Over the last two decades, astronomers have discovered more than 430 extrasolar planets. Although the initial expectation was that these planetary systems would resemble the solar system, the data speak otherwise. Most exoplanets orbit with large eccentricities or in circular orbits very close to their parent star. This article highlights the latest entry in the “bizarre planet” category.
On April 1, 2008 the SuperWASP collaboration announced the discovery of a planet dubbed WASP-12b. With a daytime temperature around 4,500 degrees Fahrenheit, it was the hottest known transiting extrasolar planet. Its mass, 41% larger than Jupiter, falls within the normal range of exoplanets. Yet, WASP-12b exceeds Jupiter’s radius by 79%, which puzzled astronomers because, given its mass, the planet should be much smaller. The orbital characteristics of the planet revealed more surprises. WASP-12b orbits its parent star at a distance only 3 times larger than the star’s radius (in contrast, Earth orbits at a distance 213 times the radius of the Sun). This short distance means WASP-12b makes a full revolution every 27 hours! Usually orbits this small are quickly circularized by tidal interactions with the host star, yet WASP-12b exhibits an eccentric orbit.
New research, published in 2010, went a long way toward explaining WASP-12b’s odd characteristics. As the planet orbits, the gravity of its host star exerts forces that squeeze and deform the planet into a shape similar to a football (think NFL, not soccer). This deformation generates tremendous heating within the planet, causing WASP-12b to expand and occupy more volume that it would otherwise. According to the article published in Nature,1 this planetary swelling leads to its outer material being transferred to its host star. In fact, WASP-12b loses roughly 10 billion metric tons each second. At this rate, WASP-12b would disappear in 10 million years—a short lifetime compared to the 4.5 billion-year-old planets in our solar system.
The material pulled from WASP-12b forms a disk that slowly spirals into the host star. Current telescope facilities have the ability to detect this disk, which would confirm the explanation for the unusual characteristics of WASP-12b and its host. Additionally, it may provide a way to determine if other smaller super-Earth planets exist within the same system.
Exciting times still lay ahead for the continuing discovery and research of exoplanets. RTB expects future discoveries to follow past trends and demonstrate how remarkably fine-tuned the solar system is to support life.
- Shu-lin Li et al., “WASP-12b as a Prolate, Inflated and Disrupting Planet from Tidal Dissipation,” Nature 463 (February 25, 2010): 1054–56.