Matt Williams, Author at Universe Today

May 27, 2016December 12, 2019 by Matt Williams

10 Interesting Facts About Earth

This view of Earth comes from NASA's Moderate Resolution Imaging Spectroradiometer aboard the Terra satellite.

Planet Earth. That shiny blue marble that has fascinated humanity since they first began to walk across its surface. And why shouldn’t it fascinate us? In addition to being our home and the place where life as we know it originated, it remains the only planet we know of where life thrives. And over the course of the past few centuries, we have learned much about Earth, which has only deepened our fascination with it.

But how much does the average person really know about the planet Earth? You’ve lived on Planet Earth all of your life, but how much do you really know about the ground underneath your feet? You probably have lots of interesting facts rattling around in your brain, but here are 10 more interesting facts about Earth that you may, or may not know.

1. Plate Tectonics Keep the Planet Comfortable:

Earth is the only planet in the Solar System with plate tectonics. Basically, the outer crust of the Earth is broken up into regions known as tectonic plates. These are floating on top of the magma interior of the Earth and can move against one another. When two plates collide, one plate will subduct (go underneath another), and where they pull apart, they will allow fresh crust to form.

The Earth's Tectonic Plates. Credit: msnucleus.org — *The Earth’s Tectonic Plates. Credit: msnucleus.org*

This process is very important, and for a number of reasons. Not only does it lead to tectonic resurfacing and geological activity (i.e. earthquakes, volcanic eruptions, mountain-building, and oceanic trench formation), it is also intrinsic to the carbon cycle. When microscopic plants in the ocean die, they fall to the bottom of the ocean.

Over long periods of time, the remnants of this life, rich in carbon, are carried back into the interior of the Earth and recycled. This pulls carbon out of the atmosphere, which makes sure we don’t suffer a runaway greenhouse effect, which is what happened on Venus. Without the action of plate tectonics, there would be no way to recycle this carbon, and the Earth would become an overheated, hellish place.

2. Earth is Almost a Sphere:

Many people tend to think that the Earth is a sphere. In fact, between the 6th cenury BCE and the modern era, this remained the scientific consensus. But thanks to modern astronomy and space travel, scientists have since come to understand that the Earth is actually shaped like a flattened sphere (aka. an oblate spheroid).

This shape is similar to a sphere, but where the poles are flattened and the equator bulges. In the case of the Earth, this bulge is due to our planet’s rotation. This means that the measurement from pole to pole is about 43 km less than the diameter of Earth across the equator. Even though the tallest mountain on Earth is Mount Everest, the feature that’s furthest from the center of the Earth is actually Mount Chimborazo in Ecuador.

The Earth's layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com — *The Earth’s layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com*

3. Earth is Mostly Iron, Oxygen and Silicon:

If you could separate the Earth out into piles of material, you’d get 32.1 % iron, 30.1% oxygen, 15.1% silicon, and 13.9% magnesium. Of course, most of this iron is actually located at the core of the Earth. If you could actually get down and sample the core, it would be 88% iron. And if you sampled the Earth’s crust, you’d find that 47% of it is oxygen.

4. 70% of the Earth’s Surface is Covered in Water:

When astronauts first went into the space, they looked back at the Earth with human eyes for the first time. Based on their observations, the Earth acquired the nickname the “Blue Planet:. And it’s no surprise, seeing as how 70% of our planet is covered with oceans. The remaining 30% is the solid crust that is located above sea level, hence why it is called the “continental crust”.

5. The Earth’s Atmosphere Extends to a Distance of 10,000 km:

Earth’s atmosphere is thickest within the first 50 km from the surface or so, but it actually reaches out to about 10,000 km into space. It is made up of five main layers – the Troposphere, the Stratosphere, the Mesosphere, the Thermosphere, and the Exosphere. As a rule, air pressure and density decrease the higher one goes into the atmosphere and the farther one is from the surface.

Winter Solstice — *Earth, as viewed from the cabin of the Apollo 11 spacecraft. Credit: NASA*

The bulk of the Earth’s atmosphere is down near the Earth itself. In fact, 75% of the Earth’s atmosphere is contained within the first 11 km above the planet’s surface. However, the outermost layer (the Exosphere) is the largest, extending from the exobase – located at the top of the thermosphere at an altitude of about 700 km above sea level – to about 10,000 km (6,200 mi). The exosphere merges with the emptiness of outer space, where there is no atmosphere.

The exosphere is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules – including nitrogen, oxygen and carbon dioxide. The atoms and molecules are so far apart that the exosphere no longer behaves like a gas, and the particles constantly escape into space. These free-moving particles follow ballistic trajectories and may migrate in and out of the magnetosphere or with the solar wind.

Want more planet Earth facts? We’re halfway through. Here come 5 more!

6. The Earth’s Molten Iron Core Creates a Magnetic Field:

The Earth is like a great big magnet, with poles at the top and bottom near to the actual geographic poles. The magnetic field it creates extends thousands of kilometers out from the surface of the Earth – forming a region called the “magnetosphere“. Scientists think that this magnetic field is generated by the molten outer core of the Earth, where heat creates convection motions of conducting materials to generate electric currents.

The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. The field can be thought of as a huge bubble, protecting us from cosmic radiation and charged particles that bombard Earth in solar winds. It's shaped by winds of particles blowing from the sun called the solar wind, the reason it's flattened on the "sun-side" and swept out into a long tail on the opposite side of the Earth. Credit: ESA/ATG medialab — *Artist’s impression of the Earth’s protective magnetic field and the dynamo effect in its core that gives rise to it. Credit: ESA/ATG medialab*

Be grateful for the magnetosphere. Without it, particles from the Sun’s solar wind would hit the Earth directly, exposing the surface of the planet to significant amounts of radiation. Instead, the magnetosphere channels the solar wind around the Earth, protecting us from harm. Scientists have also theorized that Mars’ thin atmosphere is due to it having a weak magnetosphere compared to Earth’s, which allowed solar wind to slowly strip it away.

7. Earth Doesn’t Take 24 Hours to Rotate on its Axis:

It actually takes 23 hours, 56 minutes and 4 seconds for the Earth to rotate once completely on its axis, which astronomers refer to as a Sidereal Day. Now wait a second, doesn’t that mean that a day is 4 minutes shorter than we think it is? You’d think that this time would add up, day by day, and within a few months, day would be night, and night would be day.

But remember that the Earth orbits around the Sun. Every day, the Sun moves compared to the background stars by about 1° – about the size of the Moon in the sky. And so, if you add up that little motion from the Sun that we see because the Earth is orbiting around it, as well as the rotation on its axis, you get a total of 24 hours.

This is what is known as a Solar Day, which – contrary to a Sidereal Day – is the amount of time it takes the Sun to return to the same place in the sky. Knowing the difference between the two is to know the difference between how long it takes the stars to show up in the same spot in the sky, and the it takes for the sun to rise and set once.

8. A year on Earth isn’t 365 days:

It’s actually 365.2564 days. It’s this extra .2564 days that creates the need for a Leap Year once ever four years. That’s why we tack on an extra day in February every four years – 2004, 2008, 2012, etc. The exceptions to this rule is if the year in question is divisible by 100 (1900, 2100, etc), unless it divisible by 400 (1600, 2000, etc).

9. Earth has 1 Moon and 2 Co-Orbital Satellites:

As you’re probably aware, Earth has 1 moon (aka. The Moon). Plenty is known about this body and we have written many articles about it, so we won’t go into much detail there. But did you know there are 2 additional asteroids locked into a co-orbital orbits with Earth? They’re called 3753 Cruithne and 2002 AA₂₉, which are part of a larger population of asteroids known as Near-Earth Objects (NEOs).

The asteroid known as 3753 Cruithne measures 5 km across, and is sometimes called “Earth’s second moon”. It doesn’t actually orbit the Earth, but has a synchronized orbit with our home planet. It also has an orbit that makes it look like it’s following the Earth in orbit, but it’s actually following its own, distinct path around the Sun.

Meanwhile, 2002 AA₂₉ is only 60 meters across and makes a horseshoe orbit around the Earth that brings it close to the planet every 95 years. In about 600 years, it will appear to circle Earth in a quasi-satellite orbit. Scientists have suggested that it might make a good target for a space exploration mission.

10. Earth is the Only Planet Known to Have Life:

We’ve discovered past evidence of water and organic molecules on Mars, and the building blocks of life on Saturn’s moon Titan. We can see amino acids in nebulae in deep space. And scientists have speculated about the possible existence of life beneath the icy crust of Jupiter’s moon Europa and Saturn’s moon Titan. But Earth is the only place life has actually been discovered.

But if there is life on other planets, scientists are building the experiments that will help find it. For instance, NASA just announced the creation of the Nexus for Exoplanet System Science (NExSS), which will spend the coming years going through the data sent back by the Kepler space telescope (and other missions that have yet to be launched) for signs of life on extra-solar planets.

Europa's cracked, icy surface imaged by NASA's Galileo spacecraft in 1998. Credit: NASA/JPL-Caltech/SETI Institute. — *Europa’s cracked, icy surface imaged by NASA’s Galileo spacecraft in 1998. Credit: NASA/JPL-Caltech/SETI Institute.*

Giant radio dishes are currently scan distant stars, listening for the characteristic signals of intelligent life reaching out across interstellar space. And newer space telescopes, such as NASA’s James Webb Telescope, the Transiting Exoplanet Survey Satellite (TESS), and the European Space Agency’s Darwin mission might just be powerful enough to sense the presence of life on other worlds.

But for now, Earth remains the only place we know of where there’s life. Now that is an interesting fact!

We have written many interesting articles about planet Earth here on Universe Today. Here’s What is the Highest Place on Earth?, What is the Diameter of the Earth?, What is the Closest Planet to Earth?, What is the Surface Temperature of Earth? and The Rotation of the Earth?

Other articles include how fast the Earth rotates, and here’s an article about the closest star to Earth. If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

And there’s even an Astronomy Cast episode on the subject of planet Earth.

May 26, 2016May 26, 2016 by Matt Williams

Next Time You’re Late To Work, Blame Dark Energy!

Illustration of the Big Bang Theory — The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com

Ever since Lemaitre and Hubble’s first proposed it in the 1920s, scientists and astronomers have been aware that the Universe is expanding. And from these observations, cosmological theories like the Big Bang Theory and the “Arrow of Time” emerged. Whereas the former addresses the origins and evolution of our Universe, the latter argues that the flow of time in one-direction and is linked to the expansion of space.

For many years, scientists have been trying to ascertain why this is. Why does time flow forwards, but not backwards? According to new study produced by a research team from the Yerevan Institute of Physics and Yerevan State University in Armenia, the influence of dark energy may be the reason for the forward-flow of time, which may make one-directional time a permanent feature of our universe.

Today, theories like the Arrow of Time and the expansion of the universe are considered fundamental facts about the Universe. Between measuring time with atomic clocks, observing the red shift of galaxies, and created detailed 3D maps that show the evolution of our Universe over the course of billions of years, one can see how time and the expansion of space are joined at the hip.

Artist's impression of the influence gravity has on space time. Credit: space.com — *Artist’s impression of the influence gravity has on space time. Credit: space.com*

The question of why this is the case though is one that has continued to frustrate physicists. Certain fundamental forces, like gravity, are not governed by time. In fact, one could argue without difficulty that Newton’s Laws of Motion and quantum mechanics work the same forwards or backwards. But when it comes to things on the grand scale like the behavior of planets, stars, and entire galaxies, everything seems to come down to the Second Law of Thermodynamics.

This law, which states that the total chaos (aka. entropy) of an isolated system always increases over time, the direction in which time moves is crucial and non-negotiable, has come to be accepted as the basis for the Arrow of Time. In the past, some have ventured that if the Universe began to contract, time itself would begin to flow backwards. However, since the 1990s and the observation that the Universe has been expanding at an accelerating rate, scientists have come to doubt that this.

If, in fact, the Universe is being driven to greater rates of expansion – the predominant explanation is that “Dark Energy” is what is driving it – then the flow of time will never cease being one way. Taking this logic a step further, two Armenian researchers – Armen E. Allahverdyan of the Center for Cosmology and Astrophysics at the Yerevan Institute of Physics and Vahagn G. Gurzadyan of Yerevan State University – argue that dark energy is the reason why time always moves forward.

In their paper, titled “Time Arrow is Influenced by the Dark Energy“, they argue that dark energy accelerating the expansion of the universe supports the asymmetrical nature of time. Often referred to as the “cosmological constant” – referring to Einstein’s original theory about a force which held back gravity to achieve a static universe – dark energy is now seen as a “positive” constant, pushing the Universe forward, rather than holding it back.

*Diagram showing the Lambda-CBR universe, from the Big Bang to the the current era. Credit: Alex Mittelmann/Coldcreation*

To test their theory, Allahverdyan and Gurzadyan used a large scale scenario involving gravity and mass – a planet with increasing mass orbiting a star. What they found was that if dark energy had a value of 0 (which is what physicists thought before the 1990s), or if gravity were responsible for pulling space together, the planet would simply orbit the star without any indication as to whether it was moving forwards or backwards in time.

But assuming that the value of dark energy is a positive (as all the evidence we’ve seen suggests) then the planet would eventually be thrown clear of the star. Running this scenario forward, the planet is expelled because of its increasing mass; whereas when it is run backwards, the planet closes in on the star and is captured by it’s gravity.

In other words, the presence of dark energy in this scenario was the difference between having an “arrow of time” and not having one. Without dark energy, there is no time, and hence no way to tell the difference between past, present and future, or whether things are running in a forward direction or backwards.

