Representing what may be the first long term lunar environmental impact study, recent laser ranging data from the Apache Point Observatory in New Mexico suggests the Lunar Ranging Retro Reflectors (LRRRs) left on the Moon by Apollo missions 11, 14 and 15 are beginning to shows signs of age. Read more…
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Artist impression of LCROSS approaching the Moon. Credit: NASA
Almost five months ago, the LCROSS spacecraft had an abrupt end to its flight when it impacted a crater on the Moon's south pole. But that was only the beginning of the work of principal investigator Tony Colaprete and the rest of the science teams, who have since been working non-stop to get their initial results out to the public. Look for a flood of 'water on the Moon' news to be announced at the Lunar and Planetary Science Conference this week.
"The data set from LCROSS is a lot more interesting that we thought it would be," said Colaprete, speaking on a "My Moon" webcast, sponsored by the Lunar and Planetary Institute. "A big part of our time has been making sure the data is properly calibrated. That takes a lot of time and effort, but the other side of the equation is understanding all the stuff you don't understand in the data, and there was a lot we didn't initially understand."
Read more…
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If you search around Universe Today, you'll find more than just a couple of articles here referring to Mimas as the Death Star moon. That's because it does look like the Galactic Empire's planet-blasting Death Star – round and with a large circular depression at the side. If you're from one of the younger generations, we're referring to the first Star Wars trilogy.
Mimas, which is actually one of Saturn's natural satellite, also has a large circular depression which is actually a very large crater. The crater is named Herschel, after the astronomer who discovered Mimas – William Herschel. Mimas, along with most of Saturn's moons, are named after the Titans of Greek mythology.
Herschel, the crater, is so large that at 139-km wide, it easily covers almost a third of the entire diameter of Mimas. If you want to picture that with respect to the Earth's dimensions, imagine a crater slightly wider than the area occupied by Canada. The impact of the asteroid that may have caused the crater could have been enough to shatter the moon.
Scientists believe that fractures located in the opposite side of the moon may have been caused by shock waves emanating from the point of impact. The walls of Herschel are estimated to be about 5 km high. At the center of the crater, a structure protrudes conspicuously from the the crater's floor to a height of about 6 km.
Mimas' mean radius is 198 km. For comparison, our Moon has a mean radius of 1,737 km.
Saturn has 62 moons all in all and Mimas is one of those considered as its major satellites. However, just like all the other major satellites, the size of Mimas is nothing compared to Saturn's largest satellite – Titan. Titan comprises 96% of the total mass orbiting around Saturn (and that already includes the rings).
The other major satellites, Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus , combine to constitute about 4%. The rest, about 50 plus moons all in all, are so tiny that they only make up around 0.04%.
Many of the images we've seen of Mimas were taken by the Cassini orbiter, with the closest shots captured very recently when the orbiter was only 9,500 km away. This was on February 13, 2010.
Here are some related articles from Universe Today:
Saturn's Moon Mimas
Cassini Survives Close Encounter of the Death Star Kind!
Want some more? Check out a couple of pages from NASA:
Up Close to Mimas
Cassini Set to Do Retinal Scan of Saturnian Eyeball
Tired eyes? Listen to some episodes at Astronomy Cast. Here are two that might interest you:
Stellar Roche Limits, Seeing Black Holes, and Water on Mars
The Search for Extraterrestrial Intelligence
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A moon eclipse is also known as a lunar eclipse. This is when the earth completely block out the sun allowing no light to hit the moon. This type of eclipse has interesting properties as opposed to a solar eclipse. First the lunar eclipse can be seen anywhere on the planet at night when it occurs. The next interesting thing about lunar eclipses is the various types that can occur.
The different types of eclipses are determined by the composition of the earth's shadow. The Sun is a very large object in relation to the earth so even when the earth passes between it and an object in space, not all of its light is blocked out. This creates a shadow with two parts an umbra and penumbra. The umbra is portion of the shadow where light from the sun is completely blocked out. The penumbra is an area of lighter shadow where some light is allowed. The location of the moon when it passes through the shadow the earth casts determines the kind of eclipse that will be formed.
