Posted on by Abby Cessna

What are The Outer Planets of the Solar System?

The Jovian planets of the Solar System. Credit: bork.hampshire.edu

Astronomers have divided the eight planets of our solar system into the inner planets and the outer planets. The 4 inner planets are the closest to the Sun, and the outer planets are the other four – Jupiter, Saturn, Uranus, and Neptune. The outer planets are also called the Jovian planets or gas giants. Like the inner planets, the outer planets have similar characteristics to one another.

The outer planets are so much larger than the inner planets that they make up 99 percent of the mass of the celestial bodies that orbit the Sun. Although mainly composed of gas, the outer planets also have other ingredients. Somewhere at the center is what scientist refer to as a rocky core, although it is actually composed of liquid heavy metals. While the inner planets have few or no moons, the outer planets have dozens each. The inner and outer planets are separated by the asteroid belt.

Jupiter is the largest planet in our Solar System with a mass more than three hundred times Earth’s mass. Jupiter is not only the largest planet, it also has the most moons – 63 identified so far. Jupiter is one of the brightest objects in the sky and has a very stormy atmosphere. One major storm, the Great Red Spot, is as big as the Earth.

Saturn is hard to miss with its distinctive, large rings. Although all of the outer planets have rings, Saturn’s are the most visible ones. Astronomers did not know that there any other planets with rings until 1977 when Uranus’ rings were discovered. Soon after that, astronomers discovered rings around both Jupiter and Neptune.

Uranus has the smallest mass of the outer planets, although in size it’s a little bigger than Neptune. It is the only planet to rotate on its side. Scientists are unsure why it rotates that way, although there are a couple theories. One suggests it suffered a major collision and another hypothesizes that smaller shifts during the planets’ formation caused its unusual rotation.

Neptune is the final outer planet in the solar system. Neptune’s winds are the fastest of any planets in the Solar System and can reach more than 1,200 miles per hour. While all of the outer planets’ atmospheres contain hydrogen and helium, Neptune and Uranus contain significant amounts of what astronomers call ices. These ices include water, ammonia, and methane. The methane in Neptune and Uranus is what gives the planets their blue color.

Check out these other articles from Universe Today on the outer solar system and the inner solar system.

If you are searching for more information, NASA has many articles, including one on the planets and Science Daily is also a rich resource for information on the outer planets.

Astronomy Cast has a number of episodes on the Jovian planets including this one on Jupiter.

Posted on by Abby Cessna

Life on Other Planets

Mars. Credit: NASA

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For centuries, men have pondered the possibility of life on other planets and tried to prove its existence. Even before the first shuttle or probe was launched, stories of life on other planets and life invading our own planet, were published prolifically. Whether it’s a desire to connect with others or a burning curiosity to know whether we are truly alone, the question of life on other planets fascinates people from every walk of life.

An article on extraterrestrial life would not be complete without discussing Mars. Mars has been the biggest focus of the ongoing search for life on other planets for decades. This is not just a wild assumption or fancy; there are several reasons why scientists consider Mars the best place to look for extraterrestrial life. One reason why many people, including scientists, look to Mars as a possible source of life is because they believe there may be water on the planet. Since the telescope was first invented, astronomers have been able to see the channels in the terrain that look like canals or canyons. Finding water on a planet is vitally important to proving that life exists there because it acts as a solvent in chemical reactions for carbon-based life.

Another reason astronomers consider Mars as a likely location for life is because there is a good possibility that Mars is in the habitable zone. The habitable zone is a theoretical band of space a certain distance from the Sun in which conditions are optimal for the existence of carbon-based life. Unsurprisingly, Earth is in the middle of the habitable zone. Although astronomers do not know how far this zone could extend, some think that Mars could be in it.

Most astronomers are looking for life that is carbon-based and similar to life on Earth. For instance, the habitable zone only applies to favorable conditions for supporting carbon-based life, and it is definitely possible for forms of life that do not need water to exist.

