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.
Venus is often referred to as Earth’s twin planet (evil twin planet is more like it, when you consider the scorching temperatures). It’s almost the same size, mass, gravity and overall composition. The composition of Venus is pretty similar to Earth, with a core of metal, a mantle of liquid rock, and an outer crust of solid rock.
Unfortunately, scientists have no direct knowledge about Venus composition. Here on Earth, scientists use seismometers to study how seismic waves from earthquakes propagate through the planet. How these waves bounce and turn inside the Earth tell scientists about its composition. Since the surface of Venus is hot enough to melt lead, and no spacecraft have survived on the surface for longer than a few hours, there just isn’t the information about Venus’ internal composition.
Scientists can calculate the density of Venus, though. Since it’s similar to Earth, and the other terrestrial planets, scientists guess that the internal structure of Venus is similar to Earth. One of the big differences between our two planets, however, is the lack of plate tectonics on Venus. For some reason, plate tectonics on Venus shut down billions of years ago. This has prevented the interior of Venus from losing as much heat as the Earth does, and could be the reason Venus doesn’t have an internally generated magnetic field.
Before spacecraft missions were sent to Venus, scientists had no idea what the composition of Venus was. They could calculate the planet’s density, but the surface of Venus was obscured by dense clouds. Spacecraft equipped with radar were able to penetrate the thick clouds and map out features on the planet’s surface, showing that it has impact craters and ancient volcanoes. It’s believed that Venus went through some kind of global resurfacing event about 300-500 million years ago, which is the age of the planet’s surface (calculated by the number of impact craters).
The crust of Venus is thought to be about 50 km thick, and composed of silicious rocks. Beneath that is the mantle, which is thought to be about 3,000 km thick. The composition of the mantle is unknown. And then at the center of Venus is a solid or liquid core of iron or nickel. Since Venus doesn’t have a global magnetic field, scientists think that the planet doesn’t have convection in its core. The planet doesn’t have a large difference in temperature between the inner and outer core, and so the metal doesn’t flow around and generate a magnetic field.
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The average circumference of Venus is 38,025 km.
Need some comparison? The average circumference of Earth is 40,041 km. And then if you compare the two numbers, you find that the circumference of Venus is about 95% the circumference of Earth.
If you’ll notice at the top of the article, I specified that we’re talking about the “average circumference”. That’s the number if you average out all the circumference measurements around the planet. This is normally very important when you measure the circumference of planets since they’re often spinning quite rapidly. This rotation causes them to flatten out and bulge around the equator. This means that the equatorial circumference is larger than the circumference if you measure it from pole to pole.
The average (or mean) circumference on Earth is 40,041 km. The equatorial circumference is 40,075 km, and the polar circumference is 40,008 km. So you can see, that’s a pretty big difference, and the average is very important. But here’s the thing. Venus rotates so slowly that it doesn’t bulge at the equator. While the Earth turns once on its axis every 24 hours, Venus takes 243 days to complete a day – that’s even longer than a year on Venus!
Need your numbers in miles? No problem. The circumference of Venus in miles is 23,628 miles.
The density of Venus is 5.204 grams per cubic centimeter.
Need some kind of comparison? The density of Earth is 5.515 g/cm3. So Venus is definitely less dense than Earth. And it’s even less dense than Mercury. Of course, it’s much more dense than any of the outer planets, like Jupiter or Saturn.
Scientists think that Venus has an interior structure similar to Earth, with a metal core, rocky mantle, and an outer crust. But these assumptions come purely from the density calculations. Here on Earth, scientists study the interior structure of the planet by using seismographs, and studying how seismic waves from earthquakes travel through the Earth. Since the surface of Venus is hot enough to melt lead, there’s no way to leave scientific equipment on the surface for any period of time to study the interior of the planet.
With its lower density, Venus has a lower mass than Earth. In fact, the mass of Venus is only about 81% the mass of Earth. And it’s also a little smaller than Earth. This means that the surface gravity of Venus is only 90% of what you would experience on Earth.
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The axial tilt of Venus is 177.3°. That’s a bit of a confusing number, so let’s figure out what’s going on here. Compare this number to the Earth’s axial tilt of 23.5°. Our tilt gives us such different seasons between summer and winter, so you’d expect that Venus’ much larger tilt would cause more extreme seasons.
Nope. But if you remember your high school geometry, you’ll realize what’s going on. A full circle is 360°. Half a circle is 180°. So if you subtract 177.3° from 180°, you get 2.7°. In other words, Venus is actually only tilted away from the plane of the ecliptic by only 2.7°. Venus is actually completely upside down – almost perfectly upside down.
In fact, Venus is the only planet in the Solar System that rotates backwards compared to the other planets. Seen from above, all the planets are turning in a counter clockwise direction. That’s why Asia sees the Sun first, then Europe, and then the Americas. Mars is the same, and so is Mercury, but Venus is rotating clockwise.
It’s possible that Venus was knocked upside down by a massive impact early in its history. it’s also possible that Venus just slowed down through tidal locking with the Sun, and was somehow spun slowly backwards through its interactions with the other planets.
