Torn Apart by its Own Tides: Massive Planet on a 'Death March'

Posted Feb 27, 2010 by Tea Lulic
WASP-12b, a massive planet outside of our Solar System, is slowly but surely walking towards its death as its host star is inflating its size and at the same time causing a rapid disruption of it.
Illustration of WASP-12b in orbit around WASP-12.
ESA/C Carreau
Illustration of WASP-12b in orbit around WASP-12.
A group of international astrophysicists has one-of-a-kind opportunity to observe how a planet enters its final stages of life and flounders towards its death. In fact, this is the first time astronomers are able to witness this occurrence in space.
The research was led by Shu-lin of the National Astronomical Observatories of China. Li and a research team analyzed observational data on the planet and showed that the gravity of its parent star is causing the massive growth of WASP-12b, which is in turn spurring its disruption.
WASP-12b was discovered in 2008 and deemed one of the most enigmatic of 400-plus planets that have been found outside of our Solar System in the past 15 years. It is located in the constellation Auriga, orbiting a star named WASP-12, which has a similar mass to our Sun. It is large and gaseous, resembling planets such as Saturn and Jupiter. However, WASP-12b orbits its star at a very close range – approximately 75 times closer than the Earth is to Sun, or just over 1 million miles. Also, its mass is estimated to be almost 50% larger than Jupiter’s and its 80% larger (approximately 6 times Jupiter’s volume). Furthermore, the daily temperatures on WASP-12b reach an astonishing 2500 degree Celsius. Such an astonishing size has prompted researchers to take a look at its tidal forces and focus their analysis towards them, claiming that they are strong enough to produce the effects observed on WASP-12b.
Tidal forces between the Earth and the moon cause local sea levels to rise and fall modestly twice a day. However, because WASP-12b is located so close to its parent planet, its gravitational forces are enormous. It orbits WASP-12 so quickly, it is literally being pulled apart. For example, Jupiter takes about 26 years to orbit our Sun, but WASP-12b orbits WASP-12 in 26 hours! These tidal forces, created by rapid orbital path, cause it to change its shape into a shape of an American football. Moreover, the forces create friction in its interior. This friction produces heat and cause the planet to compress and keep on expanding, transferring most of its gas to WASP-12. WASP-12 in this case acts as a "cannibal" star, sucking away life out of WASP-12b.
"This is the first time that there is direct evidence that internal heating (or 'tidal heating') is responsible for puffing up the planet to its current size," says Lin.
Due to its mass and size, WASP-12b faces an early demise. It has increased in size so much that it cannot retain its mass against the pull of its host star’s gravity.
"WASP-12b is losing its mass to the host star at a tremendous rate of six billion metric tons each second. At this rate, the planet will be completely destroyed by its host star in about ten million years. This may sound like a long time, but for astronomers it's nothing. This planet will live less than 500 times less than the current age of the Earth," explained Li.
The material that is being stripped off of WASP-12b does not directly fall onto its parent star. Instead, it forms a disk around it, which slowly spirals inwards. An analysis of its orbital motion suggests that a smaller, lower mass planet is located within this disk – a massive version of the Earth.
The results of this study have been published in the February 25 issue of Nature.