Here, There And Everywhere

It’s a day to be grateful, and the sky is one place we can always go to see our lives in perspective. Despite the usual worries and setbacks, I’m glad to be here to enjoy my bit part in the grand scheme.

The forecast doesn’t look promising tonight for our region, but it will improve as we head into the weekend. Here are some times for International Space Station (ISS) passes. For all of them, the ISS will rise in the west and cross the northern sky. Passes of the lost took kit will be much better next week.

* Tonight, Nov. 27 starting at 5:10 p.m.
* Friday, Nov. 28 at 5:37 p.m.
* Saturday, Nov. 29 at 6:04 p.m.
* Sunday, Nov. 30 at 4:55 p.m.
(Passes last 4-5 minutes)

Earth, Jupiter and Saturn all wear "caps" of aurora as seen in these NASA images.

The aurora this week got me thinking about where else in the solar system you could go to see a nice show. Turns out it’s every planet except Mercury. Most auroras are caused by the interaction between particles in the solar wind and a planet’s magnetic field. The wind is a stream of protons and electrons that literally blows away from the sun at hundreds of miles per second. When the particles get roped into the magnetic field, they follow invisible lines of force right down into a planet’s atmosphere, where they excite the atoms there. Excited atoms "calm down" by emitting light, and this is what we see as aurora.

Molten iron circulating around the Earth’s solid central core, combined with spin provided by the planet’s rotation, create an invisible but very real magnetic bubble around us. Illustration: NASA

Earth, Jupiter, Saturn, Uranus and Nepture are all surrounded by magnetic fields. Same as one of those old-fashioned horseshoe magnets. You can’t see the field — unless you sprinkle some iron filing around it — but you know it’s there, because other metal objects are drawn to the magnet. Planetary magnetism is generated by spinning an electrically conducting fluid like iron in their cores. The spin comes naturally as the planet rotates.

The tremendous pressure deep below Jupiter’s clouds turns hydrogen gas into a weird metallic form that conducts electricity and generates its field. Befitting its giant status, Jupiter’s auroras are 1000 times more powerful than Earth’s.

In these image plots by the Pioneer Venus Orbiter, the dark splotches are patches of aurora flaring away in Venus’ atmosphere. Photo: NASA

Venus and Mars are unique in the solar system. Venus rotates too slowly to produce a magnetic field but has aurora just the same. The Pioneer Venus Orbiter in the 1980s recorded glowing, auroral patches in its upper atmosphere from direct hits by solar particles. Mars is stranger yet. Although it rotates at almost the same rate as Earth, it lacks a planetary magnetic field. Instead, certain areas of its crust are very strongly magnetic. Scientists believe this magnetism is a remnant of an active magnetic field when the planet was younger. Presumably, the core cooled and any liquid metal solidified. In 2004, the Mars Express orbiter discovered an aurora only 18 miles across hovering some 78 miles above the Terra Cimmeria in the planet’s southern hemisphere. How bizarre is that?

Magnetized rock in this area of Mars southern hemisphere, known
as Terra Cimmeria, is powerful enough to create its own mini-aurora.

How a Mars aurora might look to an astronaut orbiting the night side of the planet. Illustration: M. Holmstrom (IRF)

No matter where future astronauts travel, they’ll never have to stray too far from the familiar sight of Northern Lights.

1 Response

  1. Tony M

    Hi Bob – Hope you had a great Thanksgiving. Can’t wait to see some Nothern Lights. I’m going to have to try to get away from town. Here’s to clear, dark skies. – Tony

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