In outer space, an object’s location has a huge impact on its temperature.  The closer the object is to its star, the hotter it most likely is.  Heat then plays a major role in what materials are present in that object’s atmosphere, if it has one.  Lighter elements such as hydrogen and helium and much easier to take a gaseous state and create an atmosphere.  So it came as a surprise when two different teams found much heavier elements in the atmosphere of comets that were relatively far away from the Sun.  And one of those comets happened to be from another solar system.  

Many comets are metallic, so there wasn’t much surprise that elemental metals such as iron and nickel are present on their surface.  And when metallic comets approach the sun those elements can sometimes sublimate into the cloud of dust that surrounds the comet.  Astronomers have observed this phenomena for years, and it makes sense given the temperatures involved.

UT video explaining the origin of comets.

When a team of astronomers at the University of Liège studied the atmospheres of a series of comets that were relatively far away from the solar system, they found some strange spectral lines that they couldn’t explain.  Using the European Southern Observatory’s Very Large Telescope (VLT), they were looking at comets that were three times further from the sun than Earth is, making them cold and stable compared to comets closer in.

After some further research the team realized the spectral lines they were looking at were representative of very weak signals for iron and nickel.  Strangely, the two elements were almost the same concentration, with about 1 g of iron and 1 g of nickel per 100 kg of water in the comet’s atmosphere.  Closer to the sun, where it is more common to find these heavier elements in comet’s atmospheres, there is usually about 10 times the amount of iron than there is nickel.

Image of the VLT, where the data on the comets were collected, during a lunar eclipse.
Credit: ESO / Yuri Beletsky

This could mean there is some new material that contains iron and nickel and has a much lower sublimation temperature.  Or there could be as yet unexplained reasons for the appearance of these metals.  However, the team already has some steps forward,
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