmic gem is unusually symmetric, appearing to be almost perfectly circular on the sky.

Credit: ESO

The planetary nebula Abell 33 captured using ESO’s Very Large Telescope

Astronomers using ESO’s Very Large Telescope in Chile have captured this eye-catching image of planetary nebula Abell 33. Created when an aging star blew off its outer layers, this beautiful blue bubble is, by chance, aligned with a foreground star, and bears an uncanny resemblance to a diamond engagement ring. This cosmic gem is unusually symmetric, appearing to be almost perfectly circular on the sky.

Credit: ESO

Coronal loop

The corona is the outer part of the solar atmosphere. Its name derives from the fact that, since it is extremely tenuous with respect to the lower atmosphere, it is visible in the optical band only during the solar eclipses as a faint crown (corona in Latin) around the black moon disk. When inspected through spectroscopy the corona reveals unexpected emission lines, which were first identified as due to a new element (coronium) but which were later ascertained to be due to high excitation states of iron. It became then clear that the corona is made of very high temperature gas, hotter than 1 MK(megakelvin). Almost all the gas is fully ionized there and thus interacts effectively with the ambient magnetic field. It is for this reason that the corona appears so inhomogeneous when observed in the X-ray band, in which plasma at million degrees emits most of its radiation. In particular, the plasma is confined inside magnetic flux tubes which are anchored on both sides to the underlying photosphere. When the confined plasma is heated more than the surroundings, its pressure and density increase. Since the tenuous plasma is optically thin, the intensity of its radiation is proportional to the square of the density, and the tube becomes much brighter than the surrounding ones and looks like a bright closed arch: a coronal loop.
Coronal Loops: Observations and Modeling of Confined Plasma

Credit: Fabio Reale

Coronal loop

The corona is the outer part of the solar atmosphere. Its name derives from the fact that, since it is extremely tenuous with respect to the lower atmosphere, it is visible in the optical band only during the solar eclipses as a faint crown (corona in Latin) around the black moon disk. When inspected through spectroscopy the corona reveals unexpected emission lines, which were first identified as due to a new element (coronium) but which were later ascertained to be due to high excitation states of iron. It became then clear that the corona is made of very high temperature gas, hotter than 1 MK(megakelvin). Almost all the gas is fully ionized there and thus interacts effectively with the ambient magnetic field. It is for this reason that the corona appears so inhomogeneous when observed in the X-ray band, in which plasma at million degrees emits most of its radiation. In particular, the plasma is confined inside magnetic flux tubes which are anchored on both sides to the underlying photosphere. When the confined plasma is heated more than the surroundings, its pressure and density increase. Since the tenuous plasma is optically thin, the intensity of its radiation is proportional to the square of the density, and the tube becomes much brighter than the surrounding ones and looks like a bright closed arch: a coronal loop.

Credit: Fabio Reale

Spiral galaxy ESO 137-001

This Hubble image shows ESO 137-001, a galaxy located in the southern constellation of Triangulum Australe (The Southern Triangle) — a delicate and beautiful spiral galaxy, but with a secret. The image not only captures the galaxy and its backdrop in stunning detail, but also something more dramatic — intense blue streaks streaming outwards from the galaxy, seen shining brightly in ultraviolet light.
These streaks are actually hot young stars, encased in wispy streams of gas that are being torn away from the galaxy by its surroundings as it moves through space. This violent galactic disrobing is due to a process known as ram pressure stripping — a drag force felt by an object moving through a fluid . The fluid in question here is superheated gas, which lurks at the centres of galaxy clusters.
This image combines NASA/ESA Hubble Space Telescope observations with data from the Chandra X-ray Observatory.

Credit: NASA, ESA, CXC

Spiral galaxy ESO 137-001

This Hubble image shows ESO 137-001, a galaxy located in the southern constellation of Triangulum Australe (The Southern Triangle) — a delicate and beautiful spiral galaxy, but with a secret. The image not only captures the galaxy and its backdrop in stunning detail, but also something more dramatic — intense blue streaks streaming outwards from the galaxy, seen shining brightly in ultraviolet light.