If the moon passes through the penumbra of the Earth's shadow, it is called a penumbral eclipse. Normally the casual observer will be able to tell its happening because the moon will be dimmer than normal. Also at sunsets and sunrises the moon will be read. The most rare type of penumbral lunar eclipse it a total penumbral lunar eclipse. This is when the moon passes only through the penumbra of the Earth's shadow.
If the moon passes partially through the umbra of the Earth's shadow, it is called a partial lunar eclipse. However the most well known lunar eclipse is a total lunar eclipse. This is when the moon passes through the umbra of the Earth's shadow. This eclipse last for a shorter time period than other lunar eclipses normally around 3.6 hours due to the smaller size of the umbra.
Over all lunar eclipse happen very frequently. However, the frequency depends on the type of lunar eclipse. However you can plan on when to observe the next one by checking an almanac or ephemeris. They should give you the year and date for future eclipses.
If you enjoyed this article there are several others on Universe Today that you will be sure to enjoy. There is a great article about lunar phases. There is also an interesting article on Red Moons.
There are also other resources online that you can look to for more information. You can check out NASA's lunar eclipse page. The GSU physics website also has a great article on how eclipses work.
You can also check out Astronomy Cast. Episode 160 is about Eclipses.
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Meteorites are extraterrestrial objects that enter the atmosphere, strike the Earth's surface and avoid getting totally vaporized. Thus, a meteorite impact is the event associated with collisions between such objects and the Earth.
Although extraterrestrial objects strike the Earth's atmosphere many times everyday, many of them vaporize upon impact. Hence, the number of meteorites found are nowhere near the actual number of extraterrestrial objects that bombard our planet.
Berringer Crater in Arizona
This was the reason why D.M. Barringer had difficulty proving that Barringer Crater was caused by a meteorite impact. The proof he was looking for was already vaporized!
Meteorite impact scenarios have inspired the production of Hollywood films like Deep Impact and Armageddon. Such scenarios that are devastating enough to cause massive extinction is not just a figment of imagination of Hollywood's creative minds.
There are actual scientific theories that are the basis of such scenarios. For instance, the event that totally wiped out the great dinosaurs some 65 million years ago is believed to have been caused by a meteorite impact.
This belief connects the two theories of a group of paleontologists and two groups of astronomers. The group of paleontologists believe that the extinctions that occurred over the last 250 million years are cyclical in nature.
The astronomers, on the other hand, suggest that this cyclical nature may be caused by the cyclic movement of a companion star of the Sun about their barycenter. According to the astronomers, the star (known as Nemesis) may, at a certain point during its orbit, disturb comets in the Oort cloud and cause them to travel through space. Unfortunately, their trajectories apparently coincide with ours.
Proof of massive meteorite impact scenarios can be seen on the Moon's surface as well as on other moons in the Solar System. The craters suggest that at some time or times in the past, asteroids and meteoroids rained upon the region. The same proofs are not as noticeable on Earth as they may have been eroded over time.
Hold on …An asteroid may not have wiped out the dinosaurs. We've got that story here in UniverseToday. Want to know where the biggest crater is?
Come October 9, 2009, LCROSS will perform a lunar impact. Find out which crater NASA has chosen for the impact. If you want to know more about the largest crater on the Moon, NASA's got the right stuff.
There are some interesting episodes from Astronomy Cast that we'd like to recommend:
The Source of Atmospheres, the Vanishing Moon, and a Glow After Sunset
The Moon, Part 1
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Looking for a Moon background? Here's a set of images of the Moon that you can use for your computer desktop background. Just click on an image to enlarge it, and then right-click and choose "Set as Desktop Background".
Lunar Reconnaissance Orbiter
This is an artist's illustration of NASA's Lunar Reconnaissance Orbiter, the most recently mission sent to the Moon. LRO sent an impactor crashing into the Moon to search for evidence of water, and gathered high-resolution images of the surface of the Moon.
Lunar Lander Model
This is a model of an early design of the lunar lander that NASA used to put humans on the Moon as part of the Apollo program. This prototype was called the "Bug", and had many of the features that eventually went into the final lander design.