But of course, Allahverdyan and Gurzadyan were also sure to note in their study that this is a limited test and doesn’t answer all of the burning questions. “We also note that the mechanism cannot (and should not) explain all occurrences of the thermodynamic arrow,” they said. “However, note that even when the dark energy (cosmological constant) does not dominate the mean density (early universe or today’s laboratory scale), it still exists.”

Limited or not, this research is representative of some exciting new steps that astrophysicists have been taking of late. This involves not only questioning the origins of dark energy and the expansion force it creates, but also questioning its implication in basic physics. In so doing, researchers may finally be able to answer the age-old question about why time exists, and whether or not it can be manipulated (i.e. time travel!)

Further Reading: Physical Review E

May 26, 2016May 4, 2017 by Matt Williams

How Do Volcanoes Erupt?

The 2006 Cleveland Volcano Eruption viewed from space. Credit: NASA

Volcanoes come in many shapes and sizes, ranging from common cinder cone volcanoes that build up from repeated eruptions and lava domes that pile up over volcanic vents to broad shield volcanoes and composite volcanoes. Though they differ in terms of structure and appearance, they all share two things. On the one hand, they are all awesome forces of nature that both terrify and inspire.

On the other, all volcanic activity comes down to the same basic principle. In essence, all eruptions are the result of magma from beneath the Earth being pushed up to the surface where it erupts as lava, ash and rock. But what mechanisms drive this process? What is it exactly that makes molten rock rise from the Earth’s interior and explode onto the landscape?

To understand how volcanoes erupt, one first needs to consider the structure of the Earth. At the very top is the lithosphere, the outermost layers of the Earth that consists of the upper mantle and crust. The crust makes up a tiny volume of the Earth, ranging from 10 km in thickness on the ocean floor to a maximum of 100 km in mountainous regions. It is cold and rigid, and composed primarily of silicate rock.

Beneath the crust, the Earth’s mantle is divided into sections of varying thickness based on their seismology. These consist of the upper mantle, which extends from a depth of 7 – 35 km (4.3 to 21.7 mi)) to 410 km (250 mi); the transition zone, which ranges from 410–660 km (250–410 mi); the lower mantle, which ranges from 660–2,891 km (410–1,796 mi); and the core–mantle boundary, which is ~200 km (120 mi) thick on average.

In the mantle region, conditions change drastically from the crust. Pressures increase considerably and temperatures can reach up to 1000 °C, which makes the rock viscous enough that it behaves like a liquid. In short, it experiences elastically on time scales of thousands of years or greater. This viscous, molten rock collects into vast chambers beneath the Earth’s crust.

Since this magma is less dense than the surrounding rock, it ” floats” up to the surface, seeking out cracks and weaknesses in the mantle. When it finally reaches the surface, it explodes from the summit of a volcano. When it’s beneath the surface, the molten rock is called magma. When it reaches the surface, it erupts as lava, ash and volcanic rocks.

With each eruption, rocks, lava and ash build up around the volcanic vent. The nature of the eruption depends on the viscosity of the magma. When the lava flows easily, it can travel far and create wide shield volcanoes. When the lava is very thick, it creates a more familiar cone volcano shape (aka. a cinder cone volcano). When the lava is extremely thick, it can build up in the volcano and explode (lava domes).

Another mechanism that drives volcanism is the motion the crust undergoes. To break it down, the lithosphere is divided into several plates, which are constantly in motion atop the mantle. Sometimes the plates collide, pull apart, or slide alongside each other; resulting in convergent boundaries, divergent boundaries, and transform boundaries. This activity is what drives geological activity, which includes earthquakes and volcanoes.

In the case of the former, subduction zones are often the result, where the heavier plate slips under the lighter plate – forming a deep trench. This subduction changes the dense mantle into buoyant magma, which rises through the crust to the Earth’s surface. Over millions of years, this rising magma creates a series of active volcanoes known as a volcanic arc.

Cross-section of a volcano. Credit: 3dgeography.co.uk/#! — *Cross-section of a volcano. Credit: 3dgeography.co.uk*

In short, volcanoes are driven by pressure and heat in the mantle, as well as tectonic activity that leads to volcanic eruptions and geological renewal. The prevalence of volcanic eruptions in certain regions of the world – such as the Pacific Ring of Fire – also has a profound impact on the local climate and geography. For example, such regions are generally mountainous, have rich soil, and periodically experience the formation of new landmasses.

We have written many articles about volcanoes here at Universe Today. Here’s What are the Different Types of Volcanoes?, What are the Different Parts of a Volcano?, 10 Interesting Facts About Volcanoes?, What is the Pacific Ring of Fire?, Olympus Mons: The Largest Volcano in the Solar System.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

May 25, 2016June 13, 2016 by Matt Williams

Take A Virtual Reality Tour Of Pluto

View from the surface of Pluto, showing its large moon Charon in the distance. Credit: New York Times

On July 14th, 2015, the New Horizons probe made history as it passed within 12,500 km (7,800 mi) of Pluto, thus making it the first spacecraft to explore the dwarf planet up close. And since this historic flyby, scientists and the astronomy enthusiasts here at Earth have been treated to an unending stream of breathtaking images and scientific discoveries about this distant world.

And thanks to the New York Times and the Universities Space Research Association‘s Lunar and Planetary Institute in Texas, it is now possible to take a virtual reality tour of Pluto. Using the data obtained by the New Horizon’s instruments, users will be able to experience what it is like to explore the planet using their smartphone or computer, or in 3D using a VR headset.

The seven-minute film, titled “Seeking Pluto’s Frigid Heart“, which is narrated by science writer Dennis Overbye of the New York Times – shows viewers what it was like to approach the dwarf planet from the point of the view of the New Horizon’s probe. Upon arrival, they are then able to explore Pluto’s surface, taking in 360 degree views of its icy mountains, heart-shaped plains, and largest moon, Charon.

This represents the most detailed and clear look at Pluto to date. A few decades ago, the few maps of Pluto we had were the result of close observations that measured changes in the planet’s total average brightness as it was eclipsed by its largest moon, Charon. Computer processing yielded brightness maps, which were very basic by modern standards.

In the early 2000s, images taken by the Hubble Space Telescope were processed in order to create a more comprehensive view. Though the images were rather undetailed, they offered a much higher resolution view than the previous maps, allowing certain features – like Pluto’s large bright spots and the dwarf planet’s polar regions – to be resolved for the first time.

However, with the arrival of the New Horizons mission, human beings have been finally treated to a close-up view of Pluto and its surface. This included Pluto’s now-famous heart-shaped plains, which were captured by the probe’s Long Range Reconnaissance Imager (LORRI) while it was still several days away from making its closest approach.

