Wednesday, February 6, 2013

FEB 6 Use Big Dipper’s pointers to find Polaris, the North Star





FEB 6
Use Big Dipper’s pointers to find Polaris, the North Star
If you can find the Big Dipper in the northern sky in mid to late evening tonight, you can find the North Star, Polaris. The Big Dipper will be low in the northeast sky, but it’ll climb upward during the evening hours, to reach its high point for the night in the wee hours after midnight.
The Big Dipper isn’t a constellation. Instead, it’s an asterism, just a recognizable pattern of stars on the sky’s dome. It’s part of the constellation Ursa Major, the Greater Bear.
A well-known trick for finding the North Star, or Polaris, is that the two outermost stars in thebowl of the Big Dipper point to Polaris. Those stars are Dubhe and Merak. They are well known among amateur astronomers as The Pointers.
Can’t find the Big Dipper? Yes, you can!
It really does look like a dipper, and it’s pretty bright. You just have to look for it at a time when it’s visible. And that’ll be tonight, and for many nights to come over the coming weeks and months … in the north in mid-evening. Once you find the Big Dipper, use the pointer stars to find Polaris, the North Star.

Tuesday, February 5, 2013

Asteroid 2012 DA14 to sweep close on February 15, 2013


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Asteroid 2012 DA14 to sweep close on February 15, 2013
Asteroid 2012 DA14 on February 15, 2012