LRO's First Moon Images
Here is one of the first images sent back to Earth from NASA's Lunar Reconnaissance Orbiter. It shows craters on the surface of the Moon with high resolution; it was so sensitive it could reveal images of the Apollo landing sites.
Crescent Earth
This is an image of the Earth rising up from surface of the Moon, as captured by Apollo 17. Of course, it's no possible to see the Earth rise up over the horizon, since the Moon always displays the same face to the Earth. You need to be in orbit to see this.
Image of Solar Eclipse as seen by Hinode Satellite
Here's an image of a solar eclipse photographed by the Japanese Hinode spacecraft. From our vantage here on Earth, the Sun and the Moon appear to be the same size, and this is why we can get this perfect alignment of a solar eclipse. It's cool to see it from space, though.
We've written many articles about the Moon for Universe Today. Here's how long it takes to get to the Moon, and here's an article about the distance to the Moon.
If you'd like more info on the Moon, check out NASA's World Book on the Moon, and here's a link to NASA's Lunar and Planetary Science page.
We've also recorded an entire episode of Astronomy Cast all about the Moon. Listen here, Episode 113: The Moon, Part 1.
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Gliece 581c is a planet orbiting Gliece 581, a red dwarf star in the constellation Libra. Gliese 581c first gained prominence when it was found to be within its star's habitable zone – the first low mass extrasolar (outside our Solar System) planet found in such a region.
A star's habitable zone, as the name implies, is a region around a star in which the conditions are right for water to exist and subsequently, for life to flourish. Another term commonly used for such a region is the Goldilocks zone.
More recent studies, however, led scientists to suspect that Gliese 581c's atmosphere has the runaway greenhouse effect and hence cannot be habitable. The runaway greenhouse effect is a phenomena wherein too much greenhouse gas in the atmosphere forces the surface to overheat.
This in turn promotes very rapid evaporation and an accumulation of water vapor in the atmosphere. Incidentally, water vapor is an identified greenhouse gas. Thus, the accumulation of water vapor further enhances the greenhouse effect in the planet. And this is what is known as the runaway greenhouse effect.
Because of this, some scientists believe that while water may exist in the planet, it would not be in liquid form. Rather, it would be in vapor form.
The mass of Gliese 581c is estimated to be within 5.36 to 10.4 Earth masses. Scientists are not yet sure what the radius of the planet is.
Since Gliese 581 has a bolometric luminosity of only 1.3% of our Sun's total luminosity, it is expected that its habitable zone should be much closer than our Sun's, e.g., where our Earth is. As a matter of fact, Gliese 581c is only about 11 km from Gliese 581. By comparison, the Earth is 150 km from the Sun.
This extrasolar planet is so close to its sun, that it only takes 13 Earth days for it to complete one revolution. That essentially means "one year" there is only equivalent to 13 days. Whereas here, we roughly have 365 days.
Just like many moons in our Solar System, our Moon included, Gliese 581c experiences what is known as tidal locking. Meaning, only one of its hemispheres keep on facing its sun. This is because of Gliese 581c's closeness to it. The result of this behavior is that only one side will experience day. The other side will be constantly dark.
Universe Today has an article that talks about Gliese 581 and its planets within the habitable zone.
For those who are into Twitter, you might want to check out the article entitled: Send a Tweet to Our Alien Friends on Gliese 581 D.
Of course, there's more information from NASA. Check out
Habitable World Around Gliese 581? How about an astronomy picture of the day on it instead?
Alternatively, you can also listen to an interesting episode about craters in Astronomy Cast.
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Europa. Credit: NASA
Compared to our own planet's natural satellite, the Moon, Europa is slightly smaller. Europa has a mean radius of 1,569 km while the Moon has 1,737 km. This size of Europa makes it the sixth largest moon in the entire Solar System.
Here are the top 10 largest moons in the Solar System and their respective mean radii, arranged from largest to smallest: Ganymede (2,634 km), Titan (2,575 km), Callisto (2,408 km), Io (1,818 km), Moon (1,737 km), Europa (1,569 km), Triton (1,353 km), Titania (788 km), Rhea (764 km), and Oberon (761 km).
