Universe Today

July 15, 2008April 26, 2016 by Nancy Atkinson

The “Other” Moon Rocket Some NASA Engineers Believe is Better Than Ares

Jupiter 110 and 232. From Directlauncher.com

There’s a group of NASA engineers who believe NASA is making a mistake with its new Constellation program to replace the shuttle, which will use the new Ares rockets for launches starting in 2014. Constellation is an all new program which requires everything to be built from the ground up. The group of engineers asks, why not use the systems we already have that work reliably? The engineers, who are working clandestinely after hours on their plans have been joined by business people and space enthusiasts, and they call the plan Direct 2.0. They believe this approach could be flying sooner than Ares, reducing the gap in the US’s access to space, and providing a smoother transition for the workforce. Additionally it is more powerful than Ares, has lower risks for the astronauts, adds additional servicing missions to the Hubble Space Telescope, and reduces the cost to orbit by half.

Proponents say the Direct 2.0 approach is more capable than Orion, can lift more mass into Earth orbit and boost more mass out of Earth orbit on to other destinations. The concept is simple: use the same orange external tank and booster rockets as the shuttle, but don’t use the orbiter. Put additional engines on the bottom of the tank, and the cone-shaped Orion capsule on the nose. They call the rocket system Jupiter, and not only would Jupiter have less cost per launch, but it would cost less per kilogram to put things in orbit. They also say the crew abort limits are safer than Ares 1, and would require only minor modifications to the current mobile launch platform.

Instead of having the separate Ares-I Crew Launch Vehicle (CLV) and Ares-V Cargo Launch Vehicle (CaLV) they use just one single Jupiter launcher, capable of performing both roles.

On their website, Directlauncher.com, they say “This change to NASA’s architecture completely removes the costs & risks associated with developing and operating a second launcher system, saving NASA $19 Billion in development costs, and a further $16 Billion in operational costs over the next 20 years.”

But recent articles by the Associated Press and the Orlando Sentinel say that NASA is not interested in this concept, and that its nothing more than a concept on the back of a napkin. Additionally, Ares is so far along, with test flights scheduled for next year, that there’s no turning back now.

But the Orlando Sentinel article says that NASA ended a study last fall which showed Direct 2.0 would outperform Ares. The initial results showed Direct 2.0 was superior in cost, overall performance and work-force retention, which is a big issue for Florida.

The engineers who work at NASA say they can’t speak out directly for fear of being fired, but an outside group who supports their efforts are trying to get the word out about the plan.

Check out their website includes a discussion forum, a presentation on their concept and much more. Here’s a video that explains the concept:

In short, they say the Direct 2.0 approach introduces many advantages over the current Ares Launch Vehicles, such as:

Shorter “gap” after the Shuttle retires (3 years vs. 5)
Earlier return to the Moon (2017 vs. 2019)
Deletes all risks and costs associated with a second new launch vehicle
Optimum use of the existing NASA & contractor experience

Original News Sources: AP, Orlando Sentinel, ABC’s Science and Society Blog, Directlauncher.com

July 14, 2008December 24, 2015 by Ian O'Neill

Observing an Evaporating Extrasolar Planet

Artist impression of an evaporating planet orbiting a main sequence star (NASA)

Observations of planets orbiting other stars are becoming increasingly common as astronomical techniques become more and more sophisticated. But some extrasolar planets have a stronger than normal spectroscopic signature, often stronger than their optical signature. What could be causing this? In a recent study, observations of the extrasolar planet HD 209458b (also unofficially known as “Osiris”, which orbits a star in the constellation of Pegasus) revealed the strongest ever spectroscopic signature for a giant extrasolar planet, indicating Osiris is producing a huge cloud of gas. This gas is being lost from the planet’s atmosphere; Osiris is evaporating…

Osiris orbits a star (imaginatively) called HD 209458, a yellow dwarf not too dissimilar to our Sun (with 1.1 solar masses, 1.2 solar radii and a surface temperature of 6000 K). This extrasolar planet is special in that it is readily observable during its transit period of 3.5 terrestrial days. This very short year is due to its small orbital radius of only 0.047 AU. Osiris could be called a “hot Jupiter” as it is a gas giant, approximately 60% the mass of Jupiter and it orbits within 0.05 AU of its parent star. Because of its close proximity to HD 209458, Osiris has a surface temperature of over 1000 K.

