In the News: Exoplanets & Volcano Spotting

[CraigS]

In the news today:

Can we spot volcanoes on alien worlds? Astronomers say yes"

http://www.physorg.com/news203080119.html

Now that astronomers are finding rocky worlds orbiting distant stars, they're asking the next logical questions: Do any of those worlds have volcanoes? And if so, could we detect them? Work by theorists at the Harvard-Smithsonian Center for Astrophysics suggests that the answer to the latter is a qualified "Yes."

.. and yet ....

Astronomers are decades away from being able to image the surface of an alien world, or exoplanet.

....

To look for volcanic sulfur dioxide, astronomers would rely on a technique known as the secondary eclipse, which requires the exoplanet to cross behind its star as seen from Earth. By collecting light from the star and planet, then subtracting the light from the star (while the planet is hidden), astronomers are left with the signal from the planet alone. They can search that signal for signs of particular chemical molecules.

Some time ago, Carl and I were trying to work out whether they could measure the temperature of an exoplanet of say 130 lyrs distant:
http://www.iceinspace.com.au/forum/s...ght=atmosphere
We came up with 'we don't think so' .. not until better technology gets built (the 'OWL').

From this article they say:

But any Earth-like planet less than 30 light-years away could show faint signs of volcanism when studied with the James Webb Space Telescope.

Good idea to keep track of where this sensory technology is up to in present day.

To look for volcanos at these distances they say:

Such gigantic eruptions are infrequent, so astronomers would have to monitor many Earth-sized planets for years to catch one in the act. However, if alien worlds are more volcanically active than Earth, success might be more likely.

Hmmm ... a long time .... just to find a volcano !!

Cheers

[renormalised (Carl)]

That was using the method of light curve dipping...the method they're using here is still spectroscopy, which is different. Using spectroscopy, they can quite easily determine the surface temp of a planet, from just about any distance....so long as they receive enough light from it to get a reasonable spectrum.

They would still need an OWL sized scope, even with the best of their detector technology, to gather enough light to directly detect the changes in intensity of starlight shining through an exoplanet's atmosphere. The have to be able to resolve the planet as a disk to be able to use this method...it's going to be some time before we're able to do that to Earth sized planets.

But this is an interesting set of observations that they should be pursuing. It would be interesting to be able to detect a volcanic eruption in progress on an exoplanet.

[CraigS]

Originally Posted by renormalised

That was using the method of light curve dipping...the method they're using here is still spectroscopy, which is different. Using spectroscopy, they can quite easily determine the surface temp of a planet, from just about any distance....so long as they receive enough light from it to get a reasonable spectrum.

They would still need an OWL sized scope, even with the best of their detector technology, to gather enough light to directly detect the changes in intensity of starlight shining through an exoplanet's atmosphere. The have to be able to resolve the planet as a disk to be able to use this method...it's going to be some time before we're able to do that to Earth sized planets.

But this is an interesting set of observations that they should be pursuing. It would be interesting to be able to detect a volcanic eruption in progress on an exoplanet.

I presume they're measuring the star's unimpeded light spectrum and comparing that with the spectrum of the reflected light from the planet's surface (multiple times, over years). The volcano emissions, if any, would then show up in the reflected light sulphur dioxide band as varying dips which could be seen over the years of observation data (?)

All that at a distance of 30 Lyrs !

Cheers

[renormalised (Carl)]

They take a combined spectrum....planet + star, then a star only and subtract the star only from the planet + star, leaving you with the planet spectrum. Volcanic emissions from SO2 would show up in the red/IR end of the spectrum of the planet. All the spectra I've mentioned are absorption spectra....light of various wavelengths that are absorbed by the gases present, out of the continuous spectrum of the light given off by the source.

[renormalised (Carl)]

With most exoplanets, since their orbits are so fast, they can take multiple spectrum readings per orbit. For some, in the space of a month they can take 15 or more readings, so they build up spectra rather quickly.