Astronomers do not limit themselves to our Solar System either, suggesting that we should look at different solar systems. Scientists are planning to use interferometry–an investigative technique that implements lasers, which is used in astronomy as well as other fields– to find planets in the habitable zones of other solar systems. Astronomers believe that there are hundreds of solar systems and thousands of planets, which means that statistically the odds are favorable for finding another planet that supports life. While NASA develops better probes, the search for life continues.

There are a number of sites with more information including life on other planets from Groninger Kapteyn Institute astronomy students and NASA predicts non-green plants on other planets from NASA.

Universe Today has a number of articles concerning life on other planets including searching for life on non-Earth like planets and single species ecosystem gives hope for life on other planets.

Take a look at this podcast from Astronomy Cast on the search for water on Mars.

Posted on by Abby Cessna

List of Planets

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

Mercury is the closest planet to the Sun but not the hottest. That distinction goes to Venus. The planet was named after the Roman messenger of the gods because it orbits the Sun so quickly. Mercury is a small, grayish planet that is often said to resemble the Earth’s Moon.

Venus, the second planet from the Sun, is the hottest planet because its atmosphere tends to trap heat. Named after the Roman goddess of beauty, Venus is the brightest planet. In fact, the only celestial body that is brighter is the Moon. Venus is around the same size as Earth with similar gravity, causing it to be referred to as Earth’s twin.

Earth is the third planet from the Sun. It is the only planet where life has been confirmed to exist. Roughly two-thirds of Earth’s surface is covered with oceans, and so far Earth is the only place where liquid water is known to exist.

Mars was named after the Roman god of war because of its red color, which is caused by rust in the rocks on the surface. Since it is the closest planet to Earth, people have long wondered if life could exist on Mars. Although no life has been discovered so far, some people still think that there may be life on Mars.  

Jupiter, a gas giant, is the largest planet in this solar system. It was named after the Roman king of the gods, probably because of its size. Jupiter has 63 moons, one of which, Ganymede, is the solar system’s largest moon. Jupiter is also home to an enormous storm, the Great Red Spot, which has been raging for over two hundred years.

Saturn, the sixth planet from the sun, was named after the Roman god of agriculture and harvest, Saturnus. It is also a gas giant and therefore does not have a solid surface. One distinctive feature of the planet is its rings, which are composed of small pieces of rock and ice.

Uranus, the third largest planet, is also a gas giant. One interesting fact is that its moons were named after characters from works of literature by Shakespeare and Alexander Pope. Uranus orbits very slowly; it takes the planet 84 years to circle the sun.

Neptune is the furthest planet from the Sun. It was named after the Roman god of the sea; this is not surprising because it is bright blue, reminding one of a beautiful ocean. Neptune has four rings, although they are difficult to see. When Pluto was reclassified as a dwarf planet, Neptune became the eighth and last planet in the solar system.

Universe Today has a number of other articles about this including the planets and the solar system for kids.

If you are looking for more information check out this overview of the planets and article on planets in our solar system.

Astronomy Cast also has numerous articles on the planets so take a look at this one for starters: the planet Earth.

Posted on by Abby Cessna

Heliosphere

Heliosphere

The heliosphere is often described as a kind of bubble that contains our solar system. This magnetic sphere, which extends beyond Pluto, is caused by the Sun’s solar winds. These winds spread out from the Sun at around 400 km/s until they hit what is known as interstellar space, which is also called local interstellar medium (LISM) or interstellar gas. Interstellar space is the space in galaxies that is unoccupied by either stars or planets.

When the solar winds hit local interstellar medium, a kind of bubble forms that prevents certain material from getting in. Thus, the heliosphere acts as a kind of shield that protects our solar system from cosmic rays, which are dangerous interstellar particles. The interaction between interstellar gas and solar winds depends on the pressure of the solar winds and properties of interstellar space, such as pressure, density, and qualities of the magnetic field. Astronomers believe that other solar systems have their own heliospheres caused by different stars.

