You are probably somewhat familiar with our Solar System. At least you most likely know that there are eight planets in it, including the Earth, the Sun, moons, and a number of other objects like Pluto and asteroids. However, there is a lot more beyond the Solar System of which you may not be aware.
Our galaxy is the Milky Way Galaxy, but there are also other ones including the Andromeda Galaxy. Each galaxy is a system composed of different star systems, stellar remains, and interstellar medium. Although astronomers are not certain, they estimate that there are one hundred billion galaxies in the universe. Between the galaxies is intergalactic space, which has a thin gas in it. It is no wonder that the universe is considered to be infinite when you consider how large our Solar System is and that this Solar System is just one of many in our galaxy. This really puts into perspective exactly how small the Earth, and we, are in the big picture.
The Milky Way galaxy has many stars in it. Beyond our Solar System is interstellar medium and more stars along with their star systems. Interstellar medium is the vacuum of space between different star systems, although the space is not actually an empty vacuum. It has dust and other particles in it in addition to cosmic rays and magnetic fields.
Astronomers have already discovered many extrasolar planets – planets beyond our Solar System that orbit stars other than our own. The first extrasolar planet’s existence was not confirmed until 1995, because technology was not advanced enough to detect these distant planets. Since then, 357 extrasolar planets, also known as exoplanets, have been discovered. It is estimated that only a small percentage of stars have planets, and most of these stars are similar to our own Sun.
At first, the only extrasolar planets that astronomers could find were gas giants similar to Jupiter. However, in recent years, they have found planets similar to Neptune. This strengthened the hope of astronomers who were looking for Earth-like planets. In fact, some astronomers believe that they have found Earth-like planets in the past few years. Astronomers are still trying to find a way to determine whether there is life on these planets.
While there is still much more to learn in our own Solar System – the Moon is the only place besides Earth humans have actually set foot – there are also many things to discover beyond our Solar System. Not just other stars, but also other galaxies if we can reach them.
This is a picture of the sequence of the eight planets and three of the dwarf planets. Image courtesy of IAU.
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Since 2006, due to a controversial decision by the International Astronomical Union (IAU) that demoted Pluto to a dwarf planet, we have had eight planets.
Mercury is a small planet, which can reach extreme temperatures. Since the planet is the closest one to the Sun, it can reach temperatures of 450°C. However, because the planet has almost no atmosphere due to very little gravity, the surface also drops to low temperatures of -170°C.
Venus is farther from the Sun than Mercury is, but it stays hotter due to its thick, toxic atmosphere. The main compound in Venus’ atmosphere is carbon dioxide, which creates the strongest greenhouse effect of any planet.
Undoubtedly, you already know a lot about Earth, but you may not know that our planet is the only one in our Solar System that has plate tectonics. The Earth’s outer crust is broken up into various sections called plates, which can move. These plates also take carbon out of the atmosphere and recycle it. This prevents a greenhouse effect like Venus’ and keeps the Earth from getting too hot. This is just one feature of our unique planet that helps support life.
Mars is the only inner planet, except for Earth, that has moons. Its two moons are called Phobos and Deimos. In Greek mythology, Phobos is a son of Ares (the equivalent of Mars) and Deimos is a figure that represents dread.
Jupiter is the model for gas giants as well as being the largest planet in our Solar System. It was named after the Roman king of the gods who was also the god of the sky and of thunder, which is fitting considering its size. Jupiter has 63 moons – more than any other planet in our Solar System.
Saturn is the only planet in our Solar System that has an average density less than water. Its core is actually denser than water, but its gas atmosphere balances the heavier core. You may consider floating Saturn in water, but even if you found a planet with a large enough body of water, the gases that make up Saturn’s atmosphere would simply merge with the other planet’s atmosphere.
Uranus and Neptune both belong to a class of gas giants called ice giants because they contain higher amounts of “ices” in their atmosphere. These ices include water, ammonia, and methane.
Neptune is an ice giant with the fastest winds of any planets. These winds can reach speeds of 2,100 kilometers per hour. The planet was discovered with mathematical predictions when astronomers noticed discrepancies in Uranus’ orbit.
A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions. Credit: NASA/ESA/A. Felid (STScI)).
