Category: Guide to Space

The answer to ‘how many stars are in the Solar System’ is pretty straightforward, or is it? There is only one star that has ever been observed in our solar system, but some scientists have theorized that there is a second star out beyond the Oort Cloud that only comes close enough to be observed every 32 million years. That length of time between observational periods would explain why a human has never proven its existence.

As scientists explore our galaxy, it seems that ours is a somewhat unique solar system in many ways. Most do not have as many orbiting bodies and very few are single star systems. A majority have at least two stars(binary). A system could theoretically have an unlimited amount of stars. Systems with up to six stars have been observed.

Now, a little more about the theoretical companion star within our our solar system. The other star would have to be a red or brown dwarf and has been given the name Nemesis. In 1984, a pair of scientists, Raup & Sepkoski, claimed that mass extinctions, like the one that killed the dinosaurs, occur every 32 million years. The most widely held theory for the demise of dinosaurs is an asteroid or cometary impact, so the length of time would suggest that some mechanism is needed to disturb the comets in the Oort Cloud every 32 million years. Richard Muller, among others, hypothesized that a companion that orbits the Sun in that period could be the explanation. To prove their theory, Muller and a few colleagues embarked on a search for Nemesis. The team ran into this hurdle immediately; ‘Every star of the correct spectral type and magnitude must be scrutinized. … We are currently scrutinizing 3098 fields, which we believe contain all possible red dwarf candidates in the northern hemisphere.’ With nearly 3,100 possibilities in the Northern Hemisphere alone and a limited number of clear observational days, it is easy to see how daunting this task is.

Just to be clear, there is no evidence of any kind that makes scholars think that there is a companion star in our Solar System. It is a theory based solely on a need to explain the periodic mass extinctions that our planet has experienced. So, the only answer to ‘how many stars are in the Solar System’ that can be proven through observation is one…the Sun.

Here’s an article about a possible Planet X, and how it could disrupt the Solar System (and how it probably doesn’t exist), and an article about how multiple star systems come together.

Here’s Wikipedia’s entry on Nemesis, and another answer to the question from NASA.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

References:
NASA Ask an Astrophysicist
Nineplanets.org
Wikipedia

How old is the Solar System? That is a question that cuts to the heart of it all. By studying several things, mostly meteorites, and using radioactive dating techniques, specifically looking at daughter isotopes, scientists have determined that the Solar System is 4.6 billion years old. Well, give or take a few million years. That age can be extended to most of the objects and material in the Solar System.

The United States Geological Survey(USGS) website has a lot of indepth material about how the age of the Solar System was determined. The basics of it are that all material radioactively decays into a stable isotope. Some elements decay within nanoseconds while others have projected half-lives of over 100 billion years. The USGS based their study on minerals that naturally occur in rocks and have half-lives of 700 million to 100 billion years. These dating techniques, known as radiometric dating, are firmly grounded in physics and are used to measure the last time that the rock being dated was either melted or disturbed sufficiently to re-homogenize its radioactive elements. This techniques returned an approximate age for meteorites of 4.6 billion years and Earth bound rocks around 4.3 billion years. The USGS admits that they were unable to find any rock that had not been altered by the Earths tectonic plates, so the age of the Earth could be refined in the future.

When the gasses of the early solar nebula began to cool, the first materials to condense into solid particles were rich in calcium and aluminum. Eventually solid particles of different elements clumped together to form the common building blocks of comets, asteroids, and planets. Astronomers have long thought that some of the Solar System’s oldest asteroids should be more enriched in calcium and aluminum, but, none had been identified until recently. The the Allende meteorite of 1969 was the first to show inclusions that were extremely rich in calcium and aluminum. It took 40 years for the spectra of the inclusions to be discovered and then extrapolates to very old asteroids still in orbit around the Sun. Astronomer Jessica Sunshine and colleagues made this discovery with the support of NASA and the National Science Foundation

Additionally, the Universe is thought to have been created about 13.7 billion years ago. Measuring two long-lived radioactive elements in meteorites, uranium-238 and thorium-232, has placed the age of the Milky Way at in the same time frame. From these measurements, it appears that large scale structures like galaxies formed relatively quickly after the Big Bang.