Source


It’ll pass within the moon’s distance from Earth – closer than the orbits of geosynchronous satellites. But it won’t strike us in 2013.
A near-Earth asteroid – called 2012 DA14 by astronomers – will pass very close to Earth on February 15, 2013. Astronomers estimate that, when it’s closest to us, it’ll be within the orbit of the moon (which is about 240,000 miles away), and within the orbits of geosynchronous satellites (about 26,000 miles up). 2012 DA14 will be about 21,000 miles (35,000 kilometers) away. It will not strike Earth in 2013.Astronomers’ calculations of asteroid orbitscan be trusted. After all, even decades ago, they knew enough about calculating orbits to send people to the moon and bring them safely back, and today we are able place our space vehicles in orbit around objects as small as asteroids.
So, no, 2012 DA14 won’t strike us in 2013. There was a remote possibility it might strike us in 2020, but that possibility has been ruled out also.
Asteroid 2012 DA14 will pass closest on February 15, 2013. As the image above shows, it will pass much closer than the orbit of the moon - closer even that orbiting geosynchronous satellites (22,000 miles). View larger. Image Credit: NASA
What will happen when Asteroid 2012 DA14 passes closely in 2013?
What will happen when it passes us? The short answer is … nothing. On the day it passes, most of us won’t see it or be aware of its passage, in any way. The asteroid won’t alter the tides. It won’t cause volcanoes. It’ll just sweep closely past us – as millions of asteroids have done throughout Earth’s four-and-a-half-billion-year history – some in your own lifetime.
The asteroid will be within range for small telescopes and solidly mounted binoculars, used by experienced observers who have access to appropriate stars charts. Here’s what NASA says about its visibility:
On [February 15, 2013], the asteroid will travel rapidly from the southern evening sky into the northern morning sky with its closest Earth approach occurring about 19:26 UTC when it will achieve a magnitude of less than seven, which is somewhat fainter than naked eye visibility. About 4 minutes after its Earth close approach, there is a good chance it will pass into the Earth’s shadow for about 18 minutes or so before reappearing from the eclipse. When traveling rapidly into the northern morning sky, 2012 DA14 will quickly fade in brightness.
What do we know about asteroid 2012 DA14?
Asteroid 2012 DA14 is a little guy, compared to some asteroids, although its size has not been pinned down precisely. It is thought to be about 45 meters across (nearly 150 feet across), with an estimated mass of about 130,000 metric tons.
If a space object 150 feet wide were to strike our planet, it wouldn’t be Earth-destroying. But it has been estimated that it would produce the equivalent of 2.4 megatons of TNT. How does that compare with other known impact events on Earth? In 1908, in a remote part of Russia, an explosion killed reindeer and flattened trees. But no crater was ever found. Scientists now believe a small comet struck Earth. That event has been estimated at 3 to 20 megatons. So 2012 DA14 is in the same approximate realm as the Tunguska comet(which, actually, might have been an asteroid instead). It would not destroy Earth, but it could flatten a city.
Of course, about 70% of our world is covered by oceans. That means the most likely landing spot of any incoming asteroid is in the water – not on a city or other populated area.
Astronomers at the Observatorio AstronĂ³mico de La Sagra in Spain discovered 2012 DA14 in early 2012. We know 2012 DA14′s orbit is similar to that of Earth. That is one reason the asteroid eluded astronomers until recently. You can be sure that many astronomers are carefully tracking 2012 DA14 now.
The orbit of 2012 DA14 is an inclined ellipse. In other words, it’s tilted sightly with respect to Earth’s orbit around the sun, and, like Earth’s orbit, it’s not circular but elliptical – like a circle that someone sat down on. According to Bad Astronomer Phil Plait, who appears to have used a computer program to look at its orbit:
The asteroid spends most of its time well away from our planet. However, the path of the rock does bring it somewhat close to the Earth twice per orbit, or about every six months. The last time it passed us was on February 16 [2012], when it was about 2.5 million km (1.5 million miles) away, equal to about 6 times the distance to the moon. That’s usually about the scale of these encounters — it misses us by quite a margin.
If we know it will miss us in 2013 and in 2020, why are astronomers still watching? In fact, the orbit of 2012 DA14 is not entirely pinned down, although it is known well enough to say for sure: it will not hit us next year, or in 2020.
But it will come close on February 15, 2013! It should be close enough to catch the attention of virtually everyone on Earth in February 2013, on what’s sure to be a media field day.
Will 2012 DA14 strike Earth in 2020?
No. In March 2012, when a collision between 2012 DA14 and Earth in 2020 was stillremotely possible, I asked astronomer Donald Yeomans to clarify the risk. Yeomans is, among other things, manager of NASA’s Near-Earth Object Program Office at NASA’s Jet Propulsion Laboratory. In March 2012, he told EarthSky that a 2020 collision between Earth and asteroid 2012 DA14 was …
… approximately one chance in 83,000, with additional remote possibilities beyond 2020. However, by far the most likely scenario is that additional observations, especially in 2013, will allow a dramatic reduction in the orbit uncertainties and the complete elimination of the 2020 impact possibility.
It turned out they didn’t have to wait until 2013. By May, 2012, astronomers had ruled out even the remote possibility of a 2020 collision.
Still, 2012 DA14 and asteroids like it are sobering.
Bottom line: The near Earth asteroid 2012 DA14 will have a very close pass near Earth on February 15, 2013. It will sweep approximately 21,000 miles from us – much closer than the moon’s orbit and closer than geosynchronous satellites. It will not strike Earth. Its orbit around the sun can bring it no closer to the Earth’s surface on February 15, 2013 than 3.2 Earth radii.

Magnitude 8.0 earthquake strikes off the Solomon Islands




Magnitude 8.0 earthquake strikes off the Solomon Islands
A tsunami warning is in effect for the Solomon Islands and other nearby islands. A tsunami watch is in effect for New Zealand, Australia, and elsewhere in the Pacific.
February 6, 2013 earthquake
According to the U.S. Geological Survey (USGS), a magnitude-8.0 earthquake has occurred near the Solomon Islands – near New Zealand and Australia in Earth’s southern hemisphere. The Pacific Tsunami Warning Center has issued a warning for places in the Pacific near the epicenter, and a watch elsewhere in the Pacific. According to the Pacific Tsunami Warning Center, it isn’t known that a tsunami has been generated. They generated the watch and warning only after evaluating the earthquake itself. They did comment in their bulletin:
AN EARTHQUAKE OF THIS SIZE HAS THE POTENTIAL TO GENERATE A DESTRUCTIVE TSUNAMI THAT CAN STRIKE COASTLINES NEAR THE EPICENTER WITHIN MINUTES AND MORE DISTANT COASTLINES WITHIN HOURS.

