A New Power Source for Earth’s Dynamo

News Writer: 
Lori Dajose

Magnesium-bearing minerals transported through the core up to the mantle can cause the convection that powers the geodynamo.
Credit: Joseph O’Rourke/Caltech

The earth’s global magnetic field plays a vital role in our everyday lives, shielding us from harmful solar radiation. The magnetic field, which has existed for billions of years, is caused by a dynamo—or generator—within the mostly molten iron in the earth’s interior; this liquid iron churns in a process called convection. But convection does not happen on its own. It needs a driving force—a power source. Now, graduate student Joseph O’Rourke and David Stevenson, Caltech’s Marvin L. Goldberger Professor of Planetary Science, have proposed a new mechanism that can power this convection in the earth’s interior for all of the earth’s history.

A paper detailing the findings appears in the January 21 issue of Nature.

Convection can be seen in such everyday phenomena as a pot of boiling water. Heat at the bottom of the pot causes pockets of fluid to become less dense than the surrounding fluid, and thus to rise. When they reach the surface, the pockets of fluid cool and sink again. This same process occurs in the 1,400-mile-thick layer of molten metal that makes up the outer core.

The earth consists mostly of the mantle (solid material made of oxides and silicate in which magnesium is prominent) and the core (mainly iron). These two regions are usually thought of as completely separated; that is, the mantle materials do not dissolve in the core materials. They do not mix at the atomic level, much as water does not usually mix with oil. The core has a solid inner part that has been slowly growing throughout the earth’s history, as liquid iron in the planet’s interior solidifies. The outer, liquid part of the core is a layer of molten iron mixed with other elements, including silicon, oxygen, nickel, and a small amount of magnesium. Stevenson and O’Rourke propose that the transfer of the element magnesium in the form of mantle minerals from the outer core to the base of the mantle is the mechanism that powers convection.

Magneisum is a major element in the mantle, but it has low solubility in the iron core except at very high temperatures—above 7,200 degrees Fahrenheit. As the earth’s core cools, magnesium oxides and magnesium silicates crystallize from the metallic, liquid outer core, much as sugar that has been dissolved in hot water will precipitate as sugar crystals when the water cools. Because these crystals are less dense than iron, they rise to the base of the mantle. The heavier liquid metal left behind then sinks, and this motion, Stevenson argues, may be the mechanism that has sustained convection for over three billion years—the mechanism that in turn powers the global magnetic field.

“Precipitation of magnesium-bearing minerals from the outer core is 10 times more effective at driving convection than growth of the inner core,” O’Rourke says. “Such minerals are very buoyant and the resulting fluid motions can transport heat effectively. The core only needs to precipitate upwards a layer of magnesium minerals 10 kilometers thick—which seems like a lot, but it’s not much on the scale of the inner and outer cores—in order to drive the outer core’s convection.”

Previous models assumed that the steady cooling of iron in the inner core would release heat that could power convection. But most measurements and theory in the past few years for the thermal conductivity of iron—the property that determines how efficiently heat can flow through a metal—indicates that the metal can easily transfer heat without undergoing motion. “Heating up iron at the bottom of the outer core will not cause it to rise up buoyantly—it’s just going to dissipate the heat to its surroundings,” O’Rourke says.

“Dave had the idea of a magnesium-powered dynamo for a while, but there was supposed to be no magnesium in Earth’s core,” O’Rourke says. “Now, models of planetary formation in the early solar system are showing that Earth underwent frequent impacts with giant planetary bodies. If these violent, energetic events occurred, Earth would have been experiencing much higher temperatures during its formation than previously thought—temperatures that would have been high enough to allow some magnesium to mix into liquid metallic iron.”

These models made it possible to pursue the idea that the dynamo may be powered by the precipitation of magnesium-bearing minerals. O’Rourke calculated that the amounts of magnesium that would have dissolved in the core during Earth’s hot early stages would have caused other changes in the composition of the mantle that are consistent with other models and measurements. He also calculated that the precipitation of these magnesium minerals would have enough energy to power the dynamo for four billion years.

Experimental verification of the amount of magnesium that can go into the core is still sparse, O’Rourke and Stevenson say. “Further applications of our proposed mechanism include Venus—where there is no magnetic field—and the abundant exoplanets that are more massive than the Earth but may have similar chemical compositions,” Stevenson says.

