No one seems to have been shouting too loudly about NASA’s IBEX probe. In fairness I suppose, it isn’t going to be looking at any planets or surveying any galaxies. From an astrochemical perspective though, IBEX is far more exciting than satellites like Fermi — and that’s saying something!

Because everyone likes acronyms these days, IBEX stands for Interstellar Boundary Explorer, and it’s objective is to explore the very edge of the solar system, where interstellar space begins.

As any astrochemist will happily tell you, despite being technically a vacuum, interstellar space is far from empty. In fact, it’s awash with all kinds of molecules, ions, dust grains and other lovely things that we astrochemists try very hard to identify.

So to explain exactly what IBEX will be looking at, here’s a handy little picture…

The Sun, just like all other stars, has a stellar wind (or, when talking about the Sun, a Solar wind). It’s constantly flinging streams of charged particles in all directions. The Solar wind is powerful enough that it actually blows a bubble in the interstellar medium, called a heliosphere. Some parts of the heliosphere are pictured above. For a start, it’s big. Very big. Heading outwards, well past the Kuiper Belt, the first thing you reach is the Termination Shock. This is where the Solar wind begins to slow down significantly. It starts to compress and heat up. Incidentally, the Termination Shock varies. The more sunspots and flares the Sun is giving off, the stronger the Solar wind, so the further away the Termination Shock. Voyager II actually crossed the boundary 5 times!
(It recorded some data too…)

Cross the Termination Shock and you find yourself in the Heliosheath. This is where the Voyager probes now lie. Their current aim isto study the Heliosheath itself. It’s a turbulent region, full of swirling gasses and plasmas, heated by the collision between the Solar wind and the Interstellar Medium (ISM). Though much is still unknown, it’s thought that the heliosheath is drawn into a long teardrop shape, due to the Sun’s orbit around the galaxy. The ISM pushes harder against one side, causing an elongated shape.

Finally, as the Solar wind becomes too weak to push back the ISM, you reach the Heliopause, the actual boundary of the solar system, and the edge of true interstellar space. As the Sun plows it’s way around the galaxy though, it has one final effect. Stars create Bow Shocks as they plough their way through interstellar space, exactly the way a ship’s bow cuts through water. It’s not very obvious in The Sun’s case, but it’s been observed in several other stars. The effect’s a lot more obvious if the star happens to be travelling through a nebula (like LL Orionis here)…

IBEX launches on October 19th. Let’s hope it finds some interesting things!

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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5 Responses to IBEX

  1. {
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  2. invaderxan says:

    No need to apologise. It took me a while to find the answer to that myself — it doesn’t seem to be discussed anywhere! :)
    Confusingly, the Oort cloud actually lies largely outside the heliosphere (weakly gravitationally bound to the Sun, but not necessarily made of Solar material). While the ISM does have pressure, it isn’t really high enough to affect a comet sized object much. Plus, the average distance between Oort cloud objects is estimated at around 2-5AU (if I remember rightly)…
    Theories go that Oort clouds around stars are continually stripped and replenished as the host star travels through different regions of the ISM.
    LL Orionis there, travelling through the Orion Nebula, will have had many smaller Oort cloud objects stripped off. Larger ones will probably be coated in a thin layer (a ‘mantle’) or nebula material.

  3. invaderxan says:

    Actually, it won’t take very long at all. IBEX is being put into an Earth orbit. A long elliptical orbit (taking it outside the Earth’s magnetic field), but an Earth orbit nonetheless.
    I’m hoping that means it’ll have some results back pretty quickly! ;)

  4. underwr1tten says:

    Pardon my ignorance, but I’m confused and out of touch with current astronomy. How is the Oort cloud related to all of this?

  5. Since I have no concept of timing with these launched probes, how long will it take the IBEX probe to get to it’s intended target region of interest?

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