Posted on by Fraser Cain

K-T Boundary

Chicxulub Crater

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What killed the dinosaurs? That’s a question that has puzzled paleontologists since dinosaurs were first discovered. Maybe the global climate changed, maybe they were killed by disease, volcanoes, or the rise of mammals. But in the last few decades, a new theory has arisen; an asteroid strike millions of years ago drastically changed the Earth’s environment. It was this event that pushed the dinosaurs over the edge into extinction. What’s the evidence for this asteroid impact? A thin dark line found in layers of sediment around the world; evidence that something devastating happened to the planet 65 million years ago. This line is known as the K-T boundary.

What is the K-T boundary? K is actually the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period. So the K-T boundary is the point in between the Cretaceous and Tertiary periods. Geologists have dated this period to about 65.5 million years ago.

When physicist Luis Alvarez and geologist Walter Alvarez studied the K-T boundary around the world, they found that it had a much higher concentration of iridium than normal – between 30-130 times the amount of iridium you would expect. Iridium is rare on Earth because it sank down into the center of the planet as it formed, but iridium can still be found in large concentrations in asteroids. When they compared the concentrations of iridium in the K-T boundary, they found it matched the levels found in meteorites.

The researchers were even able to estimate what kind of asteroid must have impacted the Earth 65.5 million years ago to throw up such a consistent layer of debris around the entire planet. They estimated that the impactor must have been about 10 km in diameter, and release the energy equivalent of 100 trillion tons of TNT.

When that asteroid struck the Earth 65.5 million years ago, it destroyed a region thousands of kilometers across, but also threw up a dust cloud that obscured sunlight for years. That blocked photosynthesis in plants – the base of the food chain – and eventually starved out the dinosaurs.

Researchers now think that the asteroid strike that created the K-T boundary was probably the Chicxulub Crater. This is a massive impact crater buried under Chicxulub on the coast of Yucatan, Mexico. The crater measures 180 kilometers across, and occurred about 65 million years ago.

Geologists aren’t completely in agreement about the connection between the Chicxulub impact and the extinction of the dinosaurs. Some believe that other catastrophic events might have helped push the dinosaurs over the edge, such as massive volcanism, or a series of impact events.

We have written many articles about the K-T boundary for Universe Today. Here’s an article about how the dinosaurs probably weren’t wiped out by a single asteroid, and here’s an article about how asteroids and volcanoes might have done the trick.

Here’s more information from the USGS, and an article from NASA.

We have recorded an episode of Astronomy Cast all about asteroid impacts. Listen to it here: Episode 29: Asteroids Make Bad Neighbors.

Reference:
USGS

Posted on by John Carl Villanueva

How Long is a Light Year?

This visible-light image shows the galaxy dubbed UGC 3789, which is 160 million light-years from Earth. Credit: STScI

A light year is the distance light can travel in vacuum in one year’s time. This distance is equivalent to roughly 9,461,000,000,000 km or 5,878,000,000,000 miles. This is such a large distance. For comparison, consider the circumference of the Earth when measured at the equator: 40,075 km.

You can even throw in the center to center distance between the Earth and the Moon, 384,403 km, and that value would still pale in comparison to 1 light year. Pluto, at its farthest orbit distance from the Sun, is only about 7,400,000,000 km from the center of our Solar System.

Because of its great scale, the light year is one of the units of distance used for astronomical objects. For example, Andromeda Galaxy, which is the nearest spiral galaxy from the Milky Way, is approximately 2.5 million light years away. Alpha Centauri, the nearest star system from our own Solar System is only 4.37 light years away.

Imagine using miles or kilometers when describing the diameter of the Milky Way Galaxy, some 100,000 light years. Expressed in km or mi in expanded notation, that could occupy a lot of space on this page. Just look at the first paragraph, wherein we described 1 light year, to see what I mean. Of course, one may argue that we can still use scientific notation. But well, some people easily get daunted by the mere sight of exponents.

