What I Learned Today

Jupiter’s moon Io is very active volcanically:

“A Giant plume from Io’s Tvashtar volcano composed of a sequence of five images taken by NASA’s New Horizons probe on March 1st 2007, over the course of eight minutes from 23:50 UT. The plume is 330 km high, though only its uppermost half is visible in this image, as its source lies over the moon’s limb on its far side.” (Robert Wright and Mary C. Bourke)

But what is that lava made of? What materials lie inside the moon that are being spewed out? We can’t (yet) land on Io and test its lava directly. But we can make some inferences based on remote sensing observations of the lava’s temperature. The temperature carries information about how mafic (magnesium and iron-rich) or felsic (silicon-rich) the lava may be.

The best way to test our ability to deduce composition from orbit is to do it here on Earth, where we do have the opportunity to determine the true composition by sampling the lava on the ground. Scientists Robert Wright, Lori Glaze, and Stephen M. Baloga recently reported a positive correlation between temperature observations from Earth orbit (using the Hyperion spectrometer) and ground composition observations of 13 volcanoes: “Constraints on determining the eruption style and composition of terrestrial lavas from space”. The conclusion for Io is that the lava is so hot that it is likely ultramafic: very high magnesium/iron content.

You can read more about this endeavor (and view more pictures).

Perhaps you saw the recent Venus transit of the Sun. But what about an Earth transit?

Obviously we can’t see such a phenomenon while sitting on the Earth itself. But some clever astronomers have done calculations to work out when the Earth would transit the Sun from the perspective of other bodies in the solar system, including the Moon and Jupiter.

“In January 2014, Jupiter will witness a transit of Earth. And we can see it too, the astronomers say, by training NASA’s Hubble Space Telescope on the huge planet and studying the sunlight it reflects.”
(From NBCNews, June 4, 2012)

Using Jupiter as a mirror seems a curious strategy, since the reflected light will also be influenced by the chemical makeup of Jupiter’s atmosphere. However, just as with the hunt for exoplanets, if we can stare at Jupiter for long enough before the transit occurs, we can build a good enough model so its factors can be subtracted out from the Earth+Jupiter signal during the transit. Scientists first plan to test this strategy with a Venus transit that Jupiter will see (Earth won’t) in September of this year. And I’ve seen talk that they used the Moon as a mirror to observe the recent Venus transit from the Earth vicinity — but I haven’t been able to find any images of the result yet. Here’s how it works: