A Fuzzy, Burning Star

The southern hemisphere of Venus in infrared (top) and ultraviolet. Credit: ESA/VIRTIS-VenusX IASF-INAF, Observatoire de Paris (R.Hueso, Univ. Bilbao)

The southern hemisphere of Venus in infrared (top) and ultraviolet. Credit: ESA/VIRTIS-VenusX IASF-INAF, Observatoire de Paris (R.Hueso, Univ. Bilbao)

 

Apr 23, 2014

Venus is a young, electrically active planet.

“Venus was described as a ‘hairy star,’ a ‘star that smoked’ and as ‘a stupendous prodigy in the sky.’ So it is significant that one of the earliest space-age discoveries about Venus was its ‘cometary magnetotail’, in the form of invisible ‘stringy things’, or plasma current filaments, stretching as far as the Earth’s orbit.”
Wal Thornhill

Venus has no intrinsic magnetic field. According to data from the Magellan orbiter’s magnetometer, the magnetic field strength on Venus is .000015 times Earth’s magnetic field. That field strength is trivial, so its magnetotail must be created from another source. Since its upper atmosphere contains a rather dense concentration of charged particles, the electrically charged solar wind ions induce electric current flow in the ionosphere, giving Venus a filamentary magnetotail.

Planets with magnetic fields are surrounded by magnetospheres. Magnetospheres deflect charged solar wind particles, both electrons and positively charged ions (primarily hydrogen nuclei). It is that deflection that forms the protective magnetospheric “bubble” around Earth, for example.

Earth’s magnetotail is similar to Venus: a complex electrically active structure that extends for millions of kilometers, always pointed away from the Sun. On Earth, charged particles from the Sun are captured in the magnetosphere, and along with ions generated by Earth itself, collect in a plasma sheet within the magnetotail, where they are held together by Earth’s magnetic field. However, there are cusps in Earth’s magnetosphere at each pole, where solar wind ions enter deeper into the electromagnetic field. That is the reason why aurorae occur at the poles and not the equator.

Of further interest is the fact that other planetary bodies, like Titan and Mars, have no intrinsic magnetic fields but do have magnetotails. This lends support to the electrical connection that the Sun maintains with its collection of orbiting bodies. Since other rocky bodies in the Solar System do not have magnetotails, it must be that it is atmospheric density that contributes to their formation. Venus, Mars, and Titan all possess atmospheres, where Mercury, the Moon, or Triton do not.

Venus is far more electrically active than previously thought. Several Picture of the Day articles have reported that lightning has been detected in its dense cloud layers. Venus Express found low-frequency electromagnetic bursts, lasting fractions of a second, called “whistlers“, in the clouds. A whistler is an electro-acoustic wave that is normally generated by lightning. They are called “whistlers” because they demonstrate a decreasing frequency falloff in detection equipment.

A recent press release announced that aurorae may have also been detected on Venus. It is a controversial report, since it has always been assumed that they require a magnetosphere to form. However, the THEMIS spacecraft, currently orbiting Earth, found small, fast-moving auroral “knots” of plasma that “collide” with larger formation, releasing abrupt flashes of light.

It is thought that the knots move in conjunction with a plasma jet traveling through Earth’s magnetotail. Plasma instabilities are generated when the jet reaches the magnetotail’s inner boundary. Since the five THEMIS spacecraft repeatedly fly through the magnetotail, they also confirmed the existence of plasma streams speeding toward Earth. Those packets of field aligned charged particles are called “plasma bullets”. Perhaps the same phenomenon is taking place in the magnetotail of Venus?

Since Venus also emits twice the infrared energy that it receives from the Sun, there must be a source for that heat. Its ionosphere is “stringy” because Birkeland currents carry electricity from the solar wind into the Venusian environment. With so much electrical energy pumping into it, it may be that Venus is constantly charging and discharging with an infrared glow. It also might indicate that Venus is a relatively young planet, releasing the heat of its birth as it slowly reaches equilibrium.

Stephen Smith

Click here for a Spanish translation

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