These streaks are actually hot young stars, encased in wispy streams of gas that are being torn away from the galaxy by its surroundings as it moves through space. This violent galactic disrobing is due to a process known as ram pressure stripping — a drag force felt by an object moving through a fluid . The fluid in question here is superheated gas, which lurks at the centres of galaxy clusters.

This image combines NASA/ESA Hubble Space Telescope observations with data from the Chandra X-ray Observatory.

Credit: NASA, ESA, CXC

Fire and Ice

Saturn’s largest and second largest moons, Titan and Rhea, appear to be stacked on top of each other in this true-color scene from NASA’s Cassini spacecraft.

Titan is likely differentiated into several layers with a 3,400-kilometre (2,100 mi) rocky center surrounded by several layers composed of different crystal forms of ice.Its interior may still be hot and there may be a liquid layer consisting of a “magma" composed of water and ammonia between the ice Ih crust and deeper ice layers made of high-pressure forms of ice.

Rhea is an ice-cold body of weak density (1.236 g/cm3), indicating that the moon consists of a rocky nucleus counting only for a third of the mass of Rhea, the rest being mainly some ice-cold water.

Credit: NASA/JPL-Caltech/SSI


While sunspots are relatively cool and quiescent regions on the Sun, the photosphere around them sometimes erupts with outflows of high energy particles in active regions. Most often these eruptions are in the form of loops and sheets called prominences which remain under the control of the intense magnetic fields associated with solar storms. There are other events which in a matter of minutes can release enormous amounts of energy and eject material out into space. Such violent events are called solar flares.

Images credit: TRACE/NASA

While sunspots are relatively cool and quiescent regions on the Sun, the photosphere around them sometimes erupts with outflows of high energy particles in active regions. Most often these eruptions are in the form of loops and sheets called prominences which remain under the control of the intense magnetic fields associated with solar storms. There are other events which in a matter of minutes can release enormous amounts of energy and eject material out into space. Such violent events are called solar flares.

Images credit: TRACE/NASA

Rhea: Saturn’s Mysterious Moon

Rhea, the second largest moon of Saturn, is a dirty snowball of rock and ice. The only moon with an oxygen atmosphere, thin though it may be, Rhea is one of the most heavily cratered satellites in the solar system.

A very faint oxygen atmosphere exists around Rhea, the first direct evidence of an oxygen atmosphere on a body other than Earth. The atmosphere is thin, with oxygen measuring about 5 trillion times less dense than that found on Earth. Oxygen could be released as the surface is irradiated by ions from Saturn’s magnetosphere. The source of the carbon dioxide is less clear, but could be the result of similar irradiation, or from dry ice much like comets.

On March 6, 2008, NASA announced that Rhea may have a tenuous ring system. This would mark the first discovery of rings about a moon. The rings’ existence was inferred by observed changes in the flow of electrons trapped by Saturn’s magnetic field as Cassini passed by Rhea. Dust and debris could extend out to Rhea’s Hill sphere, but were thought to be denser nearer the moon, with three narrow rings of higher density. The case for a ring was strengthened by the subsequent finding of the presence of a set of small ultraviolet-bright spots distributed along Rhea’s equator (interpreted as the impact points of deorbiting ring material).However, when Cassini made targeted observations of the putative ring plane from several angles, no evidence of ring material was found, but there’s still something around Rhea that is causing a strange, symmetrical structure in the charged-particle environment around Saturn’s second-largest moon.