It’s no secret that the universe is an extremely vast place. That which we can observe (aka. “the known Universe”) is estimated to span roughly 93 billion light years. That’s a pretty impressive number, especially when you consider its only what we’ve observed so far. And given the sheer volume of that space, one would expect that the amount of matter contained within would be similarly impressive.
But interestingly enough, it is when you look at that matter on the smallest of scales that the numbers become the most mind-boggling. For example, it is believed that between 120 to 300 sextillion (that’s 1.2 x 10²³ to 3.0 x 10²³) stars exist within our observable universe. But looking closer, at the atomic scale, the numbers get even more inconceivable.
At this level, it is estimated that the there are between 1078 to 1082 atoms in the known, observable universe. In layman’s terms, that works out to between ten quadrillion vigintillion and one-hundred thousand quadrillion vigintillion atoms.
And yet, those numbers don’t accurately reflect how much matter the universe may truly house. As stated already, this estimate accounts only for the observable universe which reaches 46 billion light years in any direction, and is based on where the expansion of space has taken the most distant objects observed.
The history of the universe starting the with the Big Bang. Image credit: grandunificationtheory.com
While a German supercomputer recently ran a simulation and estimated that around 500 billion galaxies exist within range of observation, a more conservative estimate places the number at around 300 billion. Since the number of stars in a galaxy can run up to 400 billion, then the total number of stars may very well be around 1.2×1023 – or just over 100 sextillion.
On average, each star can weigh about 1035 grams. Thus, the total mass would be about 1058 grams (that’s 1.0 x 1052 metric tons). Since each gram of matter is known to have about 1024 protons, or about the same number of hydrogen atoms (since one hydrogen atom has only one proton), then the total number of hydrogen atoms would be roughly 1086 – aka. one-hundred thousand quadrillion vigintillion.
Within this observable universe, this matter is spread homogeneously throughout space, at least when averaged over distances longer than 300 million light-years. On smaller scales, however, matter is observed to form into the clumps of hierarchically-organized luminous matter that we are all familiar with.
In short, most atoms are condensed into stars, most stars are condensed into galaxies, most galaxies into clusters, most clusters into superclusters and, finally, into the largest-scale structures like the Great Wall of galaxies (aka. the Sloan Great Wall). On a smaller scale, these clumps are permeated by clouds of dust particles, gas clouds, asteroids, and other small clumps of stellar matter.
Representation of the timeline of the universe over 13.7 billion years, and the expansion in the universe that followed. Credit: NASA/WMAP Science Team.
The observable matter of the Universe is also spread isotropically; meaning that no direction of observation seems different from any other and each region of the sky has roughly the same content. The Universe is also bathed in a wave of highly isotropic microwave radiation that corresponds to a thermal equilibrium of roughly 2.725 kelvin (just above Absolute Zero).
The hypothesis that the large-scale universe is homogeneous and isotropic is known as the cosmological principle. This states that physical laws act uniformly throughout the universe and should, therefore, produce no observable irregularities in the large scale structure. This theory has been backed up by astronomical observations which have helped to chart the evolution of the structure of the universe since it was initially laid down by the Big Bang.
The current consensus amongst scientists is that the vast majority of matter was created in this event, and that the expansion of the Universe since has not added new matter to the equation. Rather, it is believed that what has been taking place for the past 13.7 billion years has simply been an expansion or dispersion of the masses that were initially created. That is, no amount of matter that wasn’t there in the beginning has been added during this expansion.
However, Einstein’s equivalence of mass and energy presents a slight complication to this theory. This is a consequence arising out of Special Relativity, in which the addition of energy to an object increases its mass incrementally. Between all the fusions and fissions, atoms are regularly converted from particles to energies and back again.
Atom density is greater at left (the beginning of the experiment) than 80 milliseconds after the simulated Big Bang. Credit: Chen-Lung Hung
Nevertheless, observed on a large-scale, the overall matter density of the universe remains the same over time. The present density of the observable universe is estimated to be very low – roughly 9.9 × 10-30 grams per cubic centimeter. This mass-energy appears to consist of 68.3% dark energy, 26.8% dark matter and just 4.9% ordinary (luminous) matter. Thus the density of atoms is on the order of a single hydrogen atom for every four cubic meters of volume.
