  We suggest an additional possible plasma source to explain part of the
phenomena observed for the transiting hot Jupiters WASP-12b and HD 189733b in
their ultraviolet (UV) light curves. In the proposed scenario, material
outgasses from the molten surface of Trojan satellites on tadpole orbits near
the Lagrange points L$_4$ and L$_5$. We show that the temperature at the
orbital location of WASP-12b is high enough to melt the surface of rocky bodies
and to form shallow lava oceans on them. In case of WASP-12b, this leads to the
release of elements such as Mg and Ca, which are expected to surround the
system. The predicted Mg and Ca outgassing rates from two Io-sized WASP-12b
Trojans are $\approx 2.2 \times 10^{27}$ s$^{-1}$ and $\approx 2.2 \times
10^{26}$ s$^{-1}$, respectively. Trojan outgassing can lead to the apparent
lack of emission in Mg{\sc ii}\,h\&k and Ca{\sc ii}\,H\&K line cores of
WASP-12. For HD 189733b, the mechanism is only marginally possible due to the
lower temperature. This may be one of the reasons that couldn't explain the
early ingress of HD 189733b observed in the far-UV (FUV) C{\sc ii} doublet due
to absence of carbon within elements outgassed by molten lava. We investigate
the long-term stability region of WASP-12b and HD 189733b in case of planar and
inclined motion of these satellites and show that unlike the classical exomoons
orbiting the planet, Io-sized Trojans can be stable for the whole systems life
time.