Caltech News tagged with “GPS”

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Notes from a Small Island

Notes from a Small Island

Notes from a Small Island

Veering from the ludicrous to the endearing and back again, Notes From a Small Island is a delightfully irreverent jaunt around the unparalleled floating nation that has produced zebra crossings, Shakespeare, Twiggie Winkie’s Farm, and places with names like Farleigh Wallop and Titsey.Reacting to an itch common to Midwesterners since there’s been a Midwest from which to escape, writer Bill Bryson moved from Iowa to Britain in 1973. Working for such places as Times of London, among others, he has

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Writer Bill Bryson moved from Iowa to Britain

Reacting to an itch common to Midwesterners since there’s been a Midwest from which to escape, writer Bill Bryson moved from Iowa to Britain in 1973. Working for such places as Times of London, among others, he has lived quite happily there ever since. Now Bryson has decided his native country needs him–but first, he’s going on a roundabout jaunt on the island he loves.

Britain fascinates Americans: it’s familiar, yet alien; the same in some ways, yet so different. Bryson does an excellent job of showing his adopted home to a Yank audience, but you never get the feeling that Bryson is too much of an outsider to know the true nature of the country. Notes from a Small Island strikes a nice balance: the writing is American-silly with a British range of vocabulary. Bryson’s marvelous ear is also in evidence: “… I noted the names of the little villages we passed through–Pinhead, West Stuttering, Bakelite, Ham Hocks, Sheepshanks …” If you’re an Anglophile, you’ll devour Notes from a Small Island.

Great_Britain_and_Northern_Ireland

Satellite image of Great Britain and Northern Ireland in April 2002.
Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

http://visibleearth.nasa.gov

 

 

A Walk in the Woods: Rediscovering America on the Appalachian Trail

 

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Caltech Researchers Find Evidence of a Real Ninth Planet

News Writer: 
Kimm Fesenmaier

This artistic rendering shows the distant view from Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side.
Credit: Caltech/R. Hurt (IPAC)

Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system. The object, which the researchers have nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than does Neptune (which orbits the sun at an average distance of 2.8 billion miles). In fact, it would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun.

The researchers, Konstantin Batygin and Mike Brown, discovered the planet’s existence through mathematical modeling and computer simulations but have not yet observed the object directly.

“This would be a real ninth planet,” says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy. “There have only been two true planets discovered since ancient times, and this would be a third. It’s a pretty substantial chunk of our solar system that’s still out there to be found, which is pretty exciting.”

Brown notes that the putative ninth planet—at 5,000 times the mass of Pluto—is sufficiently large that there should be no debate about whether it is a true planet. Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the solar system. In fact, it dominates a region larger than any of the other known planets—a fact that Brown says makes it “the most planet-y of the planets in the whole solar system.”

Batygin and Brown describe their work in the current issue of the Astronomical Journal and show how Planet Nine helps explain a number of mysterious features of the field of icy objects and debris beyond Neptune known as the Kuiper Belt.

“Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there,” says Batygin, an assistant professor of planetary science. “For the first time in over 150 years, there is solid evidence that the solar system’s planetary census is incomplete.”

The road to the theoretical discovery was not straightforward. In 2014, a former postdoc of Brown’s, Chad Trujillo, and his colleague Scott Sheppard published a paper noting that 13 of the most distant objects in the Kuiper Belt are similar with respect to an obscure orbital feature. To explain that similarity, they suggested the possible presence of a small planet. Brown thought the planet solution was unlikely, but his interest was piqued.

He took the problem down the hall to Batygin, and the two started what became a year-and-a-half-long collaboration to investigate the distant objects. As an observer and a theorist, respectively, the researchers approached the work from very different perspectives—Brown as someone who looks at the sky and tries to anchor everything in the context of what can be seen, and Batygin as someone who puts himself within the context of dynamics, considering how things might work from a physics standpoint. Those differences allowed the researchers to challenge each other’s ideas and to consider new possibilities. “I would bring in some of these observational aspects; he would come back with arguments from theory, and we would push each other. I don’t think the discovery would have happened without that back and forth,” says Brown. ” It was perhaps the most fun year of working on a problem in the solar system that I’ve ever had.”

Fairly quickly Batygin and Brown realized that the six most distant objects from Trujillo and Shepherd’s original collection all follow elliptical orbits that point in the same direction in physical space. That is particularly surprising because the outermost points of their orbits move around the solar system, and they travel at different rates.