The properties of dark energy and dark matter are largely unknown, and could be uniformly distributed or organized in clumps like normal matter. However, it is believed that dark matter gravitates as ordinary matter does, and thus works to slow the expansion of the Universe. By contrast, dark energy accelerates its expansion.
Once again, this number is just a rough estimate. When used to estimate the total mass of the Universe, it often falls short of what other estimates predict. And in the end, what we see is just a smaller fraction of the whole.
Interaction between Venus and the solar wind. (Credit: ESA / C. Carreau)
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In many ways Venus is Earth’s twin planet. It’s only a little smaller, and made up of the same composition as Earth. But when it comes to climate, Venus couldn’t really be more different. Venus is a hellish world – the hottest planet in the Solar System, with an average temperature of more than 400°C, and a surface pressure almost 100 times what we experience here on Earth. On top of that, there are clouds of sulfuric acid and other corrosive chemicals. Visiting Venus would be the worst vacation ever.
Before the 1960s, scientists thought that the climate of Venus might be similar to Earth. It has clouds, and here Earth, clouds mean rain, water, oceans and even life. But microwave observations of Venus showed that its surface must be incredibly hot, too hot for liquid water to exist. And spacecraft visiting the planet in the 1960s and 70s confirmed that the clouds of Venus are made up almost entirely of carbon dioxide; a potent greenhouse gas keeping the planet so hot.
But you could say that Venus has a climate. It has severe winds that blow at speeds greater than 100 m/s; although, the winds don’t reach down to the surface of the planet. It has sulfuric acid clouds which send down torrents of sulfuric acid rain.
The climate of Venus wasn’t always this harsh. In fact, Venus used to have an atmosphere similar to our own. But at some point in Venus’ past, its global magnetosphere shut down. Without this global force field, the Sun’s solar wind was able to reach the planet and tear away at its atmosphere, stripping away the lighter atoms. The lightest atom is hydrogen, of course, one of the constituents of water. Recent observations by ESA’s Venus Express showed that this process is still going on today. 2 x 1024 atoms of hydrogen are being blasted off Venus into space every second.
Interaction between Venus and the solar wind. (Credit: ESA / C. Carreau)
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When astronomers first pointed their rudimentary telescopes at Venus, they saw a world shrouded in clouds. Here on Earth, clouds mean water, so early astronomers imagined a tropical world with constant rainfall. The truth, of course is that the thick atmosphere on Venus is made almost entirely of carbon dioxide. In fact, the atmospheric pressure on the surface of Venus is 92 times more than what you would experience on Earth. If the clouds are carbon dioxide, is there water on Venus.
Well, there isn’t any water on the surface of Venus, in form of rivers, lakes or oceans. The average temperature on Venus is 461.85 °C. Since water boils at 100 °C, it couldn’t be on the surface. But could water be in the clouds and atmosphere of Venus?
Astronomers have detected that the atmosphere of Venus consists of 0.002% water vapor. Compare that to the Earth’s atmosphere, which contains 0.40% water vapor.
Scientists think that Venus had a similar formation to Earth, and it was certainly bombarded by the same comets that delivered vast quantities of water to our early planet. So why has Venus lost its water, while Earth kept its water? Recent observations by ESA’s Venus Express spacecraft found that Venus has a trail of hydrogen and oxygen atoms blasted away from the planet by the Sun’s solar winds. Every second, there are 2 x 1024 hydrogen atoms streaming away from Venus. The Earth’s magnetosphere protects our atmosphere from the Sun, channeling the solar wind around the planet, and keeping it from reaching our atmosphere.
The Earth’s magnetosphere is generated by the convection of material deep inside the Earth. This happens because the large temperature difference between the outer core and the inner core. At some point, plate tectonics on Venus ceased, and the planet stopped releasing as much heat from the interior. Without a high temperature gradient, its inner convection stopped, taking away its planet-wide magnetosphere.
It’s estimated that Earth’s atmosphere and surface has 100,000 times as much water as Venus. And if we didn’t have our protective magnetosphere, we’d be losing our water too.
Artist's conception of Venus Express. Image credit: ESA
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Although humans have never made the voyage, spacecraft from Earth have visited Venus. So, how long does it take to get to Venus from Earth?