Here on Earth, the axial tilt is responsible for the seasons. When it’s winter in the northern hemisphere, the north pole is tilted away from the Sun, and less of the Sun’s radiation falls on every square meter of ground. The opposite is true in the summer. Without a significant axial tilt, Venus doesn’t experience seasons like this. The temperature of Venus is a nice even 462°C everywhere on the whole planet.
The newly discovered Green Pea galaxies. (Photo: Carolin Cardamone and Sloan Digital Sky Survey.)
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Citizen scientists from the Galaxy Zoo project have discovered rare galaxies they’re calling the “Green Peas.” They’re small in size, bright green in color, and proficient at churning out new stars — plus, they could reveal unique insights into how galaxies form stars in the early universe.
The newly discovered galaxies appear in the image at left, from Carolin Cardamone and the Sloan Digital Sky Survey.
“These are among the most extremely active star-forming galaxies we’ve ever found,” said Cardamone, an astronomy graduate student at Yale University and lead author of a new paper on the discovery. The results will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.
Galaxy Zoo users volunteer their spare time to help classify galaxies in an online image bank. Cardamone said of the one million galaxies that make up Galaxy Zoo’s image bank, the team found only 250 Green Peas.
“No one person could have done this on their own,” she said. “Even if we had managed to look through 10,000 of these images, we would have only come across a few Green Peas and wouldn’t have recognized them as a unique class of galaxies.”
The Green Peas boast “some of the highest specific star formation rates seen in the local Universe,” write Cardamone and her co-authors, “yielding doubling times for their stellar mass of hundreds of millions of years.”
The authors say evidence points to recent or ongoing mergers, adding that the Peas are similar in size, mass, luminosity and metallicity to Luminous Blue Compact Galaxies.
“They are also similar to high redshift UV-luminous galaxies, e.g., Lyman-break galaxies and Lyman-alpha emitters, and therefore provide a local laboratory with which to study the extreme star formation processes that occur in high-redshift galaxies,” they write.
The galaxies, which are between 1.5 billion and 5 billion light years away, are 10 times smaller than our own Milky Way galaxy and 100 times less massive. But they are forming stars 10 times faster than the Milky Way.
Kevin Schawinski, a postdoctoral associate at Yale and one of Galaxy Zoo’s founders, said the Green Peas would have been normal in the early universe, “but we just don’t see such active galaxies today. Understanding the Green Peas may tell us something about how stars were formed in the early universe and how galaxies evolve.”
The Galaxy Zoo volunteers who discovered the Green Peas—and who call themselves the “Peas Corps” and the “Peas Brigade”—began discussing the strange objects in the online forum. (The original forum thread was called “Give peas a chance.”)
Cardamone asked the volunteers, many of whom had no previous astronomy background or experience, to refine the sample of objects they detected in order to determine which were bona fide Green Peas and which were not, based on their colors. By analyzing their light, Cardamone determined how much star formation is taking place within the galaxies.
“This is a genuine citizen science project, where the users were directly involved in the analysis,” Schawinski said, adding that 10 Galaxy Zoo volunteers are acknowledged in the paper as having made a particularly significant contribution. “It’s a great example of how a new way of doing science produced a result that wouldn’t have been possible otherwise.”
Trojan asteroids sharing the orbits of Jupiter and Neptune. Image credit: Scott Sheppard.
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A planetesimal is an object formed from dust, rock, and other materials. The word has its roots in the concept infinitesimal, which indicates an object too small to see or measure. Planetesimals can be anywhere in size from several meters to hundreds of kilometers. The term refers to small celestial bodies formed during the creation of planets. One way to think of them is as small planets, but they are much more than that.
The planetesimal theory was suggested by the Russian astronomer Viktor Safronov. The planetesimal theory is a theory on how planets form. According to the planetesimal hypothesis, when a planetary system is forming, there is a protoplanetary disk with materials from the nebulae from which the system came. This material is gradually pulled together by gravity to form small chunks. These chunks get larger and larger until they form planetesimals. Many of the objects break apart when they collide, but some continue to grow. Some of these planetesimals go on to become planets and moons. Since the gas giants are balls of gas with liquid cores, it may seem impossible that an asteroid-like object formed them. The planetesimals formed the core of these gaseous planets, which turned molten when it enough heat was created.
Other planetesimals turn into comets, Kuiper Belt Objects (KBOs), and trojan asteroids. There is some debate as to whether KBOs and asteroids can be called planetesimals. This is one reason why nomenclature of celestial objects is so difficult. The planetesimal theory is not universally accepted though. Like many theories, there are some observations that cannot be explained, but the planetesimal theory is still very popular.
Many people think that around 3.8 billion years ago, many of the planetesimals were thrown into far away regions, such as the Oort cloud or the Kuiper Belt. Other objects collided with other objects after being affected by gas giants. Phobos and Deimos are believed to be planetesimals that were captured by Mars’ gravity and became satellites. Many of Jupiter’s moons are believed to be planetesimals as well.