“It’s almost like having six hands on a clock all moving at different rates, and when you happen to look up, they’re all in exactly the same place,” says Brown. The odds of having that happen are something like 1 in 100, he says. But on top of that, the orbits of the six objects are also all tilted in the same way—pointing about 30 degrees downward in the same direction relative to the plane of the eight known planets. The probability of that happening is about 0.007 percent. “Basically it shouldn’t happen randomly,” Brown says. “So we thought something else must be shaping these orbits.”

The first possibility they investigated was that perhaps there are enough distant Kuiper Belt objects—some of which have not yet been discovered—to exert the gravity needed to keep that subpopulation clustered together. The researchers quickly ruled this out when it turned out that such a scenario would require the Kuiper Belt to have about 100 times the mass it has today.

That left them with the idea of a planet. Their first instinct was to run simulations involving a planet in a distant orbit that encircled the orbits of the six Kuiper Belt objects, acting like a giant lasso to wrangle them into their alignment. Batygin says that almost works but does not provide the observed eccentricities precisely. “Close, but no cigar,” he says.

Then, effectively by accident, Batygin and Brown noticed that if they ran their simulations with a massive planet in an anti-aligned orbit—an orbit in which the planet’s closest approach to the sun, or perihelion, is 180 degrees across from the perihelion of all the other objects and known planets—the distant Kuiper Belt objects in the simulation assumed the alignment that is actually observed.

“Your natural response is ‘This orbital geometry can’t be right. This can’t be stable over the long term because, after all, this would cause the planet and these objects to meet and eventually collide,'” says Batygin. But through a mechanism known as mean-motion resonance, the anti-aligned orbit of the ninth planet actually prevents the Kuiper Belt objects from colliding with it and keeps them aligned. As orbiting objects approach each other they exchange energy. So, for example, for every four orbits Planet Nine makes, a distant Kuiper Belt object might complete nine orbits. They never collide. Instead, like a parent maintaining the arc of a child on a swing with periodic pushes, Planet Nine nudges the orbits of distant Kuiper Belt objects such that their configuration with relation to the planet is preserved.

“Still, I was very skeptical,” says Batygin. “I had never seen anything like this in celestial mechanics.”

But little by little, as the researchers investigated additional features and consequences of the model, they became persuaded. “A good theory should not only explain things that you set out to explain. It should hopefully explain things that you didn’t set out to explain and make predictions that are testable,” says Batygin.

And indeed Planet Nine’s existence helps explain more than just the alignment of the distant Kuiper Belt objects. It also provides an explanation for the mysterious orbits that two of them trace. The first of those objects, dubbed Sedna, was discovered by Brown in 2003. Unlike standard-variety Kuiper Belt objects, which get gravitationally “kicked out” by Neptune and then return back to it, Sedna never gets very close to Neptune. A second object like Sedna, known as 2012 VP113, was announced by Trujillo and Shepherd in 2014. Batygin and Brown found that the presence of Planet Nine in its proposed orbit naturally produces Sedna-like objects by taking a standard Kuiper Belt object and slowly pulling it away into an orbit less connected to Neptune.


A predicted consequence of Planet Nine is that a second set of confined objects should also exist. These objects are forced into positions at right angles to Planet Nine and into orbits that are perpendicular to the plane of the solar system. Five known objects (blue) fit this prediction precisely.
Credit: Caltech/R. Hurt (IPAC) [Diagram was created using WorldWide Telescope.]

But the real kicker for the researchers was the fact that their simulations also predicted that there would be objects in the Kuiper Belt on orbits inclined perpendicularly to the plane of the planets. Batygin kept finding evidence for these in his simulations and took them to Brown. “Suddenly I realized there are objects like that,” recalls Brown. In the last three years, observers have identified four objects tracing orbits roughly along one perpendicular line from Neptune and one object along another. “We plotted up the positions of those objects and their orbits, and they matched the simulations exactly,” says Brown. “When we found that, my jaw sort of hit the floor.”

“When the simulation aligned the distant Kuiper Belt objects and created objects like Sedna, we thought this is kind of awesome—you kill two birds with one stone,” says Batygin. “But with the existence of the planet also explaining these perpendicular orbits, not only do you kill two birds, you also take down a bird that you didn’t realize was sitting in a nearby tree.”

Where did Planet Nine come from and how did it end up in the outer solar system? Scientists have long believed that the early solar system began with four planetary cores that went on to grab all of the gas around them, forming the four gas planets—Jupiter, Saturn, Uranus, and Neptune. Over time, collisions and ejections shaped them and moved them out to their present locations. “But there is no reason that there could not have been five cores, rather than four,” says Brown. Planet Nine could represent that fifth core, and if it got too close to Jupiter or Saturn, it could have been ejected into its distant, eccentric orbit.

Batygin and Brown continue to refine their simulations and learn more about the planet’s orbit and its influence on the distant solar system. Meanwhile, Brown and other colleagues have begun searching the skies for Planet Nine. Only the planet’s rough orbit is known, not the precise location of the planet on that elliptical path. If the planet happens to be close to its perihelion, Brown says, astronomers should be able to spot it in images captured by previous surveys. If it is in the most distant part of its orbit, the world’s largest telescopes—such as the twin 10-meter telescopes at the W. M. Keck Observatory and the Subaru Telescope, all on Mauna Kea in Hawaii—will be needed to see it. If, however, Planet Nine is now located anywhere in between, many telescopes have a shot at finding it.

“I would love to find it,” says Brown. “But I’d also be perfectly happy if someone else found it. That is why we’re publishing this paper. We hope that other people are going to get inspired and start searching.”

In terms of understanding more about the solar system’s context in the rest of the universe, Batygin says that in a couple of ways, this ninth planet that seems like such an oddball to us would actually make our solar system more similar to the other planetary systems that astronomers are finding around other stars. First, most of the planets around other sunlike stars have no single orbital range—that is, some orbit extremely close to their host stars while others follow exceptionally distant orbits. Second, the most common planets around other stars range between 1 and 10 Earth-masses.

“One of the most startling discoveries about other planetary systems has been that the most common type of planet out there has a mass between that of Earth and that of Neptune,” says Batygin. “Until now, we’ve thought that the solar system was lacking in this most common type of planet. Maybe we’re more normal after all.”

Brown, well known for the significant role he played in the demotion of Pluto from a planet to a dwarf planet adds, “All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found,” he says. “Now we can go and find this planet and make the solar system have nine planets once again.”

The paper is titled “Evidence for a Distant Giant Planet in the Solar System.”

Caltech News tagged with “GPS”

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The National Oceanic and Atmospheric Administration’s National Weather Service Glossary

The National Oceanic and Atmospheric Administration’s National Weather Service Glossary

The National Oceanic and Atmospheric Administration's National Weather Service Glossary

This glossary contains information on more than 2000 terms, phrases and abbreviations used by the NWS. Many of these terms and abbreviations are used by NWS forecasters to communicate between each other and have been in use for many years and before many NWS products were directly available to the public. It is the purpose of this glossary to aid the general public in better understanding NWS products. Previously, this book was only availableonline as a search tool. This hardcopy edition is base

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Jason-3, an international mission led by the National Oceanic and Atmospheric Administration (NOAA) to continue U.S.-European satellite measurements of the topography of the ocean surfaces,

 

 

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Jason-3 spacecraft ready for launch

j3_still_CA_v2

http://sealevel.jpl.nasa.gov/missions/jason3/

Jason-3, an international mission led by the National Oceanic and Atmospheric Administration (NOAA) to continue U.S.-European satellite measurements of the topography of the ocean surfaces, is scheduled for launch from Vandenberg Air Force Base in California on Sunday, Jan. 17. Liftoff aboard a SpaceX Falcon 9 rocket from Vandenberg’s Space Launch Complex 4 East is targeted for 10:42:18 a.m. PST (1:42:18 p.m. EST) at the opening of a 30-second launch window. If needed, a backup launch opportunity is available on the Western Range on Jan. 18 at 10:31:04 a.m. PST (1:31:04 p.m. EST).

Jason-3 will maintain the ability to monitor and precisely measure global sea surface heights, monitor the intensification of tropical cyclones and support seasonal and coastal forecasts. Data from Jason-3 will support scientific, commercial and practical applications related to ocean circulation and climate change. Additionally, Jason-3 data will be applied to fisheries management, marine industries and research into human impacts on the world’s oceans.

The mission is planned to last at least three years with a goal of five years.

Jason-3 is a four-agency international partnership consisting of NOAA, NASA, the French Space Agency CNES (Centre National d’Etudes Spatiales) and EUMETSAT (the European Organization for the Exploitation of Meteorological Satellites). Thales Alenia of France built the spacecraft.

NOAA, in collaboration with the European partners, is responsible for the Jason-3 mission. NASA’s Jet Propulsion Laboratory in Pasadena, California, is responsible for NASA Jason-3 project management. NASA’s Launch Services Program at the agency’s Kennedy Space Center in Florida provides launch management. SpaceX of Hawthorne, California, is NASA’s launch service provider of the Falcon 9 rocket.

PRELAUNCH NEWS CONFERENCE/JASON-3 MISSION SCIENCE BRIEFING

Friday, Jan 15: The Jason-3 Mission Science Briefing and prelaunch news conference will be held starting at 4 p.m. PST (7 p.m. EST) at Vandenberg Air Force Base. The pre-launch news conference will be first at 4 p.m. PST, followed by the mission science briefing at 4:45 PST.

Both events will be carried live on NASA Television and streamed on NASA.gov and www.ustream.tv/NASAJPL2.

Participants in the pre-launch news conference will be:

  • Jim Silva, Jason-3 program manager, NOAA, Washington, D.C.
  • Sandra Smalley, director, Science Mission Directorate Joint Agency Satellite Division, NASA Headquarters, Washington
  • Tim Dunn, NASA launch manager, Kennedy Space Center, Florida
  • Hans Koenigsmann, vice president of Mission Assurance, SpaceX, Hawthorne, California
  • Parag Vaze, Jason-3 project manager, JPL
  • Lt. Joseph Round, launch weather officer, 30th Operations Support Squadron, Vandenberg Air Force Base, California

Participants in the Jason-3 Mission Science Briefing will be:

  • Laury Miller, Jason-3 program scientist and chief, NOAA Laboratory for Satellite Altimetry
  • Josh Willis, Jason-3 project scientist, JPL
  • Marc Cohen, associate director and chief of Low Earth Orbit Programmes, EUMETSAT
  • Sophie Coutin Faye, chief, Altimetry and Precise Positioning Office, CNES

NASA TELEVISION LAUNCH DAY COVERAGE

On launch day, Jan. 17, NASA TV launch commentary coverage of the countdown will begin at 8 a.m. PST (11 a.m. EST). Launch is targeted for 10:42:18 a.m. PST (1:42:18 p.m. EST). The launch window is 30 seconds in duration. Spacecraft separation from the rocket occurs 55 minutes after launch.

For information on receiving NASA TV, go to:

http://www.nasa.gov/multimedia/nasatv/index.html

NASA WEB PRELAUNCH AND LAUNCH COVERAGE

For extensive prelaunch, countdown and launch day coverage of the liftoff, including the prelaunch webcast of Jason-3 aboard the Falcon 9 rocket, go to:

http://blogs.nasa.gov/Jason3

SOCIAL MEDIA

Throughout the launch countdown, the NASA Launch Services Program and NASA JPL Twitter and Facebook accounts will be continuously updated at:

https://www.twitter.com/NASALSP

https://twitter.com/NASAKennedy

https://twitter.com/NASAJPL

https://www.facebook.com/NASALSP

https://www.facebook.com/NASAJPL

https://www.facebook.com/NASAKennedy

Live countdown coverage on NASA’s launch blog begins at 8 a.m. PST (11 a.m. EST). Coverage features real-time updates of countdown milestones, as well as streaming video clips highlighting launch preparations and liftoff.

For more information about the Jason-3 mission, visit:

http://www.nesdis.noaa.gov/jason-3/

Media contacts

Steve Cole
NASA Headquarters, Washington
202-358-0918
stephen.e.cole@nasa.gov

John Leslie
NOAA
301-713-0214
john.leslie@noaa.gov

George H. Diller
Kennedy Space Center, Fla.
321-867-2468
george.h.diller@nasa.gov

Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0474
alan.buis@jpl.nasa.gov

 

Global Climate Change – Vital Signs of the Planet – News RSS Feed

The National Oceanic and Atmospheric Administration’s National Weather Service Glossary

The National Oceanic and Atmospheric Administration's National Weather Service Glossary

This glossary contains information on more than 2000 terms, phrases and abbreviations used by the NWS. Many of these terms and abbreviations are used by NWS forecasters to communicate between each other and have been in use for many years and before many NWS products were directly available to the public. It is the purpose of this glossary to aid the general public in better understanding NWS products. Previously, this book was only availableonline as a search tool. This hardcopy edition is base

Buy from amazon

 

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