There are several different parts of the heliosphere. The heliopause is the boundary between the heliosphere and the LISM. When solar winds approach this blurred region, they slow abruptly causing a shock wave to form known as the solar wind termination shock. The action is similar to slamming down on the brakes in a car, causing people and objects in the car to fly forward. This shock wave actually causes the particles to accelerate, aiding in the formation of the heliosphere. After it has slowed down, the winds of interstellar space act on the solar winds causing them to curve forming what has been described as a comet-like tail to the Sun. This tail, which has been examined by NASA’s probes Voyager 1 and Voyager2, is called the heliosheath. The termination shock is from around 75 to 90 astronomical units (AU) from our Sun, and at its closest point, the heliosheath is approximately 80 to 100 AU from the Sun.

Astronomers monitoring the Sun have noticed that solar winds have decreased to all-time lows. This affects the heliosphere, which in turn can affect Earth and other planets in the solar system. With solar winds lessening, astronomers fear that the strength of the heliosphere will also decrease, leaving our solar system vulnerable to dangerous cosmic rays. Because solar winds are cyclical, some scientists believe that instead of permanently decreasing, the solar winds are merely experiencing a lengthy low period.

We have written many articles about the heliosphere for Universe Today. Here’s an article about how NASA’s STEREO spacecraft has mapped the heliosphere, and another article about how the heliosphere has been shrinking recently.

Here are two other articles from NASA on heliophysics and the heliosphere.

We’ve recorded a special episode of Astronomy Cast about this topic, Episode 65: The End of Our Tour Through the Solar System.

References:
NASA Solar Science: The Solar Wind
NASA Science: The Heliosphere

Posted on by Nicholos Wethington

How Did the Milky Way Form?

Computer simulation showing the development and evolution of the disk of a galaxy such as the Milky Way. Credit: Rok Roškar

The Milky Way has been around a long, long time. The age of our galaxy is approximately 13.6 billion years, give or take 800 million years. But how did the galaxy get here? What did baby photos of the Milky Way look like?

First off, there weren’t always stars in the Universe, and the Milky Way hasn’t been around forever. After the big bang happened, and the Universe cooled for a bit, all there was was gas uniformly spread throughout. Small irregularities allowed the gas to coalesce into larger and larger enough clumps, heating up and eventually starting the  nuclear fusion that powers stars. The stars started to gravitationally attract each other into larger groups. The oldest of these groups of stars are called globular clusters, and some of these clusters in the Milky Way galaxy date back to the very, very early Universe.

Not all of the stars in the Milky Way date back to the primordial Universe, though. The Milky Way produces more than 7 stars per year, but it acquired much of its mass in another fashion. The Milky Way is often referred to as a “cannibal” galaxy, because during formation it swallowed up smaller galaxies. Astronomers think that this is how many larger galaxies have come to be the size they are today.

In fact, the Milky Way is currently gobbling up another galaxy, (and a stellar cluster) at this very moment. Called the Canis Major Dwarf Galaxy, the remnant stars are 45,000 light years from the galactic center, and a mere 25,000 light years from our Sun.

Older stars in the Milky Way are to be found distributed spherically in the galactic halo, meaning that it’s likely the galaxy had a spherical shape to start out. Younger stars in the galaxy are located in the disk, evidence that as it started to get heavier, the mutual orbit of material started the galaxy spinning, which resulted in the spiral one sees in representations of the Milky Way.

To get you started on how the formation of our galaxy looked, here’s an animated simulation of what a galaxy much like the Milky Way looks like as it goes from the gas cloud at the beginning of the Universe to a beautiful barred spiral, a few billion years condensed into a couple of short minutes. And to get a handle on the formation of a spiral arms in a galaxy, check out this spiral galaxy simulator.

For more on the formation of the Milky Way and other galaxies, listen to Astronomy Cast, Episode 25: The Story of Galaxy Evolution, and Episode 99: The Milky Way.