Osiris’ size and compact orbit causes HD 209458’s luminosity to vary by 2% as the planet passes in front of the star. It is for this reason that HD 209458 has been designated as a “variable star” with the name V376 Pegasi.

However, spectroscopic analysis of the star show that emissions from elements such as neutral hydrogen and a carbon ion are dimmed far more than the 2% optical luminosity dimming. What could be causing this increase in dimming for spectroscopic emission lines? As light is produced by HD 209458, it is blocked by the Osiris planetary disk, creating the 2% dimming observed by optical instrumentation. However, something is increasing the disk cross section area, absorbing certain spectral wavelengths of stellar emission. For example, there is a 5-15% dimming effect on neutral hydrogen (H I at 121.6 nm) and a 7-13% dimming effect on both atomic oxygen (O I at 130.5 nm) and singly ionized carbon (C II at around 133.5 nm). This led astronomers to realize there was a cloud of gas surrounding Osiris, allowing most of the optical wavelengths to pass through, but absorbing some spectroscopic lines.

As Osiris is orbiting so close to its star, the X-ray and EUV emissions are exciting gases in the exosphere (the uppermost reaches of the gas giant’s atmosphere), causing heating and expansion. As the planet is strongly influenced by its star’s gravitational pull, tides will play a strong part in amplifying the expansion of Osiris’ atmosphere. At a certain point, when the planet’s “exobase” (or the base of the exosphere) reaches the Roche Limit, atmospheric gases will begin to escape the gravitational pull of the planet and the interaction with HD 209458 causes a geometrical blow-off, ejecting huge amounts of atmospheric gases into space. The atmosphere of Osiris is therefore evaporating.

This is an intriguing subject, and more details can be found in the review recently published by David Ehrenreich from the Laboratoire dâ€™astrophysique de Grenoble, Universite Joseph Fourier, France.

Source: arXiv:0807.1885v1 [astro-ph]

July 14, 2008December 24, 2015 by Nancy Atkinson

Echus Chasma From Mars Express

echus chasma. Credits: ESA/ DLR/ FU Berlin (G. Neukum)

Do these valleys on Mars come from gushes of water from past rainfall, or groundwater springs, or could they have possibly been formed from magma flows on Mars surface? That’s the debate surrounding the many valleys, chasms and dry gullies found on the Red Planet.

The majority of planetary geologists seem to favor the idea of water flowing on Mars surface in the past. The images shown here of Echus Chasma are from the European Space Agency’s Mar’s Express, and its High-Resolution Stereo Camera (HRSC). Echus Chasma is believed to be one of the largest water source regions on the Red Planet. The valleys, cut into the landscape look similar to drainage networks found on Earth.

The image here has a ground resolution of approximately 17 m/pixel, and is so clear and distinct it almost makes you feel like you’re there!

Echus Chasma is approximately 100 km long and 10 km wide. Echus Chasma is believed to be the water source region that formed Kasei Valles, a large valley which extends thousands of kilometers to the north. It’s located in the Lunae Planum high plateau, north of Valles Marineris â€“ the Grand Canyon of Mars. This image indicates elevation data, also obtained by the HRSC.

*Echus Chasma mosaic. Credits: ESA/DLR/ FU Berlin (G. Neukum)*

An impressive cliff, up to 4000 m high, is located in the eastern part of Echus Chasma. Possibly, gigantic water falls may once have plunged over these cliffs on to the valley floor. The remarkably smooth valley floor was later flooded by basaltic lava.

