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When we look at the Moon, we see these amazing variations of light and dark. And depending on your orientation on Earth, you might see the famous “Man in the Moon”, or maybe the “Rabbit in the Moon”. The darker areas are known as maria, smooth lava fields created by ancient volcanic eruptions on the Moon.
But why do we see this face of the Moon, and not a different side?
The Moon’s rotation is tidally locked to the Earth. This means that the Moon always presents the same side to us, completing one orbit around the Earth in the exact same amount of time it takes to turn once on its axis. From our perspective, the Moon never rotates, always displaying the “Man in the Moon”.
And before the space age, it was assumed that the entire Moon looked like this. When the first spacecraft were sent from Earth to orbit the Moon, they sent back surprising photographs that revealed a completely different landscape from what we’re used to. Instead of the dark splotches of lunar maria we see on the near side – the “Man in the Moon” – the far side is merely covered in craters.
So why is the maria-side facing us, while the crater-side faces away? Is it just a coincidence?
Researchers from the California Institute of Technology think that it’s not about luck at all, but the way the Moon’s rotation slowed down after its formation. Oded Aharonson, a professor of planetary science at Caltech, and his team created a simulation that calculated how the rotation of the Moon slowed down after its formation.
Although the Moon looks like a sphere, it actually has a slight bulge. And billions of years ago, when the Moon was rotating much more quickly, showing its entire surface to the inhabitants of Earth, the Earth’s gravity tugged at this bulge with each rotation, slowing it down slightly each time until the Moon’s rotation was completely stopped from our perspective.
In every simulation that the Caltech did, thanks to the orientation of this lunar bulge, either the Moon’s maria-side or crater-side ended up facing Earth. But the rate at which it slowed down – how fast it dissipated its rotational energy – defined our chances of seeing the “Man in the Moon”.
If the Moon slowed down quickly, it would have been a 50/50 chance. But because the Moon slowed down more gradually, we had a much higher chance of seeing the maria-side as the final result. The maria-side was twice as likely to be our final view over the crater-side. The results of this research was published in the February 27th edition of the Journal Icarus.
You can read a more detailed article from the Caltech news release.
A type of worm from the Dorvilleids family. The first known species to consume Archaea.
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A couple of consumption stories crossed my desk today, so I thought I’d merge them together. The bottom line is that everything’s on the menu. If there’s energy to be extracted from something, life is going to find a way to consume it.
We’ve got a deep sea worm that seems to be able to thrive from any of the three main branches of life on Earth – the first known example of a creature that consumes Archaea.
And then there’s the discovery of a fungus capable of consuming large amounts of polyurethane plastic.
Eating from all three branches of the tree of life
The first example of this comes from research done at Oregon State University about a single-celled microorganism called Archaea. This class of life is one of the three basic “domains of life” on Earth, including bacteria and eukaryota (multi-celled creatures like us).
Scientists believed that Archaea were completely disconnected from the food web – the circle of life just didn’t include them – but researchers at Oregon State University tried feeding two varieties of Archaea to a type of deep sea worms that live near the “black smoker” vents off the coast of North America.
To their surprise, these worms were perfectly happy eating Archaea, as well as standard meals of bacteria, spinach or rice. They grew at the same rate, regardless of what branch their food was hanging from on the tree of life.
Researchers from Yale University have discovered a variety of fungi in the Amazon Rainforest (where else?), that can “eat” a common form of plastic known as polyurethane. This, of course, would be the holy grail of recycling, since there’s no natural process that will get rid of plastic.
While exploring the Amazon, they discovered a fungus in the rainforest of Ecuador and brought it back to the lab for analysis. They experimented with it a bit and discovered just how quickly it could consume plastic. In one report, the fungus was only 10 days old and had significantly consumed about a quart’s worth of plastic – without needing any oxygen.
The puzzling part, of course, is trying to figure out what this fungus normally eats in the wild, since it’s not growing on plastic trees.