Planetesimals are very valuable to scientists because they can provide information about the creation of our Solar System. The exterior of planetesimals have been bombarded with solar radiation, which can change their chemistry, for billions of years. Inside though, there is material that has been untouched since the object was first formed. Using this material, astronomers hope to learn about the condition of the nebulae from which our Solar System was formed.
The symbols of the eight planets, and Pluto, Credit: insightastrology.net
In our long history of staring up at the stars, human beings have assigned various qualities, names, and symbols for all the objects they have found there. Determined to find patterns in the heavens that might shed light on life here on Earth, many of these designations ascribed behavior to the celestial bodies.
When it comes to assigning signs to the planets, astrologists and astronomers – which were entwined disciplines in the past -made sure that these particular symbols were linked to the planets’ names or their history in some way.
Consider the planet Mercury, named after the Roman god who was himself the messenger of the gods, noted for his speed and swiftness. The name was assigned to this body largely because it is the planet closest to the Sun, and which therefore has the fastest rotation period. Hence, the symbol is meant to represent Mercury’s helmet and caduceus – a herald’s staff with snakes and wings intertwined.
Mercury, as imaged by the MESSENGER spacecraft, which was named after the messenger of the gods because it has the fastest orbit around the Sun. Image Credit: NASA/JHU/Carnegie Institution.
Venus:
Venus’ symbol has more than one meaning. Not only is it the sign for “female”, but it also represents the goddess Venus’ hand mirror. This representation of femininity makes sense considering Venus was the goddess of love and beauty. The symbol is also the chemical sign for copper; since copper was used to make mirrors in ancient times.
Earth:
Earth’s sign also has a variety of meanings, although it does not refer to a mythological god. The most popular view is that the circle with a cross in the middle represents the four main compass points. It has also been interpreted as the Globus Cruciger, an old Christian symbol for Christ’s reign on Earth.
This symbol is not just limited to Christianity though, and has been used in various culture around the world. These include, but are not limited to, Norse mythology (where it appears as the Solar or Odin’s Cross), Native American cultures (where it typically represented the four spirits of direction and the four sacred elements), the Celtic Cross, the Greek Cross, and the Egyptian Ankh.
In fact, perhaps owing to the simplicity of the design, cross-shaped incisions have made appearances as petroglyphs in European cult caves dating all the way back to the beginning of the Upper Paleolithic, and throughout prehistory to the Iron Age.
Mars, as photographed with the Mars Global Surveyor, is identified with the Roman god of war. Credit: NASA
Mars:
Mars is named after the Roman god of war, owing perhaps to the planet’s reddish hue, which gives it the color of blood. For this reason, the symbol associated with Mars represents the god of wars’ shield and spear. Additionally, it is the same sign as the one used to represent “male”, and hence is associated with self-assertion, aggression, sexuality, energy, strength, ambition and impulsiveness.
Jupiter:
Jupiter’s sign, which looks like an ornate, oddly shaped “four,” also stands for a number of symbols. It has been said to represent an eagle, which is Jupiter’s bird. Additionally, the symbol can stand for a “Z,” which is the first letter of Zeus – who was Jupiter’s Greek counterpart.
The line through the symbol is consistent with this, since it would indicate that it was an abbreviation for Zeus’ name. And last, but not least, there is the addition of the swirled line which is believed to represent a lighting bolt – which just happens to Jupiter’s (and Zeus’) weapon of choice.
Saturn:
Like Jupiter, Saturn resembles another recognizable character – this time, it’s an “h.” However, this symbol is actually supposed to represent Saturn’s scythe or sickle, because Saturn is named after the Roman god of agriculture.
Jupiter, the largest planet in the Solar System, is appropriately named after the Roman father of the gods. Credit: NASA/ESA/A. Simon (Goddard Space Flight Center)
Uranus:
The sign for Uranus is a combination of two other signs – Mars’ sign and the symbol of the Sun – because the planet is connected to these two in mythology. Uranus represented heaven in Roman mythology, and this ancient civilization believed that the Sun’s light and Mars’ power ruled the heavens.
Neptune:
Neptune’s sign is linked to the sea god Neptune, who the planet was named after. Appropriately, the symbol represents this planet is in the shape of the sea god’s trident.
Pluto:
Although Pluto was demoted to a dwarf planet, it still has a symbol. Pluto’s sign is a combination of a “P” and a “L,” which are the first two letters in Pluto as well as the initials of Percival Lowell, the astronomer who discovered the planet.
Other Objects:
The Moon is represented by a crescent shape, which is a clear allusion to how the Moon appears in the night sky more often than not. Since the Moon is also tied to people’s perceptions, moods, and emotional make-up, the symbol has also come to represents the mind’s receptivity.
A full moon captured July 18, 2008. Credit: NASA/Sean Smith
And then there’s the sun, which is represented by a circle with a dot in the middle. In the case of the Sun, this symbol represents the divine spirit (circle) surrounding the seed of potential, which is a direct association with ancient Sun worship and the central role Sun god’s played in ancient pantheons.
The planets have played an important role in the culture and astrological systems of every human culture. Because of this, the symbols, names, and terms that denote them continue to hold special significance in our hearts and minds.