Here are the details of the event from USGS.
Event Time
2013-02-06 01:12:23 UTC
2013-02-05 19:12:23 UTC-06:00 system time
Location
10.752°S 165.089°E
depth=5.8km (3.6mi)
February 6, 2013 earthquake strikes near Solomon Islands (February 5 in U.S. and Europe).
The region around the Pacific Ocean is known as theRing of Fire. It is extremely geologically active, with most of the world’s volcanoes and earthquakes occurring there. Read more about this image, and about magnitude 8.0 earthquakes since 1900, from USGS.
Here is the bulletin from the Pacific Tsunami Warning Center:
TSUNAMI BULLETIN NUMBER 001
PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS
ISSUED AT 0118Z 06 FEB 2013
THIS BULLETIN APPLIES TO AREAS WITHIN AND BORDERING THE PACIFIC OCEAN AND ADJACENT SEAS…EXCEPT ALASKA…BRITISH COLUMBIA…WASHINGTON…OREGON AND CALIFORNIA.
… A TSUNAMI WARNING AND WATCH ARE IN EFFECT …
A TSUNAMI WARNING IS IN EFFECT FOR
SOLOMON ISLANDS / VANUATU / NAURU / PAPUA NEW GUINEA / TUVALU /
NEW CALEDONIA / KOSRAE / FIJI / KIRIBATI / WALLIS AND FUTUNA
A TSUNAMI WATCH IS IN EFFECT FOR
MARSHALL ISLANDS / HOWLAND AND BAKER / POHNPEI / TOKELAU /
SAMOA / KERMADEC ISLANDS / NEW ZEALAND / AMERICAN SAMOA /
TONGA / AUSTRALIA / NIUE / COOK ISLANDS / INDONESIA /
WAKE ISLAND / CHUUK / JARVIS ISLAND / GUAM / NORTHERN MARIANAS /
PALMYRA ISLAND / YAP / JOHNSTON ISLAND / MINAMITORISHIMA /
BELAU
FOR ALL OTHER AREAS COVERED BY THIS BULLETIN… IT IS FOR INFORMATION ONLY AT THIS TIME.
Bottom line: A magnitude 8.0 earthquake struck near the Solomon Islands on February 6, 2013 (February 5 in the U.S. and Europe). The Pacific Tsunami Warning Center has issued a tsunami warning.Source

Sunday, February 3, 2013

The Untold Story: Columbia Shuttle Disaster and Mysterious 'Day 2 Object'

Space Shuttle Left Wing
These detailed views represent a space shuttle left wing with Reinforced Carbon-Carbon, or RCC, panels with only those panels numbered 1 through 10, 16 and 17 shown. Each wing's leading edge had 22 RCC panels.
CREDIT: NASA 


A decade has passed since the ill-fated Columbia space shuttle orbiter and its seven-person crew ended their journey in catastrophe. During its Feb. 1, 2003 plunge back to Earth, the vehicle broke apart, with wreckage strewn across east Texas and western Louisiana.

Painstaking work by the Columbia Accident Investigation Board (CAIB) later identified the physical cause of the disaster as damage to Columbia's left wing that occurred just 81.9 seconds after launch.

A piece of insulating foam separated from the left "bipod ramp" that connected the shuttle's fuel tank to the orbiter, gouging a hole in a reinforced carbon-carbon (RCC) panel on the leading edge of Columbia's left wing.


Now, 10 years later, new information is coming to light on an event early in Columbia's mission, often termed the "Flight Day 2 Object."