The smaller valleys, also called sapping canyons, are believed to originate from the discharge of groundwater.

Original News Source: ESA

July 14, 2008April 26, 2016 by Nancy Atkinson

Where Do Meteorites Come From?

If you’ve ever held a real meteorite in your hand, you probably wanted to know, “Where has this rock been in space and where did it come from?” Until now, no one has been able to definitively establish where the majority of meteorites found on Earth came from because of the changes that occur in meteorites after they are ejected from the asteroids they were originally part of. The most common type of meteorite found on Earth, about 75% of those identified, are chondrites, stony bits of space rocks that didn’t undergo any melting while out in space. Two astronomers say have determined that most of these meteorites come from the asteroid belt between Mars and Jupiter. Using the GEMINI telescope, they found that asteroids in that region are similar to chondrites found on Earth.

This discovery is the first observational match between the most common meteorites and asteroids in the main belt. It also confirms the role of space weathering in altering asteroid surfaces.

To find the parent asteroid of a meteorite, the astronomers compared the spectra of a meteorite specimen to those of asteroids. This is a difficult task because meteorites and their parent asteroids underwent different processes after the meteorite was ejected. In particular, surfaces of asteroids are known to be altered by a process called â€œspace weatheringâ€, which is probably caused by micrometeorite and solar wind action that changes the surface and spectra of asteroid surfaces.

Meteoroids are created, usually when there is a collision between asteroids. When an impact of a large asteroid occurs, the fragments broken off can follow the same orbit as the primary asteroid. These groups of fragments are called â€œasteroid families.â€ Until recently, most of the known asteroid families have been very old (they were formed 100 million to billions of years ago), and younger families are more difficult to detect because asteroid fragments are closer to each other.

In 2006, four new, extremely young asteroid families were identified, with an age ranging from 50,000 to 600,000 years. The astronomers, Thais MothÃ©-Diniz from Brazil and David NesvornÃ½ from the US observed these asteroids, obtaining visible spectra. They compared the asteroids spectra to the spectra of an ordinary chondrite (the Fayetteville meteorite, shown in the top photo) and found they matched.

Identifying the parent asteroid of a meteorite is a unique tool when studying the history of our solar system because one can infer both the time of geological events (from the meteorite that can be analyzed through dating techniques) and their location in the solar system (from the location of the parent asteroid).

Meteorites are also a major tool for knowing the history of the solar system because their composition is a record of past geologic processes that occurred while they were still incorporated in the parent asteroid.

Original News Source: Astronomy and Astrophysics

July 14, 2008December 24, 2015 by Ian O'Neill

Binary Asteroid Glides Past Earth

A rare event has given astronomers a great view of a binary asteroid system. Tonight, asteroid 2008 BT18 passed 1.4 million miles from Earth, shining like a 13th magnitude star. Before July 7th, astronomers believed 2008 BT18 was “just another” near-Earth asteroid, but then the Arecibo radio telescope obtained a “delay-Doppler” image of the asteroid and found it in fact had a binary partner. Although binaries are fairly common in the Solar System, this was a rare opportunity for a ground-based telescope to capture such a clear view…

Only last week, Nancy wrote about binary asteroids and double craters found on Earth may be evidence that our planet has been hit by binaries in the past. As the article was being written, the Arecibo radio telescope in Puerto Rico was taking a detailed look at a binary asteroid approaching Earth. Although asteroid 2008 BT18 posed no threat to Earth, astronomers are very keen to learn more about binary asteroids to understand how they form and how they may be deflected from a collision course with Earth should a binary get too close.

About 16% of asteroids in the Solar System are thought to be binaries, so this event was a great opportunity for Arecibo to image 2008 BT18 and it could be seen by amateur astronomers as a 13th magnitude star. The Arecibo observatory has discovered 53% of all near-Earth binaries, so this seasoned radio telescope is an important component in the observation of these objects.