Our evolving understanding of Pluto, represented by images taken by Hubble in 2002-3 (left), and images taken by New Horizons in 2015 (right). Credit: theguardian.com — *Our changing impression of Pluto, represented by images taken by Hubble in 2002-3 (left), and images taken by the New Horizons mission in 2015 (right). Credit: theguardian.com*

This was then followed-up by very clear images of its surface features and atmosphere, which revealed floating ice hills, mountains and icy flow plains, and surface clouds composed of methane and tholins. From all of these images, we now know what the surface of this distant world looks like with precision. All of this has allowed scientists here at Earth to reconstruct, in stunning detail, what it would be like to travel to Pluto and stand on its surface.

Amazingly, only half of New Horizon’s images and measurements have been processed so far. And with fresh data expected to arrive until this coming October, we can expect that scientists will be working hard for many years to analyze it all. One can only imagine what else they will learn about this mysterious world. And one can only hope that any news findings will be uploaded to the app (and those like it)!

The VR app can be downloaded at the New York Times VR website, and is available for both Android and Apple devices. It can also be viewed using headset’s like Google Cardboard, a smartphone, and a modified version exists for computer browsers.

May 25, 2016February 8, 2019 by Matt Williams

Finding Aliens May Be Even Easier Than Previously Thought

Accroding to new research, the Milky Way may still bear the marks of "ancient impacts". Credit: NASA/Serge Brunier

Finding examples of intelligent life other than our own in the Universe is hard work. Between spending decades listening to space for signs of radio traffic – which is what the good people at the SETI Institute have been doing – and waiting for the day when it is possible to send spacecraft to neighboring star systems, there simply haven’t been a lot of options for finding extra-terrestrials.

But in recent years, efforts have begun to simplify the search for intelligent life. Thanks to the efforts of groups like the Breakthrough Foundation, it may be possible in the coming years to send “nanoscraft” on interstellar voyages using laser-driven propulsion. But just as significant is the fact that developments like these may also make it easier for us to detect extra-terrestrials that are trying to find us.

Not long ago, Breakthrough Initiatives made headlines when they announced that luminaries like Stephen Hawking and Mark Zuckerberg were backing their plan to send a tiny spacecraft to Alpha Centauri. Known as Breakthrough Starshot, this plan involved a refrigerator-sized magnet being towed by a laser sail, which would be pushed by a ground-based laser array to speeds fast enough to reach Alpha Centauri in about 20 years.

In addition to offering a possible interstellar space mission that could reach another star in our lifetime, projects like this have the added benefit of letting us broadcast our presence to the rest of the Universe. Such is the argument put forward by Philip Lubin, a professor at the University of California, Santa Barbara, and the brains behind Starshot.

In a paper titled “The Search for Directed Intelligence” – which appeared recently in arXiv and will be published soon in REACH – Reviews in Human Space Exploration – Lubin explains how systems that are becoming technologically feasible on Earth could allow us to search for similar technology being used elsewhere. In this case, by alien civilizations. As Lubin shared with Universe Today via email:

“In our SETI paper we examine the implications of a civilization having directed energy systems like we are proposing for both our NASA and Starshot programs. In this sense the NASA (DE-STAR) and Starshot arrays represent what other civilizations may possess. In another way, the receive mode (Phased Array Telescope) may be useful to search and study nearby exoplanets.”

DE-STAR, or the Directed Energy System for Targeting of Asteroids and exploRation, is another project being developed by scientists at UCSB. This proposed system will use lasers to target and deflect asteroids, comets, and other Near-Earth Objects (NEOs). Along with the Directed Energy Propulsion for Interstellar Exploration (DEEP-IN), a NASA-backed UCSB project that is based on Lubin’s directed-energy concept, they represent some of the most ambitious directed-energy concepts currently being pursued.

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity's first interstellar voyage. Credit: breakthroughinitiatives.org — *Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org*

Using these as a template, Lubin believes that other species in the Universe could be using this same kind of directed energy (DE) systems for the same purposes – i.e. propulsion, planetary defense, scanning, power beaming, and communications. And by using a rather modest search strategy, he and colleagues propose observing nearby star and planetary systems to see if there are any signs of civilizations that possess this technology.

This could take the form of “spill-over”, where surveys are able to detect errant flashes of energy. Or they could be from an actual beacon, assuming the extra-terrestrials us DE to communicate. As is stated in the paper authored by Lubin and his colleagues:

“There are a number of reasons a civilization would use directed energy systems of the type discussed here. If other civilizations have an environment like we do they might use DE system for applications such as propulsion, planetary defense against “debris” such as asteroids and comets, illumination or scanning systems to survey their local environment, power beaming across large distances among many others. Surveys that are sensitive to these “utilitarian” applications are a natural byproduct of the “spill over” of these uses, though a systematic beacon would be much easier to detect.”

According to Lubin, this represents a major departure from what projects like SETI have been doing during the last few decades. These efforts, which can be classified as “passive” were understandable in the past, owing to our limited means and the challenges in sending out messages ourselves. For one, the distances involved in interstellar communication are incredibly vast.

The Very Large Telescoping Interferometer firing it's adaptive optics laser. Credit: ESO/G. Hüdepohl — *Directed-energy technology, such as the kind behind the Very Large Telescoping Interferometer, could be used by ET for communications.* *Credit: ESO/G. Hüdepohl*

Even using DE, which moves at the speed of light, it would still take a message over 4 years to reach the nearest star, 1000 years to reach the Kepler planets, and 2 million years to the nearest galaxy (Andromeda). So aside from the nearest stars, these time scales are far beyond a human lifetime; and by the time the message arrived, far better means of communication would have evolved.

Second, there is also the issue of the targets being in motion over the vast timescales involved. All stars have a transverse velocity relative to our line of sight, which means that any star system or planet targeted with a burst of laser communication would have moved by the time the beam arrived. So by adopting a pro-active approach, which involves looking for specific kinds of behavior, we could bolster our efforts to find intelligent life on distant exoplanets.

But of course, there are still many challenges that need to be overcome, not the least of which are technical. But more than that, there is also the fact that what we are looking for may not exist. As Lubin and his colleagues state in one section of the paper: “What is an assumption, of course, is that electromagnetic communications has any relevance on times scales that are millions of years and in particular that electromagnetic communications (which includes beacons) should have anything to do with wavelengths near human vision.”

In other words, assuming that aliens are using technology similar to our own is potentially anthropocentric. However, when it comes to space exploration and finding other intelligent species, we have to work with what we have and what we know. And as it stands, humanity is the only example of a space-faring civilization known to us. As such, we can hardly be faulted for projecting ourselves out there.

Here’s hoping ET is out there, and relies on energy beaming to get things done. And, fingers crossed, here’s hoping they aren’t too shy about being noticed!

Further Reading: arXiv

May 22, 2016June 13, 2016 by Matt Williams

What is the Highest Place on Earth?