References:
http://www.nasa.gov/centers/goddard/news/topstory/2006/milkyway_seven.html
http://www.eso.org/public/news/eso0425/

Posted on by Fraser Cain

Triangulum Galaxy

The Triangulum Galaxy. Image credit: NASA/JPL-Caltech/University of Arizona

There are three large spiral galaxies in our Local Group of galaxies. Our Milky Way is one, of course, and we’re joined by the Andromeda Galaxy. The third large spiral galaxy is the Triangulum Galaxy (Messier 33 or NGC 598).

The Triangulum Galaxy, also known as the Pinwheel Galaxy, is located about 3 million light-years away in the constellation Triangulum. In very bright skies you can see this galaxy with the unaided eye; although, there were no historical records of it before the invention of the telescope. It was probably first discovered by Giovanni Battista Hodierna in the 17th century, but it was first identified by Charles Messier in 1764.

Astronomers have estimated that Triangulum measures about 50,000 light-years across. That’s half the diameter of the Milky Way. It has an estimated mass between 10 and 40 billion solar masses.

While most galaxies are being carried away from the Milky Way by the expansion of the Universe, Triangulum is actually drifing towards us. Well, more specifically, it’s drifting towards the Andromeda Galaxy, and Andromeda is moving towards us. It’s approaching our galaxy at a speed of 24 km/second.

We have written many articles about galaxies for Universe Today. Here’s an article about the Triangulum galaxy.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

Posted on by Fraser Cain

Starburst Galaxy

All galaxies are going through some rate of star formation. New stars are being formed every year in the Milky Way. But some galaxies, classified as “starburst galaxies” are undergoing furious rates of star formation. Some are so active, they’re forming thousands of new stars every year.

So why do starburst galaxies form, when our own Milky Way has a relatively slow rate of new star formation? The most popular theory is that a galaxy is put into a starburst phase when it makes a close encounter with another galaxy. The gravitational interaction sends shockwaves through giant clouds of gas, causing them to collapse and form star forming regions. These create some of the most massive stars in the Universe; monster blue stars with more than 100 solar masses.

These massive stars live short lives and detonate as supernovae, blasting out more shockwaves into the galaxy. This creates a chain reaction that cascades through the galaxy. Within a few million years, the galaxy is forming stars at tens or even hundreds of times the rate of formation in a normal galaxy. And then when the gas is used up, within about 10 million years, the period of star formation ends.

Starburst galaxies are rare today, but astronomers have found that they were very common in the early Universe, when galaxies were closer and interacted more.

Thousands of starburst galaxies have been discovered across the Universe. One of the best known starburst galaxies is M82, located about 12 million light-years away in the constellation Ursa Major. The Hubble Space Telescope imaged the galaxy in 2005, and found 197 massive clusters of star formation going off simultaneously in the starburst core. The changes in M82 are being driven by its gravitationally interaction with nearby M81 galaxy.

We have written many articles about galaxies for Universe Today. Here’s an article about the starburst galaxy M82.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

Posted on by Fraser Cain

Galaxy Core

NGC 4314. Image credit: Hubble

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A typical spiral galaxy is shaped like a flat spinning disk – think of a record. It has a bulging galactic core surrounded by a flat rotating disk of stars. For example, our own Milky Way measures about 100,000 light-years across. Our Sun is thought to be about 25,000 light-years away from the galaxy core.

Studying the galaxy core is very difficult for astronomers. That’s because the regions surrounding the central core are shrouded in thick gas and dust that blocks visible light. In order to study the center of the galaxy, astronomers used to have to look at other galaxies that were similar in structure to the Milky Way. But in the last few decades, astronomers have been finally able to study the galaxy core in other wavelengths, like infrared and x-rays, which can pass through gas and dust.

And what they found surprised them.

Researchers discovered that the stars at the galactic core are orbiting an object with an enormous amount of mass. That object turned out to be a supermassive black hole, with 4.1 million times the mass of the Sun. Since that discovery, astronomers have located supermassive black holes in the galactic cores of many galaxies, and theorized that they’re in all galaxies.

Active galaxies, known as quasars (as well as other names), occur when the supermassive black hole is actively feeding on infalling material. This material heats up to millions of degrees and blazes with more radiation than all of the stars in the galaxy. And then when the supermassive black hole at the galaxy core runs out of fuel, it goes quiet again.

