The Case for a Creator: Hot Jupiters

The Case for a Creator: Hot Jupiters December 24, 2009

The Case for a Creator, Chapter 7

In chapter 3, I chastised Jonathan Wells, a trained biologist, for making deceptive arguments whose answers he unquestionably already knows. I have to send a similar criticism Guillermo Gonzalez’s way, because in this chapter, he makes an argument that any beginner student in astronomy would be able to answer easily.

The argument has to do with the nature of extrasolar planets, of which we currently know over 400. Gonzalez concedes that this means our solar system is not unique when it comes to having planets orbiting a star – a point he’s clearly reluctant to yield – but he still maintains that what we have discovered reinforces his claim about the uniqueness of Earth.

“…the expectation was that astronomers would find giant gas planets in large circular orbits, much like Jupiter… However, we’re finding that the planets circling other stars are quite different from Jupiter. They orbit over a full range of distances, from just a tiny fraction of an Astronomical Unit – which is the distance between the Earth and the sun – out to several Astronomical Units. Most of their orbits are highly elliptical; very few are circular. These strongly non-circular orbits utterly surprised astronomers… they had expected that other planetary systems would be just like ours. And that expectation was basically dashed.” [p.173]

Strobel lets this comment pass without asking for any examples of astronomers who had allegedly expected this. I doubt he would have gotten any if he had.

It’s true that most of the extrasolar planets we’ve found so far are “hot Jupiters”, or gas giants with orbits that take them very close to their parent stars. (Most hot Jupiters do, in fact, have circular orbits, so Gonzalez is wrong on that point.) But that’s not because every extrasolar planet is like that. Rather, it’s because the detection methods we use are most sensitive to this type of planet.

One of the most successful ways of detecting extrasolar planets is the radial-velocity method. As a massive planet orbits its star, the gravity of the planet tugs the star back and forth. This causes a small, but detectable, Doppler shift in the frequency of the star’s light as observed from Earth. Because gravity is proportional to mass and inversely proportional to distance, the planets with the largest gravitational effects on their parent stars – the ones that are easiest to detect – are very large and orbit very close: in other words, hot Jupiters.

Planet-finding instruments like HARPS have astounding sensitivity, able to detect velocity shifts in stars as small as 1 m/s. But even they aren’t sensitive enough to detect the minuscule Doppler shifts that Earth-size planets would cause. Finding terrestrial exoplanets will have to wait for next-generation instruments like NASA’s Terrestrial Planet Finder mission – although, as our methods improve, we’re finding more and more exoplanets in a category called super-Earths – rocky worlds much smaller than gas giants, but with up to ten times the mass of our own planet.

Searching for these planets is like sweeping the ocean with a net to catch fish. The more finely-woven your net, the smaller the fish you’ll be able to catch. Our “net” is still fairly coarse, able to catch only the larger fish. Strobel and his creationist allies would claim that this proves that only large fish live in the ocean. But we’re getting better at weaving finer and finer nets, and every year we’re catching smaller and smaller fish. This is an area where the science is progressing very rapidly, and we’re in the very rare position of being able to know, possibly within just a few years, exactly how wrong the creationists are.

Having spent all this time discussing religious pseudoscience, I just have to cleanse my palate now by talking about some real science, especially since there’s such an abundance to be had. Feast your eyes on the first ever visible-light image of a planet outside our solar system:

This composite image, taken by the Hubble Space Telescope’s Advanced Camera for Surveys, shows a dust disk surrounding the bright star Fomalhaut (see also), about 25 light-years from Earth in the constellation Piscis Australis. The star itself has been blocked out from the image, so that its light doesn’t drown out the far dimmer object orbiting it: the planet named Fomalhaut b, which is about the same mass as Jupiter and orbits its parent once every 872 years, four times as far as Neptune is from our own sun.

Fomalhaut is a young, hot white star, similar to Vega and Sirius. It’s only about 200 million years old – which means Fomalhaut b must be similarly young – but is expected to burn for no more than another billion years or so. The star is surrounded by a vast disk of dust, which very likely resembles the one that coalesced into the planets of our own solar system. Fomalhaut b’s gravity has shepherded the particles of this disk, which accounts for the relatively sharp inner edge visible in the Hubble photo. The disk also radiates strongly in the infrared, which may indicate heat being radiated from the collision of small rocky bodies and planetesimals – implying that planet formation may be occurring around Fomalhaut, or even that other young planets exist within this system that have yet to be observed.

One more intriguing fact is that Fomalhaut b is significantly brighter than expected for a planet of its mass. A possible explanation is that the planet, like Saturn, has a ring system that reflects starlight (though, one of the scientists who theorized this said that its rings could dwarf Saturn’s by comparison).

These are the kind of discoveries that creationists wave off, insisting that there’s nothing new or interesting worth finding beyond our own world. A worldview that already has all the answers has no place for curiosity. But the universe is greater than they imagine, and every day, real scientists are making discoveries that further reveal to us our true place in the cosmos. There are countless worlds waiting to be explored. Who knows what wonders may yet lie hidden on those other shores?

Image of Jupiter via Wikimedia Commons/NASA; image of Fomalhaut via NASA/STScI.

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