The asteroid binary was fairly sizeable but passed about six times the Earth-Moon distance from us. “The sizes of the two components are 600m for the primary and >200m for the secondary,” said Lance Benner, a scientist from NASA’s Jet Propulsion Laboratory (JPL). “The primary looks spheroidal, but we don’t yet know about the shape of the secondary.”

Other telescopes are analyzing the binary orbit, asteroid masses and density of the two objects, such as NASA’s Goldstone radar in the Mojave Desert, California. Although Goldstone is smaller than Arecibo, there is a strong echo for scientists to analyze the data collected from the passage of the asteroid pair. According to spaceweather.com, observers in the Southern Hemisphere had the opportunity to see 2008 BT18 pass through the constellation of Canis Major, heading south.

Source: Spaceweather.com

July 13, 2008December 24, 2015 by Tammy Plotner

Comet W1 Boattini Now Visible For Northern Skies

I wanted to see it myself before I said anything – but now it’s confirmed. Comet W1 Boattini is now visible in the northern hemisphere! So what if you have to get up before dawn? While its overall brightness is good enough to be seen with the unaided eye, I needed a lot of help, and maybe you’d like some, too?

Make no mistake. Fresh from its trip around the Sun and still holding a respectable 5.5 magnitude puts Comet W1 Boattini right in the ballpark of being visible without optical aid, but its size makes it invisible against dawn’s glow. But don’t be discouraged. If you have a decent southeastern skyline, you can catch Boattini with even small binoculars!

Let the one thing you can’t miss in the sky by your guide – the Pleiades. The view you see here is roughly what your horizon will look like before dawn. Although your own local time will vary a bit, that’s about 4:30 – 5:00 a.m. here. Take your binoculars out with you and begin scanning along the horizon for the Pleiades. Once you find them, locate Alpha Ceti. How can you be sure? It’s easy. Menkar is an optical double. Now begin looking with Menkar to the right of your field of view and scan slowly towards the Pleiades. Comet W1 Boattini will pop out and look like a small, unresolved globular cluster! It’s not big, and it doesn’t have a tail – but it sure is sweet.

If you’re good with sky charts, use this to help aid you. This is the rough track that Boattini will be following for the next few weeks – but don’t wait around to find it. In just a few days the Moon will also begin to interfere with the morning darkness and your chances of easily spotting the comet are going to become less. Once you locate it in binoculars, it’s easy to pick it up again in an optical finder on a telescope and take a closer look.

Good luck!

Many thanks to Joe Brimacombe and Guilherme Venere for the W1 Boattini images!

July 12, 2008December 24, 2015 by Tammy Plotner

StarGazer’s Telescope: So Long, Saturn…

As the summer nights in the northern hemisphere grow short, Saturn fades quickly to the west and with it takes our great views of the solar system’s most serene and restful planet. If you were to walk out tonight and point a small telescope Saturn’s way, what would you see? Step right up the the StarGazer’s Telescope and let’s look…

Saturn, the sixth planet from the Sun, has the most spectacular set of rings in the solar system – ones which are easily seen in even the smallest of telescopes. Even at roughly 793 million miles away, we can still see this thin band of icy particles and rubble circling the magnificent planet. Maybe it was a comet that ventured too close… Perhaps Saturn’s moons collided… But no matter what the explanation is, the gentle yellow serenity of Saturn is something to behold.

Can you see Saturn’s gentle, yellow color? Much of the atmosphere of Saturn is made of hydrogen and helium, but there is also water vapor, methane, ammonia, and nitrogen. While it looks warm by nature, these cloudtops are quite cold, about â€“220Â° Fahrenheit. Winds in the upper atmosphere reach 500 meters (1,600 feet) per second in the equatorial region which is about five times faster than any hurricane force wind ever encountered here on Earth. These super-fast winds, combined with heat rising from within the planet’s interior, cause the yellow and gold bands visible in the atmosphere.