Mt. Chimborazo, located in Equator, is technically the highest point on Earth. Sorry, Everest! Credit: gerdbreitenbach.de

Whenever the question is asked, what is the highest point on planet Earth?, people naturally assume that the answer is Mt. Everest. In fact, so embedded is the notion that Mt. Everest is the highest point on the world that most people wouldn’t even think twice before answering. And even when we talk of other huge mountains in the Solar System (like Mars’ Olympus Mons), we invariably compare them to Mt. Everest.

But in truth, Everest does not hold the record for being the highest point on Earth. Due to the nature of our planet – which is not shaped like a perfect sphere but an oblate spheroid (i.e. a sphere that bulges at the center) – points that are located along the equator are farther away than those located at the poles. When you factor this in, Everest and the Himalayas find themselves falling a bit short!

Earth as a Sphere:

The understanding that Earth is spherical is believed to have emerged during the 6th century BCE in ancient Greece. While Pythagoras is generally credited with this theory, it is equally likely that it emerged on its own as a result of travel between Greek settlements – where sailors noticed changes in what stars were visible at night based on differences in latitudes.

Earth - Western Hemisphere — *Planet Earth, as seen from space above the Western Hemisphere. Credit: Reuters*

By the 3rd century BCE, the idea of a spherical Earth began to become articulated as a scientific matter. By measuring the angle cast by shadows in different geographical locations, Eratosthenes – a Greek astronomer from Hellenistic Libya (276–194 BCE) – was able to estimate Earth’s circumference within a 5% – 15% margin of error. With the rise of the Roman Empire and their adoption of Hellenistic astronomy, the view of a spherical Earth became widespread throughout the Mediterranean and Europe.

This knowledge was preserved thanks to the monastic tradition and Scholasticism during the Middle Ages. By the Renaissance and the Scientific Revolution (mid 16th – late 18th centuries), the geological and heliocentric views of Earth became accepted as well. With the advent of modern astronomy, precise methods of measurement, and the ability to view Earth from space, our models of its true shape and dimensions have come to be refined considerably.

Modern Models of the Earth:

To clarify matters a little, the Earth is neither a perfect sphere, nor is it flat. Sorry Galileo, and sorry Flat-Earthers (not sorry!), but it’s true. As already noted, it is an oblate spheroid, which is a result of the rotation of the Earth. Basically, its spin results in a flattening at the poles and a bulging at its equatorial. This is true for many bodies in the Solar System (such as Jupiter and Saturn) and even rapidly-spinning stars like Altair.

Data from the Earth2014 global relief model, with distances in distance from the geocentre denoted by color. Credit: Geodesy2000 — Data from the Earth2014 global relief model, with distances from the geocenter represented in color. Credit: Geodesy2000

Based on some of the latest measurements, it is estimated that Earth has a polar radius (i.e. from the middle of Earth to the poles) of 6,356.8 km, whereas its equatorial radius (from the center to the equator) is 6,378.1 km. In short, objects located along the equator are 22 km further away from the center of the Earth (geocenter) than objects located at the poles.

Naturally, there are some deviations in the local topography where objects located away from the equator are closer or father away from the center of the Earth than others in the same region. The most notable exceptions are the Mariana Trench – the deepest place on Earth, at 10,911 m (35,797 ft) below local sea level – and Mt. Everest, which is 8,848 meters (29,029 ft) above local sea level. However, these two geological features represent a very minor variation when compared to Earth’s overall shape – 0.17% and 0.14% respectively.

Highest Point on Earth:

To be fair, Mt. Everest is one of the highest points on Earth, with its peak ascending to an altitude of 8,848 meters (29,029 ft) above sea level. However, due to its location within the Himalayan Mountain Chain in Nepal, some 27° and 59 minutes north of the equator, it is actually lower than mountains located in Ecuador.

It is here, where the land is dominated by the Andes mountain chain, that the highest point on planet Earth is located. Known as Mt. Chiborazo, the peak of this mountain reaches an attitude of 6,263.47 meters (20,549.54 ft) above sea level. But because it is located just 1° and 28 minutes south of the equator (at the highest point of the planet’s bulge), it receives a natural boost of about 21 km.

Mount Everest from Kalapatthar. Photo: Pavel Novak — *Mount Everest, imaged from Kalapatthar. Credit: Pavel Novak*

In terms of how far they are from the geocenter, Everest lies at a distance of 6,382.3 kilometers (3,965.8 miles) from the center of the Earth while Chimborazo reaches to a distance of 6,384.4 kilometers (3,967.1 miles). That’s a difference of about 2.1 km (1.3 miles), which may not seem like much. But if we’re talking about rankings and titles, it pays to be specific.

Naturally, there are those who would stress that Mt. Everest is still the tallest mountain, measured from base to peak. Unfortunately, here too, they would be incorrect. That prize goes to Mauna Kea, a dormant volcano located on the island of Hawaii. Measuring 10,206 meters (33,484 ft) from base to summit, it is the highest mountain in the world. However, since its base is several thousand meters below seat level, we only see the top 4,207 m (13,802 ft) of it.

But if one were to say that Everest was tallest mountain based on its altitude, they would be correct. In terms of its summit’s elevation above sea level, Everest is ranked as being as the tallest mountain in the world. And when it comes to the sheer difficulty of ascending it, Everest will always be ranked no. 1, both in the records books and in the hearts of climbers everywhere!

We have written many interesting articles about the Earth and mountains here at Universe Today. Here’s Planet Earth, What is the Earth’s Diameter?, The Rotation of the Earth, and Mountains: How Are They Formed?

For more information, be sure to check out NASA’s Visible Earth, and “Highest Mountain in the World” at Geology.com.

Astronomy Cast also has a great episode on the subject – Episode 51: Earth.

May 21, 2016May 4, 2017 by Matt Williams

What is the Surface Temperature of Neptune?

Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL

Our Solar System is a fascinating place. Between its eight planets and many dwarf planets, there are some serious differences in terms of orbit, composition, and temperature. Whereas conditions within the inner Solar System, where planets are terrestrial in nature, can get pretty hot, planets that orbit beyond the Frost Line – where it is cold enough that volatiles (i.e. water, ammonia, methane, CO and CO²) condense into solids – can get mighty cold!

It is in this environment that we find Neptune, the Solar System’s most distance (and hence most cold) planet. While this gas/ice giant has no “surface” to speak of, Earth-based research and flybys have been conducted that have managed to obtain accurate measurements of the temperature in the planet’s upper atmosphere. All told, the planet experiences temperatures that range from approximately 55 K (-218 °C; -360 °F) to 72 K (-200 °C; -328 °F), making it the coldest planet in the Solar System.

Orbital Characteristics:

Of all the planets in the Solar System, Neptune orbits the Sun at the greatest average distance. With a very minor eccentricity (0.0086), it orbits the Sun at an semi-major axis of approximately 30.11 AU (4,504,450,000,000 km), ranging from 29.81 AU (4.459 x 10⁹ km) at perihelion and 30.33 AU (4.537 x 10⁹ km) at aphelion.