Although the light year has a more familiar ring to us, having perhaps heard about it quite often in sci-fi films or in magazines, it is not the most widely used unit of distance in astrometry, the branch of astronomy that deals with measurements and positions of celestial bodies. That assignment is given to the parsec. 1 parsec is approximately equal to 3.26 light years.

Another commonly used unit of distance is the astronomical unit or AU, wherein 1 AU is the average distance between the Earth and the Sun, and is roughly equivalent to 150,000,000 km. It is normally used when describing distances within the Milky Way.

Always remember that the ‘year’ we have been referring to here is not based in the internationally-accepted Gregorian Calendar. Instead, ‘year’ here refers to the Julian year. 1 Julian year is equivalent to 365.25 days or 31,557,600 seconds. The Julian calendar does not designate dates, hence is different from the Gregorian Calendar.

We have some related articles here in Universe Today. Here are the links:

Here are the links of two more articles from NASA:

Here are two episodes at Astronomy Cast that you might want to check out as well:

Source: NASA

Posted on by John Carl Villanueva

What are Plate Boundaries?

In Plate Tectonic Theory, the lithosphere is broken into tectonic plates, which undergo some large scale motions. The boundary regions between plates are aptly called plate boundaries. Based upon their motions with respect to one another, these plate boundaries are of three kinds: divergent, convergent, and transform.

Divergent Boundaries:

Divergent boundaries are those that move away from one another. When they separate, they form what is known as a rift. As the gap between the two plates widen, the underlying layer may be soft enough for molten lava underneath to push its way upward. This upward push results in the formation of volcanic islands. Molten lava that succeeds in breaking free eventually cools and forms part of the ocean floor.

Some formations due to divergent plate boundaries are the Mid-Atlantic Ridge and the Gakkel Ridge. On land, you have Lake Baikal in Siberia and Lake Tanganyika in East Africa.

Convergent Boundaries:

Convergent boundaries are those that move towards one another. When they collide, subduction usually takes place. That is, the denser plate gets subducted or goes underneath the less dense one. Sometimes, the plate boundaries also experience buckling. Convergent boundaries are responsible for producing the deepest and tallest structures on Earth.

Among those that have formed due to convergent plate boundaries are K2 and Mount Everest, the tallest peaks in the world. They formed when the Indian plate got subducted underneath the Eurasian plate. Another extreme formation due to the convergent boundary is the Mariana Trench, the deepest region on Earth.

Transform Boundaries:

Transform boundaries are those that slide alongside one another. Lest you imagine a slippery, sliding motion, take note that the surfaces involved are exposed to huge amounts of stress and strain and are momentarily held in place. As a result, when the two plates finally succeed in moving with respect to one another, huge amounts of energy are released. This causes earthquakes.

The San Andreas fault in North America is perhaps the most popular transform boundary. Transform boundary is also known as transform fault or conservative plate boundary.

Movements of the plates are usually just a few centimeters per year. However, due to the huge masses and forces involved, they typically result in earthquakes and volcanic eruptions. If the interactions between plate boundaries involve only a few centimeters per year, you could just imagine the great expanse of time it had to take before the land formations we see today came into being.

You can read more about plate boundaries here in Universe Today. Here are the links:

Here are the links of two more articles from USGS:

Here are two episodes at Astronomy Cast that you might want to check out as well:

Sources:
Plate Boundaries
http://pubs.usgs.gov/gip/dynamic/understanding.html

Posted on by Fraser Cain

What is a Volcanic Neck?

Devils Tower, a volcanic neck.

Remember that strange rock formation in Close Encounters of the Third Kind. It looked like the top of a toothpaste tube, but made of solid rock. That’s a volcanic neck, and it has nothing to do with space aliens. In reality, a volcanic neck is the solidified magma trapped inside a volcano. After millions of years, the softer outer layer of the volcano erodes, and all that remains is the volcanic neck. The structure in Close Encounters is Devil’s Tower, located in Wyoming.

