In the search for distant planetary systems, astronomers employ a special method to discover planets beyond the range of our telescopes. Thanks to the theory of general relativity, astronomers have access to gravitational lenses that far outstrip the power of any telescope they can build. But even with the amazing detection capabilities afforded to us by gravitational lensing, scientists have yet to discover a planetary system as hospitable to life as our own.
What Is Gravitational Lensing?
Gravitational lensing exists in three forms: strong (or macro) lensing, weak lensing, and microlensing. Strong gravitational lensing occurs whenever a giant galaxy or a cluster of galaxies lies along the line of sight between us and a distant quasar or galaxy. The strong gravitational field of the giant galaxy or cluster of galaxies bends and magnifies the light emitted by the more distant quasar or galaxy. The magnified light of the distant quasar or galaxy, if perfectly aligned, appears as a circle of light, termed an Einstein ring, around the giant galaxy or cluster of galaxies. Figure 1 shows such an Einstein ring.
Figure 1: This Einstein ring occurred as the gravity of a large red galaxy gravitationally distorted the light from a much more distant blue galaxy into a ring.
Image credit: NASA/ESA/Hubble
In weak gravitational lensing, either the alignment is much less than perfect or the gravitational field of the intervening galaxy or galaxy cluster is relatively weak so that the magnified light of the distant galaxy or galaxies fails to form a circle or a set of bright spots. Instead, what astronomers see is a general distortion of images surrounding the intervening galaxy or galaxy cluster (see figure 2).
Figure 2: Image distortion resulting from weak gravitational lensing
Image credit: Wikimedia Commons/TallJimbo
In the case of gravitational microlensing, no distortion in the shape of the image occurs. Light from a distant star is bent by the gravitational field of a closer star that lies in the line of sight (see figure 3). The presence of a planet orbiting the closer star affects the degree of bending of light from the more distant star in a periodic manner. By measuring the period of the change in light bending and the degree of the change, astronomers can determine both the orbit and the mass of the planet.
Figure 3: Gravitational microlensing influenced by an orbiting planet
Image credit: NASA
Advantages and Effectiveness of Gravitational Lensing
The first planet to be detected by gravitational microlensing was OGLE-2003-BLG-235Lb. Discovered in April 2004, the planet appears to be a gas giant planet (similar to Jupiter) that is located approximately 4.3 AU away from its parent star. Unlike other planet detection methods, gravitational microlensing can discover planets tens of thousands of light-years away from Earth and even find planets in other galaxies. Another advantage over alternate detection methods is the ease with which low mass planets and planets that are farther away from their host stars can be located.
The advantages of the microlensing technique give astronomers an opportunity to build a relatively unbiased sample of exoplanets for statistical analysis. Such analysis can help answer the question of whether or not our solar system is unique among planetary systems in manifesting the characteristics needed for complex life to exist on one of the planets in the system.
So far, only 30 planets have been discovered by the microlensing technique. Nevertheless, this sample prompted the three largest microlensing research teams (the OGLE collaboration, the MOA collaboration, and the MiNDSTEp collaboration) to jointly publish the first statistical analysis of their research.1 They reported three findings:
1. Thirty-eight percent of stars host cold super-Earths or cold Neptunes.
2. Forty percent of planets found by microlensing are either cold Neptunes or cold sub-Saturns.
3. Cold super-Earths and cold Neptunes are about seven times more abundant than cold Jupiters.
Here, a cold planet is defined as one that is at least 1.6 times more distant from its host star than Earth is from the Sun. A super-Earth is a planet 1–10 times Earth’s mass. A Neptune is a planet around 10–30 times Earth’s mass. A cold sub-Saturn is a planet that is 30–80 times Earth’s mass. And a cold Jupiter is a planet approximately 100–3,000 times Earth’s mass.
With only 30 planets in the microlensing catalogs, these results are preliminary. Time will reveal the degree to which these initial statistical findings are confirmed.
How Do Exoplanets Size Up to Ours?
By comparison, our solar system possesses no super-Earths at all; it has as many cold Jupiters as it has cold Neptunes, namely two; and our system’s cold Neptunes are located more than 18 times Earth’s distance from the Sun, as compared to less than nine times Earth’s distance for the sample of cold Neptunes in the microlensing catalogs. All of these distinct features of our solar system are critical for enabling advanced life to exist on Earth.
The fact that no other planetary system out of the 1,349 discovered so far possesses the configuration of planets needed for advanced life to possibly exist within that system is evidence that a supernatural, superintelligent Creator personally designed our solar system so that humans and all advanced plant and animal life could exist and thrive on Earth.2 The expanding microlensed planet catalogs yield yet another demonstration that the more we learn about exoplanets and exoplanetary systems the more evidence we accumulate for the handiwork of God in designing the solar system for the specific benefit of human beings.
Food for Thought
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