How Magnetic Tornadoes Might Regenerate Mercury’s Atmosphere

by Brian Ventrudo on June 3, 2009

Want to stay on top of all the space news? Follow @universetoday on Twitter

mercury-magnetic-tornadoes

This diagram shows magnetic tornadoes forming in Mercury's magnetic field. The tornadoes are corkscrew-shaped bundles of twisted magnetic fields and plasma. The pink area represents the boundary of Mercury's magnetic field, called the magnetopause. The tornadoes, also called "flux transfer events" (twisted lines) form at the magnetopause and "plasmoids" (yellow areas) when they form in the long magnetic "tail" extending from the night-side of Mercury.. The flux transfer events act as open channels through which the solar wind can flow down to the surface of the planet and sputter neutral atoms into Mercury’s atmosphere.

Compared to Earth, Mercury doesn’t have much of an atmosphere.  The smallest rocky planet has weak surface gravity, only 38% that of Earth.  And the scorching-hot daytime surface temperatures of 800 degrees Fahrenheit (approximately 450 degrees Celsius) should have boiled away any trace of Mercury’s atmosphere long ago.  Yet recent flybys of the MESSENGER spacecraft clearly revealed Mercury somehow retains a thin layer of gas near its surface.   Where does this atmosphere come from?

“Mercury’s atmosphere is so thin, it would have vanished long ago unless something was replenishing it,” says Dr. James A. Slavin of NASA’s Goddard Space Flight Center, Greenbelt, Md., a co-investigator on NASA’s MESSENGER mission to Mercury.

The solar wind may well be the culprit.  A thin gas of electrically charged particles called a plasma, the solar wind blows constantly from the surface of the sun at some 250 to 370 miles per second (about 400 to 600 kilometers/second).  According to Slavin, that’s fast enough to blast off the surface of Mercury through a process called “sputtering”, according to Slavin.  Some sputtered atoms stay close enough to the surface to serve as a tenuous yet measurable atmosphere.

But there’s a catch – Mercury’s magnetic field gets in the way. MESSENGER’s first flyby on January 14, 2008, confirmed that the planet has a global magnetic field, as first discovered by the Mariner 10 spacecraft during its flybys of the planet in 1974 and 1975.  Just as on Earth, the magnetic field should deflect charged particles away from the planet’s surface.  However, global magnetic fields are leaky shields and, under the right conditions, they are known to develop holes through which the solar wind can hit the surface.

During its second flyby of the planet on October 6, 2008, MESSENGER discovered that Mercury’s magnetic field can be extremely leaky indeed. The spacecraft encountered magnetic “tornadoes” – twisted bundles of magnetic fields connecting the planetary magnetic field to interplanetary space – that were up to 500 miles wide or a third of the radius of the planet.

“These ‘tornadoes’ form when magnetic fields carried by the solar wind connect to Mercury’s magnetic field,” said Slavin. “As the solar wind blows past Mercury’s field, these joined magnetic fields are carried with it and twist up into vortex-like structures. These twisted magnetic flux tubes, technically known as flux transfer events, form open windows in the planet’s magnetic shield through which the solar wind may enter and directly impact Mercury’s surface.”

Venus, Earth, and even Mars have thick atmospheres compared to Mercury, so the solar wind never makes it to the surface of these planets, even if there is no global magnetic field in the way, as is the case for Venus and Mars. Instead, it hits the upper atmosphere of these worlds, where it has the opposite effect to that on Mercury, gradually stripping away atmospheric gas as it blows by.

The process of linking interplanetary and planetary magnetic fields, called magnetic reconnection, is common throughout the cosmos. It occurs in Earth’s magnetic field, where it generates magnetic tornadoes as well. However, the MESSENGER observations show the reconnection rate is ten times higher at Mercury.

“Mercury’s proximity to the sun only accounts for about a third of the reconnection rate we see,” said Slavin. “It will be exciting to see what’s special about Mercury to explain the rest. We’ll get more clues from MESSENGER’s third flyby on September 29, 2009, and when we get into orbit in March 2011.”

Slavin’s MESSENGER research was funded by NASA and is the subject of a paper that appeared in the journal Science on May 1, 2009.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and after flybys of Earth, Venus, and Mercury will start a yearlong study of its target planet in March 2011. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory, Laurel, Md., built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.

Source:  NASA

Anaconda June 10, 2009 at 4:16 AM

@ Jon Hanford:

“Space is filled with a network of currents which transfer energy and momentum over large or very large distances.”