Pluto and its cohorts in the icy-asteroid-rich Kuiper Belt beyond the orbit of Neptune. Credit: NASA — *Neptune and the icy-asteroid-rich Kuiper Belt that lies beyond its orbit. Credit: NASA*

Neptune takes 16 hours 6 minutes and 36 seconds (0.6713 days) to complete a single sidereal rotation, and 164.8 Earth years to complete a single orbit around the Sun. This means that a single day lasts 67% as long on Neptune, whereas a year is the equivalent of approximately 60,190 Earth days (or 89,666 Neptunian days).

Because Neptune’s axial tilt (28.32°) is similar to that of Earth (~23°) and Mars (~25°), the planet experiences similar seasonal changes. Combined with its long orbital period, this means that the seasons last for forty Earth years. In addition, the planets axial tilt also leads to variations in the length of its day, as well as variations in temperature between the northern and southern hemispheres (see below).

“Surface” Temperature:

Due to their composition, determining a surface temperature on gas or ice giants (compared to terrestrial planets or moons) is technically impossible. As a result, astronomers have relied on measurements obtained at altitudes where the atmospheric pressure is equal to 1 bar (or 100 kilo Pascals), the equivalent of air pressure here on Earth at sea level.

In this image, the colors and contrasts were modified to emphasize the planet’s atmospheric features. The winds in Neptune’s atmosphere can reach the speed of sound or more. Neptune’s Great Dark Spot stands out as the most prominent feature on the left. Several features, including the fainter Dark Spot 2 and the South Polar Feature, are locked to the planet’s rotation, which allowed Karkoschka to precisely determine how long a day lasts on Neptune. (Image: Erich Karkoschka) — *Color-contrasted photo showing Neptune’s atmospheric features. Credit: Erich Karkoschka*

It is here on Neptune, just below the upper level clouds, that pressures reach between 1 and 5 bars (100 – 500 kPa). It is also at this level that temperatures reach their recorded high of 72 K (-201.15 °C; -330 °F). At this temperature, conditions are suitable for methane to condense, and clouds of ammonia and hydrogen sulfide are thought to form (which is what gives Neptune its characteristically dark cyan coloring).

But as with all gas and ice giants, temperatures vary on Neptune due to depth and pressure. In short, the deeper one goes into Neptune, the hotter it becomes. At its core, Neptune reaches temperatures of up to 7273 K (7000 °C; 12632 °F), which is comparable to the surface of the Sun. The huge temperature differences between Neptune’s center and its surface create huge wind storms, which can reach as high as 2,100 km/hour, making them the fastest in the Solar System.

Temperature Anomalies and Variations:

Whereas Neptune averages the coldest temperatures in the Solar System, a strange anomaly is the planet’s south pole. Here, it is 10 degrees K warmer than the rest of planet. This “hot spot” occurs because Neptune’s south pole is currently exposed to the Sun. As Neptune continues its journey around the Sun, the position of the poles will reverse. Then the northern pole will become the warmer one, and the south pole will cool down.

Neptune’s more varied weather when compared to Uranus is due in part to its higher internal heating, which is particularly perplexing for scientists. Despite the fact that Neptune is located over 50% further from the Sun than Uranus, and receives only 40% its amount of sunlight, the two planets’ surface temperatures are roughly equal.

*Four images of Neptune taken a few hours apart by the Hubble Space Telescope on June 25-26, 2011. Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA)*

Deeper inside the layers of gas, the temperature rises steadily. This is consistent with Uranus, but oddly enough, the discrepancy is larger. Uranus only radiates 1.1 times as much energy as it receives from the Sun, whereas Neptune radiates about 2.61 times as much. Neptune is the farthest planet from the Sun, yet its internal energy is sufficient to drive the fastest planetary winds seen in the Solar System. The mechanism for this remains unknown.

And while temperatures on Pluto have been recorded as reaching lower – down to 33 K (-240 °C; -400 °F) – Pluto’s status as a dwarf planet mean that it is no longer in the same class as the others. As such, Neptune remains the coldest planet of the eight.

We have written many articles about Neptune here at Universe Today. Here’s The Gas (and Ice) Giant Neptune, What is the Surface of Neptune Like?, 10 Interesting Facts About Neptune, and The Rings of Neptune.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

May 21, 2016May 4, 2017 by Matt Williams

What is the Difference Between Lava and Magma?

Few forces in nature are are impressive or frightening as a volcanic eruption. In an instant, from within the rumbling depths of the Earth, hot lava, steam, and even chunks of hot rock are spewed into the air, covering vast distances with fire and ash. And thanks to the efforts of geologists and Earth scientists over the course of many centuries, we have to come to understand a great deal about them.

However, when it comes to the nomenclature of volcanoes, a point of confusion often arises. Again and again, one of the most common questions about volcanoes is, what is the difference between lava and magma? They are both molten rock, and are both associated with volcanism. So why the separate names? As it turns out, it all comes down to location.

Earth’s Composition:

As anyone with a basic knowledge of geology will tell you, the insides of the Earth are very hot. As a terrestrial planet, its interior is differentiated between a molten, metal core, and a mantle and crust composed primarily of silicate rock. Life as we know it, consisting of all vegetation and land animals, live on the cool crust, whereas sea life inhabits the oceans that cover a large extent of this same crust.

However, the deeper one goes into the planet, both pressures and temperatures increase considerably. All told, Earth’s mantle extends to a depth of about 2,890 km, and is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. Although solid, the high temperatures within the mantle cause pockets of molten rock to form.

This silicate material is less dense than the surrounding rock, and is therefore sufficiently ductile that it can flow on very long timescales. Over time, it will also reach the surface as geological forces push it upwards. This happens as a result of tectonic activity.

Basically, the cool, rigid crust is broken into pieces called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries. These are known as convergent boundaries, at which two plates come together; divergent boundaries, at which two plates are pulled apart; and transform boundaries, in which two plates slide past one another laterally.

Interactions between these plates are what is what is volcanic activity (best exemplified by the “Pacific Ring of Fire“) as well as mountain-building. As the tectonic plates migrate across the planet, the ocean floor is subducted – the leading edge of one plate pushing under another. At the same time, mantle material will push up at divergent boundaries, forcing molten rock to the surface.

Magma:

As already noted, both lava and magma are what results from rock superheated to the point where it becomes viscous and molten. But again, the location is the key. When this molten rock is still located within the Earth, it is known as magma. The name is derived from Greek, which translate to “thick unguent” (a word used to describe a viscous substance used for ointments or lubrication).

It is composed of molten or semi-molten rock, volatiles, solids (and sometimes crystals) that are found beneath the surface of the Earth. This vicious rock usually collects in a magma chamber beneath a volcano, or solidify underground to form an intrusion. Where it forms beneath a volcano, it can then be injected into cracks in rocks or issue out of volcanoes in eruptions. The temperature of magma ranges between 600 °C and 1600 °C.

