Did Astronomers Just See Mercury's Tail?

Mercury has a shining dragon tail of sodium atoms that, scientists say, is more than seven times longer than ever imagined.

Observations of Mercury's tail, which streams like a kite's long tail in the solar wind, placed it at roughly 100 times the Earth's size itself.

It is assumed that the neutral sodium atoms that make up Mercury's 2.5 million kilometer-long tail are blasted by the light and micro-meteor impacts off the surface. These convey sufficient energy for the atoms to blast into orbit.

Some components are in the tail as well. But it is the sodium that shines up and is detectable.

It disperses photons like crazy, giving it a perfect clue to the different processes at work on and off the planet.

Shorter Tail Previously Seen

The tail of Mercury has been observed before. Still, astronomers overlooked its great length as they aimed at a piece of the sky that was too thin, says Boston University researcher Jeffrey Baumgardner.

Baumgardner is the lead author of a 2008 article in the journal Geophysical Science Letters on Mercury's sodium tail. Using a telescope at McDonald's Observatory in Texas that is about 16 full-moons high, his team produced an 8°-wide image. The real 2° tail of sodium is as long as four total stars.

Mercury is blurred out in the picture since the sodium tail outshines the brightness. It would be less than a pixel in diameter if Mercury were seen to scale in the photograph. Baumgardner claims the Earth's own sodium light is itself produced by the constant supply of meteors that burn up in the atmosphere.

Two Hot Places for Sodium

Baumgardner's team has created close-up sodium-glow photographs of Mercury to better understand how Mercury's tail is formed. This showed that the Earth, both at high latitudes, has two sodium hot spots.

These may be the result of the mineralogy. Mercury's topography may have anything to do with how the planet's magnetic field channels from the sun into particles.

That's close to how Earth does the same thing and displays near the poles to produce aurora.

Per Sprague, the secrets of these areas are likely to be discovered by the Messenger starship.

In January, Messenger made a near fly-by of the planet and is planned for March 2011 to settle into orbit.

Most of Messenger's task would be to map out the geological content of the fast-shifting Earth.

Other Worlds Have Tails

Mercury, Baumgardner states, is not the only celestial entity with a sodium tail. Neutral sodium from the sodium blasted from its tiny and hyper-volcanic moon Io is also seen creating a haze around Jupiter.

Venus has a tail-like structure with ionized oxygen as the solar wind blows in the correct direction. Blowing from comets is observed, too. And there is even a sodium tail on the Earth's Moon, naked and exposed by the solar breeze, but it is not as big or lush as Mercury's.

Because tails in our solar system are synonymous with rocky planets, they may someday help planet hunters find rocky worlds around other stars, Sprague says.

What Makes the Tail of Mercury so Special?

For a particular cause, Mercury's tail is unique. We will learn about the seasonal changes in Mercury's exosphere and how phenomena such as solar flares and coronal mass ejections impact the tiny planet by observing it at various periods during the planet's orbit.

Since sodium tails are mostly correlated with rocky structures, hence, the discovery of sodium in systems around other stars could allow us to monitor and determine rocky exoplanets' possible habitability.

Every planet in the Solar System, including Uranus and Neptune, has its own idiosyncrasies. It's a wonderful reminder of how many different planets can be from each other. Each and every person is a special and precious individual; knowing how and why in the broader World is a step towards understanding planets and planetary systems.

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