When added to the wealth of information already known about how the Columbia accident occurred, this story reinforces a picture of technical slip-ups, a lack of effective communications and a failure of early detection and reaction to anomalies, all of which contributed to the disaster. [Video: Astronaut Jerry Ross Remembers Columbia]





















Panel 8
Reinforced Carbon-Carbon (RCC) Panel #8
Scott Hubbard, Columbia Accident Investigation Board member, inspects damaged Reinforced Carbon-Carbon (RCC) panel #8 following test.
CREDIT: NASA/CAIB

About a day after launch on Jan. 16, 2003, with Columbia's crew settling into its mission, an object roughly the size of a notebook computer drifted away from the orbiter out into space.
According to a source that asked not to be named, "due to a procedural issue" the object was not recognized during Columbia’s 16-day mission by the Air Force Space Command (AFSPC). That AFSPC procedure was later corrected.
The Flight Day 2 object, according to a source then working with the CAIB to help discern the cause of the Columbia calamity, was a fragment of the RCC panel on the orbiter's wing. A team of experts concluded that the departing piece had been lodged within the left wing by aerodynamic forces on Columbia's liftoff. It was set adrift after the orbiter reached space.
The CAIB made the final conclusion that the foam-shedding incident on Columbia's takeoff affected panel 8 of the RCC heat-shielding, which was located on the orbiter's leading edge. That foam strike punctured a hole in the RCC panel roughly 16 inches (41 centimeters) by 16 inches. Analysts estimated that a hole as small as 10 inches (25 cm) across could have caused the orbiter to be destroyed on re-entry through Earth's atmosphere.

That left-wing damage permitted the penetration of hot, re-entry gases, which led to the loss of Columbia and its crew. Superheated air entered the leading-edge insulation and progressively melted the aluminum structure of the left wing, until increasing aerodynamic forces led to loss of control, failure of the wing and disintegration of the orbiter.
From a re-entry standpoint, Columbia broke up very late, at a low altitude, roughly 30 to 35 miles (50 to 55 kilometers) above Earth, where heating had almost ceased. The breakup was primarily mechanical, due to localized heating that occurred earlier in the re-entry process.

Serendipitous observations
Space Shuttle Columbia Over Maui
Image of space shuttle Columbia in orbit during mission STS-107 were taken by the U.S. Air Force Maui Optical and Supercomputing (AMOS) site on Jan. 28, four days before Columbia's re-entry, as the spacecraft flew above the island of Maui in the Hawaiian Islands.
CREDIT: NASA/U.S. Air Force

A number of experts who studied the loss of Columbia and its crew shared their theories on the cause of the Flight Day 2 incident with SPACE.com.

Early on, experts had thought that perhaps a piece of orbital debris hit the shuttle.

In post-disaster work, an Air Force Space Command Space Analysis Center team worked with the Space Surveillance Network (SSN), a worldwide system of U.S. Army, Navy and Air Force-operated ground-based radars and optical sensors.

That team and SSN operators went back after Columbia's demise to see if there had been any serendipitous observations taken the orbiter during its mission by accident, among the wealth of photos of the sky during that period.

Indeed, that team did find some observations and noted there was another piece of debris in orbit with Columbia starting on Day 2 of its flight. Aiding in this identification was the fact that Columbia had been in a unique orbit, for not only the shuttle but virtually any other satellite, so there wasn't much else in the orbit.

After noting the Day 2 object, researchers began an investigation to determine the object's separation velocity and its time of release from Columbia.

Investigators hoped to see if the object departed the orbiter at high velocity, indicating a possible collision, or if it came off at low velocity, signifying something drifting away, perhaps out of Columbia's cargo bay.





















Radar information
FEMA Official Surveys Shuttle Debris
FEMA official surveys shuttle debris along with the Columbia Accident Investigation Board near Nacogdoches, Texas.
CREDIT: Mark Wolfe/FEMA

With radar information on hand concerning the object's size, and measurements of how quickly it decayed in Earth orbit, analysts could tell it was something with the dimensions of a notebook computer. Best estimates are that the Flight Day 2 object decayed from orbit on Jan. 20, disintegrating as it fell down through Earth's atmosphere. The item was never given a satellite catalogue number since it decayed before its discovery.