The first spacecraft ever launched towards Venus was the Soviet Venera 1 spacecraft. It was launched on February 12, 1961 on course to Venus. Unfortunately, scientists lost contact with the spacecraft on February 17th. Mission controllers didn’t get a chance to put in a course correction that would have directed it closer to Venus, so it’s thought to have passed within 100,000 km of the planet on May 19th. That’s a total time of 97 days; just over 3 months.
The first successful Venus flyby was NASA’s Mariner 2. This spacecraft was launched on August 8th, 1962 and made a successful flyby on December 14, 1962. So that calculates to 110 days from launch to arrival at Venus.
The most recent spacecraft to fly to Venus was ESA’s Venus Express. It was launched on November 9th, 2005, and took 153 days to make the journey to Venus.
Why is there such a big difference in travel times to Venus? It all comes down to the launch speed and trajectory. Both Earth and Venus are traveling on orbits around the Sun. You don’t just point your spacecraft directly at Venus and fire your rockets. You have to travel on a transfer orbit that moves you between Earth’s orbit and Venus’ orbit, catching up with Venus, ideally going into orbit. To make the trip with a smaller, less expensive rocket, you have to make a longer trip, taking more time.
Humans have never made the trip to Venus, but maybe someday they will; although, the planet would be extremely unpleasant to try and land on. Maybe just a flyby would be nice.
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Want to lose some weight? Travel to Venus and you’ll feel lighter right away. Well, the high temperatures, intense pressures, and corrosive chemicals will make the experience unpleasant (and kill you instantly), but you’ll definitely be lighter on the scales. So what would your weight be on Venus?
The force of gravity on the surface of Venus is 90% the force of gravity you experience on Earth. In other words, if your bathroom scale reads 100 kg, it would only read 90 kg on Venus. For you imperial folks, if you weighed 150 pounds on Earth, you would weigh 135 pounds on Venus.
If Earth and Venus are considered twin planets, why wouldn’t you weigh the same? Well, Venus and Earth are very similar, but they’re not actually twin planets. Venus is only 95% the size of Earth, and 81% of its mass. With the smaller size and mass, the force of gravity pulling you on the surface is lower.
To get your weight on Venus, just multiply your current weight by 0.9. That’s why 100 pounds becomes 90 pounds. You can also do the reverse calculation and figure out how high you could jump, or what you could carry on Venus by dividing a number by 0.9. For example, the world record high jump is currently 2.45 meters. If that was done on Venus, it would be 2.72 meters (2.45 / 0.9).
Just one last thing. It’s important to note that kilograms are a measure of mass; how much stuff an object has. Your mass doesn’t change when you travel from planet to planet, or anywhere in the Universe. It would be more accurate to measure your weight in newtons, but bathroom scales don’t have that option. That’s why we say that your weight in kilograms changes from planet to planet.
From our perspective here on Earth, Venus is completely covered in clouds. So what’s inside Venus? For most of history, scientists had no idea what’s inside of Venus. The earliest telescopes showed hazy cloud tops, and even the largest telescopes didn’t improve the view. Some astronomers thought they might have caught a glimpse of the surface through the clouds, or maybe the peak of a tall mountain poking up through the clouds. But we now know those were just observation errors.
It wasn’t until the first spacecraft from Earth arrived at Venus, and started gathering scientific data about the inside of Venus. NASA’s Mariner 2 helped scientists calculate that the density of Venus is very similar to the density of Earth. Although there were no direct observations of Venus’ interior, scientists assume that it must be similar to Earth. The inside of Venus is thought to contain a solid/liquid core of metal 3,000 km across. This is surrounded by a mantle of rock 3,000 km thick. And then there’s a thin crust of rock about 50 km thick.
When NASA’s Magellan spacecraft was launched to Venus in 1989, it was carrying a suite of powerful radar mapping instruments. These tools could pierce through the thick clouds surrounding Venus and reveal the surface of the planet in great detail. Magellan found that the surface of Venus is actually quite young, and was probably resurfaced 300-500 million years ago, based on the number of impact craters found on its surface.