Europa is mainly composed of silicate rock but is believed to have an iron core. Interestingly, images of Europa show that its surface is very smooth; in fact, one of the smoothest in the Solar System. Although there are noticeably fewer craters on its surface than what is normally seen in popular moons like our own, Europa is striated by cracks and streaks.
Above the surface is a weak atmosphere composed primarily of oxygen. This thin atmosphere provides a very week atmospheric pressure, about 10-12 times that of Earth's. Its atmosphere also has a charged layer, known as an ionosphere.
Mainly because of the smoothness of Europa's surface, some scientists suggest that this moon may have a huge body of water underneath. Now, whenever water is mentioned, some people are quick to point out, and rightfully so, the possibility of biological life.
Most of what we know of Europa were results of fly-by missions of the unmanned spacecraft, Galileo. Due to the possibility of finding extraterrestrial life there, Europa is among the celestial bodies that are being seriously considered for future exploratory missions.
One of the future missions being considered may entail the use impactors. These are parts of orbiters that are deployed into a controlled crash on the surface of interest. The moment the impactor strikes the surface, it could release a plume of debris. Data from the plume could then be collected by another spacecraft trailing the impactor.
Want to know more about the largest moon in the Solar System? We have an article about it here in Universe Today. If you're more interested in Jupiter's neighbor, Saturn, you might want to know what Saturn's rings are made of.
Here's a closer look of another moon in the Solar System from NASA: Dione at NASA. Here's another one of Dione from the same site.
Relax and listen to some interesting episodes at Astronomy Cast. Want to know more about Ultraviolet Astronomy? How different is it from Optical Astronomy?
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Saturn's moon Dione. Credit: NASA
Cassini, who along with Robert Hooke is credited for the discovery of the Great Red Spot in Jupiter, named Saturn's moons collectively as Sidera Lodoicea. Dione was discovered on the same day as another moon of Saturn, on March 21, 1684. The two other moons, Iapetus and Rhea, were discovered earlier – on October 25, 1671 and December 23, 1672 respectively.
Sidera Lodoicea, which means Louisian Stars, was chosen by Cassini to honor his benefactor as patron of the Paris Observatory, France's King Louis XIV. Cassini was the director of Paris Observatory during King Louis XIV's reign.
Dione is believed to be made mostly of high density water ice. However, it is also believed that silicate rock may be found underneath. Dione's water ice has a high density because gravity is pulling the massive structure together.
Also known as Saturn IV, Dione has a mean radius of about 561 km. It's much smaller than our own Moon, which has a mean radius of 1,737 km. It's mass is only 1.095 x 1021 kg, and has an escape velocity of 0.510 km/s.
It is easy to understand why all of the water on the Dionean surface is frozen. This moon has a temperature of only 87 K or -186°C.
There are three main types of geological features that can be found on Dione: Chasmata or chasms, Lineae or wispy features, and the almost ever-present craters.
Dione's surface reveal the same violent past as the Moon's, wherein these celestial bodies may have been heavily bombarded with asteroids and meteoroids as evidenced by the craters on its surface. Many of Dione's craters have radii over 100 km in diameter.
The craters in Dione have a peculiar concentration, i.e. most of the highly cratered regions can be found in the trailing hemisphere. It is peculiar because tidally locked satellites like Dione are expected to suffer heavier bombardment on their leading hemisphere. Tidally locked satellites are those that have one side always facing the planet they orbit.
Scientists believe that, due to Dione's small size, the moon spun during the period of heavy bombardment. In other words, the current trailing hemisphere may have been the leading hemisphere before.
Want to know what is the largest moon in the Solar System? Find the answer here in Universe Today. If you're more interested in Saturn, you might want to know what Saturn's rings are made of.
Here's a closer look of Dione at NASA. Here's another one of Dione from the same site.
Relax and listen to some interesting episodes at Astronomy Cast. Want to know more about Ultraviolet Astronomy? How different is it from Optical Astronomy?
