The old Moon in the New Moon’s arms
Contributed by Jamie Cooper from Dustin, England
Solar Eclipses Can (Slightly) Change Weather on Earth
Moon’s shadow causes winds to slow, alter direction, study says.
In the image: Children gaze at a partial solar eclipse over Manila Bay, the Philippines, in 2009.
The moon, that giant lump of rock that has fascinated poets and scientists alike, may be about to get even more interesting. A new analysis of isotopes found in lunar minerals challenges the prevailing view of how Earth’s nearest neighbor formed.
Most scientists believe Earth collided with a hypothetical, Mars-sized planet called Theia early in its existence, and the resulting smash-up produced a disc of magma orbiting our planet that later coalesced to form the moon. This is called the giant impact hypothesis. Computer models indicate that, for the collision to remain consistent with the laws of physics, at least 40% of the magma would have had to come from Theia.
One way to test the hypothesis is to look at the isotopes of particular elements in rocks returned from the moon. Atoms of most elements can occur in slightly different forms, called isotopes, with slightly different masses. Oxygen, for example, has three isotopes: 16O, 17O and 18O, indicating differences in the number of neutrons each nucleus contains. Compare any two samples of oxygen found on Earth and you’ll find the proportions of 16O, 17O and 18O isotopes are almost identical in the two samples. The proportions found in samples from meteorites and other planets like Mars, however, are usually different. So if you find that a sample has the same oxygen isotope composition as one from Earth, then it’s very likely the sample came from our world.
Previous research has established that the oxygen isotope composition of lunar samples is indistinguishable from that of Earth. Since 40% of the moon is supposed to have come from Theia (which presumably would have had a different isotope composition), this might spell trouble for the giant impact hypothesis. But it’s possible that Earth may have exchanged oxygen gas with the magma disk that later formed the Moon shortly after the collision, explaining why the results are the same.
In the new research, published online today in Nature Geoscience, geochemists led by Junjun Zhang at the University of Chicago in Illinois, together with a colleague at the University of Bern in Switzerland, looked at titanium isotopes in 24 separate samples of lunar rock and soil. The proportion of 50Ti to 47Ti is another good indicator of whether a sample came from Earth, and, just as with oxygen, the researchers found the moon’s proportion was effectively the same as Earth’s and different from elsewhere in the solar system. Zhang explains that it’s unlikely Earth could have exchanged titanium gas with the magma disk because titanium has a very high boiling point. “The oxygen isotopic composition would be very easily homogenized because oxygen is much more volatile, but we would expect homogenizing titanium to be very difficult.”
So, if the giant impact hypothesis doesn’t explain the moon, how did it get there? One possibility is that a glancing blow from a passing body left Earth spinning so rapidly that it threw some of itself off into space like a shot put, forming the disk that coalesced into the moon. This would explain why the moon seems to be made entirely of Earth material. But there are problems with this model, too, such as the difficulty of explaining where all the extra angular momentum went after the moon formed, and the researchers aren’t claiming to have refuted the giant impact hypothesis.
Planetologist Matthias Meier of Lund University in Sweden, who was not involved in the new study, finds the research persuasive, but he’s not ready to give up on the giant impact hypothesis either. “I think the general idea of having an impact forming a disk and this disk then forming a moon is probably right,” he says, “but this paper shows us that we still don’t understand exactly what the mechanism is, and there is a lot of work to be done in that field.”
This story provided by ScienceNOW, the daily online news service of the journal Science.
Image: New research sheds light on how the moon formed. (Cosmic Collisions Space Show/Rose Center for Earth and Space/AMNH)
Behold, a beautiful example of Earthshine
You’re looking at a stunning example of something astronomers and stargazers called “Earthshine.” Known by some as “the old Moon in the new Moon’s arms,” Earthshine is a phenomenon first formally described by Leonardo da Vinci some 500 years ago.
In the image: Animation of Tethys passing in front of Dione from Cassini’s point of view.
Saturn’s moon Tethys passes in front of its slightly larger sister Dione in this animation made from 25 raw images acquired by Cassini on March 14, 2012. Pretty cool!
Tethys and Dione are similar in diameter, being 1,062 kilometers (660 miles) wide and 1,123 kilometers (698 miles) wide, respectively. Both are heavily cratered, ice-rich worlds.
In this view, Tethys’ enormous Odysseus crater can be seen on its northern hemisphere. 400 km (250 miles) across, Odysseus is two-fifths the diameter of Tethys itself, suggesting that it was created early in the moon’s history when it was still partially molten — or else the impact would have shattered the moon apart entirely.
