The Earth's layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com
Like all the other terrestrial planets, (Mercury, Venus, and Mars) the Earth is made up of many layers. This is the result of it undergoing planetary differentiation, where denser materials sink to the center to form the core while lighter materials form around the outside. Whereas the core is composed primarily of iron and nickel, Earth’s upper layer are composed of silicate rock and minerals.
This region is known as the mantle, and accounts for the vast majority of the Earth’s volume. Movement, or convection, in this layer is also responsible for all of Earth’s volcanic and seismic activity. Information about structure and composition of the mantle is either the result of geophysical investigation or from direct analysis of rocks derived from the mantle, or exposed mantle on the ocean floor.
What if someone were to tell you that at any given moment, you were traveling at speeds well in excess of the speed of sound? You might think they were crazy, given that – as best as you could tell – you were standing on solid ground, and not in the cockpit of a supersonic jet. Nevertheless, the statement is correct. At any given moment, we are all moving at a speed of about 1,674 kilometers an hour, thanks to the Earth’s rotation,
By definition, the Earth’s rotation is the amount of time that it takes to rotate once on its axis. This is, apparently, accomplished once a day – i.e. every 24 hours. However, there are actually two different kinds of rotation that need to be considered here. For one, there’s the amount of time it take for the Earth to turn once on its axis so that it returns to the same orientation compared to the rest of the Universe. Then there’s how long it takes for the Earth to turn so that the Sun returns to the same spot in the sky.
Our Sun in all its intense, energetic glory. When life appeared on Earth, the Sun would have been much different than it is now; a more intense, energetic neighbor. Image: NASA/SDO.
The early Solar System was a much different place than it is now. Chaos reigned supreme before things settled down into their present state. New research shows that the young Sun was more chaotic and expressive than it is now, and that Earth’s magnetic field was key for the development of life on Earth.
Researchers at the Harvard Smithsonian Centre for Astrophysics have been studying a star called Kappa Ceti, about 30 light years away in the Cetus constellation. Kappa Ceti is in many ways similar to our own Sun, but it’s estimated to be between 400 million to 600 million years old, about the same age as our Sun when life appeared on Earth. Studying Kappa Ceti gives scientists a good idea of the type of star that early life on Earth had to contend with.
Kappa Ceti, at its young age, is much more magnetically active than our 4.6 billion year old Sun, according to this new research. It emits a relentless solar wind, which the research team at Harvard says is 50 times as powerful as the solar wind from our Sun. It’s surface is also much more active and chaotic. Rather than the sunspots that we can see on our Sun, Kappa Ceti displays numerous starspots, the larger brother of the sunspot. And the starspots on Kappa Ceti are much more numerous than the sunspots observed on the Sun.
We’re familiar with the solar flares that come from the Sun periodically, but in the early life of the Sun, the flares were much more energetic too. Researchers have found evidence on Kappa Ceti of what are called super-flares. These monsters are similar to the flares we see today, but can release 10 to 100 million times more energy than the flares we can observe on our Sun today.
So if early life on Earth had to contend with such a noisy neighbour for a Sun, how did it cope? What prevented all that solar output from stripping away Earth’s atmosphere, and killing anything alive? Then, as now, the Earth’s electromagnetic field protected it. But in the same way that the Sun was so different long ago, so was the Earth’s protective shield. It may have been weaker than it is now.
The researchers found that if the Earth’s magnetic field was indeed weaker, then the magnetosphere may have been only 34% to 48% as large as it is now. The conclusion of the study says “… the early magnetic interaction between the stellar wind and the young Earth planetary magnetic field may well have prevented the volatile losses from the Earth exosphere and created conditions to support life.”
Or, in plain language: “The early Earth didn’t have as much protection as it does now, but it had enough,” says Do Nascimento.
The Moon's shadow is cast across Indonesia in this view from the DSCOVR spacecraft, March 9, 2016. (Courtesy of the DSCOVR EPIC team.)
On March 8, 2016 (March 9 local time) the Moon briefly blocked the light from the Sun in what was the only total solar eclipse of the year. The event was visible across portions of southeast Asia, Indonesia, and Micronesia, and was observed by both skywatchers on the ground in person and those watching live online around the world. While to most the view was of a silhouetted Moon slowly carving away the disk of the Sun before totality revealed a shimmering corona, the view from space looking back at Earth showed the Moon’s dark shadow passing over islands, clouds, and sea.
An artist's image of an asteroid Impact. Image Credit: University of California Observatories/Don Davis.
All over the Earth, there is a buried layer of sediment rich in iridium called the Cretaceous Paleogene-Boundary (K-Pg.) This sediment is the global signature of the 10-km-diameter asteroid that killed off the dinosaurs—and about 50% of all other species—66 million years ago. Now, in an effort to understand how life recovered after that event, scientists are going to drill down into the site where the asteroid struck—the Chicxulub Crater off the coast of Mexico’s Yucatan Peninsula.
The end-Cretaceous extinction was a global catastrophe, and a lot is already known about it. We’ve learned a lot about the physical effects of the strike on the impact area from oil and gas drilling in the Gulf of Mexico. According to data from that drilling, released on February 5th in the Journal of Geophysical Research: Solid Earth, the asteroid that struck Earth displaced approximately 200,000 cubic km (48,000 cubic miles) of sediment. That’s enough to fill the largest of the Great Lakes—Lake Superior—17 times.
The Chicxulub impact caused earthquakes and tsunamis that first loosened debris, then swept it from nearby areas like present-day Florida and Texas into the Gulf basin itself. This layer is hundreds of meters thick, and is hundreds of kilometers wide. It covers not only the Gulf of Mexico, but also the Caribbean and the Yucatan Peninsula.
In April, a team of scientists from the University of Texas and the National University of Mexico will spend two months drilling in the area, to gain insight into how life recovered after the impact event. Research Professor Sean Gulick of the University of Texas Institute for Geophysics told CNN in an interview that the team already has a hypothesis for what they will find. “We expect to see a period of no life initially, and then life returning and getting more diverse through time.”
Scientists have been wanting to drill in the impact region for some time, but couldn’t because of commercial drilling activity. Allowing this team to study the region directly will build on what is already known: that this enormous deposit of sediment happened over a very short period of time, possibly only a matter of days. The drilling will also help paint a picture of how life recovered by looking at the types of fossils that appear. Some scientists think that the asteroid impact would have lowered the pH of the oceans, so the fossilized remains of animals that can endure greater acidity would be of particular interest.
The Chicxulub impact was a monumental event in the history of the Earth, and it was extremely powerful. It may have been a billion times more powerful than the atomic bomb dropped on Hiroshima. Other than the layer of sediment laid down near the site of the impact itself, its global effects probably included widespread forest fires, global cooling from debris in the atmosphere, and then a period of high temperatures caused by an increase in atmospheric CO2.
We already know what will happen if an asteroid this size strikes Earth again—global devastation. But drilling in the area of the impact will tell us a lot about how geological and ecological processes respond to this type of devastation.
The eight planets of our Solar System vary widely, not only in terms of size, but also in terms of mass and density (i.e. its mass per unit of volume). For instance, the 4 inner planets – those that are closest to the Sun – are all terrestrial planets, meaning they are composed primarily of silicate rocks or metals and have a solid surface. On these planets, density varies the farther one ventures from the surface towards the core, but not considerably.
By contrast, the 4 outer planets are designated as gas giants (and/or ice giants) which are composed primarily of of hydrogen, helium, and water existing in various physical states. While these planets are greater in size and mass, their overall density is much lower. In addition, their density varies considerably between the outer and inner layers, ranging from a liquid state to materials so dense that they become rock-solid.
Asteroids represent a real danger to Earth. But is targeting them with missiles, maybe nuclear, a good idea? Image: NASA/JPL/CalTech
In a shocking announcement, Russian scientists say they want to test improved ballistic missiles on the asteroid Apophis, which is expected to come dangerously close to Earth in 2036. If this doesn’t send chills down your spine, you haven’t read enough science fiction.