Image credit: NASA/JPL-Caltech/SSI,Gordan Ugarkovic

The Submillimeter Array telescope unveils how small cosmic seeds grow into big stars

New images from the Smithsonian’s Submillimeter Array (SMA) telescope provide the most detailed view yet of stellar nurseries within the Snake Nebula. These images offer new insights into how cosmic seeds can grow into massive stars.
Stretching across almost 100 light-years of space, the Snake Nebula is located about 11,700 light-years from Earth in the direction of the constellation Ophiuchus. In images from NASA’s Spitzer Space Telescope, it appears as a sinuous dark tendril against the starry background. It was targeted because it shows the potential to form many massive stars (stars heavier than eight times our Sun).
Full Article

Image Credit: Spitzer/GLIMPSE/MIPS, Herschel/HiGal, Ke Wang (ESO)

The Submillimeter Array telescope unveils how small cosmic seeds grow into big stars

New images from the Smithsonian’s Submillimeter Array (SMA) telescope provide the most detailed view yet of stellar nurseries within the Snake Nebula. These images offer new insights into how cosmic seeds can grow into massive stars.

Stretching across almost 100 light-years of space, the Snake Nebula is located about 11,700 light-years from Earth in the direction of the constellation Ophiuchus. In images from NASA’s Spitzer Space Telescope, it appears as a sinuous dark tendril against the starry background. It was targeted because it shows the potential to form many massive stars (stars heavier than eight times our Sun).

Full Article

Image Credit: Spitzer/GLIMPSE/MIPS, Herschel/HiGal, Ke Wang (ESO)

A Change Of Perspective

This animation was composed of 6 color frames taken on February 3rd, 2007 over the course of 2 hours by Cassini’s wide angle camera.
Cassini was moving from below the ring plane towards the ring plane crossing and moving away from the planet at the same time.
At the start of the sequence the phase angle was 16.8 deg and distance was 1.070 mil km. This increased to 17.5 deg and 1.080 mil km at the end, respectively. During that period Saturn can be seen rotating, notice particularly the streaky clouds just below the ring shadows.

Image Credit: Gordan Ugarkovic

A Change Of Perspective

This animation was composed of 6 color frames taken on February 3rd, 2007 over the course of 2 hours by Cassini’s wide angle camera.

Cassini was moving from below the ring plane towards the ring plane crossing and moving away from the planet at the same time.

At the start of the sequence the phase angle was 16.8 deg and distance was 1.070 mil km. This increased to 17.5 deg and 1.080 mil km at the end, respectively. During that period Saturn can be seen rotating, notice particularly the streaky clouds just below the ring shadows.

Image Credit: Gordan Ugarkovic

Enceladus and Saturn

Cassini Narrow Angle camera (NAC) clear filter frame colorized to approximate the appearance of Saturn’s limb and emphasize Enceladus’ grayish color in contrast. 

Image credit: Gordan Ugarkovic

Enceladus and Saturn

Cassini Narrow Angle camera (NAC) clear filter frame colorized to approximate the appearance of Saturn’s limb and emphasize Enceladus’ grayish color in contrast.

Image credit: Gordan Ugarkovic


Neptune is the eighth planet from the Sun and the smallest of the gas giants. Neptune was the first planet found by mathematical prediction after unexpected changes in the orbit of Uranus were observed. Neptune is named after the Roman god of the sea.
The blue coloring is the result of methane in the atmosphere, though the exact reason for the vividness of the blue is still unknown. The winds that whip around Neptune are on average nine times faster than those on Earth and are believed to be the strongest winds in the solar system.
Storms much like the Great Red Spot on Jupiter have been seen on Neptune. Unlike the Great Red Spot, which has been observed for over 300 years, the storms on Neptune seem to come and go. In 1986 the Voyager 2 discovered the Great Dark Spot, a storm in the Southern Hemisphere. However, later images from the Hubble Space Telescope show that the Great Dark Spot no longer exists and that a new storm formed in the Northern Hemisphere. Also, there is a group of white clouds referred to as The Scooter which races around the planet every 16 hours. The Scooter is thought to be a plume from lower in the atmosphere, though its true origin is unknown.

Image Credit: Steve Albers, NOAA/GSD

Neptune is the eighth planet from the Sun and the smallest of the gas giants. Neptune was the first planet found by mathematical prediction after unexpected changes in the orbit of Uranus were observed. Neptune is named after the Roman god of the sea.