The more extensively-cratered trailing side of Dione is visible here, its signature “wispy lines“ rotated out of view. Since it makes sense that a moon’s leading face should be more heavily cratered, it’s thought that Dione has been spun around by an impact event in the distant past.
If you look closely, a slight rotation in Tethys can also be discerned from the first frame to the last.
Credit: NASA/JPL/SSI. Animation by Jason Major.
Colorful Map Details Volcano-Studded Surface of Io
After a six-year effort, researchers have released the first geologic map of the solar system’s most volcanically active object, Jupiter’s moon Io.
Crescent shape of Dione, orbiting Saturn, on December 12, 2011. (NASA/JPL) #
Photos of Saturn’s icy moon Rhea.
NASA’s Cassini spacecraft took this raw, unprocessed image of Saturn’s moon Rhea on March 10, 2012. The camera was pointing toward Rhea at 26,019 miles (41,873 kilometers) away. [See More Images]
Awe-inspiring images of the moon
1. The magnificent moon
The moon has been a source of wonder and mystery ever since the first cave dwellers turned their eyes to the glowing orb in the night sky. But for the past 50 years, we have been able to explore our planet’s only natural satellite as never before. From the Soviet’s first flyby of the moon in 1959 to the future missions of exploration, we now understand the moon perhaps better than any other celestial body. The Galileo spacecraft sent back images of the moon on its way to Jupiter in 1992, and this is a colored-enhanced composite of those images. (Text: Katherine Butler)
2. The mineral moon
This is another color-enhanced image of the moon captured by the Galileo spacecraft. It shows the different changes in color on the northern hemisphere of the moon according to its mineral composition. According to NASA, “Bright pinkish areas are highlands materials. Blue to orange shades indicate volcanic lava flows.” The moon has been continually assaulted by comets, asteroids and meteoroids because it has no atmosphere to slow them down.
3. Coronal and zodiacal light on the moon
This image shows the coronal and zodiacal light (CZL) on the moon as seen by the Clementine spacecraft. The white area is the CZL and the bright object in space is the planet Venus. The CZL glow of the moon was noticed by several astronauts. It is a lunar horizon glow that occurs when the moon is out of the sun’s direct light. Since the moon has no atmosphere, experts aren’t entirely sure why it happens. Further, it is not always seen. NASA hopes that the launch of the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft will clear up the mystery of the CZL glow.
4. Lunar eclipse from Earth
The photo was taken on Dec. 21, 2010, in the early stages of a rare lunar eclipse that coincided with the winter solstice. While most experts believe the moon formed when a giant object hit Earth, others think it could have been created at the same time as the other planets in our solar system. Even others believe the young Earth was spinning so fast that it threw off a chunk of itself, forming our natural satellite. One thing is certain — the moon will continue to be an object of wonder and exploration for all of humanity.
A Sliver of Saturn’s Moon Enceladus
NASA’s Cassini spacecraft snapped this picture of a dark Enceladus, the sixth-largest of Saturn’s moons and one of the most interesting to scientists because of the presence of water ice on its surface and geological activity. In the image, some of this icy geological action is visible at the moon’s southern end where plumes of water-ice spray up from the terrain. Cassini took the picture at a distance of 83,000 miles on February 20, 2012.
Witness the Moon’s breathtaking 4.5-billion-year evolution in less than three minutes
When we gaze up at the Moon, we expect a certain degree of consistency. Sure, it moves through its phases, shifting in and out of darkness over the course of the month, but generally speaking, the Moon’s surface looks the same to us — night after night, year after year. But the Moon has not always looked the way it does now.
In the last 4.5 billion years, the Moon has transformed from a roiling mass of ejected terrestrial matter, to an unblemished orb, to the heavily cratered, volcanic-crust laden entity we know and love today. We know these things occurred because the Moon’s surface features tell a story, and for close to three years now, NASA’s Lunar Reconnaissance Orbiter has been getting an up close look at what those features have to say.
Now, the folks at NASA’s Goddard Multimedia team have used the latest data on the Moon’s history, acquired by LRO, to packr 4.5 billion years of lunar evolution into the stunning video you see up top.
Pretty much everyone can rattle off the names of our solar system’s eight (formerly nine) planets, but ask the average person to list some moons and you’ll be lucky if they can tell you more than two or three.
Now, you obviously can’t expect people to remember the name of every single satellite in the solar system (after all, they outnumber the planets by around 20 to 1), but if you have even the slightest interest in astronomy, it wouldn’t kill you to be familiar with at least an even ten. So with that in mind, we’ve assembled this reference guide to ten of the solar system’s most noteworthy moons.