In a February 11th article in the Russian state-owned news agency TASS, Sabit Saitgarayev, the lead researcher at the Makeyev Rocket Design Bureau, says Russian scientists are developing a program to upgrade Inter-Continental Ballistic Missiles (ICBMs) to destroy near-Earth meteors from 20-50 metres in size. Apophis’ approach in 2036 would be a test for this program.
ICBM’s are the kind of long range nukes that the USSR and the USA had pointed at each other for decades during the Cold War. They still have some pointed at each other, and they can be launched quickly. This program would take that technology and improve it for anti-asteroid use.
Typical rockets of the type that take payloads into space are not good candidates for intercepting asteroids. They require too much lead time to meet the threat of an incoming asteroid that might be detected only days before impact. They can take several days to fuel. But ICBM’s are different. They can stand at the ready for long periods of time, and be launched at a moment’s notice. But to be suitable for use as asteroid killers, they have to be upgraded.
Design work on the asteroid-killing ICBM’s has already begun, admitted Saitgarayev, but he did not say whether the money has been committed or whether the authorization has been given to go ahead with the project. But like a lot of things that are said and done by Russia, it’s difficult to know exactly where the truth lies.
There’s no question that being prepared to prevent an asteroid strike on Earth is of the utmost importance. No matter where on Earth one was to strike, the effects could be global. But one thing’s certain: the development and testing of missiles designed to be used in space is unsettling.
It’s also unsettling in light of the January 16th TASS article stating that “The international scientific community has asked Russian scientists to develop an asteroid deflection system on the basis of nuclear explosions in space.” Taken together, the two announcements point towards a program of weaponizing space, something the international community has agreed should be avoided. In fact, there is a ban on nuclear explosions in space.
We don’t want to be alarmist. There are only a handful of countries in the world that have the capacity to develop some protective system against asteroids, and Russia is definitely one of them. And if Earth were threatened by an asteroid, the weaponization of space would be the least of our concerns.
The fact that Russia wants to develop a missile system with nuclear warheads, and employ it in space, is not entirely unreasonable. But it should make us stop and think. What will happen if something goes wrong?
It’s easy to imagine a scenario where an atomic explosion went off in low-Earth orbit. What would the consequences be? And what are the consequences to having one country develop this capability, rather than an international group? How can this whole endeavour be managed responsibly?
Special Guest: Dr. Or Graur, Research Associate at the Center for Cosmology and Particle Physics at New York University; Researches what type of star leads to a thermonuclear, or “Type Ia,” supernova.
Jupiter takes a beating from Comet Shoemaker-Levy 9. Credit: NASA/Hubble Space Telescope team.
I’ve always liked the idea that Jupiter has acted like a protector to its little brother, Earth. That it has used its massive gravitational pull to divert asteroids and comets from a collision course with Earth. Maybe Jupiter even felt bad when one got through, and doomed the dinosaurs to extinction. But a new study has cast this idea into doubt.
The idea of Jupiter as a protector has been around for a while. The images of comet Shoemaker-Levy 9 breaking apart and crashing into Jupiter in 1994 reinforced the idea. But according to Kevin Grazier, at the Jet Propulstion Laboratory (JPL), rather than acting solely as a shield, re-directing comets and other objects away from the inner solar system, Jupiter may have actually directed planetesimals into the inner solar system.
Illustration of a rocky planet being bombarded by comets. (Image credit: NASA/JPL-Caltech)
In the early days of the Solar System, there was much more debris around than there is now. The early days would have been a race between planetesimals to gather enough mass to form the planets we see today. After planets were formed, there would still have been plenty of planetesimals left. This new study shows that, rather than clearing the inner solar system from all this debris that could collide with Earth, Jupiter nudged many of these planetesimals towards Earth, helping to create Earth as we know it.
As reported in January 2016 in Astrobiology, Glazier created a simulator of the solar system, and ran 30,000 particles through this simulation. All of the particles began in “non life-threatening” trajectories, but a significant number of them ended the simulation in orbits that crossed the orbit of the Earth.
