Saturday, January 28, 2006

 Earthlike my ass 

When my Uncle Bill passed away 4 years ago, among other things I inherited his collection of VHS tapes of Cosmos, by Carl Sagan, that he recorded off TV when it was originally broadcast back in the early '80s. I had watched the show as a youngster back then, but hadn't seen it since. Well finally, this past week I started re-watching the series, and am surprised at how well the series has aged, in spite of the advances in astronomy and science in the past 25 years. Sagan was smart enough to make the scientific method and the spirit of free rational inquiry the real emphases of the series, and not focus solely on the latest summation of what has been learned by science at the time.

In one installment of the 13-part series, he speaks in front of a grade school class (he was quite good in that setting, better than you might think), talking to them about how planets around other stars will be discovered in the near future. He knew full well what he was talking about, for his predictions then have come to fruition in the past decade, with the discovery of over 100 so-called extrasolar planets. This is a burgeoning field of study, although most of the planets discovered thus far have been quite different from anything in our own solar system; the main methodologies can find bloated gas-giants that would make Jupiter shrivel in fear much easier than they can find smaller rocky spheres like Venus, Earth, or Mars. In time, that may change, but for now, that's all that can be done.

Still, refinements continue, and the limits keep getting pushed back. Earlier this week Nature published an article by over 70 collaborators from 30 institutions about the discovery of another extrasolar planet, this time using a method called gravitational microlensing, whereby the light of a more distant object is distorted by the gravitational field of the planet in question; and even though the planet itself cannot be seen directly, its existence can be safely inferred by the observed distortions of the light from that object, using Einstein's General Theory of Relativity. All in all, a very impressive accomplishment:

Located more than 20,000 light years away in the constellation Sagittarius, close to the center of our Milky Way galaxy, planet OGLE-2005-BLG-390Lb is approximately five-and-a-half times the mass of Earth.

Orbiting a star one-fifth the mass of the sun at a distance almost three times that of Earth's orbit, the newly discovered planet is frigid: the estimated surface temperature is -364 degrees Fahrenheit (-220 degrees Celsius).

Although astronomers doubt this cold body could sustain organisms, researchers believe gravitational microlensing will bring opportunities for observing other rocky planets in the "habitable zones" of stars - regions where temperatures are perfect for maintaining liquid water and spawning life.

But here's what chaps my hide. The discoverers of course report that they have found "one of the most earth-like planets yet", which is true as far as it goes. But what does the traditional media say in their reports on this story?

Washington Post - Earth-like Planet Found Outside Solar System
CNN - New Technique Finds Earth-like Planet
Albuquerque Tribune - Team Spots Earth-Like Planet
BBC News - Small Earth-like Planet Found

Hell, even the US State Department - yes, Condi Rice's State Department - exacerbated the misperception with their release entitled, "Astronomers Find Distant Icy Earth-like Planet". Ugh.

Let's review this planet's resume: OGLE-2005-BLG-390Lb (OGLE for short) orbits a star one-fifth as massive as our sun at a distance of about 300 million miles. A star that small will also have far less luminosity than our sun, since smaller stars have lower internal pressures and therefore maintain lower rates of nuclear energy generation. Basically, OGLE has a dimmer sun, and they orbit much further from that dim sun than we orbit ours. As a result, the surface temperature can't be much warmer than -350 degrees Fahrenheit. Oh, and OGLE is also 5 times as massive as the Earth, which means its gravity would be 5 times stronger.

So, would someone tell me how all this makes this planet "earth-like"?

Here's the deal - using the term "earth-like" is just a shorthand in planetary science circles for saying that the object is mostly solid material with a limited or non-existent atmosphere, in contrast to gas giants like Jupiter or Saturn, or other proto-stars like brown dwarfs. (Or Yavin, for all you Star Wars buffs.) However, I would submit that "earth-like" means something else entirely to the public at large - that it means having oceans, a breathable nitrogen and oxygen atmosphere, that it has landforms and volcanos and maybe palm trees and sandy beaches and all the ingredients you'd need to make margueritas and basically that it looks like our own Blue Marble. Such a planet is not what was found here, and it makes me wonder, what would the media say when such a planet were found? They've already shot their wad by claiming that we've found an "earth-like" planet. Are they going to say, "No, this time we mean it, a really REALLY earth-like planet has been found."

Maybe we should save our breathless headlines for the time when we really do find an "earth-like planet." Jus' sayin'.

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