Volcanic necks are somewhat rare because when a magma plug forms within a volcano, it often leads to an explosive eruption, like what happened with Krakatoa, or more recently with Mount St. Helens. The plug is broken up and ejected as ash and rock in a split second. But if the pressure isn’t great enough to actually detonate the top of the volcano, the plug cools and hardens deep within the Earth.

There are some very famous volcanic necks around the world. Probably the most famous is Devils Tower in Wyoming. It rises 386 meters above the surrounding landscape, a lone prominence of rusty red rock. I’ve actually stood beside it, and it’s one of the most impressive geologic features I’ve ever seen.

The type of erosion will define the shape of the volcanic neck. For example, glaciers will erode away one side of the volcanic neck, but leave a long tail behind.

We have written many articles about volcanoes for Universe Today. Here’s an article about the largest volcano in the Solar System, and here’s an article about the largest volcano on Earth.

You can also find out more information about volcanic necks from the USGS.

We have also recorded an episode of Astronomy Cast dealing with volcanoes on Earth and across the Solar System. Check out Episode 141 – Volcanoes, Hot and Cold.

Posted on by Brian Ventrudo

Magnetic Fields Have Key Influence on Star Formation

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When a giant cloud of interstellar gas and dust collapses to form a new cluster of stars, only a small fraction of the cloud’s mass ends up in stars. Scientists have never been sure why.  But a new study provides insights into the role magnetic fields might play in star formation, and suggests more than the influence of gravity should be taken into account in computer models of stellar birth.

Gravity favors star formation by drawing material together, so if most material does not coalesce into stars, some additional force must hinder the process. Magnetic fields and turbulence are the two leading candidates. Magnetic fields channel flowing gas, making it hard to draw gas from all directions, while turbulence stirs the gas and induces an outward pressure that counteracts gravity.

“The relative importance of magnetic fields versus turbulence is a matter of much debate,” said astronomer Hua-bai Li of the Harvard-Smithsonian Center for Astrophysics. “Our findings serve as the first observational constraint on this issue.”

Li and his team studied 25 dense patches, or cloud cores, each one about a light-year in size. The cores, which act as seeds from which stars form, were located within molecular clouds as much as 6,500 light-years from Earth.

The degree of polarization of light from the clouds is influenced by the direction and strength of the local magnetic fields, so the researchers measured polarization to determine magnetic field strength. The fields within each cloud core were compared to the fields in the surrounding, tenuous nebula.

The magnetic fields tended to line up in the same direction, even though the relative size scales (1 light-year-sized cores versus 1000 light-year-sized nebulas) and densities were different by orders of magnitude. Since turbulence would tend to churn the nebula and mix up magnetic field directions, their findings show that magnetic fields dominate turbulence in influencing star birth.

“Our result shows that molecular cloud cores located near each other are connected not only by gravity but also by magnetic fields,” said Li. “This shows that computer simulations modeling star formation must take strong magnetic fields into account.”

In the broader picture, this discovery aids understanding of how stars and planets form and, therefore, how the universe has come to look the way it is today.

Source: Harvard-Smithsonian Center for Astrophysics

Posted on by Fraser Cain

Mantle Plume

Hotspot

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One of the mysteries of Earth science is hotspots. While most volcanoes are found at plate boundaries, where two tectonic plates are rubbing against each other, volcanic hotspots can be anywhere, even in the middle of continents. What causes volcanic hotspots? One theory is the idea of a mantle plume.

A mantle plume is kind of like what’s going on inside a lava lamp. As the light heats up the wax in a lava lamp, it rises up through the oil in large blobs. These blobs reach the top of the lamp, cool and then sink back down to be heated up again.

Inside the Earth, the core of the Earth is very hot, and heats up the surrounding mantle. Heat convection in the mantle slowly transports heat from the core up to the Earth’s surface. These rising columns of heat can come up anywhere, and not just at the plate boundaries. Geologists did fluid dynamic experiments to try and simulate mantle plumes, and they found they formed long thin conduits topped by a bulbous head.

