“Discovering Mercury’s Elongated Comet-like Tail in the Night Sky”

2023-05-01 08:55:41

▲ Mercury’s comet-like tail across the sky. Taken on April 12th. (Source: Dr. Sebastian Voltmer)

Recently, as Mercury, the Sun’s first planet, reached perihelion, the closest point to the Sun, a majestic comet-like tail revealed its gigantic tail in the night sky, captured by an astrophotographer’s lens.

Comets are orbiting clumps of frozen rock and dust, and are always characterized by two distinct tails behind them. One is made of gas emitted from the inside, and the other is made of dust from the surface. These two tails are driven in the same direction by the solar wind of charged particles expelled from the sun.

Mercury, the smallest planet in the solar system, has a comet-like tail made up of sodium ions scattered from the planet’s surface by the solar wind and tiny meteor impacts.

▲ Mercury’s tail was photographed using a special filter to increase visibility. (Credit: Dr. Sebastian Voltmer)

Researchers have known about the existence of Mercury’s tail since 2001, and have since discovered that Mercury’s tail gets longer as it gets closer to the Sun.

According to Spaceweather.com, the tail extends to 24 million kilometers at its longest, which is more than 60 times the Earth-Moon distance.

Mercury’s tail is so elongated because it has a very thin atmosphere and is so close to the sun that the solar wind can easily tear through the planet’s surface.

▲ An animation showing how the moon’s sodium ‘tail’ appears from Earth. It is the tail that is visible from Earth just a few days after each new moon as the Moon moves between the Earth and the Sun. (Source: James O’Donoghue)

According to Spaceweather.com, Mercury’s tail is best visible from Earth exactly 16 days after Mercury’s perihelion, for reasons yet to be determined. Mercury reached perihelion on April 1, meaning its tail appeared brightest on April 17.

But astrophotographer Sebastian Boltmer captured this stunning image of the planet’s tail on April 12 near Spicheren in northeastern France.

Mercury’s tail was not discovered until the 21st century because it is very difficult for the casual observer to see. But Voltmer was able to photograph the giant planetary plume thanks to a special filter sensitive to the yellow wavelengths of light given off by excited sodium particles in its tail. “Without these filters, Mercury’s tail is barely visible to the naked eye,” Voltmer said.

But Mercury isn’t the only object in the solar system with a comet-like tail. The Moon can also be seen wearing a scarf-like tail, which is only seen once a month when the Earth passes through the Moon. The lunar tail, like Mercury, is made up of millions of sodium atoms.

Lee Kwang-sik, science columnist [e-mail]

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