Magma is also known to exist on other terrestrial planets in the Solar System (i.e. Mercury, Venus and Mars) as well as certain moons (Earth’s Moon and Jupiter’s moon Io). In addition to stable lava tubes being observed on Mercury, the Moon and Mars, powerful volcanoes have been observed on Io that are capable of sending lava jets 500 km (300 miles) into space.

Igneous rock (aka. "fire rock") is formed from cooled and solidified magma. Credit: geologyclass.org — *Igneous rock (aka. “fire rock”) is formed from cooled and solidified lava. Credit: geologyclass.org*

Lava:

When magma reaches the surface and erupts from a volcano, it officially becomes lava. There are actually different kinds of lava depending on its thickness or viscosity. Whereas the thinnest lava can flow downhill for many kilometers (thus creating a gentle slope), thicker lavas will pile up around a volcanic vent and hardly flow at all. The thickest lava doesn’t even flow, and just plugs up the throat of a volcano, which in some cases cause violent explosions.

The term lava is usually used instead of lava flow. This describes a moving outpouring of lava, which occurs when a non-explosive effusive eruption takes place. Once a flow has stopped moving, the lava solidifies to form igneous rock. Although lava can be up to 100,000 times more viscous than water, lava can flow over great distances before cooling and solidifying.

The word “lava” comes from Italian, and is probably derived from the Latin word labes which means “a fall” or “slide”. The first use in connection with a volcanic event was apparently in a short written account by Franscesco Serao, who observed the eruption of Mount Vesuvius between May 14th and June 4th, 1737. Serao described “a flow of fiery lava” as an analogy to the flow of water and mud down the flanks of the volcano following heavy rain.

Such is the difference between magma and lava. It seems that in geology, as in real estate, its all about location!

We have written many articles about volcanoes here at Universe Today. Here’s What is Lava?, What is the Temperature of Lava?, Igneous Rocks: How Are They Formed?, What Are The Different Parts Of A Volcano? and Planet Earth.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

May 20, 2016April 17, 2017 by Matt Williams

The Orbit of Jupiter. How Long is a Year on Jupiter?

When it comes to the other planets that make up our Solar System, some pretty stark differences become apparent. In addition to being different in terms of their sizes, composition and atmospheres from Earth, they also differ considerably in terms of their orbits. Whereas those closest to the Sun have rapid transits, and therefore comparatively short years, those farther away can take many Earth to complete a single orbit.

This is certainly the case when it comes to Jupiter, the Solar System largest and most massive planet. Given its considerable distance from the Sun, Jupiter spends the equivalent of almost twelve Earth years completing a single circuit of our Sun. Orbiting at this distance is part of what allows Jupiter to maintain its gaseous nature, and led to its formation and peculiar composition.

Orbit and Resonance:

Jupiter orbits the Sun at an average distance (semi-major axis) of 778,299,000 km (5.2 AU), ranging from 740,550,000 km (4.95 AU) at perihelion and 816,040,000 km (5.455 AU) at aphelion. At this distance, Jupiter takes 11.8618 Earth years to complete a single orbit of the Sun. In other words, a single Jovian year lasts the equivalent of 4,332.59 Earth days.

However, Jupiter’s rotation is the fastest of all the Solar System’s planets, completing a rotation on its axis in slightly less than ten hours (9 hours, 55 minutes and 30 seconds to be exact. Therefore, a single Jovian year lasts 10,475.8 Jovian solar days. This orbital period is two-fifths that of Saturn, which means that the two largest planets in our Solar System form a 5:2 orbital resonance.

Seasonal Changes:

With an axial tilt of just 3.13 degrees, Jupiter also has one of the least inclined orbits of any planet in the Solar System. Only Mercury and Venus have more vertical axes, with a tilt of 0.03° and 2.64° respectively. As a result, Jupiter does not experience seasonal changes the way the other planets do – particularly Earth (23.44°), Mars (25.19°) and Saturn (26.73°).

As a result, temperatures do not vary considerably between the northern or southern hemispheres during the course of its orbit. Measurements taken from the top of Jupiter’s clouds (which is considered to be the surface) indicate that surface temperatures vary between 165 K and 112 K (-108 °C and -161 °C). However, temperatures vary considerably due to depth, increasing drastically as one ventures closer to the core.

Formation:

Jupiter’s composition and position in the Solar System are interrelated. According to Nebular Theory, the Sun and all the planets of our Solar System began as a giant cloud of molecular gas and dust (called a solar nebula). Then, about 4.57 billion years ago, something happened that caused the cloud to collapse, which could have been the result of anything from a passing star to shock waves from a supernova.

Young stars have a disk of gas and dust around them called a protoplanetary disk. Out of this disk planets are formed, and the presence of water ice in the disc affects where different types of planets form. Credit: NASA/JPL-Caltech

From this collapse, pockets of dust and gas began to collect into denser regions. As the denser regions pulled in more and more matter, conservation of momentum caused them to begin rotating, while increasing pressure caused them to heat up. Since temperatures across this protoplanetary disk were not uniform, this caused different materials to condense at different temperatures, leading to different types of planets forming.

The dividing line for the different planets in our solar system is known as the “Frost Line”, a point in the Solar System beyond which volatiles (such as water, ammonia, methane, carbon dioxide and carbon monoxide) are able to exist in a frozen state. As a result, planets like Jupiter, which are located beyond the Frost Line, condensed out of denser materials first (like silicate rock and minerals), then were able to accumulate gases in a liquid state.

In addition to ensuring that Jupiter was able to become the massive gas giant it is today, its distance from the Sun is also what makes its orbital period much longer than that of Earth’s.

We have written many articles about Jupiter here at Universe Today. Here’s The Gas Giant Jupiter, Ten Interesting Facts About Jupiter, Jupiter Compared to Earth, How Long Does it Take to get to Jupiter?, Could We Terraform Jupiter?

If you’d like more information on Jupiter, check out Hubblesite’s News Releases about Jupiter. And here’s an article about Jupiter on the NASA Solar System Exploration Guide.

We have also recorded an episode of Astronomy Cast about Jupiter. You can listen here, Episode 56: Jupiter.

May 19, 2016October 7, 2018 by Matt Williams

What is the Closest Planet to Earth?

At a closest average distance of 41 million km (25,476,219 mi), Venus is the closest planet to Earth. Credit: NASA/JPL/Magellan

A common question when looking at the Solar System and Earth’s place in the grand scheme of it is “which planet is closest to Earth?” Aside from satisfying a person’s general curiosity, this question is also of great importance when it comes to space exploration. And as humanity contemplates mounting manned missions to neighboring planets, it also becomes one of immense practicality.

If, someday, we hope to explore, settle, and colonize other worlds, which would make for the shortest trip? Invariable, the answer is Venus. Often referred to as “Earth’s Twin“, Venus has many similarities to Earth. It is a terrestrial planet, it orbits within the Sun’s habitable zone, and it has an atmosphere that is believed to have once been like Earth’s. Combined with its proximity to us, its little wonder we consider it our twin.