A High-resolution Look over Mercury's Northern Horizon. Credit: MESSENGER team
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When you look at an image of Mercury, it looks like a dry, airless world. But you might be surprised to know that Mercury does have an atmosphere. Not the kind of atmosphere that we have here on Earth, or even the thin atmosphere that surrounds Mars. But Mercury’s atmosphere is currently being studied by scientists, and the newly arrived MESSENGER spacecraft.
Mercury’s original atmosphere dissipated shortly after the planet formed 4.6 billion years ago with the rest of the Solar System. This was because of Mercury’s lower gravity, and because it’s so close to the Sun and receives the constant buffeting from its solar wind. Its current atmosphere is almost negligible.
What is Mercury’s atmosphere made of? It has a tenuous atmosphere made up of hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor. Astronomers think this current atmosphere is constantly being replenished by a variety of sources: particles of the Sun’s solar wind, volcanic outgassing, radioactive decay of elements on Mercury’s surface and the dust and debris kicked up by micrometeorites constantly buffeting its surface. Without these sources of replenishment, Mercury’s atmosphere would be carried away by the the solar wind relatively quickly.
Mercury atmospheric composition:
Oxygen 42%
Sodium 29%
Hydrogen 22%
Helium 6%
Potassium 0.5%
With trace amounts of the following:
Argon, Carbon dioxide, Water, Nitrogen, Xenon, Krypton, Neon, Calcium, Magnesium
In 2008, NASA’s MESSENGER spacecraft discovered water vapor in Mercury’s atmosphere. It’s thought that this water is created when hydrogen and oxygen atoms meet in the atmosphere.
Two of those components are possible indicators of life as we know it: methane and water vapor(indirectly). Water or water ice is believed to be a necessary component for life. The presence of water vapor in the atmosphere of Mercury indicates that there is water or water ice somewhere on the planet. Evidence of water ice has been found at the poles where the bottoms of craters are never exposed to light. Sometimes, methane is a byproduct of waste from living organisms. The methane in Mercury’s atmosphere is believed to come from volcanism, geothermal processes, and hydrothermal activity. Methane is an unstable gas and requires a constant and very active source, because studies have shown that the methane is destroyed in less than on Earth year. It is thought that it originates from peroxides and perchlorates in the soil or that it condenses and evaporates seasonally from clathrates.
Despite how small the Mercurian atmosphere is, it has been broken down into four components by NASA scientists. Those components are the lower, middle, upper, and exosphere. The lower atmosphere is a warm region(around 210 K). It is warmed by the combination of airborne dust(1.5 micrometers in diameter) and heat radiated from the surface. This airborne dust gives the planet its ruddy brown appearance. The middle atmosphere contains a jetstream like Earth’s. The upper atmosphere is heated by the solar wind and the temperatures are much higher than at the surface. The higher temperatures separate the gases. The exosphere starts at about 200 km and has no clear end. It just tapers off into space. While that may sound like a lot of atmosphere separating the planet from the solar wind and ultraviolet radiation, it is not.
Helping Mercury hold on to its atmosphere is its magnetic field. While gravity helps hold the gases to the surface, the magnetic filed helps to deflect the solar wind around the planet, much like it does here on Earth. This deflection allows a smaller gravitational pull to hold some form of an atmosphere.
The atmosphere of Mercury is one of the most tenuous in the Solar System. The solar wind still blows much of it away, so sources on the planet are constantly replenishing it. Hopefully, the MESSENGER spacecraft will help to discover those sources and increase our knowledge of the innermost planet.
Neptune's system of moons and rings visualized. Credit: SETI
Neptune is one of four planets in our Solar System with planetary rings. Neptune was not discovered until 1846 and its rings were only discovered definitively in 1989 by the Voyager 2 probe. Although the rings were not discovered until the late 1900’s, William Lassell who discovered Titan recorded that he had observed a ring. However, this was never confirmed. The first ring was actually discovered in 1968, but scientists were unable to determine if it was a complete ring. The Voyager’s evidence was the definitive proof for the existence of the rings.
