What is Magnetic Field ?

As we’ve discussed before, scientists have wondered for decades why the temperature of the Sun’s corona, or outer atmosphere, is so much hotter than its photosphere, or visible surface. Defying all logic, the surface of the Sun has a temperature around 6,000 Kelvin (about 6,000 degrees Celsius, or 10,000 °F), while the corona often becomes 300 times hotter. “That’s a bit of a puzzle,” said Jeff Brosius, a space scientist at NASA’s Goddard Space Flight Center in Maryland. “Things usually get cooler farther away from a hot source. When you’re roasting a marshmallow you move it closer to the fire to cook it, not farther away.”

The Standard International (SI) unit used to measure magnetic fields is the Tesla, while smaller magnetic fields are measured in terms of Gauss (1 Tesla = 10,000 Guass).

scientists recently found strong evidence that nanoflares, and the energetic particles produced by them, are at least part of the source of the extra heat. Although nanoflares are the tiny cousins of solar flares (which may heat solar plasma to tens of millions of degrees in only seconds), they still produce small, quick bursts of heat and energy almost constantly. We can’t see them directly yet, but that problem may be solved when NASA’s NuSTAR space telescope takes high-energy X-ray portraits of them. But scientists can’t take those pictures until the Sun is quieter; otherwise, all the energetic activity may hide the action of the nanoflares.

Mathematically, a magnetic field is defined in terms of the amount of force it exerted on a moving charge.

Until then, the Interface Region Imaging Spectrograph (IRIS) gives us the best way to detect nanoflares indirectly by looking at coronal loop footpoints. A coronal loop is a hot plasma loop reaching out from the surface of the Sun into the corona that glows brightly in ultraviolet and X-rays. A footpoint occurs where magnetic loops meet the Sun’s surface. IRIS can’t see the actual coronal heating events, but it does see the telltale rapid, small brightenings at the coronal loop footpoints.

The measurement of this force is consistent with the Lorentz Force Law, which can be expressed as F= qvB, where F is the magnetic force, q is the charge, v is the velocity, and the magnetic field is B.

This relationship is a vector product, where F is perpendicular (->) to all other values.

Rocks can tell us a lot about a protoplanet’s evolution because they can only be formed under specific conditions. NASA’s spacecraft Dawn recently gave us information on the puzzling dark matter that’s spread all over Vesta’s surface.

Magnetic fields may be represented by continuous lines of force (or magnetic flux) that emerge from north-seeking magnetic poles and enter south-seeking poles.

It absorbs light like soot. But our scientists were curious to know what it was made of and where it came from. That might give them some insight into why Vesta started to become a planet over four billion years ago but never made the evolutionary leap beyond protoplanet.

The density of the lines indicate the magnitude of the field, being more concentrated at the poles (where the field is strong) and fanning out and weakening the farther they get from the poles.

That one mineral solves some of the mystery of Vesta’s formation. The dark matter can’t have come in contact with high levels of heat because temperatures above 400 degrees Celsius (700 °F) would destroy serpentine. We already know that Vesta was quite hot at one time, so the dark matter couldn’t have come from Vesta itself.

A uniform magnetic field is represented by equally-spaced, parallel straight lines.

That leaves a relatively slow impact from a carbon-rich asteroid as the only logical explanation. If the impact had been high-speed, then the serpentine would have been destroyed by the resulting high temperature. The dispersion of dark material on Vesta is also consistent with a low-speed impact from an asteroid.

These lines are continuous, forming closed loops that run from north to south, and looping around again.

That leaves a relatively slow impact from a carbon-rich asteroid as the only logical explanation. If the impact had been high-speed, then the serpentine would have been destroyed by the resulting high temperature. The dispersion of dark material on Vesta is also consistent with a low-speed impact from an asteroid.

The direction of the magnetic field at any point is parallel to the direction of nearby field lines, and the local density of field lines can be made proportional to its strength.

“This work all started with a mystery from 1978,” said Glyn Collinson from NASA’s Goddard Space Flight Center in Maryland. “When Pioneer Venus Orbiter moved into orbit around Venus, it noticed something very, very weird—a hole in the planet’s ionosphere. It was a region where the density just dropped out, and no one has seen another one of these things for 30 years.”

Magnetic field lines resemble a fluid flow, in that they are streamlined and continuous, and more (or fewer lines) appear depending on how closely a field is observed.

The ionosphere is a layer of atmosphere on Venus that’s electrically charged. When the European Space Agency’s Venus Express began to orbit Venus in recent years, it was in a much higher orbit than that of its predecessor. But even at the higher altitude, Venus Express saw the same holes. That meant these holes had drilled farther down into the atmosphere than once believed. In addition, Pioneer Venus Orbiter observed the holes at the solar maximum, when solar activity is at its peak. But Venus Express saw holes during the solar minimum which means these holes are more prevalent than we realized.

A magnetic field is generated when electric charge carriers such as electrons move through space or within an electrical conductor.

Field lines are useful as a representation of magnetic fields, allowing for many laws of magnetism (and electromagnetism) to be simplified and expressed in mathematical terms.

To interpret what’s happening to Venus, it’s necessary to understand that the side of its ionosphere facing the Sun is hammered constantly by solar wind, a stream of charged particles flowing from the Sun. The ionosphere acts like a thin boundary that extends from the front of Venus around the planet until tailing off in the back like a comet. Think of the ionosphere as the air streaming around a golf ball that’s in flight.

The geometric shapes of the magnetic flux lines produced by moving charge carriers (electric current) are similar to the shapes of the flux lines in an electrostatic field.

A simple way to observe a magnetic field is to place iron filings around an iron magnet.