So not only did Jupiter—and Saturn—re-direct material into the inner Solar System, but the simulation also showed that Jupiter slowed that material to a speed which allowed it to contribute mass to Earth.
But these planetesimals would have contributed more than just mass to Earth. They would have carried volatiles with them. Volatiles are chemical elements and molecules with low boiling points. They are associated with the atmosphere and the crust. These volatiles, which include nitrogen, hydrogen, carbon dioxide, and others, make up a large portion of the Earth’s crust. Without them, Earth would be a very different place. It may never have developed the atmosphere that has allowed life to flourish.
It’s clear that Jupiter has contributed to the evolution of Earth and the Solar System as we know it. As the largest planet by far, its influence is undeniable. As a result of this study, we better understand the dual-role Jupiter has played. While it no doubt has played the role of protector, by changing the direction of some objects on a collision course with Earth, Jupiter’s presence has also been responsible for slowing and diverting planetesimals—and their life-friendly volatiles—directly into Earth.
From Lunar orbit, Earth is obviously habitable. But from a distant point in the galaxy, not so much. Image: NASA/LRO.
Right now, we’re staring hard at a small section of the sky, to see if we can detect any planets that may be habitable. The Kepler Spacecraft is focused on a tiny patch of sky in our Milky Way galaxy, hoping to detect planets as they transit in front of their stars. But if alien astronomers are doing the same, and detect Earth transiting in front of the Sun, how habitable would Earth appear?
You might think, because, well, here we are, that the Earth would look 100% habitable from a distant location. But that’s not the case. According to a paper from Rory Barnes and his colleagues at the University of Washington-based Virtual Planetary Laboratory, from a distant point in the galaxy, the probability of Earth being habitable might be only 82%.
Illustration of the Kepler spacecraft.(NASA/Kepler mission/Wendy Stenzel)
Barnes and his team came up with the 82% number when they worked to create a “habitability index for transiting planets,” that seeks to rank the habitability of planets based on factors like the distance from its star, the size of the planet, the nature of the star, and the behaviour of other planets in the system.
The search for habitable exo-planets is dominated by the idea of the circumstellar habitable zone—or Goldilocks Zone—a region of space where an orbiting planet is not too close to its star to boil away all the water, and not so far away that the water is all frozen. This isn’t a fixed distance; it depends on the type and size of the star. With an enormous, hot star, the Goldilocks Zone would be much further away than Earth is from the Sun, and vice-versa for a smaller, cooler star. “That was a great first step, but it doesn’t make any distinctions within the habitable zone,” says Barnes.
Comparing a star’s habitable zone based on its size. Credit: Fine Art America/Detlev Van Ravenswaay.
Kepler has already confirmed the existence of over 1,000 exo-planets, with over 4,700 total candidate planets. And Kepler is still in operation. When it comes time to examine these planets more closely, with the James Webb Space Telescope and other instruments, where do we start? We needed a way to rank planets for further study. Enter Barnes and his team, and their habitability index.
To rank candidates for further study, Barnes focused on not just the distance between the planet and the host star, but on the overall energy equilibrium. That takes into account not just the energy received by the planet, but the planet’s albedo—how much energy it reflects back into space. In terms of being warm enough for life, a high-albedo planet can tolerate being closer to its star, whereas a low-albedo planet can tolerate a greater distance. This equilibrium is affected in turn by the eccentricity of the planet’s orbit.
The habitability index created by Barnes—and his colleagues Victoria Meadows and Nicole Evans—is a way to enter data, including a planet’s albedo and its distance from its host star, and get a number representing the planet’s probability of being habitable. “Basically, we’ve devised a way to take all the observational data that are available and develop a prioritization scheme,” said Barnes, “so that as we move into a time when there are hundreds of targets available, we might be able to say, ‘OK, that’s the one we want to start with.’”
So where does the Earth fit into all this? If alien astronomers are creating their own probability index, at 82%, Earth is a good candidate. Maybe they’re already studying us more closely.
