Universe Today

August 10, 2009December 29, 2015 by Nancy Atkinson

Carnival of Space #115

This week’s Carnival of Space is hosted by New Frontier News.

Click here to read the Carnival of Space #115.

And if you’re interested in looking back, here’s an archive to all the past Carnivals of Space. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to [email protected], and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. And if you really want to help out, let Fraser know if you can be a host, and he’ll schedule you into the calendar.

Finally, if you run a space-related blog, please post a link to the Carnival of Space. Help us get the word out.

August 10, 2009December 24, 2015 by Nancy Atkinson

Have You Ever Seen a Moonbow?

Photo of a Lunar Rainbow taken from the Zambia side of Victoria Falls. The constellation Orion is visible behind the top of the moonbow. Credit: Calvin Bradshaw

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They are elusive, but powerful to see. “Moonbows” are rainbows created by light from the Moon. Conditions have to be just right, and there are only a small number of places in the world where they regularly materialize, such as Victoria Falls on the border between Zambia and Zimbabwe as seen above, Cumberland Falls in Kentucky, Yosemite Falls in California, and Waimea on Hawaii. Because they are so faint, moonbows are difficult to see with the naked eye (they usually appear just white). But with long-exposure photography, all the colors of moonbows can be seen. Below, check out a gorgeous video of stars, a moonbow and rainbow over Torres del Paine in Patagonia, Chile, and more moonbow images at Environmental Graffiti.

August 10, 2009December 24, 2015 by Abby Cessna

Radius of the Planets

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One way to measure the size of the planets is by radius. Radius is the measurement from the center of an object to the edge of it.

Mercury is the smallest planet with a radius of only 2,440 km at its equator. Mercury is not that much larger than the Moon, and it is actually smaller than some of our Solar System’s larger satellites, such as Titan. Despite Mercury’s small size, it is actually dense with higher gravity than you would expect for its size.

Venus has a radius of 6,052 kilometers, which is only a few hundred kilometers smaller than Earth’s radius. Most planets have a radius that is different at the equator than it is at the poles because the planets spin so fast that they flatten out at the poles. Venus has the same diameter at the poles and at the equator though because it spins so slowly.

Earth is the largest of the four inner planets with a radius of 6,378 kilometers at the equator. This is over two times larger than the radius of Mercury. The radius between the poles is 21.3 km less than the radius at the equator because the planet has flattened slightly since it only takes 24 hours to rotate.

Mars is a surprisingly small planet with a radius of 3,396 kilometers at the equator and 3,376 kilometers at the poles. This means that Mars’ radius is only about half of Earth’s radius.

Jupiter is the largest of all the planets. It has a radius of 71,492 kilometers at the equator and a radius of 66,854 kilometers at the poles. This is a difference of 4,638 kilometers, which is almost twice Mercury’s radius. Jupiter has a radius at the equator 11.2 times Earth’s equatorial radius.

Saturn has an equatorial radius of 60,268 kilometers and a radius of 54,364 kilometers at the poles making it the second largest planet in our Solar System. The difference between its two radiuses is a little more than twice the radius of Mercury.

Uranus has an equatorial radius of 25,559 kilometers and a radius of 24,973 kilometers at the poles. Although this is much smaller than Jupiter’s radius, it is around four times the size of Earth’s radius.

Neptune’s equatorial radius of 24,764 kilometers makes it the smallest of the four outer planets. The planet has a radius of 24,341 kilometers at the poles. Neptune’s radius is almost four times the size of Earth’s radius, but it is only about a third of Jupiter’s radius.

Universe Today has articles on the radius of Neptune and the size of the planets.

If you are looking for more information, check out NASA’s Solar System exploration page, and here’s a link to NASA’s Solar System Simulator.

Astronomy Cast has an episode on Venus and more on all the planets.

August 10, 2009December 24, 2015 by Abby Cessna

Volume of the Planets

Planets and other objects in our Solar System. Credit: NASA.

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There are a number of measurements that astronomers use, including mass, surface area, diameter, and radius, to determine the the size of the planets. Volume is one measurement of the size of a planet. It is a measurement of how much three-dimensional space an object occupies. The volumes of the planets, along with other measurements, help astronomers discover the physical composition of the planets in addition to other information about them.

Mercury is the littlest planet in our Solar System with the smallest volume of any planet. It has a volume of 6.083 x 10¹⁰ cubic kilometers, which is only 5.4% of Earth’s volume.