The Air Force and SSN analysts worked closely with Air Force Research Laboratory (AFRL) specialists, all focused on understanding the object's makeup and attempting to tag likely materials that had the right density. A final determination, according to a SPACE.com source, was that it was a piece of Columbia's carbon-carbon leading edge.

"That determination encouraged NASA to continue their testing of firing foam at the leading edge … finally getting a result that very closely matched our analysis," the source, who asked not to be named, said.

A post-disaster review of Columbia's movements on Day 2 showed the detached object appeared to separate after the orbiter undertook a couple of maneuvers to change its orientation.

The Space Analysis Center team believed that aerodynamic forces on ascent had pushed the Day 2 object back into the wing and Columbia's maneuvers subsequently shook the object loose.




















Foam impact

Another view of the situation at the time is offered by a Columbia Accident Investigation Board (CAIB) member, Scott Hubbard, then director of the NASA Ames Research Center and currently professor of aeronautics and astronautics at Stanford University.

Hubbard played an instrumental role in spotlighting the cause of Columbia's demise. To do so, he relied on computational modeling, reinforced by experimental testing with a large compressed-gas gun done by Southwest Research Institute (SwRI) scientists and engineers in San Antonio, Texas. During the tests, scientists fired a piece of foam at a target at speeds comparable to what a falling piece of debris from the shuttle would have experienced. Researchers then observed the damage.

Hubbard oversaw those tests, which showed that a chunk of falling insulating foam from the large, exterior fuel tank could indeed punch a hole in the leading edge of the orbiter's left wing — panel 8 of the RCC thermal protection system, to be exact.

"My decision to direct as definitive a test as possible of the foam impact on Columbia was driven by the desire to provide the crew and shuttle program with a clear, physical cause so that 'return to flight' could be carried out without hesitation," Hubbard told SPACE.com.

While there was a significant collection of circumstantial evidence — film of launch, "black box" data and collected debris — Hubbard said he had the strong sense that NASA was not converging on an answer to such basic parameters as the size of the falling foam.


Uncertainty of observations

"During the CAIB deliberations, the radar data and analysis by AFRL was occasionally presented to the board, but the uncertainty of the observations and myriad initial interpretations did little to convince us that the mysterious 'second day' object was part of the orbiter," Hubbard said. [Columbia Shuttle Disaster Explained (Infographic)]

"I can state quite unequivocally that the AFRL examination of the radar profile had no influence on the selection of the SwRI test parameters. Computational fluid dynamics analysis, the 35mm film data and emerging debris information had already convinced my team and me to aim at Panel 8 of the RCC."

The AFRL did not issue their final summary report until July 20, 2003, nearly two weeks after the definitive SWRI tests, Hubbard said.