The blue coloring is the result of methane in the atmosphere, though the exact reason for the vividness of the blue is still unknown. The winds that whip around Neptune are on average nine times faster than those on Earth and are believed to be the strongest winds in the solar system.

Storms much like the Great Red Spot on Jupiter have been seen on Neptune. Unlike the Great Red Spot, which has been observed for over 300 years, the storms on Neptune seem to come and go. In 1986 the Voyager 2 discovered the Great Dark Spot, a storm in the Southern Hemisphere. However, later images from the Hubble Space Telescope show that the Great Dark Spot no longer exists and that a new storm formed in the Northern Hemisphere. Also, there is a group of white clouds referred to as The Scooter which races around the planet every 16 hours. The Scooter is thought to be a plume from lower in the atmosphere, though its true origin is unknown.

Image Credit: Steve Albers, NOAA/GSD


Uranus is the seventh planet from the Sun and was the first planet to be discovered with the use of a telescope. Uranus’ most unique feature is that its axis sideways in comparison to other planets. Uranus is named after the Greek god of the sky.
Uranus has 27 moons, all of which were named after characters from the stories of Shakespeare and Alexander Pope. The atmosphere of Uranus is composed of 83% hydrogen, 15% helium and 2% methane. Unlike Saturn and Jupiter, two other gas planets, it appears that Uranus does not have a rocky core. Instead, it is thought that Uranus’ mass is evenly distributed throughout the area of planet. One feature that is similar to the other gas planets is the fast moving winds that blow the clouds around in the atmosphere.

Image Credit: Steve Albers, NOAA/GSD

Uranus is the seventh planet from the Sun and was the first planet to be discovered with the use of a telescope. Uranus’ most unique feature is that its axis sideways in comparison to other planets. Uranus is named after the Greek god of the sky.

Uranus has 27 moons, all of which were named after characters from the stories of Shakespeare and Alexander Pope. The atmosphere of Uranus is composed of 83% hydrogen, 15% helium and 2% methane. Unlike Saturn and Jupiter, two other gas planets, it appears that Uranus does not have a rocky core. Instead, it is thought that Uranus’ mass is evenly distributed throughout the area of planet. One feature that is similar to the other gas planets is the fast moving winds that blow the clouds around in the atmosphere.

Image Credit: Steve Albers, NOAA/GSD

 The Bolshoi Simulation

What if you could fly through the universe and see dark matter? While the technology for taking such a flight remains under development, the technology for visualizing such a flight has taken a grand leap forward with the completion of the Bolshoi Cosmological Simulation.
After 6 million CPU hours, the world’s seventh fastest supercomputer output many scientific novelties including the above flight simulation. Starting from the relatively smooth dark matter distribution of the early universe discerned from the microwave background and other large sky data sets, the Bolshoi tracked the universe’s evolution to the present epoch shown above, given the standard concordance cosmology. The bright spots in the simulation above are all knots of normally invisible dark matter, many of which contain normal galaxies. Long filaments and clusters of galaxies, all gravitationally dominated by dark matter, become evident.
Statistical comparison between the Bolshoi and current real sky maps of actual galaxies show good agreement. Although the Bolshoi simulation bolsters the existence of dark matter, many questions about our universe remain, including the composition of dark matter, the nature of dark energy, and how the first generation of stars and galaxies formed.
For more information about the Bolshoi Cosmological Simulation, click here.

Credit:  A. Klypin (NMSU), J. Primack (UCSC) et al., Chris Henze (NASA Ames), NASA’s Pleiades Supercomputer

The Bolshoi Simulation

What if you could fly through the universe and see dark matter? While the technology for taking such a flight remains under development, the technology for visualizing such a flight has taken a grand leap forward with the completion of the Bolshoi Cosmological Simulation.

