Posted on by Abby Cessna

The Brightest Planet

Venus. From the Pioneer Venus Orbiter

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When you look up into the sky, if you are lucky, you see shining stars on a field of blue-black. Not all of these objects are stars though. Venus, which can be seen with the unaided eye from Earth, is the brightest planet in our Solar System. Venus was given the nickname evening star and morning star because of its bright, consistent presence. It is often called Earth’s twin because it is similar in shape and size to our own planet. The only objects brighter than Venus are the Moon and the Sun. Sirius, the brightest star that can be seen in the sky, is much dimmer than Venus is. People have known that Venus existed for centuries. The planet was named after the Roman goddess of love and this shining planet has long been associated with femininity.

A planet’s brightness is determined by how much light is reflected by the planet. The term albedo refers to the balance between how much light is absorbed and how much light is reflected by the planet. As the brightest planet, Venus has a very high albedo. Seventy percent of the light that hits Venus is reflected back into space. Why does Venus have such a high albedo though? There are droplets of sulfuric acid and acidic crystals in the atmosphere of Venus. The smooth surfaces of these droplets of sulfuric acid and crystals reflect light very well, which is one reason why Venus is so bright. There is a lot more to this planet than its shimmering appearance though.

The same atmosphere that causes Venus to shine like a beacon also prevents us from getting a look at the planet’s surface. Astronomers did not know what the planet looked like until probes checked out the surface in the last few decades. Because the surface of Venus could not be seen, scientists and writers imagined that it was a tropical, lush landscape. That was not the case though. In addition to hiding the surface and reflecting light, Venus’ atmosphere traps heat from the Sun, turning the planet into a raging furnace. Reaching temperatures of over 460°C, Venus is the hottest planet in the Solar System. Its landscape is similar to that of Mercury and the Moon – rocky, barren terrain with no sign of life. Venus has long enchanted viewers with its beauty and shining presence. Try looking for this planet in the sky; you may find yourself captivated by this shining beauty like many before you.

Universe Today has many articles on Venus including the atmosphere of Venus  and how to find Venus in the sky.

For more information check out these articles from NASA on an overview of Venus and from Nine Planets on the brightest planet.

Astronomy Cast has an episode on Venus you should take a look at.

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