Did you know Saturn was the most distant of the five planets known to the ancients? In 1610, Galileo Galilei was the first to gaze at Saturn through a telescope and his view wasn’t even as close to as good as what we see here. In 1659, Christiaan Huygens, used a far more powerful telescope and announced that Saturn was surrounded by a thin, flat ring. A few years later in 1675, Jean-Dominique Cassini discovered a ‘division’ between what are now called the A and B rings. Thanks to modern science, we now know the gravitational influence of Saturn’s moon Mimas is what’s responsible for the black band known as Cassini Division. Can you see it peeking in and out when the atmosphere gets steady? Even from all these millions of miles away, we’re still able to resolve a feature which is 4,800 kilometers (3,000 miles) wide.

Do you want a real rush? While you’re looking at Saturn, click here. This is an audio file of radio emissions from Saturn. The Cassini spacecraft began detecting these radio emissions in April 2002, when Cassini was 374 million kilometers (234 million miles) from the planet, using the Cassini radio and plasma wave science instrument. Isn’t it creepy? It’s also kind of beautiful too… Like listening to whale songs.

Now move over… It’s my turn at the eyepiece.

July 12, 2008December 24, 2015 by Tammy Plotner

Cosmic Monster – N44 by Don Goldman

Deep in the large Magellanic Cloud a 325 light-year sized cosmic monster is born. Its open maw spans some 250 light years across, and from it spews massive particle winds. Held in its glowing gas jaws could be the expanding shells of old supernovae and it has even coughed forth hot X-ray emitting gas. What exactly is this wide-mouthed creature? Step inside…

In the area of open star cluster NGC1929, a complex nebula known as the N44 superbubble has been the controversial study of many telescopes and scientists over the years. This “super bubble” may have formed when one or more massive stars in the central cluster exploded as supernovae, blowing a hole through the nearby turbulent gas complex. But a lot of uncertainties of its evolution still remain. “When we look at the speed of gases in this cloud we find inconsistencies in the size of the bubble and the expected velocities of the winds from the central cluster of massive stars,” says astronomer Phillip Massey, “Supernovae, the ages of the central stars, or the orientation and shape of the cloud might explain this, but the bottom line is that there’s still lots of exciting science to be done here.”

So what’s at home in this area? Try Wolf-Rayet stars, evolved massive stars, O-type supergiants, high mass double-lined binaries, luminous blue variables and luminous B(e) stars. These are massive stars that have formed very quickly but at differing metallicities. Winds and intense radiation from hot, young, luminous stars in N44F excite and sculpt filaments and streamers of the glowing nebular gas.

Buried in it’s mouth is an OB association of stars known as LH47. According to Wills (et al), “The IMF of the stars outside the shell shows a slightly steeper slope than inside the shell. The slope of the IMF is very similar to values found for other associations and open clusters as well as in the solar neighborhood, thus supporting the idea of an universal shape of the IMF. LH47 turns out to be a well behaved young association embedded in a molecular cloud.”

So it it possible that N44F is actually a “super shell” instead of a superbubble? According to studies done by E.A. Magnier (et al); “Superbubbles are the shells found around OB associations. Supergiant shells are the shells found around large stellar “complexes”. Both may contain hot gas, but the heating history and cooling timescales are likely to be very different. N44 and LMC-2 in the Large Magellanic Cloud are the only resolved superbubble and supergiant shell to have been observed. These two structures are generally similar, morphologically, but have very different size. There have been reports of blowouts in both structures.”

But supernovae – the death explosions of the massive short lived stars – have also likely contributed to the region’s enormous, blown-out shapes. According to Georgelin (et al): “The bubbles of unknown origin have line ratios greater than those of the H II regions and thus appear to fill the gap between thermal and nonthermal radio sources. All the bubbles or filamentary nebulae have important internal kinematical motions. The large complex nebulae have values similar to simple H II regions in their brightest parts, while the faintest parts exhibit greater dispersions and conspicuous splittings and broadenings. The ionized bubbles appear to be intermediate between classical young H II regions and supernova remnants.”