After 6 million CPU hours, the world’s seventh fastest supercomputer output many scientific novelties including the above flight simulation. Starting from the relatively smooth dark matter distribution of the early universe discerned from the microwave background and other large sky data sets, the Bolshoi tracked the universe’s evolution to the present epoch shown above, given the standard concordance cosmology. The bright spots in the simulation above are all knots of normally invisible dark matter, many of which contain normal galaxies. Long filaments and clusters of galaxies, all gravitationally dominated by dark matter, become evident.

Statistical comparison between the Bolshoi and current real sky maps of actual galaxies show good agreement. Although the Bolshoi simulation bolsters the existence of dark matter, many questions about our universe remain, including the composition of dark matter, the nature of dark energy, and how the first generation of stars and galaxies formed.

  • For more information about the Bolshoi Cosmological Simulation, click here.

Credit: A. Klypin (NMSU), J. Primack (UCSC) et al., Chris Henze (NASA Ames), NASA’s Pleiades Supercomputer


Saturn is the sixth planet from the Sun and is named after the Roman god of wealth. Saturn is the second largest planet in the solar system and is best known for its fabulous rings. The rings were not known to exist until Galileo first observed them in 1610.
Like Jupiter and the other gas planets, Saturn has a banded appearance in its coloration due to high winds in the atmosphere. The bands are not as distinct as those on Jupiter, however, they are very wide at the equator and easy to detect. Another similarity to Jupiter is the storms that are visible on Saturn’s surface in the form of white or red ovals. However, none of these storms seem to be as long-lived as the Great Red Spot on Jupiter.

Image Credit: Oscar Malet

Saturn is the sixth planet from the Sun and is named after the Roman god of wealth. Saturn is the second largest planet in the solar system and is best known for its fabulous rings. The rings were not known to exist until Galileo first observed them in 1610.

Like Jupiter and the other gas planets, Saturn has a banded appearance in its coloration due to high winds in the atmosphere. The bands are not as distinct as those on Jupiter, however, they are very wide at the equator and easy to detect. Another similarity to Jupiter is the storms that are visible on Saturn’s surface in the form of white or red ovals. However, none of these storms seem to be as long-lived as the Great Red Spot on Jupiter.

Image Credit: Oscar Malet


Jupiter is the fifth planet from the Sun and is the largest planet in the solar system, like the other four outer planets Jupiter is a gas giant. Jupiter is named after the king of the Roman gods – Jupiter has also been known as Zeus the Greek god of thunder and Marduk the Mesopotamian god and patron of the city of Babylon. 
Jupiter has been described as its own little solar system because of the vast number of moons orbiting the planet. There are 63 moons around Jupiter, the most of any planet in the solar system. Four in particular, Io, Europa, Ganymede, and Callisto, are planet sized. In 2003 alone, 23 new moons were discovered. Reasons for this incredible number of moons include the strong gravitational force of the planet at 20.87 m/s2, more than double the gravitational force on Earth, and also the large magnetic field of the planet, which extends into Saturn’s orbit. Like Saturn, Jupiter also has rings, though they are only visible when backlit by the sun and believed to be comprised of dust kicked up from meteor collisions with the four biggest moons.

Image Credit: Steve Albers, NOAA/GSD

Jupiter is the fifth planet from the Sun and is the largest planet in the solar system, like the other four outer planets Jupiter is a gas giant. Jupiter is named after the king of the Roman gods – Jupiter has also been known as Zeus the Greek god of thunder and Marduk the Mesopotamian god and patron of the city of Babylon. 

Jupiter has been described as its own little solar system because of the vast number of moons orbiting the planet. There are 63 moons around Jupiter, the most of any planet in the solar system. Four in particular, Io, Europa, Ganymede, and Callisto, are planet sized. In 2003 alone, 23 new moons were discovered. Reasons for this incredible number of moons include the strong gravitational force of the planet at 20.87 m/s2, more than double the gravitational force on Earth, and also the large magnetic field of the planet, which extends into Saturn’s orbit. Like Saturn, Jupiter also has rings, though they are only visible when backlit by the sun and believed to be comprised of dust kicked up from meteor collisions with the four biggest moons.

Image Credit: Steve Albers, NOAA/GSD