Here’s an article from Universe Today that gives more information about the radioactive dating process of studying meteorites, and another article about how the solar nebula probably lasted about 2 million years.

Here’s a great article from the USGS that explains how the dating process works, and a great series from UC San Diego.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

References:
U.S. Geological Survey
NASA: How Old is the Universe?
NASA Earth Guide: Age of the Solar System

Where did the Solar System come from? How did we go from space to a star with planets orbiting around it? Before we can look at the formation of the Solar System, we have to see what this region looked like.

Throughout the Milky Way, there are clouds of cold gas and dust, just sitting there, doing nothing. At some point in the distant past, this cloud was disturbed; either through the collision of another galaxy, or the explosion of a massive star.

The explosion would have sent waves through space that squeezed the gas and dust together. The clumping material was able to attract more material with its gravity, and started to collect into the solar nebula. The mutual movement of all the atoms in the cloud gave the solar nebula a direction to spin.

The Sun formed out of the largest collection of mass at the center of the solar nebula. Because it was spinning quickly, the rest of the nebula collected into a flattened disk around the newborn Sun – astronomers call this an accretion disk. Within the accretion disk, additional clumps gathered together; these would eventually form the planets.

The planets started out as tiny specks of dust that clumped together. As they continued to gather together, they became pebbles, rocks, boulders and eventually planetoids. These planetoids violently collided together to become the planets we know today.

By studying the decay of radioactive elements in meteorites, astronomers have been able to determine that the Solar System formed about 4.6 billion years ago.

When astronomers look out into the Universe, they see other Solar Systems forming at different stages. Some are large clouds of cold dust, others are starting to collapse. Others have accretion disks, and some might even have planets clearing out paths in the dust of the disk. We can’t see the formation of our own Solar System, but we can see it happening everywhere we look, so we assume our Solar System formed in the same way.

Here’s an article from Universe Today about planetary formation, and another about how the gas giants might have formed quickly.

Here’s an article from Wikipedia about the formation of the Solar System, and a link to NASA’s Solar System Simulator.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

The hottest place in the Solar System is the Sun, obviously. And the hottest part of the Sun is its core. The surface of the Sun is a mere 5,800 Kelvin, while the center of the Sun is around 15 million Kelvin. That’s hot.

Although the surface of the Sun is relatively cool, the corona can get much hotter. This is the region just above the surface of the Sun, where flares and coronal mass ejections come from. Temperatures in this region can get upwards of 2 million Kelvin.

Okay, outside of the Sun, the hottest place in the Solar System is the core of Jupiter. Once again, while the cloud tops of Jupiter are more than 100 degrees below zero, the core of the planet could be up to 30,000 Kelvin. This high temperature comes from the intense pressure that comes from the entire mass of the planet bearing down on the core and compressing it.

What’s the hottest surface in the Solar System? That would have to be the surface of Venus, which is always an average temperature of 461 °C. In fact, Venus is even hotter than the planet Mercury when it’s in the Sun. Noontime temperatures on the surface of Mercury only get up to 426 °C.

Here’s an article from Universe Today about the hottest place on Earth, and more about the Sun.

Here’s more information about the Sun, and just how hot Venus is.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Pluto used to be the smallest planet, but it’s not a planet any more. That makes Mercury the smallest planet in the Solar System. The second smallest planet in the Solar System is Mars, measuring 6792 km across.

With all the focus and exploration of Mars, you’d think it’s a really big planet, but actually it’s pretty small. Mars has only 53% the diameter of Earth, and about 1/10th the mass. It only has 15% the volume of Earth. In other words, you could fit 6 planets the size of Mars into Earth, and still have room to spare.

Since Mars is relatively small compared to Earth, and it has a fraction of our planet’s mass, the force of gravity on Mars is very low. If you could walk on the surface of Mars, you would experience only 38% the force of gravity you feel pulling you down on Earth. In other words, if you weighed 100 kg on Earth, you’d feel like you only weighed 38 kg on Mars.