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Solar eclipse. Credit: NASA
There are four types of solar eclipses: total, annular, hybrid, and partial. The occurrence of each solar eclipse as per observer will depend on three main factors: the position of the Earth and Moon along their orbital paths (i.e., whether near its apogee, near its perigee, or somewhere in between), the location of the observer on Earth, and the alignment between the Earth, Sun, and Moon.
In this article, we'll focus on the effect of the positions of the Earth and Moon along their orbital paths. Their positions will determine whether the eclipse witnessed by an observer on Earth will be total, annular, or hybrid.
Recall that the Earth's and Moon's orbits are elliptical in shape. That means, in some instances, the Earth can be at its farthest position from the Sun (known as its apogee), while in others, it can be at its nearest (perigee). In still other instances (in fact, more frequent than the other two), the Earth can be located somewhere in between the two extremes.
When the Earth is at its farthest, the Sun will naturally appear smallest to an observer than if the Earth were at its nearest. Hence, all things considered equal, the Moon will be able to cover a greater part of the Sun when the Earth is at this position.
Now, since the Moon's orbital path about the Earth is also elliptical, there should be a position wherein the Moon will appear largest – its perigee. The nearer the Moon, the bigger it will appear from an observer on Earth, and the bigger its obstruction (if ever) of the Sun. As we can see, the positions of the Earth and Moon along their orbital paths are crucial in producing the type of solar eclipse.
So, at which extreme positions of the Earth and Moon can we have the smallest Sun and largest Moon?
The Sun is smallest when the Earth is at its apogee while the Moon is largest when the Moon is at its perigee. Thus, if these two scenarios happen at the same time while the Earth, Sun, and Moon are fully aligned, many of us will experience the most total solar eclipse there can ever be.
We have a nice collection of solar eclipse articles here in Universe Today. Here it is:
Of course, NASA has a good one too. Here it is:
Here's a nice episode from Astronomy Cast if you want to put your ears to work for a change:
Dangerous Solar Flares, Higgs Boson Insights, and Light Speed Flashlights
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Solar eclipse. Credit: NASA
If the Moon, Sun, and Earth are fully aligned and the Moon manages to cover the Sun entirely, the event is known as a total eclipse. Otherwise, if they are fully aligned but the Moon still isn't able to cover the Sun entirely, i.e., the Sun forms a ring around the Moon, the event is called an annular eclipse.
The occurrence of total and annular solar eclipses depend on the relative distances between the Earth, Sun, and Moon. If their relative distances are such that the apparent size of the Sun is small enough (or the Moon's apparent size big enough) for the Moon to cover it entirely, then we'll have a total solar eclipse. Otherwise, we'll only get to see an annular eclipse.
There's also what we call a hybrid eclipse, which occurs between a total eclipse and an annular eclipse. At some points on the Earth, observers will see a total eclipse, while at others, they'll see an annular eclipse.
Although solar eclipses are very rare for a specific location on Earth, happening only once every 370 years, they can occur more frequently if we consider the entire planet. That is, on the average, solar eclipses can take place more than once every year. Mostly, the solar eclipses are partial eclipses, i.e., those that occur when the Sun, Moon, and Earth are not fully aligned.
By the way, the occurrence of solar eclipses is not limited to Earth. Other planets which also have satellites like the Moon will also experience these events.
More specific terms are however used. If the passing satellite has an apparent size larger than the Sun, then the event is called an occultation. If the apparent size is smaller than the Sun, the term used is transit.
For the planet Jupiter, which has multiple satellites orbiting around it, five of them can cause occultation-type solar eclipses. All the other satellites, which are much smaller, can only result in transit-type solar eclipses when they pass between the Sun and Jupiter.
Solar eclipses on other planets like Jupiter can be observed from the Earth through telescopes. Observers typically observe the shadow transit that the passing satellite casts on the planet. Jupiter is a nice planet to observe solar eclipses because (due to the sheer size of the planet and the number of satellites) they occur quite frequently there.