Neptune has five rings: Galle, Le Verrier, Lassell, Arago, and Adams. Its rings were named after the astronomers who made an important discovery regarding the planet. The rings are composed of at least 20% dust with some of the rings containing as much as 70% dust; the rest of the material comprising the rings is small rocks. The planet’s rings are difficult to see because they are dark and vary in density and size. Astronomers think Neptune’s rings are young compared to the age of the planet, and that they were probably formed when one of Neptune’s moons was destroyed.
The Galle ring was named after Johann Gottfried Galle, the first person to see the planet using a telescope. It is the nearest of Neptune’s rings at 41,000–43,000 km. The La Verrier ring was named after the man who predicted Neptune’s position. Very narrow, this ring is only about 113 kilometers wide. The Lassell ring is the widest of Neptune’s rings. Named after William Lassell, it lies between 53,200 kilometers and 57,200 kilometers from Neptune, making it 4,000 kilometers wide. The Arago ring is 57,200 kilometers from the planet and less than 100 kilometers wide.
The outer ring, Adams, was named after John Couch Adams who is credited with the co-discovery of Neptune. Although the ring is narrow at only 35 kilometers wide, it is the most famous of the five due to its arcs. Adams’ arcs are areas where the material of the rings is grouped together in a clump. Although the Adams ring has five arcs, the three most famous ones are Liberty, Equality, and Fraternity. The arcs are the brightest parts of the rings and the first to be discovered. Scientists are unable to explain the existence of these arcs because according to the laws of motion they should distribute the material uniformly throughout the rings.
The rings of Neptune are very dark, and probably made of organic compounds that have been baked in the radiation of space. This is similar to the rings of Uranus, but very different to the icy rings around Saturn. They seem to contain a large quantity of micrometer-sized dust, similar in size to the particles in the rings of Jupiter.
It’s believed that the rings of Neptune are relatively young – much younger than the age of the Solar System, and much younger than the age of Uranus’ rings. They were probably created when one of Neptune’s inner moons got to close to the planet and was torn apart by gravity.
The innermost ring of Neptune orbits at a distance of 41,000 km from the planet, and extends to a width of 2,000 km. It’s named after Johann Gottfried Galle, the first person to see Neptune through a telescope. The next ring is the narrower LeVerrier ring, named after Neptune’s co-discoverer, Urbain Le Verrier. It’s only 113 km wide. Then comes the Lassell ring, the widest ring in the system at about 4,000 km. Then comes the Arago ring, and finally the very thin Adams ring, named after Neptune’s other co-discoverer.
Five of the planets in the night sky are easy to see with the unaided eye, and have been known since ancient times. Uranus is just bright enough that you can see it in a perfectly dark place if you know where to look. But Neptune can only be seen in a telescope. And since telescopes have only been around for a few hundred years, Neptune was discovered recently. So, who discovered Neptune?
The mathematician Alexis Bouvard published a series of astronomical tables detailing the orbit of Uranus. Over time, several astronomers realized that there had to be some additional planet deeper out in the Solar System that was influencing the motion of Uranus with its gravity. They set to work calculating where this additional planet might be located in the Solar System.
Two astronomers, Britain’s John Couch Adams and France’s Urbain Le Verrier had worked out the position of the hypothetical 8th planet independently from each other. And both had a difficult time convincing their colleagues to spend any time actually looking where they suggested the planet might be.
The Berlin Observatory astronomer Johann Gottfried Galle used the calculations by Le Verrier to find Neptune within just 1° of its predicted location, and just 12° of Adams’ predictions. Both astronomers claimed that they were the first to discover the planet, and it led to an international dispute.
After the discovery, there was rivalry between England and France about who should get credit for finding Neptune, Adams or Le Verrier. The international astronomy community agreed that the two astronomers should share credit for the discovery. Eventually both Le Verrier and Adams were given credit for discovering Neptune in 1846.
The planet was named after the Roman god of the oceans; the same as the Greek God Poseidon.
Of course, this is just a shortened version of the discovery of Neptune. If you’d like to read more, check out this article that talks about the mathematical discovery of planets. And here’s more information on Le Verrier.