Within a parsec of the galactic core, there are thousands of stars. Most of these are old main sequence stars, there are many massive stars too. In fact, more than 100 of the brightest, hottest types of stars have been discovered around the galaxy core. Astronomers used to think that massive tidal forces from the supermassive black hole at the center of the galaxy would prevent their formation, but there they are.

We have written many articles about galaxies for Universe Today. Here’s an article about how a collision between galaxies creates a dark matter core.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

Sources: SEDS, UCLA Galactic Center Group, NASA

Posted on by Fraser Cain

How Do Galaxies Get Named?

Traveling to distant locations, like Andromeda, could have interesting consequences. Credit: NASA

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Andromeda, M31, Triangulum, NGC 2403 the Whirlpool… have you ever wondered how galaxies get their names?

Galaxies usually have several names. That’s because there are several catalogs that maintain the names. For example, there’s the Messier catalog of objects. This was a list of 110 fuzzy objects that Charles Messier maintained that could be confused with comets.

There’s another list that starts with NGC. For example, NGC 7331, a galaxy that has been called a twin of the Milky Way because of its similarity. The NGC catalog is short for New General Catalogue, and it’s a list of 7,840 interesting objects in the night sky.

So let’s take a look at an object like Andromeda. It’s named the Andromeda Galaxy because it’s located in the constellation of Andromeda. Many galaxies are named after the constellation they’re located in. Andromeda also has the designation M31, or Messier 31, since it’s the 31st object on Messier’s list of things that look like comets but aren’t comets. Andromeda is also designated as NGC 224 in the New General Catalogue.

There are also specialty catalogs that describe objects in other wavelengths, like x-ray and even gamma rays. And many galaxies will have “names” in those directories as well.

So a galaxy can have many names. It just depends on which name you want to use.

If you discover a galaxy, do you get to name it? Unfortunately, no. The official names for astronomical objects are maintained by the International Astronomical Union. Just how you can’t officially name a star after yourself, you can’t name a galaxy either.

We have written many articles about galaxies for Universe Today. Here’s a more information about naming a star.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

Posted on by Fraser Cain

Galactic Alignment

Artist impression of the Milky Way.

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Just like the Earth orbits the Sun, the Sun itself is part of the Milky Way galaxy. It takes about 220 million years for the Sun to complete a single journey around the Milky Way. But the Sun also bobs up and down as it travels in orbit around the center of the galaxy. The oscillation takes a total of 64 million years to complete. And there’s a moment when the Sun passes directly through the galactic disk and there’s a perfect galactic alignment between the Sun and the center of the galaxy.

When’s that galactic alignment going to happen? It’s almost impossible to know exactly. The Milky Way is 100,000 light-years across, but only 1,000 light-years thick. So during the course of that 64 million year cycle, the Sun rises above the galactic plane 500 light-years, passes down through the galactic plane, until it’s 500 light-years below and then comes back up again.

There has to be a moment when everything’s in perfect alignment, but the timescales are so long that astronomers couldn’t calculate it. Of course, this alignment with the center of the galaxy doesn’t have an effect on the Earth or the Solar System, it’s just like crossing an imaginary line in space, like traveling from Canada to the United States in your car.

There’s another type of galactic alignment. This is where the Earth, Sun and the center of the galaxy are in perfect alignment from our perspective. This actually happens every year during the winter solstice, on December 21st. Because of a wobble in the Earth’s orbit, the positions of the constellations slowly shift from year to year. The most perfect galactic alignment between the Earth, Sun and the center of the Milky Way happened back in 1998, but now we’re slowly shifting away from that alignment. In the coming decades, the perfect alignment will shift to another day.

Again, the alignment of these objects is purely a coincidence.

We have written many articles about galaxies for Universe Today. And we’ve written many articles about the 2012 myth. Here’s even more info on the supposed 2012 planet alignment.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

Sources:
NASA: Solar and Galactic Motion
NASA: Size of the Milky Way