Venus’ Orbit:

Venus orbits the Sun at an average distance (semi-major axis) of 108,208,000 km (0.723 AUs), ranging between 107,477,000 km (0.718 AU) at perihelion and 108,939,000 km (0.728 AU) at aphelion. This makes Venus’ orbit the least eccentric of all the planets in the Solar System. In fact, with an eccentricity of less than 0.01, its orbit is almost circular.

When Venus lies between Earth and the Sun, it experiences what is known as an inferior conjunction. It is at this point that it makes its closest approach to Earth (and that of any planet) with an average distance of 41 million km (25,476,219 mi). On average, Venus achieves an inferior conjunction with Earth every 584 days.

And because of the decreasing eccentricity of Earth’s orbit, the minimum distances will become greater over the next tens of thousands of years. So not only is it Earth’s closest neighbor (when it makes its closest approach), but it will continue to get cozier with us as time goes on!

Venus vs. Mars:

As Earth’s other neighbor, Mars also has a “close” relationship with Earth. Orbiting our Sun at an average distance of 227,939,200 km (1.52 AU), Mars’ highly eccentric orbit (0.0934) takes it from a distance of 206,700,000 km (1.38 AU) at perihelion to 249,200,000 km (1.666 AU) at aphelion. This makes its orbit one of the more eccentric in our Solar System, second only to Mercury

For Earth and Mars to be at their closest, both planets needs to be on the same side of the Sun, Mars needs to be at its closest distance from the Sun (perihelion), and Earth needs to be at its farthest (aphelion). This is known as opposition, a time when Mars appears as one of the brightest objects in the sky (as a red star), rivaling that of Venus or Jupiter.

The eccentricity in Mars' orbit means that it is . Credit: NASA — *The eccentricity in Mars’ orbit means that it is . Credit: NASA*

But even at this point, the distance between Mars and Earth ranges considerably. The closest approach to take place occurred back in 2003, when Earth and Mars were only 56 million km (3,4796,787 mi) apart. And this was the closest they’d been in 50,000 years. The next closest approach will take place on July 27th, 2018, when Earth and Mars will be at a distance of 57.6 million km (35.8 mi) from each other.

It has also been estimated that the closest theoretical approach would take place at a distance of 54.6 million km (33.9 million mi). However, no such approach has been documented in all of recorded history. One would be forced to wonder then why so much of humanity’s exploration efforts (past, present and future) are aimed at Mars. But when one considers just how horrible Venus’ environment is in comparison, the answer becomes clear.

Exploration Efforts:

The study and exploration of Venus has been difficult over the years, owing to the combination of its dense atmosphere and harsh surface environment. Its surface has been imaged only in recent history, thanks to the development of radar imaging. However, many robotic spacecraft and even a few landers have made the journey and discovered much about Earth’s closest neighbor.

The first attempts were made by the Soviets in the 1960s through the Venera Program. Whereas the first mission (Venera-1) failed due to loss of contact, the second (Venera-3) became the first man-made object to enter the atmosphere and strike the surface of another planet (on March 1st, 1966). This was followed by the Venera-4 spacecraft, which launched on June 12th, 1967, and reached the planet roughly four months later (on October 18th).

*The first color pictures taken of the surface of Venus by the Venera-13 space probe. Credit: NASA*

NASA conducted similar missions under the Mariner program. The Mariner 2 mission, which launched on December 14th, 1962, became the first successful interplanetary mission and passed within 34,833 km (21,644 mi) of Venus’ surface. Between the late 60s and mid 70s, NASA conducted several more flybys using Mariner probes – such as the Mariner 5 mission on Oct. 19th, 1967 and the Mariner 10 mission on Feb. 5th, 1974.

The Soviets launched six more Venera probes between the late 60s and 1975, and four additional missions between the late 70s and early 80s. Venera-5, Venera-6, and Venera-7 all entered Venus’ atmosphere and returned critical data to Earth. Venera 11 and Venera 12 detected Venusian electrical storms; and Venera 13 and Venera 14 landed on the planet and took the first color photographs of the surface. The program came to a close in October 1983, when Venera 15 and Venera 16 were placed in orbit to conduct mapping of the Venusian terrain with synthetic aperture radar.

By the late seventies, NASA commenced the Pioneer Venus Project, which consisted of two separate missions. The first was the Pioneer Venus Orbiter, which inserted into an elliptical orbit around Venus (Dec. 4th, 1978) to study its atmosphere and map the surface. The second, the Pioneer Venus Multiprobe, released four probes which entered the atmosphere on Dec. 9th, 1978, returning data on its composition, winds and heat fluxes.

In 1985, the Soviets participated in a collaborative venture with several European states to launch the Vega Program. This two-spacecraft initiative was intended to take advantage of the appearance of Halley’s Comet in the inner Solar System, and combine a mission to it with a flyby of Venus. While en route to Halley on June 11th and 15th, the two Vega spacecraft dropped Venera-style probes into Venus’ atmosphere to map its weather.

NASA’s Magellan spacecraft was launched on May 4th, 1989, with a mission to map the surface of Venus with radar. In the course of its four and a half year mission, Magellan provided the most high-resolution images to date of the planet, was able to map 98% of the surface and 95% of its gravity field. In 1994, at the end of its mission, Magellan was sent to its destruction into the atmosphere of Venus to quantify its density.

Venus was observed by the Galileo and Cassini spacecraft during flybys on their respective missions to the outer planets, but Magellan was the last dedicated mission to Venus for over a decade. It was not until October of 2006 and June of 2007 that the MESSENGER probe would conduct a flyby of Venus (and collect data) in order to slow its trajectory for an eventual orbital insertion of Mercury.

The Venus Express, a probe designed and built by the European Space Agency, successfully assumed polar orbit around Venus on April 11th, 2006. This probe conducted a detailed study of the Venusian atmosphere and clouds, and discovered an ozone layer and a swirling double-vortex at the south pole before concluding its mission in December of 2014. Since December 7th, 2015, Japan’s Akatsuki has been in a highly elliptical Venusian orbit.

Because of its hostile surface and atmospheric conditions, Venus has proven to be a tough nut to crack, despite its proximity to Earth. In spite of that, NASA, Roscosmos, and India’s ISRO all have plans for sending additional missions to Venus in the coming years to learn more about our twin planet. And as the century progresses, and if certain people get their way, we may even attempt to send human colonists there!

We have written many articles about Earth and its closest neighbor here at Universe Today. Here’s The Planet Venus, Venus: 50 Years Since Our First Trip, And We’re Going Back, Interesting Facts About Venus, Exploring Venus By Airship, Colonizing Venus With Floating Cities, and How Do We Terraform Venus?

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

Astronomy Cast also has an interesting episode on the subject. Listen here, Episode 50: Venus.