Wednesday, May 11, 2016

Magnesium and Calcium from Evaporating Trojans

WASP-12b is a hot-Jupiter with a remarkably high equilibrium temperature of over 2500 K. It orbits its host star only two stellar radii from the star's surface. Observations of the host star of WASP-12b in ultraviolet wavelengths indicate that the host star appears dark at certain wavelengths that correspond to absorption by magnesium and calcium. This points to the presence of a cloud of magnesium ions, calcium ions, and various other ions that is surrounding the star and absorbing stellar radiation.

A study by Kislyakova et al. (2016) suggests that material outgassed from the surface of rocky Trojan satellites on tadpole orbits near the L4 and L5 Lagrange points of WASP-12b can account for such a cloud of magnesium and calcium ions surround the star. At the location of WASP-12b, temperatures are high enough to melt the surface of rocky Trojan satellites to create magma oceans that can thermally released materials such as magnesium, silicon, calcium, iron, etc. These materials are then ionised by stellar radiation and energetic electrons to form a cloud of plasma around the host star.

The result is a cloud of magnesium and calcium ions along the orbit of WASP-12b that is expected to be extended enough to cover the entire stellar disk. The absorption of stellar emission at some ultraviolet wavelengths is also predicted to occur in other exoplanetary systems that have transiting hot-Jupiters with extremely high equilibrium temperatures that exceed 2000 K.

Two configurations were considered in this study. The first configuration consists of two rocky Trojan satellites similar in size to Jupiter's moon Io around the L4 and L5 Lagrange points. The second configuration is comprised of two Trojan swarms consisting of 100 rocky bodies, each measuring 100 km in radius. The configuration with two Io-sized Trojan satellites has greater stability on long time scales, while the configuration with two Trojan swarms can more readily generate an extended cloud of magnesium and calcium ions.

Kislyakova et al. (2016), "On the ultraviolet anomalies of the WASP-12 and HD 189733 systems: Trojan satellites as a plasma source", arXiv:1605.02507 [astro-ph.EP]