1. Moon: Europa
Parent Planet: Jupiter
Why You Should Know it: Despite being covered by distinctive, criss-crossing cracks and ridges, Europa’s water-ice surface is largely free of craters, making it perhaps the smoothest solid body in the entire solar system. More interesting than Europa’s frozen exterior, however, is what lies hidden beneath it.
2. Moon: Io
Parent Planet: Jupiter
Why You Should Know it: Io is very close in size to our own moon, but it couldn’t be more different. Despite having a mean surface temperature of less than -250 degrees Fahrenheit, Io is home to over 400 raging volcanos, making it the single most geologically active object in the solar system.
3. Moon: Mimas
Parent Planet: Saturn
Why you should know it: This list is an important reference for any self-respecting science geek, but Mimas is especially relevant for fans of science fiction for what should be obvious reasons. In brief: Mimas is no space station. It’s a moon. Like many of Saturn’s orbiting bodies, Mimas is small and icy, but it’s also home to “Herschel” — the name astronomers have given the massive crater situated on the moon’s leading hemisphere.
4. Moon: Enceladus
Parent Planet: Saturn
Why You Should Know it: Enceladus is one wacky little moon. Like Europa, its surface is covered in water ice, but it’s also home to some of the most impressive geysers in the solar system. Scientists had suspected for years that Enceladus was venting water vapor from its surface, but it wasn’t until 2005 that they had direct visual confirmation that the moon was doing so by spewing jets of the stuff from geysers on its surface.
5. Moon: Triton
Parent Planet: Neptune
Why You Should Know it: Of all the biggest, “major” moons in the solar system, Triton is the only one that orbits in a direction opposite that of its parent planet’s rotation. Astrophysicists call this a “retrograde orbit,” and it’s typical of moons that have been “captured” by their parent planet.
6. Moon: Iapetus
Parent Planet: Saturn
Why You Should Know it: Iapetus may be one of the most mysterious moons we’ve ever discovered. For one thing, it is two completely different colors; the moon’s trailing hemisphere is as bright and reflective as snow, but its leading hemisphere is as dark as freshly poured asphalt — a characteristic that has led many astronomers to refer to it as the “painted” or “yin-yang” moon.
7. Moon: Phobos
Parent Planet: Mars
Why You Should Know it: Mars’ moon Phobos may not be the biggest moon on this list. It may not have the most interesting geology, or the most peculiar orbit, or the most promising environment when it comes to harboring extraterrestrial life. Be that as it may, there is a very, very good chance that it will become the second moon — and the third cosmic body — to host human travelers on mankind’s journey out into the Universe.
8. Moon: Titan
Parent Planet: Saturn
Why You Should Know it: If moons could be considered for reclassification under planetary status, Titan would be the first to come under review. It is the only moon in the entire solar system with a dense atmosphere (which can be clearly seen in the form of an enveloping haze in many recent Cassini images, including the one featured here); it experiences rain and snow; and it’s even home to geological features like lakes, valleys, plains and deserts. In fact, according to NASA’s Dr. Rosaly Lopes, “Titan looks more like the Earth than any other body in the Solar System.”
9. Moon: Hyperion
Parent Planet: Saturn
Why You Should Know it: Phil Plait — astronomer extraordinair and master of ceremonies over at Bad Astronomy — once called Hyperion “the solar system’s weirdest moon” — and that’s saying something. For one thing, Saturn is home to some pretty wonky moons (just look at how many of the natural satellites on this list orbit the ringed planet); secondly, Phil Plait has written about some weird moons in his day — so what makes Hyperion the weirdest? Well, a lot of things, but for starters: the loofah-like moon happens to be weirdly foamy.
10. Moon: Moon
Parent Planet: Earth
Why You Should Know it: It’s hard to go wrong with the original. Sure, it’s the first moon humans ever observed, but it wasn’t until the 1950s that we finally managed to get a glimpse of its far side; and just last week we learned that the Moon may have been partly responsible for sinking the Titanic, demonstrating that our Moon has been — and will always be — a source of wonder and mystery. [Photo, and top photo, by Rick Baldridge via NASA]
Southern Moon Lights
Moons Tethys and Rhea are visible beyond Saturn’s southern hemisphere. They orbit in the plane of the planet’s rings, but from this vantage point appear to be below the planet. Tethys is near the center of the image, and Rhea is on the lower right. Image taken June 29,2010
Image: NASA/JPL/Space Science Institute