But taken an even closer look and you’ll see there’s another bubble as well. It is believed that as superbubbles expand and age their surface brightness fades. Finally it is thought that superbubbles can trigger new star formation in areas of the shells where gases condense. According to Sally Oey of the University of Michigan, X-ray-emitting gas is escaping from N44F with a temperature of about 1,000,000 Kelvin. While established massive stars may very well be key contributors to the diffuse hot gas throughout space, Oey and Massey report: “We examined the stellar population which is associated with a superbubble region in the N44. We find no evidence that an unusual stellar population gave rise to the shell morphology of the gas.”

So what exactly is going on with this cosmic monster? We know N44 contains the X-ray-brightest superbubble and the break-out structure at the southern rim of the superbubble has been confirmed by the nebular dynamics and plasma temperature variations. However, Sungeun Kim and associates also have their own take; “The total kinetic energy of the neutral and ionized gas of Shell 1 is still more than a factor of 5 lower than expected in a pressure-driven superbubble. It is possible that the central OB association was formed in a molecular cloud, and a visible superbubble was not fully developed until the ambient molecular gas had been dissociated and cleared away. This hypothesis is supported by the existence of a molecular cloud toward N44 and the fact that the apparent dynamic age of the superbubble Shell 1 is much shorter than the age of its OB association LH 47.”

Even though it is a safe160,000 light years away, the combined action of stellar winds hurling forth a storm of particles moving at about 7 million kilometers per hour and multiple supernova explosions is frightening enough. Combined with several compact star-forming regions at the rim and a central star ejecting more than a 100 million times more mass per second than our Sun is only part of what makes this “cosmic monster” both beautiful and terrifying to behold.

Many thanks to MRO/AORAIA member, Don Goldman for producing this incredibly inspiring image and allowing us to share your work!

July 12, 2008December 24, 2015 by Ian O'Neill

NASA Needs to Take Space Sex Seriously

The US space agency needs to have better consideration for the sexual needs of their astronauts during long missions in space. Also, more research needs to be done to investigate human embryo development in zero-gravity or low-gravity environments, especially if NASA is serious about setting up a colony on Mars in the next 30 years. These warnings have been issued by a NASA advisor at a time when the agency doesn’t have enough funds allocated for human space physiology. These concerns are by no means trivial, basic human needs and the ability to procreate beyond Earth may be critical for missions lasting years…

At a time when the question “Can we have sex in space?” is becoming more and more popular by the future space tourists hoping to become a member of the 100-mile high club, a serious issue is beginning to surface for our long-term presence in space. Humans have needs, and although the astronauts selected by NASA, ESA and the other international space agencies are highly professional individuals, Dr Jason Kring, a NASA advisor and assistant professor at Embry-Riddle Aeronautical University in Florida, has pointed out that sexual desire is as potent as the need for water and food. “But the bottom line is that, like hunger and thirst, sex is a basic biological motive,” he said in an interview with the UK’s Sunday Telegraph. “The potential round-trip mission to Mars could take three years. It doesnâ€™t make sense to assume that these men and women are going to have no thoughts of it for three years. Nasa and other space agencies should address this in their training and in crew selection.” Kring suggests our future long-term space explorers should replicate what the early polar explorers did and take a colleague as a lover to minimize sexual frustration.

It is difficult to predict the stresses long-term missions into space and to other planets may cause, but there is a very practical reason for this worry. Heightened stress on a spaceship will create an increased risk of confrontations, lack of focus and mission failure. When considering a possible 3-year mission to Mars, mission scientists will want the crew to be as calm and stress-free as possible.