When the top of a mantle plume reaches the base of the Earth’s lithosphere, it flattens out and melts a large area of basalt magma. This whole region can form a continental flood basalt, which only lasts for a few million years. Or it can maintain a continuous stream of magma to a fixed location; this is a hotspot.

As the lithosphere continues to move through plate tectonics, the hotspot appears to be shifting its position over millions of years. But really the hotspot is remaining in a fixed location, and the Earth’s plates are shifting above it.

Two of the most famous places that might have mantle plumes underneath them are the Hawaiian Islands and Iceland.

We have written many articles about volcanoes and the interior of the Earth for Universe Today. Here’s an article about the difference between magma and lava, and here’s an article about magma chambers.

Here’s a great resource on mantle plumes, and here’s another.

We have recorded an entire episode of Astronomy Cast about volcanoes around the Solar System. Listen to it here: Episode 141: Volcanoes, Hot and Cold.

Posted on by Fraser Cain

Atmosphere Layers

Atmosphere layers. Image credit: NASA
Atmosphere layers. Image credit: NASA

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Seen from space, the Earth’s atmosphere is incredibly thin, like a slight haze around the planet. But the atmosphere has several different layers that scientists have identified; from the thick atmosphere that we breathe to the tenuous exosphere that extends out thousands of kilometers from the Earth. Let’s take a look at the different atmosphere layers.

Scientists have identified 5 distinct layers of the atmosphere, starting with the thickest near the surface, and then thinning out until it eventually merges with space.

The troposphere is the first layer above the surface of the Earth, and it contains 75% of the Earth’s atmosphere, and 99% of its water. Breathe in, that’s the troposphere. The average depth of the troposphere is about 17 km high. It gets deeper in the tropical regions, up to 20 km, and then shallower near the Earth’s poles – down to 7 km thick. Temperature and pressure are at the their highest at sea level, and then decrease with altitude. The troposphere is also where we experience weather.

The next atmosphere layer is the stratosphere, extending above the troposphere to an altitude of 51 km. Unlike the troposphere, temperature actually increases with height. Commercial airlines will typically fly in the stratosphere because it’s very stable; above weather, and allows them to optimize burning jet fuel. You might be surprised to know that bacterial life survives in the stratosphere.

Above that is the mesosphere, which starts at about 50-85 km above the Earth’s surface and extends up to an altitude of 80-90 km. Temperatures decrease the higher you go in the mesosphere, reaching a low of -100 °C, depending on the latitude and season.

Next comes the thermosphere. This region starts around 90 km above the Earth and goes up to about 320 and 380 km. The International Space Station orbits within the thermosphere. This is the region of the atmosphere where ultraviolet radiation causes ionization, and we can see auroras. Temperatures in the thermosphere can actually reach 2,500 °C; however, it wouldn’t feel warm because the atmosphere is so thin.

The 5th and final layer of the Earth’s atmosphere is the exosphere. This starts above the thermosphere and extends out for hundreds and even thousands of kilometers. Air molecules in this region can travel for hundreds of kilometers without bouncing into another particle.

We have written many articles about the Earth’s atmosphere for Universe Today. Here’s an article about the composition of the Earth’s atmosphere, and here’s information about the Earth’s early atmosphere.

Here’s a great article from NASA that explains the different layers of the atmosphere, and here’s more information from NOAA.

We have done a whole episode of Astronomy Cast just about Earth. Listen to it here, Episode 51 – Earth.

Posted on by Fraser Cain

Super Earths

An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra. Credit: NASA

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The holy grail in the search for extrasolar planets will be the discovery of Earthlike planets orbiting other stars. With better telescopes and techniques, astronomers will eventually be able to even detect the atmospheres of extrasolar planets and determine if there’s life there. Although Earth-sized planets are impossible to detect with current observatories, astronomers are now finding super earths.

