Many evolutionists have long hoped to find evidence of life in space. They reason that if life evolved on Earth, then it could have evolved elsewhere.1
If, as the argument goes, there are countless planets throughout the universe that have formed via natural processes, there must be other Earth-like planets. Many think that finding such a planet outside our solar system would be almost like finding evidence of life in space.
Scientists have searched for years for planets orbiting other stars. These are called extrasolar planets, or ‘exoplanets’. Astronomers first obtained evidence suggesting extrasolar planets around 1995 while studying the sun-sized star 51-Pegasi.2 Today there are research teams around the world searching for extrasolar planets with greatly refined research techniques. There are now over 450 objects catalogued in exoplanet lists.3,4
Creationists need to answer two main questions regarding exoplanets. 1) Do they exist? and 2) How did they form? The first question has to do with experimental evidence, but the second has to do with origins science. Scripture does not tell us whether other stars have planets, so we must apply the best observational science we can to answer the question.
On the other hand, Scripture is clear that God supernaturally created the earth and the universe in four consecutive, normal-length days and that the universe is relatively young.5 Thus, if the observational evidence for exoplanets is sound, which I believe it is (see box), creationists will differ with secular scientists about how and when they formed, not whether they exist.
As scientists came to the conclusion that extrasolar planets exist, they faced challenges in explaining their origin. From a creation point of view, it is most likely that God created exoplanets on Day 4 of Creation Week, along with the luminaries, and He could have created them with any characteristics He wished. Our own solar system is special because of Earth—our system and our planet are designed to be a safe and stable environment for life. Isaiah 45:18 acknowledges this, “He did not create it [Earth] to be empty; he formed it to be inhabited.”
There are significant scientific problems with attempts to explain the formation of stars and planets from clouds of gas and dust.6,7 One main issue is that the hypothetical disk of gas and dust tends to dissipate too fast for the resulting planets to become as large as they are observed to be. There are other major problems:
Many extrasolar planets orbit extremely close to their stars—even closer than Mercury is to the sun. Thus they are far too hot for many materials to condense and pull together by gravity. A few exoplanets even lose matter to the star or from their gases being essentially “boiled away”.
To address this problem, evolutionary astronomers proposed that planets could form far away from the star and then the orbit could move inward. This is referred to as orbit migration. This would allow the planets to form in a cooler region of their stellar system, but then the orbit would shrink, due to friction from the dust disk slowing the planet, to put the planet where we see it now.
The idea can also be applied in other ways. For example, in our own solar system, astronomers realize that there would have been too little material at the distance of Uranus and Neptune to form these giants, so they proposed that they formed closer to our sun, then migrated outward to their current orbits.8
Orbit migration theories have difficulties because the dust disk around the star tends to dissipate before the planet can grow large enough or before it can come to its observed position.9
A new problem for planet origin theories has surfaced in recent months. A technique has been developed to determine a planet’s orbital tilt relative to the equator of the star. Several exoplanets actually have retrograde orbits10—in the opposite direction of the star’s spin. Other exoplanets have very large orbital inclinations (slants), some more than 80 degrees.
These strange orbits create a serious problem for planet origins models because a planet is said to get the momentum for its orbit from the dust disk that it formed from. Thus planet orbits should initially be in the same plane as the equator of the star, and in the same direction as the star’s rotation. But there is no plausible way that a dust disk can give rise to a planet with an orbital tilt of 80 degrees, let alone a reverse direction orbit.
Evolutionary planetary scientists are generally trying to answer this by assuming that where the planet orbit is highly inclined or retrograde, there was once one or more other planets (or possibly stars) in the stellar system that were also at highly inclined orbits. If there are multiple objects (stars or planets) in various highly inclined orbits, then this could possibly cause some complex orbit changes.11 Some scientists believe that where there are three or more stars and planets in a system, it is possible for a planet’s orbit to become highly inclined. But this must assume that objects once existed in these systems at large distances from their star, which we cannot or do not observe (and where did they come from?). It is also questionable that this highly unlikely process could happen for all the known cases of retrograde planets.
Certainly extrasolar planetary systems differ from our solar system. They show that God created variety in the universe and that our own planet was created with design and purpose. Astronomers are getting closer to being able to detect an Earth-sized planet. But we must not confuse an Earth-sized planet as being a truly Earth-like planet. It is no accident that Earth is in the so-called “habitable zone” in our solar system—a narrow range of distances from the sun where liquid water can exist.
No known extrasolar planets are considered habitable—lifeless Venus and Mars are more ‘Earth-like’. In fact, even if a planet very much like Earth were eventually discovered, with an appropriate atmosphere and liquid water, that does not in and of itself mean that life could evolve on such a planet. We depend on our Creator for the planet we have and to create and sustain life.
Although there were initially false claims about exoplanets due to bias, wishful thinking and leaps in logic,12 there is now sound observational evidence for the existence of planets orbiting other stars. This evidence has come from two primary methods, and a third more recent addition:
Astronomers measure very precisely the spectrum of the star’s light. An extrasolar planet can cause a periodic change in the motion of the star as it orbits, essentially making the star wobble and causing tiny variations in the colour of the light,13 due to the Doppler effect.14 If a planet is more massive or it is close to the star, then it causes a larger “wobble” on the star than if it were smaller or farther away. Planets that are farther away from their stars cause slower wobbles because the planets orbit more slowly.15 Astronomers have used this technique to discover many exoplanets and sometimes multiple planets. But while the Doppler method can estimate a planet’s mass and distance from its star, it can’t tell us the planet’s composition.
This measures the slight drop in a star’s brightness as a planet passes in front of it. This won’t work for most stars, because the planet must block Earth’s line of sight. (Transit measurements have revealed exoplanets orbiting about 100 stars.) The silhouette of a planet transiting a star gives the planet’s size and the star’s light skirting the planet can indicate the composition of any atmosphere.
Many of the exoplanets studied this way seem to be large gaseous planets like Jupiter or Saturn in our own solar system. Combining a planet’s diameter with the estimate its mass gives its density. There is at least one known case of an exoplanet that has a similar density to Earth.16 A significant portion of this planet’s mass must be rock.
If the transit dimming of a star is in time with wobbling, this is especially strong evidence for a planet.
In recent years, telescopes have been launched into space to obtain photographs of extrasolar planets as they orbit their stars. In 2009, NASA launched the Kepler Mission, a space observatory designed for very precise transit measurements of extrasolar planets.
One photographed exoplanet orbits a nearby star called Fomalhaut. Called Fomalhaut b, it orbits just inside a dust ring.17 The Hubble Space Telescope took photos over two years, showing that this object was in motion around the star. The Spitzer Space Telescope has also detected infrared radiation from two hot Jupiter-like exoplanets.18
Direct imaging is likely to discover more exoplanets, and to verify claims from the other methods.