The life and death of a planet

Scientists have discovered a new planet, and it is spiraling to its doom, or so the predictions go. WASP-18b, so named because it was discovered by the United Kingdom’s ‘Wide Angle Search for Planets’ program, is destined to crash into its parent star, aptly named WASP-18. Fortunately for us, this planet is not in our solar system and its parent star is not our sun. But still…wow.

WASP-18b, described in the August 27 issue of the international journal Nature, is not an insignificant planet. It is ten times the mass of our Jupiter.

The trouble for poor WASP-18b is that it orbits way too close to WASP-18, a mere 1.4 million miles away. Ok, 1.4 million miles seems pretty far. But, WASP-18b is so close to WASP-18 that it can complete its orbit in just over 22 hours. It takes the Earth 8760 hours, or 365 of our so-called days (a.k.a. 1 year), to orbit our sun. The concept of a ‘day’ depends on how fast we are spinning on our Earth axis; our day is 24 hours. It takes 24 hours for us to see the sun, spin all the way around, and see the sun in the same position again. A day on WASP-18b is going to be remarkably different, because it spins on its axis slower than it traverses its orbit. So, a ‘day’ lasts longer than a ‘year’. Too bad, since ‘daytime’ temperatures on WASP-18b reach a broiling 3,800°F.

WASP-18b will be pulled to its doom, and relatively soon by planetary terms, by the gravitational forces that exist between the two bodies. These are the same sorts of gravitational forces that exist between the Earth and our Moon, and subsequently cause the tides. However, our moon orbits the Earth much more slowly than the Earth itself is rotating, thusly our moon is actually moving ever so slowly away from us. At the blinding speed of 0.2 seconds a century (so don’t lose sleep over this).

However, WASP-18b is spiraling inward, and its spin is speeding up. Because of the distance between WASP-18b and WASP-18, WASP-18b experiences gravitational forces so strong that there is huge a bulge at its equator literally dragging behind the planet. Thus, the real mystery is why it has not been sucked into the center of WASP-18 already.

Scientists admit that there is another alternative for the outcome of WASP-18b – it could be shredded to bits by gravitational pull, creating rings of gas and debris not unlike the rings of Saturn.

The really cool thing about the discovery of WASP-18b is that scientists will know if their predictions will be borne out in the next 5 to 10 years. No, the crash is not that eminent. But, the change in trajectory of WASP-18b will be.

So, how often are new planets discovered? Well, 30 more were discovered just in 2009. WASP-18b is number 374 on the list maintained by the Paris Observatory. WASP-17b was discovered on August 11 of this year. It is twice the size of Jupiter, but has only half the mass, earning it the truly adorable designation of ‘puffy planet’.