A super Earth is a terrestrial planet orbiting a distant star. But instead of having the mass of our own planet, it might have 2, 5, or even 10 times the mass of the Earth. Although that makes them large, very massive planets, they’re not as large or massive as gas giants.

And just because they’re called super Earths doesn’t mean they’re habitable, or even Earthlike in climate at all. Super Earths could be orbiting close to their parent star, or well outside the solar system’s habitable zone.

Scientists haven’t completely settled on a definition for super Earths. Some believe a planet should be considered a super Earth if it’s a terrestrial planet between 1 and 10 Earth masses, while others think it should be between 5 and 10 Earth masses.

The first super Earth ever discovered was found in 1991 orbiting a pulsar. Obviously that wouldn’t really be a very habitable place to live. The first super earth found orbiting a main sequence star was found in 2005, orbiting the star Gliese 876. It’s estimated to have 7.5 times the mass of the Earth, and orbits its parent star every 2 days. With such a short orbital period, you can expect that it’s orbiting very close to its parent star. Temperatures on the surface of the planet reach 650 kelvin.

The first super earth found within its star’ habitable zone was Gliese 581 c. It’s estimated to have 5 Earth masses, and orbits its parent star at a distance of 0.073 astronomical units (1 AU is the average distance from the Earth to the Sun). That’s pretty close to the star, and Gliese 581 c would probably have a runaway greenhouse effect, similar to Venus. But right beside that is Gliese 581 d, with a mass of 7.7 Earths and an orbit of 0.22 AU. This planet could very well have liquid water on its surface.

The smallest super Earth discovered so far is MOA-2007-BLG-192Lb, which has only 3.3 times the mass of the Earth, and was orbiting a brown dwarf star. But this record will probably be beaten by the time you read this, as planet hunters get better. It’s only a matter of time before a true Earthlike planet is discovered.

We have written many articles about super Earths. Here’s an article speculating on the kinds of atmospheres that super Earths might have, and another article about how similar super Earths really are to our own planet.

Here’s an artist’s impression of a super Earth features on NASA’s Astronomy Picture of the Day website, and here’s an article from NASA about super Earths.

We also recorded an episode of Astronomy Cast dealing with the different kinds of extrasolar planets you can find. Listen to it here. Episode 125: A Zoo of Extrasolar Planets.

Source: Wikipedia

Posted on by Nancy Atkinson

Create Your Own Galaxy Mashup With New Galaxy Zoo Tool

M81. Image credit: NASA/JPL-Caltech/ESA/Harvard-Smithsonian CfA

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If you haven’t yet succumbed to the temptation of Galaxy Zoo, a new add-on to the popular citizen scientist project just might catapult you into joining the thousands of people who are clicking and classifying. Galaxy Zoo has now teamed up with Microsoft’s World Wide Telescope to allow users to immerse themselves in the universe and be able to easily create videos and sky tours that can be customized and shared with friends and family. “Now there is an easy way to inflict your favorites on others,” said Galaxy Zoo team member Dr. Pamela Gay.

The new Sky Tour tool, available here was created by two of Gay’s students at Southern Illinois University Edwardsville, sophomores Jarod Luebbert and Mark Sands.

On Galaxy Zoo, the Zooites work with isolated images of galaxies to classify them by shape and other features. Coordinating with WWT allows users to see the galaxies in their home environments on the sky. “It’s so easy to classify a few hundred — or even a few thousand galaxies and think you’ve seen a reasonable chunk in the sky,” Gay told Universe Today. “But then you start looking at them in WWT and realize each galaxy is just a pinhead of light in a vast, vast sky. Jarod and Mark’s work really gives us a since of scale and how small we all are.”

To give you a taste of how this interface works, Luebbert and Sands created a great teaser video.

Galaxy Zoo – WorldWide Telescope Mashup! from Galaxy Zoo on Vimeo.

(The music on the video is great! Even though the video says “Starts Tomorrow,” tomorrow has now arrived, and the Sky Tour tool is available to use.)