[/caption] Mass: 1.98892 x 1030 kg Diameter: 1,391,000 kilometers Radius: 695,500 km Surface gravity of the Sun: 27.94 g Volume of the Sun: 1.412 x 1018 km3 Density of the Sun: 1.622 x 105 kg/m3
How Big is the Sun?
The Sun is the largest object in the Solar System, accounting for 99.86% of the mass.
As stars go, the Sun is actually a medium-sized, and even smallish star. Stars with much more mass can be much larger than the Sun. For example, the red giant Betelgeuse, in the constellation of Orion is thought to be 1,000 times larger than the Sun. And the largest known star is VY Canis Majoris, measuring approximately 2,000 times larger than the Sun. If you could put VY Canis Majoris into our Solar System, it would stretch out past the orbit of Saturn.
The size of the Sun is changing. In the future when it runs out of usable hydrogen fuel in the core, it will become a red giant as well. It will engulf the orbits of Mercury and Venus, and possibly even the orbit of the Earth. For a few million years, the Sun will be about 200 times bigger than its current size.
After the Sun becomes a red giant, it will shrink down to become a white dwarf star. Then the size of the Sun will only be roughly the size of the Earth.
Mass of the Sun
The mass of the Sun is 1.98892 x 1030 kilograms. That’s a really big number, and it’s really hard to put it into context, so let’s write out the mass of the Sun, with all the zeros.
Still need to wrap your head around this? Let’s give you some comparisons. The mass of the Sun is 333,000 times the mass of the Earth. It’s 1,048 times the mass of Jupiter, and 3,498 times the mass of Saturn.
In fact, the Sun accounts for 99.8% of all the mass in the entire Solar System; and most of that non-Sun mass is Jupiter and Saturn. To say that the Earth is an insignificant speck is an understatement.
When astronomers try to gauge the mass of another star-like object, they use the mass of the Sun for comparison. This is known as a “solar mass”. So the mass of objects, like black holes, will be measured in solar masses. A massive star might have 5-10 solar masses. A supermassive black hole could have hundreds of millions of solar masses.
Astronomers will refer to this with an M beside a symbol that looks like a circle with a dot in the middle – M⊙. To show a star that has 5 times the mass of the Sun, or 5 solar masses, it would be 5 M⊙. Eta Carinae, one of the most massive stars known. Image credit: NASA
The Sun is massive, but it’s not the most massive star out there. In fact, the most massive star we know of is Eta Carinae, which has a mass of 150 times the mass of the Sun.
The Sun’s mass is actually slowly decreasing over time. There are two processes at work here. The first is the fusion reactions in the core of the Sun, converting atoms of hydrogen into helium. Some of the Sun’s mass is lost through the fusion process, as atoms of hydrogen are converted into energy. The warmth we feel from the Sun, is the Sun’s lost mass. The second way is the solar wind, which is constantly blowing protons and electrons into outer space.
Mass of the Sun in kilograms: 1.98892 x 1030 kg
Mass of the Sun in pounds: 4.38481 x 1030 pounds
Mass of the Sun in tons: 2.1924 x 1027 tons
Diameter of the Sun
The diameter of the Sun is 1.391 million kilometers or 870,000 miles.
Again, let’s put this number into perspective. The diameter of the Sun is 109 times the diameter of the Earth. It’s 9.7 times the diameter of Jupiter. Really, really big.
Pardon the pun, but the Sun doesn’t hold a candle to some of the largest stars in the Universe. The biggest star we know of is called VY Canis Majoris, and astronomers think it could be 2,100 times the diameter of the Sun. The Earth compared to Sunspot 1312 on 10-10-11. Credit: Ron Cottrell.
Diameter of the Sun in kilometers: 1,391,000 km
Diameter of the Sun in miles: 864,000 miles
Diameter of the Sun in meters: 1,391,000,000 meters
Diameter of the Sun compared to Earth: 109 Earths
Radius of the Sun
The radius of the Sun, the measurement from the exact center of the Sun out to its surface, is 695,500 kilometers.