Kring adds that future manned spacecraft to the Moon and Mars should be designed to optimize the privacy of astronauts so relationships can be consummated. This basic human need was recognized by explorers here on Earth where South Pole expedition members took on “expedition spouses” as sexual partners for the duration. When the expedition was over, the explorers would return home to their families and spouses. Pairing up with a colleague therefore sidesteps the biological issues of the possibility of “going without” for months, or years at a time. There are obvious questions surrounding the psychological effect of taking on “expedition spouses” (especially the effect on the partners waiting here on Earth for the astronauts return!), but the biological question will at least have an answer.

The fact remains however, that we are naive of the effects of sex in space, let alone if it is even a pleasurable experience. The mechanics of “human docking procedures” (as described by tests carried out by the Russian space agency) are a lot more complicated when in zero gravity. NASA researchers have pointed out that additional problems include motion sickness, increased sweating and a drop in blood pressure – all of which are big problems for astronauts in space.

There are also huge ethical questions hanging over possible pregnancies in space. Zero-G tests on rat embryos produced decreased skeletal and brain development, the effects on a human embryo will remain a mystery. Also, even if astronauts are having sex for purely recreational reasons, the effectiveness of oral contraception has been brought into question, making the whole procedure highly problematic, risking accidental pregnancies (something no space agency is prepared for, especially during missions to the Moon or Mars).

The fact remains that NASA continues to cut back biological research in favor of future Moon missions, so much about human sexuality in space will remain a mystery. This point is highlighted by a NASA spokesperson who stated, “We don’t study sexuality in space.”

Source: Sunday Telegraph

July 11, 2008April 4, 2016 by Matt Williams

What is the Largest Moon in the Solar System?

Many people think that the answer to ‘what is the largest moon in the Solar System’ is our Moon. It is not. Our Moon is the fifth largest natural satellite. Ganymede, a moon of Jupiter, is the largest in this solar system. At 5,268 km at the equator, it is larger than Mercury, the dwarf planet Pluto, and three times larger than the Moon orbiting Earth. According to information from NASA,if Ganymede were to break free of Jupiter’s gravitational pull it would be classified as a planet.

Ganymede has an iron-metallic core that generates a magnetic field. The core is surrounded by a mantle of rock, which is, in turn, covered by a thick shell of ice and rock. The outer shell is up to 800 km thick. On top of the outer shell is a thin layer of material(accreted?) that is a mixture of ice and rock. In images taken by the Hubble Space Telescope in 1996, astronomers discovered a tenuous atmosphere of oxygen. The atmosphere would not support known life forms, but its very existence is interesting to science.

Through spacecraft observation, there are several facts known about the surface of Ganymede. Its surface shows two types of terrain. Forty percent of the surface is covered with highly cratered dark regions, while the remainder is covered by light grooved terrain. The light grooving forms intricate patterns across surface of the moon, some of which are thousands of km long. Sulcus, a term that means a groove or burrow, is often used to describe the grooving. This portion of the terrain was most likely formed by tensional faulting or the release of water from beneath the surface. Ridges as high as 700 m have been observed. The dark regions are heavily cratered, old and rough, and are believed to be the original crust of the moon.

Ganymede was discovered by Galileo on January 7, 1610. He made the discovery, along with three other Jovian moons. It marked the first time a moon was discovered orbiting a planet other than Earth. The discovery contributed to the acceptance of the heliocentric viewpoint over the geocentric that held sway prior to that.

Now you know the answer to ‘what is the largest moon in the Solar System’ and a few interesting facts about Ganymede. Jupiter has 63 moons, so there are plenty more facts for you to discover.

Here’s another article about Ganymede, and one about Ganymede’s lumpy interior.

Here’s a list of all the largest moons in the Solar System, and a listing of the largest moons and smallest planets at Solar Views.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

References:
NASA Solar System Guide: Ganymede
Wikipedia: Ganymede
NASA Multimedia