"It is worth noting that the SWRI tests did produce a large section of RCC that, had it floated away from the orbiter, may have resembled the 2nd day piece," Hubbard said. "However, this observation is definitely post hoc and was not a test prediction."
Air Force Space Command response
FEMA and Texas Officials Survey Damage Caused by Shuttle Material
FEMA and State of Texas officials survey damage caused by falling shuttle material.
CREDIT: Mark Wolfe/FEMA
According to CAIB report findings, the Day 2 object was discovered after the accident during Air Force processing of space surveillance network data, which yielded 3,180 separate radar or optical observations from Air Force and Navy sensors. It was the post-accident, detailed examination of these observations that revealed the Day 2 object.
After SPACE.com requested help in clarifying why the Day 2 object was not recognized during the mission, and what procedural error had since been fixed, an Air Force Space Command spokesperson responded with a statement.
"The Space Control Center (now Joint Space Operations Center) did change a
space situational awareness process involving space shuttle missions after the space shuttle Columbia accident," the AFSC statement notes. "Before the Columbia accident, the Space Control Center did conjunction analysis (collision avoidance) during space shuttle missions using NASA positional data which better modeled the predicted position of Columbia for the conjunction screenings since it was more accurate than the data from AF sensors."
Determined in hindsight
The AFSC statement explains that the NASA positional data came from their sensors, which could more accurately detect and model small orbital adjustments of the shuttle during missions than could other methods. Since NASA provided this positional data, the Space Control Center processed AF sensor data for Columbia using only basic astrodynamic algorithms and models. These, however, failed to provide high enough fidelity to definitely separate potential debris from the space shuttle orbiter.
"After the space shuttle Columbia investigation, the Space Control Center, in conjunction with NASA, decided to add additional analyst time to search for objects in close proximity to the shuttle, using both NASA positional data and Air Force sensor data," the statement explains.
"It was determined in hindsight that while the previous process of using NASA positional data made space shuttle collision avoidance better, it degraded the possibility of cataloguing debris near the space shuttle during missions. Changing the process to use both NASA positional data and Air Force sensor data improved the ability to possibly detect debris near the space shuttle during missions," the statement concludes.
Leonard David has been reporting on the space industry for more than five decades. He is former director of research for the National Commission on Space and has written for SPACE.com since 1999. He reported on the Columbia accident in 2003 and subsequent hearings of the Columbia Accident Investigation Board.

Sunday, January 20, 2013

What is Lunar X?

What is Lunar X



Lunar X via Raven Yu, January 19, 2013

Alien visitation? No. Lunar X is an example of how lighting and topography can combine to produce a pattern that seems familiar to the human eye.


Ron Bee photo of Lunar X on November 17, 2007.

Lunar X is a famous optical feature on the moon, visible through telescopes. When the terminator – or line between light and dark on the moon – is located in just the right place, it appears as the letter X on the moon’s surface. A sign of an alien visitation? No. Lunar X is a great example of how lighting and topography can combine on a planet or moon to produce a pattern that seems familiar to the human eye. In reality, the illusion of Lunar X is created by sunlight falling on the rims/ridges between the craters La Caille, Blanchinus, and Purbach.

In the case of Lunar X, the pattern repeats at each cycle of the moon, but only for a short time. The X is observable for about 4 hours around the first quarter moon phase.


EarthSky Facebook friend Raven Yu in Quezon City, Philippines took this photo of Lunar X on January 19, 2013. Thank you, Raven! View larger.

Bottom line: Lunar X is an optical feature on the moon, an apparent X on the moon’s surface, visible through telescopes. It’s caused by sunlight falling on the rims/ridges between the craters La Caille, Blanchinus, and Purbach.


source

Earth is undergoing true polar wander, scientists say

Earth is undergoing true polar wander, scientists say


Scientists developed a computer model to identify four possible instances of true polar wander in the past. And, they say, true polar wander is happening now.




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In late 2012, scientists based in Germany and Norway published new results about a geophysical theory known as true polar wander. That is a drifting of Earth’s solid exterior – an actual change in latitude for some land masses – relative to our planet’s rotation axis. These scientists used hotspots in Earth’s mantle as part of a computer model, which they say is accurate for the past 120 million years, to identify four possible instances of true polar wander in the past. And, they say, true polar wander is happening now. These scientists published their results in the Journal for Geophysical Research.

The scientists – including Pavel V. Doubrovine and Trond H. Torsvik of the University of Oslo, and Bernhard Steinberger of the Helmholtz Center in Potsdam, Germany – established what they believe is a stable reference frame for tracking true polar wander. Based on this reference frame, they say that twice – from 90 to 40 million years ago – the solid Earth traveled back and forth by nearly 9 degrees with respect to our planet’s axis of rotation. What’s more, for the past 40 million years, the Earth’s solid outer layers have been slowly rotating at a rate of 0.2 degrees every million years, according to these scientists.





