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Mega-volcanoes might be detectable on alien Earths

If a volcano with the explosive power of 600,000 Hiroshima atomic bombs blew up on a planet 30 light-years away, would we notice?
Image: Big Tambora volcano
/ Source: Discovery Channel

If a volcano with the explosive power of 600,000 Hiroshima atomic bombs blew up on a planet 30 light-years away, would we notice?

Nope, considering that nearly all the exoplanets cataloged so far have been discovered by their invisible gravitational tug, or shadows from stellar transits.

But a new generation of large-aperture space based telescopes might begin to gather clues to catastrophic events on other worlds.

WIDE ANGLE: The Age of the Exoplanet

I’m not talking about direct imaging of an exo-Earth. It will be many decades before we are ever able to take a detailed snapshot of what such a planet looks like. This would require a budget-busting space-based armada of gigantic optical telescopes working in unison.

Instead, Lisa Kaltenegger at colleagues at the of the Harvard-Smithsonian Center for Astrophysics are already thinking about ways of detecting geologic upheavals on any nearby super-Earths without waiting for photos.

NASA’s planned James Webb Space Telescope (JWST) will be able to measure the chemical composition of the atmosphere on any nearby terrestrial planet that passes in front of and behind its star.

JWST astronomers will first collect infrared light from the star and planet. They will then subtract the light from the star when the planet passes behind. Researchers will be left with the signal from the planet alone. When the planet’s light is divided into its component colors, astronomers will tease out the spectral fingerprints of certain atmospheric gases. This kind of observation is already being accomplished with the Hubble and Spitzer space telescopes as proof of concept.

Kaltenegger proposes that JWST could chemically identify an eruption 10 times the size of the largest volcanic event ever recorded on Earth. That was the 1815 Tambora, Indonesia explosion (the crater of which is imaged top). A 13,000 foot-high volcano blew its top off with the power of over 100 Mt. St. Helens eruptions.

Image: Venus volcano

Kaltenegger and her Harvard colleagues, Wade Henning and Dimitar Sasselov, developed a model for eruptions on an Earth-like exoplanet based on the present-day Earth. They found that sulfur dioxide from a very large eruption is potentially measurable because a lot of gas is produced. With ejecta being deposited tens of miles high into the atmosphere, it would take years to wash out.

Why should we care? A geologically active terrestrial planet may be more suitable for life. It recycles crust, unleashes greenhouse gasses, opens new environmental niches, and generally provides a dynamic environment for advantageous life forms. Earth would have remained a frozen snowball 650 million years ago if not for volcanism busting the surface ice apart. Perhaps not coincidentally the Cambrian Explosion of multi-celled life forms soon followed.

There are some big caveats here. First, JWST's capabilities are limited at best to a few nearby Earths orbiting red dwarf stars. Even gathering data from one of these planets would require a very long observation for JWST. And, just such a nearby planet hasn't even been found yet.

Ideally you’d want to be lucky enough to have data about the planet before and after the eruption. The odds of nature cooperating are astronomically low unless you were able to conduct long-term monitoring, which is unlikely for JWST’s anticipated demanding schedule for observing time.

Planet hunters could really use something more like an 18-meter optical space telescope dedicated to a long term surveillance of the most promising nearby Earth-like targets. But this facility is at least two decades away.

If alien super-Earths are more volcanically active than our world, success might be more likely. What's more, a super-Earth orbiting a red dwarf might be an analog to the moon Io that orbits Jupiter. Io has continuous volcanism because it is tidally heated by the gravitational squeeze of Jupiter and the other major Galilean moons. A red dwarf’s super-Earth might always be belching out sulfur dioxide.

Interestingly, if an extraterrestrial civilization is located at the star Delta Crateris — 195 light-years away — they would only just now be measuring the effects of the Tambora explosion on Earth’s atmosphere.

In addition to serving as a blogger for Discovery News, Ray Villard is news director for the Space Telescope Science Institute, which is involved in planning for the James Webb Space Telescope mission.