This radius is essentially the same however you measure it, from the center to the equator, or the from the center to the Sun’s poles. But you need to be careful with other objects, however, because the speed of their rotation affects the radius.
The Sun takes about 25 days to turn once on its axis. Because it rotates relatively slowly, the Sun doesn’t flatten out at all. The distance from the center to the poles is almost exactly the same as the distance from the center to the equator.
There are stars out there which are dramatically different, though. For example, the star Achernar, located in the constellation Eridanus, is flattened by 50%. In other words, the distance from the poles is half the distance across the equator. In this situation, the star actually looks like spinning-top toy.
So, relative to out stars out there, the Sun is almost a perfect sphere.
Astronomers use the Sun’s radius, or “solar radius” to compare the sizes of stars and other celestial bodies. For example, a star with 2 solar radii is twice as large as the Sun. A star with 10 solar radii is 10x as large as the Sun, and so on. VY Canis Majoris. The biggest known star.
Polaris, the North Star, is the brightest star in the constellation Ursa Minor (Little Dipper) and, because of its proximity to the north celestial pole, is considered the current northern pole star. Polaris is primarily used for navigation and has a solar radius of 30. That means, it is 30 times bigger than the Sun.
Sirius which is the brightest star in the night sky. In terms of apparent magnitude, the second brightest star, Canopus, has only half that of Sirius’. No wonder it really stands out. Sirius is actually a binary star system, with Sirius A having a solar radius of 1.711 and B, which is much smaller, at about 0.0084.
Radius of the Sun in kilometers: 695,500 km
Radius of the Sun in miles: 432,200 miles
Radius of the Sun in meters: 695,500,000 meters
Radius of the Sun compared to Earth: 109 Earths
Gravity of the Sun
The Sun has an enormous amount of mass, and so it has a lot of gravity. In fact, the mass of the Sun is 333,000 times more than the mass of the Earth. Forget that the surface temperature of the Sun is 5,800 Kelvin and made of hydrogen – what would you feel if you could walk on the surface of the Sun? Think about this, the gravity of the Sun at the surface is 28 times the gravity of the Earth.
In other words, if your scale says 100 kg on Earth, it would measure 2,800 kg if you tried to walk on the surface of the Sun. Needless to say, you would die pretty quickly just from the pull of gravity, not to mention the heat, etc.
The Sun’s gravity pulls all of its mass (mostly hydrogen and helium) into an almost perfect sphere. Down at the core of the Sun, the temperatures and pressures are so high that fusion reactions are possible. The tremendous amount of light and energy pouring out of the Sun counteracts the pull of gravity trying to collapse it down. The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA
Astronomers define the Solar System as the distance under the influence of gravity from the Sun. We know that the Sun holds distant Pluto in orbit (5.9 billion km away on average). But astronomers think that the Oort Cloud extends out to a distance of 50,000 astronomical units (1 AU is the distance from the Earth to the Sun), or 1 light-year. In fact, the influence of the Sun’s gravity could extend out to 2 light-years away, the point at which the pull from other stars is stronger.
Surface gravity of the Sun: 27.94 g
Density of the Sun
The density of the Sun is 1.4 grams per cubic centimeter. Just to give you a comparison, the density of water is 1 g/cm3. In other words, if you could find a pool large enough, the Sun would sink down and not float. And this seems kind of counter-intuitive. Isn’t the Sun made of hydrogen and helium, the two lightest elements in the Universe? So how can the density of the Sun be so high?
Well, it all comes down to gravity. But first, let’s calculate the density of the Sun for ourselves.
Formula for density is to divide mass by volume. The mass of the Sun is 2 x 1033 grams, and the volume is 1.41 x 1033 cm3. And so, if you do the math, the density of the Sun works out to be 1.4 g/cm3. Interior of the Sun. Image credit: NASA
The Sun holds itself together with gravity. Although the outermost layers of the Sun might be less dense, the intense gravity crushes the inner regions to enormous pressures. At the core of the Sun, the pressure is more than 1 million metric tons/cm sq – that’s equivalent to more than 10 billion times the atmosphere of the Earth. And once you get those kinds of pressures, fusion can ignite.
Density of the Sun: 1.622 x 105 kg/m3
Volume of the Sun
The volume of the Sun is 1.412 x 1018 km3. That’s a lot of cubic kilometers. Do you need something to compare this with? The volume of the Sun is so great that it would take 1.3 million planets the size of the Earth to fill it up. Or you could fill it with almost 1000 planets the size of Jupiter.
Volume of the Sun in cubic kilometers: 1.412 x 1018 km3
Volume of the Sun compared to Earth: 1,300,000
Circumference of the Sun
The circumference of the Sun is 4,379,000 km.
Just for comparison, the equatorial circumference of the Earth is 40,075 km. So, the circumference of the Sun is 109 times larger than the circumference of the Earth. And the circumference of the Sun is 9.7 times bigger than the circumference of Jupiter.
An atomic clock; a relic of a bygone age? Image credit: NIST
[/caption] Do you find that you’re always having to adjust the clocks in your house? Why can’t someone just make a clock that’s accurate? How about a clock that would never lose time in, say, the entire age of the Universe? Well, that’s just what researchers from the University of New South Wales are proposing.
According to their calculations, a neutron orbiting around the atomic nucleus of an atom would do the trick. In fact, this “atomic clock” would be so accurate, it wouldn’t gain or lose 1/20th of a second in 14 billion years – that’s the age of the Universe.
Obviously a clock like this wouldn’t have any value for home use, but in science, accurate clocks are everything. And this single atom clock would be 100 times more accurate than anything scientists have access to right now. They’d be able to record time down to 19 decimal places: 0.0000000000000000001 of a second.
One of the most important places that clocks are used is GPS. The Global Positioning System uses clocks to time how long signals take to reach your GPS unit from various satellites. The satellites are broadcasting very accurate times, which can then be used to triangulate your position. More accurate clocks mean more accurate position.
So how exactly would they do it? Lasers, of course. All the cool science is done with lasers. According the researchers:
“Atomic clocks use the orbiting electrons of an atom as the clock pendulum. But we have shown that by using lasers to orient the electrons in a very specific way, one can use the orbiting neutron of an atomic nucleus as the clock pendulum, making a so-called nuclear clock with unparalleled accuracy.”
Here’s the trick. The neutron of an atom is so tightly bound to the nucleus that it’s almost completely unaffected by outside forces. Electrons, on the other hand, can be affected and so the clocks can be less accurate.
Light can do some pretty strange stuff, like pass through objects and bounce off them; it can be broken up and recombined. In fact, everything we “see” is actually the end result of reflection and refraction of light. Time to understand how it all works.
Remember that we record every episode of Astronomy Cast as a live Google+ Hangout on Mondays at 12 pm PST / 3 pm EST / 2000 GMT. You can watch us record the episode and even jump into the Hangout and ask us some questions. Follow Fraser on Google+ to see when it happens.
Quantum theory is plenty strange, but one of the strangest discoveries is the realization that there’s a limit to how much you can measure at any one time. This was famously described by Werner Heisenberg, with his uncertainty principle: how you can never know both the position and motion of a particle at the same time.
We record Astronomy Cast live every Monday at 12 pm PST / 3 pm EST / 2000 GMT. If you want to join in our recording, just make sure you’ve got Fraser circled on Google+, then the show will show up in your stream. You can also watch us live at Cosmoquest.
Another week, another space roundup. This week we talk about the redefinition of the term “Earthlike”, salty soil on Mars, how you can participate in SETI, asteroid dust from Hayabusa, and the dangers of a warp drive.
Just a warning, we somehow lost the first 10 minutes or so of the video, so you’ll have to imagine Ian’s awesome description of the scientists concerned with the definition “Earthlike”, and how that might be changed. We didn’t miss too much of the conversation, though.
Remember, we record this show live every Thursday at 10:00am PST / 1:00 pm EST / 1800 UTC. Join us at Cosmoquest Hangouts, or watch Fraser’s Google+ stream for the show to start.
