Finding twin Earths may be harder than we thought...but it probably doesn't matter all that much

Friday, March 20, 2009

2008 is over; time to update the chart.

From Spaceref:

Does a twin Earth exist somewhere in our galaxy? Astronomers are getting closer and closer to finding an Earth-size planet in an Earth-like orbit. NASA's Kepler spacecraft just launched to find such worlds. Once the search succeeds, the next questions driving research will be: Is that planet habitable? Does it have an Earth-like atmosphere? Answering those questions will not be easy.

Due to its large mirror and location in outer space, the James Webb Space Telescope (scheduled for launch in 2013) will offer astronomers the first real possibility of finding those answers. In a new study, Lisa Kaltenegger (Harvard-Smithsonian Center for Astrophysics) and Wesley Traub (Jet Propulsion Laboratory) examined the ability of JWST to characterize the atmospheres of hypothetical Earth-like planets during a transit, when part of the light of the star gets filtered through the planet's atmosphere. They found that JWST would be able to detect certain gases called biomarkers, such as ozone and methane, only for the closest Earth-size worlds.

"We'll have to be really lucky to decipher an Earth-like planet's atmosphere during a transit event so that we can tell it is Earth-like," said Kaltenegger. "We will need to add up many transits to do so -- hundreds of them, even for stars as close as 20 light-years away."
This is true, but in my opinion the mere discovery of Earth-sized planets will be sufficient to create an epic shift in the way we view the universe (from an inhospitable void with weird planets to an inhospitable void with planets that resemble ours quite a bit), which is the most important part for humanity as a whole. Even when we have found out quite a bit about the atmosphere of other planets in other solar systems we still won't be entirely sure about the surface conditions there, and we will probably have a number of Venus-like unpleasant surprises where a planet is much more inhospitable than we originally thought...and a few pleasant surprises on the other end where a planet that we thought should be too cold to support life may actually turn out to have a thicker atmosphere than we thought, or more tidal heating than we thought enabling it to retain a liquid ocean, etc. I expect a huge increase in funding for observatories and space telescopes that are capable of finding out more about these planets once we have found them in the first place.

One other interesting part of the article refers to something I've written about quite a bit, that the first discoveries we make of Earth-like planets and the ones we will know the most about will be those orbiting red dwarfs:
An Earth-like world would have to orbit close to a red dwarf to be warm enough for liquid water. As a result, the planet would orbit more quickly and each transit would last a couple of hours to mere minutes. But it would undergo more transits in a given amount of time. Astronomers could improve their chances of detecting the atmosphere by adding the signal from several transits, making red dwarf stars appealing targets because of their more frequent transits.

An Earth-like world orbiting a star like the Sun would undergo a 10-hour transit once every year. Accumulating 100 hours of transit observations would take 10 years. In contrast, an Earth orbiting a mid-sized red dwarf star would undergo a one-hour transit once every 10 days. Accumulating 100 hours of transit observations would take less than three years.

"Nearby red dwarf stars offer the best possibility of detecting biomarkers in a transiting Earth's atmosphere," said Kaltenegger.
So that means in the next few years we're going to become very acquainted with all sorts of red dwarfs, and I suspect that we might even begin to see our own Sun as not so much a normal G-type star, but a yellow giant. After all, if red dwarfs are the most common stars in the universe, doesn't that make them the norm?

Quoth Wikipedia:
Once regarded as a small and relatively insignificant star, the Sun is now known to be brighter than 85% of the stars in the galaxy, most of which are red dwarfs.
If you're larger that 85% of the rest then that makes you a giant, does it not?


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