Yet more planet transits

Last week, I posted a guest blog entry from astronomer Jay Pasachoff about observing Venus transits from Jupiter and Saturn later this year. A reader, Mike, responded with a question: "What about also looking at transits by Earth and Mars from Jupiter, and transits by Earth, Mars, and Jupiter from Saturn?" I thought that was a very good question and sent that and a few others back to Jay.

So: Are there more transits of more planets as seen from other planets? Yes. In the time period between 2012 and 2117 (the year of the next Venus transit as seen from Earth), Jupiter will see Venus transit the Sun 15 times, and Earth transit 10 times. Saturn will see 21 Venus and 6 Earth transits. Here's a few notable upcoming transits:

• Transit of Venus as seen from Jupiter: September 20, 2012, and then not until May 26, 2024
• Transit of Earth as seen from Jupiter: January 5, 2014 and then not until January 10, 2026
• Transit of Venus as seen from Saturn: May 6 and December 21, 2012 and then not until: January 14, 2028
• Transit of Earth as seen from Saturn: July 20, 2020
• Transit of Mars as seen from Saturn: May 17, 2024
• Transit of Jupiter as seen from Saturn: not until March 17, 7571!

Why is a transit of Venus particularly interesting? Jay explained that transits of both Venus and Earth are most interesting because of their atmospheres. The goal is to see if we can detect Venus' and Earth's atmospheres as they transit, because we'd like to use similar techniques to detect atmospheres around Earth-size planets orbiting other stars. Jay now reports that their proposal to observe the next transit of Venus as seen from Jupiter with Hubble was turned down; it is very competitive to get time on Hubble. He said they intend to apply again to observe the January 5, 2014 transit of Earth as seen from Jupiter.