GZ users need to classify at least 100 galaxies before the Sky Tour tool works with their “favorites.”

Tours can be created and customized with music, pictures, and logos. Other new features include sharing directly to networking sites, and competition with other Galaxy Zoo users.

But how do college students get a chance to work on a project with Microsoft and world class astronomers?

“We knew the job opportunity had become available that they wanted two teammates who would work well together for an excellent and educational project dealing with GalaxyZoo,” Sands told Universe Today. “Jarod and I being close friends, were encouraged to apply for this position by a fellow Zoo team member, Scott Miller. After being hired, we were accepted by the rest of the team and got right to work.”

Gay and Galaxy Zoo founder Chris Lintott presented the two students with a proposal they had sent to Microsoft explaining a very detailed approach to integrating Microsoft WorldWide Telescope with GalaxyZoo.

“The synopsis was simple, and we were to merge the creation of WorldWide Telescope tours with GalaxyZoo user favorites,” Sands said, “as well as implement a WordPress (a popular blogging software) plugin for educators to create WWT tours for podcasts (a project to be released in December). With no strict direction, Pamela allowed us to go wild and be creative with our own ideas.”

The two students began formulating ideas and creating dozens of mockups. Then in July, Sands and Luebbert found themselves arriving at Microsoft Research Building 99 in Redmond, WA collaborating directly with the architects of WorldWide Telescope.

Sands said WWT architect Jonathan Fay and Peter Turcan were readily available to help with the Galaxy Zoo project and were extremely helpful, as well as Kim Rush. Yan Xu from Microsoft worked directly with Gay and Lintott on the GalaxyZoo proposal.

“It was a blast to work with them and they helped us out a lot,” said Luebbert. “Even though the original idea came from Pamela and Chris, Mark and I added our own touches as we went along.”

“Working with Microsoft was an unimaginable experience,” Sands said. “There are some fantastic people who work there and deserve just as much attention as we do. I speak for both of us when I say we had a lot of fun working with them, even if it only lasted two weeks.”

The GZ/WWT integration has received great reviews from the users. “The ability of Galaxy Zoo’s volunteers to find interesting objects never ceases to amaze me,” said Lintott. “I’m looking forward to sitting back and enjoying their tours of the Universe.”

The citizen scientists of Galaxy Zoo have classified more than 100 million classifications galaxies since its launch in July 2007. Additionally, results from users have inspired more than 15 scientific papers to date.

Posted on by Fraser Cain

ISS Tracking

International Space Station. Credit: NASA

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The International Space Station, or ISS, is the largest object every built by humans in space. And because it’s so large, it’s also very bright; easily visible with the unaided eye. The ISS also follows an orbital track that takes over different parts of the Earth. That means if you know the right time, you can go out and watch the station pass right over. But you need to know the right time, and that requires some kind of ISS tracking tool. Let’s take a look at some ISS tracking tools you can use to tell you when you should head outside and look up.

The best place to track ISS is from NASA’s human space flight ISS tracking page. This site will tell you the current location of the International Space Station, and space shuttles currently in flight, and the Hubble Space Telescope. The problem is that this tells you where the space station is right now, and not when it’s going to be passing through your skies… at night.

A better tool for that is the ISS sightings page. You download an applet that lets you put in your place on Earth and it gives you some upcoming dates and times that the station will be passing overhead. There’s also a quick drop down box, where you can select your location from many places in the world.

Another great tool is Heavens Above. It allows you to track the current position of thousands of satellites, including ISS and the space shuttles, when they’re in orbit.

So use one of these tools for ISS tracking, and then head outside and see if you can see the station with your own eyes.

We have written many articles about the International Space Station. Here’s an article about how you can actually see ISS in the daytime; it’s just that bright. And here’s an image of ISS and the shuttle transiting the Sun.

We have recorded an episode of Astronomy Cast that talks about the Space Station’s orbit.