Magellan also found evidence of a large number of volcanoes; they number in the thousands and maybe even in the millions. The shield volcanoes found across the surface of Venus indicate that the inside of Venus is still active, with magma pushing to the surface around the planet.
It’s believed that the event that resurfaced Venus 300-500 million years ago might have also shut down plate tectonics on Venus. Without the movement of plates to release trapped heat, the inside of Venus remained much hotter than it would be. It’s thought that this increase in heat also shut down the convection of metal around the core of Venus. It’s this convection in the Earth’s core that’s thought to run our planet’s magnetic field.
Venus is a tricky place to study because it’s shrouded in a thick atmosphere that hides its surface. And if you can’t even see its surface, imagine how difficult it must be to study the interior of Venus. But scientists have been making steady progress towards understanding the interior of the planet, and learn about the core of Venus.
Here on Earth, scientists study the core of the planet by measuring how seismic waves move through the planet after earthquakes. As they pass through the different layers of the Earth’s interior; the core, the mantle, and the crust, the waves reflect or bend depending on the change of density that they’re passing through. Well, the surface of Venus is hot enough to melt lead, and spacecraft are destroyed within a few hours of reaching the surface of Venus, so no readings have been gathered about Venus’ core directly.
Instead, scientists assume that the core of Venus exists based on calculations of its density. The density of Venus is only a little less than the density of Earth. This means that Venus probably has a core of metal about 3,000 km across, surrounded by a 3,000 km thick mantle and a 50 km thick crust.
Scientists aren’t sure if the core of Venus is solid or liquid, but they have a few hints. That’s because Venus doesn’t have a planet wide magnetic field like the Earth. It’s believed that the Earth’s magnetic field is generated by the convection of liquid in the Earth’s core. Since Venus doesn’t have a planetary magnetic field, it’s possible that Venus’ core is made of solid metal, or maybe there isn’t enough of a temperature gradient between the inner and outer core to made this convection happen.
It’s believed that a global resurfacing event that occurred about 300-500 million years ago might have something to do with this. The entire surface of Venus was resurfaced, shutting down plate tectonics. This might have led to a reduced heat flux through the crust, trapping the heat inside the planet. Without the big heat difference, there’s little heat convection, and so no magnetic field coming from the core of Venus.
Take a look at Venus in even the most powerful telescope, and all you’ll see is clouds. There are no surface features visible at all. It wasn’t until the last few decades, when radar equipped spacecraft arrived at Venus, that scientists finally had a chance to study the geology of Venus in great detail.
Spacecraft like NASA’s Magellan mission are equipped with radar instruments that let it penetrate down through the clouds on Venus and reveal the surface below. Magellan found that the surface of Venus does have many impact craters and evidence of past volcanism. But the total number of craters showed that the surface of Venus is actually pretty young. It’s likely that some catastrophic event resurfaced Venus about 300-500 million years ago, wiping out old craters and volcanoes.
Unlike Earth, Venus doesn’t have plate tectonics. It’s possible that the planet had them in the ancient past, but rising temperatures shut them down and helped the planet go into a runaway greenhouse cycle. Carbon on Earth is trapped by plants, and is then recycled into the Earth through plate tectonics. But on Venus, the tectonic system shut down, so carbon was able to build up to tremendous levels. This cycle thickened the atmosphere, raised temperatures with its greenhouse effect, releasing more carbon, raising temperatures even higher… etc.
There are volcanoes on Venus; scientists have identified more than 100 isolated shield volcanoes. And there are thousands and maybe even millions of smaller volcanoes less than 20 km across. Many of these have a strange dome-shaped structure, believed to have formed when plumes of magma thrust the crust upward and then collapsed.
Scientists can’t be exactly sure what the internal structure of Venus is like, but based on its density, Venus is probably similar to Earth in composition. It’s believed to have a solid or liquid core of metal 3,000 km across. This is surrounded by a mantle of rock 3,000 km thick, and then a thin crust of solid rock about 50 km thick.
One big difference between Earth and Venus is the lack of a planetary magnetic field at Venus. It’s believed that the Earth’s magnetic field is driven by the convection of liquid metal at the Earth’s core. If true, it means that Venus probably doesn’t have the same kind of temperature differences at its core, and lacks the convection to sustain a planetary magnetic field.