We have a nice collection of solar eclipse articles here in Universe Today. Here it is:
Of course, NASA has a good one too. Here it is:
Here's a nice episode from Astronomy Cast if you want to put your ears to work for a change:
Dangerous Solar Flares, Higgs Boson Insights, and Light Speed Flashlights
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This video surfaced today on NASA Watch, but there's not a lot of details about Project M. According to the America Space website, Project M is a program being developed out of the Johnson Space Center Engineering Directorate to put a lander on the moon with a robot. Supposedly, the mission could be done within a 1,000 days once the project got the go-ahead.
Read more…
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Ares V rocket
Good.
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It's time to update your computer's desktop wallpaper. Here's a good wallpaper: Moon. Click on any picture you want to get a bigger version. Then right-click on the image and choose "Set as Desktop Background".
Buzz Aldrin with the American Flag
Here's an image of Buzz Aldrin standing on the Moon with the American Flag. You can see one leg from the Eagle lander on the left-hand side of the image.
Lunar Orbiter
This is a computer illustration of NASA's Lunar Orbiter mission. This was a spacecraft sent before the Apollo landings to help study and map the surface of the Moon.
Footprints on the Moon
Here's one of the most iconic images in all of space exploration: the image of the Apollo 11 astronaut footprints on the Moon. More than a billion people watched this event live on television.
Moon - North Polar Mosaic, Color
The destination for NASA's Galileo spacecraft was Jupiter, but it took a bunch of pictures before it left the neighborhood. Here's a picture of the Moon captured by Galileo as it was speeding away from Earth.
Moonrise
This is an image of the Moon rising above the atmosphere of the Earth. It was captured by the crew of the space shuttle Columbia during its ill-fated journey back from orbit. The shuttle broke up on re-entry on Feb. 1, 2003, killing all 7 astronauts on board.
We've written many articles about the Moon for Universe Today. Here's an article about the discovery of water on the Moon, and here's an article about the Moon compared to Earth.
If you'd like more info on the Moon, check out NASA's World Book on the Moon, and here's a link to NASA's Lunar and Planetary Science page.
We've also recorded an entire episode of Astronomy Cast all about the Moon. Listen here, Episode 113: The Moon, Part 1.
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Many space programs are looking to set up bases on the moon in the not too distant future. However this would be a daunting task under most plans. The main goal would be that the moon base or colony would need to at least support human life for long enough periods of time for supplies to be restocked. What would be ideal would be for it to be self sufficient. The other problem is getting building materials to the moon.
Space exploration is still in its relative infancy and current space craft are very expensive to operate. This raises the transportation cost for significant amounts of building materials to an astronomical level. So what are the ways that we can work around these challenges?
The first solution is more international cooperation. Unless given a very valid reason, few countries would see the point in investing all the resources needed to build a moon base on their own. Like what was done with the International Space Station, a collaborative effort by the world's various space agencies.
They would need to deal with what materials to use and how to get them to the moon. Part of the problem could be solved by simply using what is there. The moon is rich in oxides and water as well as high grade minerals. Some experiments have been done mixing lunar regolith with carbon nanotubes. The resulting mixture produced a form concrete that is much lighter and stronger than its equivalent on earth. However there would still be the challenge of processing the material into a usable form.
The next challenge would be energy. The best route would be solar power but the moon has a much longer rotation period than the Earth. This would mean a potential moon base would have to deal with long periods of time with out sunlight. One solution suggested would be to place the base near the lunar pole. This region that constantly get day light all day and year round.
While the building a moon base would be a major challenge the potential benefits could be worth the effort. One is that the moon can help produce oxygen and water for longer space voyages making it a launching point for mission to Mars and beyond. It can also serve as a new training center for astronauts helping them get real world experience with extraterrestrial conditions.
If you enjoyed this article there are several others on Universe Today that you will love to read. There is a great article about the challenges of building a moon base. There is also an interesting are about some of the possible structures for a moon base.
There are also some great resources online. There is an interesting article on the history web page of NASA.gov that talks about the possibility of returning to the moon. There is also an article on the New Scientist web site that talks about potential challenges that may prevent NASA from setting up its planned moon base.
You can also check out Astronomy Cast. Episode 149 Talks about the Constellation Program.
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