What does that mean to you?

ND June 10, 2009 at 6:12 AM

Anaconda,

I think you have some questions to answer first. Like some quantifiable EU/PC models that can be compared to astronomical observations. Currently the consensus is that such models are lacking despite the hupla you and other proponents have been making.

Nereid2 June 10, 2009 at 10:41 AM

I have discovered that at least one person has tried to explain to you that not all currents are Birkeland currents, and not all currents *in plasmas* are Birkeland currents … it seems that you didn’t understand what they were trying to tell you …

At the moment I can’t find the “electric power cables in space” quote from Hannes Alfven, but I do have this one that is an equivalent:

“In order to understand the phenomena in a certain plasma region, it is necessary to map not only the magnetic but also the electric field and the electric currents. Space is filled with a network of currents which transfer energy and momentum over large or very large distances. The currents often pinch to filamentary or surface currents. The latter are likely to give space, as also interstellar and intergalactic space, a cellular structure.” — Hannes Alfven, plasma physicist, 1970 Nobel Prize winner

Source: Wikipedia, foot noted for source of above quote.

Why do you think this is equivalent to the statement you gave earlier (supposedly by Alfvén)?

@ Nereid:

What Hannes Alfven and others focussed on was the electron/ion electricity dynamic.

That should be clear to you, now, but I see you still are into passive/aggressive questions.

I am much more clued up now, Anaconda … it seems that much of what you write is simply your own, personal, ideas, formed in part by applying a narrow selection of stuff that you mis-remember from your school days, and using faulty logic (the fallacy of false dichotomy, for example).

In any case, what examples can you give (at least one please) of “currents which transfer energy and momentum over large or very large distances” in astronomy? Please, exclude the solar system.

Anaconda June 10, 2009 at 3:15 PM

@ Nereid:

The double helix that comes out of the Milky Way’s Active Galactic Nucleus.

Nereid asks: “Why do you think this is equivalent to the statement you gave earlier (supposedly by Alfvén)?”

Simple, that’s what “electric cables” do, they transfer electrical energy over large distances, it’s an analogy.

Nereid2 June 11, 2009 at 8:06 AM

Thanks for the reply, Anaconda.

[me] what examples can you give (at least one please) of “currents which transfer energy and momentum over large or very large distances” in astronomy?

[Anaconda] The double helix that comes out of the Milky Way’s Active Galactic Nucleus.

I was not aware that the Milky Way has an AGN; may I ask if you made this up, or you read it somewhere? If the latter, would you be kind enough to provide the source?

What is “The double helix“?

How did you conclude that this thing is “current(s) which transfer energy and momentum over large or very large distances”?

IVAN3MAN June 11, 2009 at 11:40 AM

@ Nereid2,

“Nereid2″? Twin brother of Nereid? :-)

Anyway, I think that this is what Anaconda is referring to: Double Helix Nebula.

IVAN3MAN June 11, 2009 at 12:38 PM

@ Nereid,

Here’s a more detailed article linked at the bottom of the Wikipedia article:
Double Helix Nebula Near Center of the Milky Way.

IVAN3MAN June 11, 2009 at 1:58 PM

@ Anaconda,

Both of those articles refer to a super-massive black hole at the centre of the Milky Way galaxy. So there! :P

Jon Hanford June 11, 2009 at 3:19 PM

@Anacona: One more time, the Milky Way Galaxy, the galaxy in which we reside, does not currently have an Active Galactic Nucleus! It may have once been an AGN and it may become an AGN in the future, but it is in no way is it considered to currently exhibit Active Galactic activity at this time. If you have a properly referenced paper that states otherwise, I’d be more than glad to admit my error. You have repeatedly made this exact error in previous posts and then admit you may have been in error. Note to Anaconda: THERE IS CURRENTLY NO AGN AT THE CENTER OF OUR GALAXY.

Nereid2 June 12, 2009 at 4:55 AM

@IVAN3MAN: for you, I will be Nereid’s (dizygous) twin brother … or anyone else you wish me to be … (well, not ANYONE); after all, as the saying goes, on the internet no one knows you’re a dog! :-)

Or you can accept a more mundane explanation, such as me being away from home, and not having taken my WP PW with me (and so having had a need to create a new account …).

IVAN3MAN June 17, 2009 at 12:09 AM

@ Nereid,

Oops! :|

Comments on this entry are closed.

Previous post:

Next post: