Friday, December 27, 2013
Monday, December 16, 2013
Tuesday, December 10, 2013
When an astronomer says a far-off planetary system is like ours, what he means is that it is completely different. For example, see the recent press releases about the seven planet system KOI-135 (aka Kepler 90).
This system has a planet the size of Jupiter in an orbit almost the same as our Earth’s. Since the star is a little bigger (and hotter) than the sun, the orbit takes less time, but the orbital radius is just like ours.
Inside of that, in an orbit about the size of Venus’s orbit, is a Saturn sized gas giant planet.
Inboard of the Saturn-sized planet are three mini-Neptunes. Our solar system doesn’t have any planets of this type, but they seem to be fairly common in the rest of the galaxy. These are gas rich planets smaller than Neptune and Uranus, but still much larger than Earth. One of them has an orbit substantially larger than that of Mercury, one substantially smaller, and one about the same radius, but much more circular (Mercury has quite an elliptical orbit).
Finally, inside of that, are two earth-sized planets that orbit screamingly close to the planet. The inner planet is more than five times closer to its star than Mercury is to the Sun, and its orbit (e.g. its year) is only a week long. The other planet is only slightly farther out, in a 9 day orbit.
It is not known if there are more planets farther out- Kepler’s detection method would not pick them up.
So you gotta wonder, if that is Earthlike, then what are the strange ones like?
In fact, the whole framing of exoplanetary research as “counting up the Galaxy’s Earths” is a bit disingenuous. By presenting a scientific study as having a foregone conclusion (e.g. there are Earths everywhere), NASA takes a lot of the suspense and excitement out of the search. Furthermore, it makes trying to fit otherwise interesting discoveries into the Earthcount box awkward, and it diminishes the wonder and diversity of just what is out there.
In fact, the NASA exo-Earth search program is a lot like going to
to find a person just like your mother.
After all, China
has billions of people, and they were all born more or less the same way as
your mother, so odds are, the place must be crawling with women just like mom.
Imagine how tedious a travel documentary of
China would be
when viewed in this way. “Our way south to Beijing to look for mom-analogs was blocked
by some kind of wall- fortunately we managed to avoid it).” You would have
progress press releases, “Some people in China confirmed to be women.” “New mission shows some Chinese women to be
mothers.” Newly discovered Chinese woman
likes fried rice, just like your mom.”
This narcissistic approach misses the whole point of travel and exploration. We investigate far-off places because they are foreign, because they expose the assumptions on which our beliefs are based, and because the let us discover new and wondrous things that were beyond the scope of our imaginations.
This is what exoplanetary research does. Everything we have discovered in planetary science, from the first Moon probes to the discovery of planets 2500 light years away, has been wonderful and new and different to expectations and awe-inspiring. But the current framing of the science does not allow this amazement to be conveyed to the public who fund the research. And this is a terrible shame.
Thursday, December 05, 2013
A recent cartoon/poster on xkcd tries to estimate what the population of habitable zone planets in our stellar neighborhood looks like. Unfortunately, despite labeling the poster as “all habitable zone planets”, there are a couple of very important omissions. The center of the picture should look like this:
When discussing the habitable zone, and how it applies to exoplanets, one needs to remember that the definition of habitable zone is sufficiently wide that it covers both Mars and Venus, the closest planets to Earth. In fact, despite discovering thousands of exoplanets and exoplanet candidates, we still do not have any planets as earthlike as Venus. It is hard to say much about exo-Mars equivalents, as exoplanet detection technology has trouble finding a planet that small and far from its host star.
Most of the planets shown in the chart have not been discovered yet. Even among those which have, very little data about the planets is available. It will be years, perhaps even decades, before we have the technology to pick an exo-Earth from an exo-Venus. But framing the exo-planet debate as an Earth versus Venus relative distribution would be a mistake. Chances are, the vast majority of these planets are completely unlike either planet.
Our solar system is strange. It is missing the most abundant type of planet in our galaxy- those which are larger than Earth, but smaller than Uranus. These worlds are often, albeit deceptively, referred to as “super-earths”. But as Systemic has shown, those which we have data for are not only completely different to anything in our solar system, they are often quite different from each other.
The omission of Venus and Mars is therefore important, because it gives the false impression that planets in the habitable zone are going to be Earthlike. Neither of the habitable zone planets in our solar system are particularly Earthlike, and everything we know about exoplanets so far suggests that they will be far stranger still.