Venus is only slightly smaller than Earth with a volume of 9.38 x 10¹¹ km³. That is 86% of the Earth’s volume. This may not seem like Venus is that close in size to our planet, but Venus is closer in size to Earth than any other planet is.

Earth is the largest of the four inner planets, although it is nothing compared to the gas giants. Earth has a volume of 1.08 x 10¹² cubic kilometers.

Mars is actually a rather small planet with a volume of 1.6 x 10¹¹ cubic kilometers. While that is larger than Mercury’s volume and pretty big in general, it is only 15% of Earth’s volume. You could put over six planets the size of Mars inside the Earth.

The largest planet in our Solar System, Jupiter’s size is astounding. Jupiter has a volume of 1.43 x 10¹⁵ cubic kilometers. To show what this number means, you could fit 1321 Earths inside of Jupiter. It is hard to imagine how large that actually is.

Saturn is the second largest planet in the Solar System. It has a volume of 8.27 x 10¹⁴ cubic km. Although it is only a fraction of the size of Jupiter, you could fit 764 Earths inside of the gas giant.

Uranus is a large planet with a volume of 6.833 x 10¹³ cubic kilometers. You could fit a little more than 63 Earths inside of Uranus, but like the other gas giants, it is not very dense. Comprised mostly of gas, the planet is only about 14.5 times more massive than Earth is.

Neptune is the smallest gas giant in our Solar System, but it is still much larger than any of the inner planets. Neptune has a volume of 6.3 x 10¹³ cubic kilometers, which is equal to about 57 Earths. Even though Neptune’s volume is much greater than the Earth’s is, the gravity on Neptune is only about 14% greater than it is on Earth. This is due to the gas giant’s small mass.

Universe Today has articles on size of the planets and mass of the planets.

Check out an overview of the Solar System and all about the planets.

Astronomy Cast has an episode on Jupiter and episodes on all the planets.

August 10, 2009December 19, 2016 by Abby Cessna

What are Planetoids?

Planetoid is another term for asteroids, which are also called minor planets. Planetoids are small celestial bodies that orbit the Sun. Planets are simply defined as asteroids, but the term asteroid is not well defined either. In 2006, The International Astronomical Union (IAU) defined it as a “small Solar System body” (SSSB), which does not really tell us anything either. Webster’s Dictionary defines an asteroid as, “any of the thousands of small planets ranging from 1,000 km (621 mi) to less than one km (0.62 mi) in diameter, with orbits usually between those of Mars and Jupiter; minor planet; planetoid.”

Asteroids – planetoids – were first discovered in 1801, and many more have been discovered since then. Up until 1977, almost all the asteroids discovered were near Jupiter. However, then astronomers began to discover planetoids even farther out and started calling them centaurs and trans-Neptunian objects (TNOs). When a region of space in the outer Solar System filled with celestial bodies was discovered, it was called the Kuiper Belt and the objects in it were called Kuiper Belt Objects (KBOs). The large number of synonyms for planetoids is one reason why keeping these terms straight is so difficult.

Some of the largest planetoids are spherical and look like tiny versions of planets. The smaller ones are irregular in shape though. The objects range in size from around ten meters to hundreds of kilometers in diameter. Objects smaller than ten meters are called meteoroids. Unfortunately, astronomers do not know that much about the materials that make up planetoids. They are believed to be composed of various materials including ice, rock, and different metals.

Most planetoids are in a region called the asteroid belt, which is situated between Mars and Jupiter. There are millions of planetoids in this region. Despite the millions of objects, all of them combined are believed to have a mass of only about 4% of the Moon’s mass. After being discovered, the planetoids are given a temporary designation. If they are officially recognized, they are given a number and maybe a name. The first few planetoids were given symbols just like the planets. All except one of the first fifteen asteroids were given extremely complex symbols. For example, one symbol was a star with a plant growing out of it. However, that soon ended when astronomers realized that there were many more planetoids. Planetoids, and other celestial bodies, are a subject of study by astronomers who hope to learn more about how the universe was formed from these ancient rocks.

Universe Today has articles on minor planets and planetesimals.

Check out articles on asteroids and planetoids beyond Pluto.

Astronomy Cast has an episode on asteroids.

References:
NASA StarChild: The Asteroid Belt
Planet-Like Body Discovered at Fringes of Our Solar System

August 10, 2009December 24, 2015 by Abby Cessna

Mythology of the Planets

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Thousands of years ago, ancient civilizations turned to the heavens, marveling at their wonders. These ancient people worshipped various gods and often linked their gods with planets in the sky, which they considered to be “wandering stars.”

Mercury gets its name from the winged messenger of the gods. He was also the god of thievery, commerce, and travel. Most likely, the planet got its name from the rate at which it spins.

Venus was the Roman goddess of love and beauty, so it is a fitting name for this brightly shining planet. The only objects in our Solar System brighter than Venus are the Sun and the Moon. Ancient civilizations thought that Venus was two different objects – the Morning Star and the Evening Star. Other civilizations have also associated the planet with love. The Babylonians called the planet Ishtar after their goddess of womanhood and love.

Earth is the only planet not named after a Roman god or goddess, but it is associated with the goddess Terra Mater (Gaea to the Greeks). In mythology, she was the first goddess on Earth and the mother of Uranus. The name Earth comes from Old English and Germanic. It is derived from “eor(th)e” and “ertha,” which mean “ground.” Other civilizations all over the world also developed terms for our planet.

Mars is named after the Roman god of war. The planet got its name from the fact that it is the color of blood. Other civilizations also named the planets for its red color.

Jupiter was the Roman king of the gods. Considering that Jupiter is the largest planet in our Solar System, it makes sense that the planet was named after the most important god.

Saturn was named after the Roman god of agriculture and harvest. While the planet may have gotten its name from its golden color, like a field of wheat, it also had to do with its position in the sky. According to mythology, the god Saturn stole the position of king of the gods from his father Uranus. The throne was then stolen by Jupiter.

Uranus was not discovered until the 1800’s, but the astronomers in that time period continued the tradition of naming planets after Roman gods. In mythology, Uranus was the father of Saturn and was at one time the king of the gods.

While Neptune almost ended up being named after one of the astronomers credited with discovering it – Verrier – that was greatly disputed, so it was named after the god of the sea. The name was probably inspired by its blue color.

Pluto is no longer a planet, but it used to be. The dark, cold, former planet was named after the god of the underworld. The first two letters of Pluto are also the initials of the man who predicted its existence, Percival Lowell.

Universe Today has articles on names of the planets and all the planets.

For more information on the planets check out all about the planets and mythology of the planets.

Astronomy Cast has episodes on all the planets including Saturn.

August 10, 2009December 24, 2015 by Nancy Atkinson

NASA May Have to Revamp Science Plans Without RTGs

A radioisotope thermalelectric generator schematic. Source: Internet Encyclopedia of Science

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As if things weren’t tight enough at NASA, now the US House and Senate have decided to cut the funding to restart production of plutonium-238 (Pu-238), the power source for many of NASA’s robotic spacecraft. Under the Atomic Energy Act of 1954, only the US Department of Energy is allowed to possess, use and produce nuclear materials and facilities, and so NASA must rely on the DOE to produce these power sources and the fuel. A report by the National Research Council says “the day of reckoning has arrived” and that NASA has already been forced to limit deep space missions due to the short supply of Pu-238.

Pu-238 is needed for radioisotope thermoelectric generators (RTGs) that supply power for systems and instruments on spacecraft travel too far from the Sun to rely on solar energy or land on surfaces with long “nights.” For example, the Voyager spacecraft utilize RTGs and are still able to communicate and return science data after over 30 years of operation, and now are at the outer edges of our solar system.

Pellet of Pu-238. RTGs are constructed using marshmallow-sized pellets of Pu-238. As it decays, interactions between the alpha particles and the shielding material produce heat that can be converted into electricity.

Pu-238 is expensive to produce, but it gives off low-penetration alpha radiation, which is much easier to shield against than the radiation produced by other isotopes.

Pu-238 does not occur in naturally, and the United States has not produced any since the late 1980s. It purchased Pu-238 for NASA missions from Russia during the 1990s, but those supplies reportedly are now exhausted. The NRC based its estimate of NASA’s Pu-238 requirements on a letter NASA sent to DOE on April 29, 2008 detailing space science and lunar exploration missions planned for the next 20 years.

The cost of restarting production appears to be the major reason for the cut, as estimates are it would cost at least $150 million.

The DOE requested $30 million in FY2010 to restart production, but the House cut that to $10 million when it passed the FY2010 Energy and Water appropriations bill (H.R. 3183) on July 17. The Senate went even further (S. 1436), completely cutting funds for restarting production of Pu-238.

Both the House and Senate Appropriations Committees complained that DOE had not explained how it would use the funds.

But if funds aren’t made available soon, NASA may have to revamp its plans significantly for the New Frontiers missions, lunar rovers, and other deep space missions. There are other isotopes that have been used in the past, such as strontium-90, but Pu-238 has been found to work the best. NASA has also solicited ideas for alternative power sources, as well.

Source: Space Policy Online

August 10, 2009December 24, 2015 by Tammy Plotner

2009 Perseid Meteor Shower – Double Peaks This Year!

2009 Perseid Meteor Shower Preview by John Chumack

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Are you ready for this year’s Perseid Meteor Shower? What will be the best place to watch and when will be the best date to see the most “shooting stars”? Follow along and let’s find out…

The Perseid meteor shower has a wonderful and somewhat grisly history. Often referred to as the “Tears of St. Lawrence” this annual shower coincidentally occurs roughly about the same date as the saint’s death is commemorated on August 10. While scientifically we know the appearance of the shooting stars are the by-products of comet Swift-Tuttle, our somewhat more superstitious ancestors viewed them as the tears of a martyred man who was burned for his beliefs. Who couldn’t appreciate a fellow who had the candor to quip “I am already roasted on one side and, if thou wouldst have me well-cooked, it is time to turn me on the other.” while being burned alive? If nothing else but save for that very quote, I’ll tip a wave to St. Lawrence at the sight of a Perseid!

While the fall rate – the number of meteors seen per hour – of the Perseids has declined in recent years since Swift-Tuttle’s 1992 return, the time to begin your Perseid watch is now. The random rate has already increased sharply and there is no guaranteed that skies will be clear on the predicted peak time – traditionally August 12 at approximately 11:00 GMT. The tears of St. Lawrence are already beginning to fall! Let’s join John Chumack via his Northeast Sky Camera #2 in his backyard Observatory in Dayton, Ohio, USA, for a look. This 5 hour movie was compressed to 10 seconds for web viewing.

Says John, “The brightest one occurred when the radiant was low on the horizon around 1:27 a.m. This fireball was at around -8 magnitude or greater, even with all the strong moonlight, some of the meteors are very bright! This one had a double explosion too!”

Astronomers are now estimating a double peak this year for viewers in the eastern portion of North America on Wednesday morning the 12th of August 2009. One peak should occur around 1:00 a.m. EST and the other peak around 5:30 a.m. EST. However, let’s assume that not all of us can be in that place and be up at that time… So let’s take a more practical look at observing the Perseid Meteor Shower.

Perseid meteor activity begins about midnight no matter where you live, but they can happen earlier, too. Because we are also contending with a Moon which will interfere with fainter meteors, the earlier you can observe, the better. There is no harm in beginning Tuesday night before the Moon rises. The general direction to face will be east around midnight and the activity will move overhead as the night continues. While waiting for midnight or later for activity to pick up to begin isn’t a pleasant prospect, by then we are looking more nearly face-on into the direction of the Earth’s motion as it orbits the Sun, and the radiant – the constellation of the meteor shower origin – is showing well. However, it won’t be long until the Moon also begins to show very well, indeed! Put an obstruction such as the edge of a house or a tree between you and Selene… Even if you just open an umbrella, the very act of shielding some of the light will most certainly help you to see far more meteors than if you don’t. For those of you who prefer not to stay up late? Try getting up early instead!

How many can you expect to see? A very average and cautiously stated fall rate for this year’s Perseids would be about 30 per hour, but remember – this is a collective estimate. It doesn’t mean that you’ll see one every two minutes, but rather you may see four or five in quick succession with a long period of inactivity in between. You can make your observing sessions far more pleasant by planning for inactive times in advance. Bring a radio along, a thermos of your favorite beverage, and a comfortable place to observe from. The further you can get away from city lights, the better your chances will be. If you’re cloud out on the peak date, don’t stop watching – because activity continues on for several days!

Will this 2000 year-old meteor shower be a sparkling success or a total dud? You’ll never know unless you go out and try yourself. One thing we do know is the Perseids are one of the most predictable of all meteor showers and even an hour or so of watching should bring a happy reward! Wishing you clear skies and good luck…

August 9, 2009December 24, 2015 by Abby Cessna

Surface of the Planets

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People have been intrigued for centuries by whether life could exist on other planets. While we now know that it is very unlikely that life as we know it could exist on other planets in our Solar System, many people do not know the surface conditions of these various planets.

Mercury resembles nothing so much as a larger version of the Moon. This planet is so close to the Sun that it is actually difficult to observe. The Hubble Space Telescope cannot look at it because it would permanently damage the lens.

Venus’ atmosphere of thick, toxic clouds hides the planet’s surface from view. Scientists and amateurs alike used to think that the planet was covered with thick forests and flora like tropical rainforests on Earth. When they were finally able to send probes to the planet, they discovered that Venus’ surface was actually more like a vision of hell with a burning landscape that is dotted with volcanoes.

Mars has very diverse terrain. One of the planet’s most famous features is its canals, which early astronomers believed were “man”-made and contained water. These huge canyons were most likely formed by the planet’s crust splitting. Mars is also famous for its red color, which is iron oxide (rust) dust that covers the surface of the entire planet. The surface of Mars is covered with craters, volcanoes, and plains. The largest volcanoes of any planet are on Mars.

Jupiter is a gas giant, so it has no solid surface just a core of liquid metals. Astronomers have created a definition for the surface – the point at which the atmosphere’s pressure is one bar. This region is the lower part of the atmosphere where there are clouds of ammonia ice.

Saturn is also a gas giant so it has no solid surface only varying densities of gas. Like Jupiter, almost all of Saturn is composed of hydrogen with some helium and other elements in trace amounts.

Uranus and Neptune are also gas giants, but they belong to the subcategory of ice giants because of the “ices” in their atmospheres. Uranus’ surface gets its blue color from the methane in the atmosphere. Methane absorbs light that is red or similar to red on the color spectrum leaving only the light near the blue end of the spectrum visible.

Neptune is also blue due to the methane in its atmosphere. Its “surface” has the fastest winds of any planet in the Solar System at up to 2,100 kilometers per hour.

Universe Today has a number of articles including surface of Mars and surface of Mercury.

Check out NASA’s Solar System exploration page, and here’s a link to NASA’s Solar System Simulator.

Astronomy Cast has an episode on each planet including Earth.

August 9, 2009December 24, 2015 by Abby Cessna

Protoplanets

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Protoplanets are small celestial objects that are the size of a moon or a bit bigger. They are small planets, like an even smaller version of a dwarf planet. Astronomers believe that these objects form during the creation of a solar system.

The most popular theory of how a solar system is formed says that a giant cloud of molecular dust collapsed, forming one or more stars. Then a cloud of gas forms around the new star. As a result of gravity and other forces, the dust and other particles in this cloud collide and stick together forming larger masses. While some of these objects break apart on impact, a number of them continue to grow. Once they reach a certain size – around a kilometer – these objects are large enough to attract particles and other small objects with their gravity. They continue to get larger until they form protoplanets. Some protoplanets continue colliding and growing until they form planets while others stay that size.

As the protoplanets grew to become planets, parts of them melted due to radioactivity, gravitational influences, and collisions. Where the objects had melted, the composition of the planets changed. Heavier elements sank, forming the cores of the planets, and lighter objects rose to the surface. This process is called planetary differentiation and explains why planets have heavy cores. Astronomers have discovered that even some asteroids have differentiated, so their cores are heavier than their surfaces.

Protoplanets used to be highly radioactive due to how they were formed. However, over thousands of years, the radioactivity of these objects has greatly decreased because of radioactive decay. Astronomers are still discovering new protoplanets, and most likely, they will discover many more. With better technology, astronomers are now able to find protoplanets in other star systems. Last year, scientists discovered a protoplanet HL Tau b that will probably turn into an actual planet one day. Astronomers say that will not happen for about a million years though because the protoplanet’s star is also very young. In its final form, HL Tau b will look like Jupiter – a gas giant around the same size as that massive planet. It is hard to believe that thousands of years ago our planets were objects about the size of a moon, which were slowly evolving and growing. Astronomers continue to study protoplanets, the same way they study planetesimals, to find out more about how the Solar System was formed.

Universe Today has articles on Earth-sized planets and planetesimals.

You will also want to check out a new protoplanet and forming gas giants.

Astronomy Cast has an episode on how old the universe is.

References:
When is an Asteroid Not an Asteroid?
From Planetesimals to Terrestrial Planets: Habitable Planet Formation in Binary Star Systems