Great Image: Double Transit of the Sun

The transit of Mercury across the sun was interesting to watch last week, as is the transit of the International Space Station. In fact, both transits are shown in the image above. 

Here is the full story from APOD:

This sharp video frame composite was taken from a well-chosen location in Philadelphia, USA. It follows the space station, moving from upper right to lower left, as it crossed the Sun's disk in 0.6 seconds. Mercury too is included as the small, round, almost stationary silhouette just below center. In apparent size, the International Space Station looms larger from low Earth orbit, about 450 kilometers from Philadelphia. Mercury was about 84 million kilometers away.

Image Credit & Copyright: Thierry Legault

Mercury's Transit of the Sun

Don't go blind today trying to watch Mercury transit the Sun because it cannot be seen with the naked eye anyway. NASA has it covered with a live video here. The transit will started at 7:15 EST and last a little over seven hours. This event happens only 13 times a century and scientists are using it to study Meecury's exo-atmosphere. Yes, as with exoplanets, such transits in front of a sun are very informative.

Learning About Home From Exoplanets

New Scientist magazine recently had an interesting article on how our study of exoplanets has raised questions about the beginnings of our own solar system.  In the piece, Mercury May Be the Sole Survivor of a Planetary Pile-up, the author notes that a number of planetary systems being seen elsewhere in the galaxy have small, rocky planets in an orbit closer to their suns than Mercury is to our sun.  The speculation now is that this may be the normal order of things in younger solar systems and over time the collision of these smaller planets may create one larger survivor such as Mercury.  Of course, these rocky planets could also pulverize one another into dust unless they are made of stronger stuff, which may explain why Mercury survived given its considerable iron core. 

This is another fascination off-shoot of our search for other planets and potential life in our galaxy.  While we are looking at the present situation in our neighborhood, we may learn quite a bit about our past as well.  And we are in the very early stages of our search.

Image Credit:  NASA Discovery Program.  Shows the process of collision and accretion created the four rocky, or terrestrial, planets of our inner solar system — Mercury, Venus, Earth, and Mars.