Mars is so small that its core cooled down billions of years ago, and so it doesn’t have a magnetic field any more. Earth’s magnetic field helps push away the Sun’s solar wind, which is trying to carry away our atmosphere. When you match this with its very low amount of gravity, and Mars has lost almost all its atmosphere. The pressure of the atmosphere on Mars is 1% what we experience on Earth.

Here’s an article that explains why Pluto isn’t a planet any more. And here’s the smallest planet in the Solar System.

Want more information? Here’s another article about the biggest planet in the Solar System, and the smallest planet in the Solar System.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

The biggest planet in the Solar System is Jupiter. But the title for the second biggest planet in our Solar System goes to Saturn.

Just for a comparison, Jupiter measures 142,984 km across its equator. Saturn for comparison is only 120,536. So Jupiter is only 1.18 times as big of Saturn. Saturn is big, but it has a much lower mass. Once again, Jupiter is 3.34 times as massive as Saturn.

Since Saturn is so big, but has so little mass, it has a very low density. In fact, if you had a pool big enough, Saturn would float. The density of Saturn is less than water. And this means that you wouldn’t experience a lot of gravity if you tried to walk on the “surface of Saturn”. If you were standing on the surface of Saturn (I know, that’s impossible), you would experience only 91% the force of Earth’s gravity.

If you wanted to compare Saturn to Earth, it’s 9.4 times as big as the Earth, and 95 times as massive. It it was just a hollow shell, you could pack 763 Earths inside Saturn, with a little room to spare.

Wanna see Jupiter? Here are amazing telescopes from Amazon.com which you can buy at reasonable prices:

Here’s the article about how Jupiter is the biggest planet. And here’s another article about just how big planets can get.

If you’d like more info on Saturn, check out Hubblesite’s News Releases about Saturn, and another page on Saturn from NASA’s Solar System Exploration Guide.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Saturn is easily the most beautiful planet in the Solar System. To celebrate this natural wonder, lets look at some beautiful pics of Saturn.

But if you want to see Saturn by yourself, you can check out these cool telescopes that will help you see the beauty of planet Saturn.

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Let’s start with one of the most beautiful photos of Saturn ever taken. This image of Saturn was taken by NASA’s Cassini spacecraft when it was behind Saturn. In other words, the Sun is completely obscured by Saturn, and illuminating it from behind. The tiny speck in the upper, left-hand side of Saturn’s rings is our own home planet Earth.

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This is a picture of Saturn taken by the ground-based Keck telescope, located atop Mauna Kea in Hawaii. It’s one of the most powerful telescopes on Earth. The Saturn photo was taken in infrared, and shows the strange hot spot located at Saturn’s south pole.

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It’s not the best picture, but you’re looking at one of the first ever images of Saturn captured up close by NASA’s Pioneer 11. During its mission, Pioneer 11 passed just 20,000 km above the cloud tops of Saturn, and captured the first close-up images of Saturn.

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This is an example of a beautiful picture of Saturn taken by NASA’s Voyager 1 spacecraft in 1980. As you can see, the quality has improved significantly over the image captured by Pioneer 11. Both Voyager 1 and Voyager 2 made quick flybys of Saturn and then sped off into space. When Voyager 1 completed its flyby of Saturn, it sped off into the depths of space, while Voyager 2 went on to visit Uranus and Neptune as part of its Grand Tour of the Solar System.

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Here’s another image of Saturn captured by NASA’s Cassini spacecraft. This photograph was taken in May 2004, when Cassini had almost arrived at Saturn. The spacecraft spent another 4 years orbiting Saturn as part of its primary mission, and at the time of this writing, it’s still going strong.

We have written many articles about Saturn for Universe Today. Here are some facts about Saturn.

Saturn couldn’t be more different from Earth; it’s mostly made of hydrogen and helium and has nearly 100 times more mass. And those rings…

You can also check out these cool telescopes that will help you see the beauty of planet Saturn.

But Saturn’s axis is tilted, just like Earth. While Earth’s axis is tilted at an angle of 23.4°, Saturn’s tilt is 26.7°. That’s pretty close.

And just like Earth, Saturn’s axial tilt gives the planet seasons. In fact, we can see Saturn’s tilt by the position of the rings. When Saturn’s northern hemisphere is experiencing summer, we can see the rings at their widest point. And then, as Saturn works its way through its 30-year orbit around the Sun, the angle to the rings decreases until they’re almost invisible – just a line through the planet.

The changing seasons on Saturn also affect the planet’s weather patterns. NASA’s Voyager spacecraft originally clocked wind speeds near Saturn’s equator at nearly 1,500 km/h. But when Cassini showed up 15 years later, they’d slowed down to only 1,100 km/h.

Here’s an article from Universe Today about long term changes on Saturn, and three views of Saturn over a long period of time.

Here’s a nice photograph from Astronomy Picture of the Day of Saturn, and another captured by Cassini, showing the planet’s southern hemisphere being illuminated.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

Saturn is easily visible with the unaided eye, so it’s hard to say when the planet was first discovered. The Romans named the planet after Saturnus, the god of the harvest – it’s the same as the Greek god Kronos.

You can also check out these cool telescopes that will help you see the beauty of planet Saturn.

Nobody realized the planet had rings until Galileo first turned his rudimentary telescope on the planet in 1610. Of course, Galileo didn’t realize what he was looking at, and thought the rings were large moons on either side of the planet.

It wasn’t until Christian Huygens used a better telescope to see that they were actually rings. Huygens was also the first to discover Saturn’s largest moon Titan.

Jean-Domanique Cassini uncovered the gap in Saturn’s rings, later named the Cassini Division, and he was the first to see 4 more of Saturn’s moons: Iapetus, Rhea, Tethys, and Dione.

There weren’t many more major discoveries about Saturn until the spacecraft flybys in the 70s and 80s. NASA’s Pioneer 11 was the first spacecraft to visit Saturn, getting within 20,000 km of the planet’s cloud layers. It was followed by Voyager 1 in 1980, and Voyager 2 in August 1981.

It wasn’t until July 2004 that NASA’s Cassini spacecraft arrived at Saturn, and began the most detailed exploration of the system. Cassini has performed multiple flybys of many of Saturn’s moons, and sent back thousands of images of the planet and its moons. It has discovered 4 new moons, a new ring, and saw liquid hydrocarbon seas on Titan.

This article was published when Cassini had finished half its primary mission, and discusses many of the discoveries made so far, and another article when its primary mission was complete.

This article has a timeline of Saturn history, and more history from NASA.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

Like the rest of the planets, Saturn formed from the solar nebula about 4.6 billion years ago. This solar nebula started out as a vast cloud of cold gas and dust which was disturbed somehow – perhaps by colliding with another cloud, or the shock wave from a supernova.

You can also check out these cool telescopes that will help you see the beauty of planet Saturn.

The cloud compressed down, forming a protostar in the center, surround by a flattened disk of material. The inner part of this disk contained more heavier elements, and formed the terrestrial planets, while the outer region was cold enough for ices to remain intact.

These ices came together, forming larger and larger planetesimals. And these planetesimals collided together, merging into planets. At some point in Saturn’s early history, a moon roughly 300 km across might have been torn apart to create the rings that circle the planet today.

Since Saturn was smaller than Jupiter, it cooled down more quickly. Astronomers think that once its outer atmosphere reached about 15 K, helium condensed into droplets that fell towards its core. The friction from these droplets heated up the planet to the point that it gives off roughly 2.3 times the amount of energy it receives from the Sun.

Here’s an article from Universe Today about how the gas giant planets might have consumed their moons early on, and another article about how gas giant planets might form around other stars.

Here’s an article about the formation of Saturn’s rings, and an article about what Saturn’s moons might tell scientists about planet formation.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.