Diagram showing solid-body rotation of the Earth with respect to a stationary spin axis due to true polar wander. This diagram is greatly exaggerated. According to Doubrovine and his team, Earth’s solid outer layers have been slowly rotating at a rate of 0.2 degrees every million years. Diagram via Wikimedia Commons.

True polar wander is not:
A geomagnetic reversal, or reversal of Earth’s magnetic field, known to have happened before in Earth history.
Plate tectonics, which describes the large-scale motions of great land plates on Earth and is thought to be driven by the circulation of Earth’s mantle.
Precession of the Earth, whereby our world’s axis of rotation slowly moves, tracing out a circle among the stars, causing the identity of our North Star changes over time.

True polar wander is a geophysical theory, a way of thinking about Earth processes that might happen and that these scientists believe do happen. The theory suggests that if an object of sufficient weight on Earth – for example, a supersized volcano or other weighty land mass – formed far from Earth’s equator, the force of Earth’s rotation would gradually pull the object away from the axis around which Earth spins. A supersized volcano far from Earth’s equator would create an imbalance, in other words. As explained at Princeton.edu:

If the volcanoes, land and other masses that exist within the spinning Earth ever became sufficiently imbalanced, the planet would tilt and rotate itself until this extra weight was relocated to a point along the equator.

That’s the theory of true polar wander. It would cause a movement of Earth’s land masses, but for a different reason than the reason the continents drift in the theory of plate tectonics (formerly called “continental drift”). In the theory of plate tectonics, the continents drift because the layer of Earth underlying our planet’s crust, called the mantle, is convective. That is, it circulates, slowly – like water about to boil. In true polar wander, on the other hand, a similar-seeming movement of land masses on Earth’s crust happens in order to correct an imbalance of weight with respect to Earth’s spin.

Scientists’ understanding of true polar wander overlaps with their understanding of plate tectonics in various ways. That’s understandable, since it’s all the same Earth.

Scientists delving into true polar wander want to know when, in which direction, and at what rate the Earth’s solid exterior might be rotating due to true polar wander. To sort it out, they say, you would need a stable frame of reference to which observations of relative motion might be compared. Doubrovine and his team say they found one: volcanic hotspots.




Hotspot forming an island chain. As land plates drift, a successive of volcanoes form over the hotspot. Image via Wikimedia Commons.

In geology, hotspots are volcanic regions fed by Earth’s underlying mantle. For example, the Hawaiian islands are believed to have formed over a hotspot in the mantle. The hotspot created a volcano, but then – as that land plate drifted over time, as described by the theory of plate tectonics – the volcano drifted, too, and was eventually cut off from the hotspot. Gradually, another volcano begins to form over the hotspot, right next to the first one. And then it moves on … and another one forms … and so on … and so on. Earth’s crust produces first one, then another volcano over the hotspot until a long chain of volcanoes forms, such as in Hawaii. Hotspots have long been used to understand the motion of tectonic plates.

Doubrovine and colleagues went a step further in order to understand true polar wander. Instead of treating the hot spots as static – frozen in place at one spot above Earth’s mantle – their computer model let the hotspots’ positions drift slowly. According to these scientists, this drifting is what produced a model of a stable reference frame, which in turn let them draw conclusions about true polar wander.

They say their model does a good job of matching observations of real hotspot tracks on Earth – the path drawn by each hotspot’s island chain – which gives them confidence their results about true polar wander are accurate.




The Hawaiian islands are believed to have formed over a hotspot – a particularly hot place in Earth’s underlying mantle. Scientists expanded on previous thinking about hotspots to suggest that Earth’s solid surface is drifting, minutely, with respect to our planet’s rotation axis.

Bottom line: German and Norwegian scientists have incorporated hotspots in Earth’s mantle into a computer model being used to study true polar wander. They say their work established a stable reference frame for this study that lets them conclude Earth is undergoing true polar wander today.

Read the original paper: Absolute plate motions in a reference frame defined by moving hot spots in the Pacific, Atlantic and Indian oceans