Magnesium Critical for the Formation of Low-Mass Planets

An international collaboration of
astronomers established in a new study that several metals play a key
role in the formation and development of low-mass extrasolar planets.
The team was led by EXOEarths experts at the Centro de Astrofísica da
Universidade do Porto's (CAUP).

In order to arrive at this conclusion, investigators analyzed spectral
readings provided by the European Southern Observatory's (ESO) High
Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph
instrument, which is installed on a 3.6-meter telescope, at the La Silla
Observatory in Chile.

The dataset covered 1,111 stars similar to our Sun, of which 109 are
known to harbor varied numbers of Jupiter-class exoplanets in their
orbits. An addition 26 host exoplanets about the size of Neptune.




After analyzing high-resolution spectra covering all these stellar
objects, the team lead by CAUP research scientist Vardan Zh. Adibekyan
found that a chemical ratio could be derived from the results, which
indicated the stars most likely to host exoplanets.

The research was focused on studying so-called alpha elements, a class
of chemicals that includes magnesium (Mg), silicon (Si) and titanium
(Ti), among others. Scientists also quantified how much iron was
available in each of the 1,111 stars.

The ratio of alpha elements to iron was found to be consistently higher
in the case of Sun-like stars that hosted exoplanets. The highest
discrepancy was observed for magnesium, the research group indicates.

“These findings indicate that some metals other than iron are involved
in the process of planet formation, especially when the amount of iron
is lower than solar,” Adibekyan comments.

“These results may provide strong constraints for the models of planet
formation, especially for planets with low mass,” adds the astronomer,
who was also the lead author of a new paper detailing the results.

The main implication of the new research is that low-mass planets need a
minimum amount of metals so that they can continue forming. According
to existing models, protoplanets appear from the constant clumping of
larger and larger particles, inside a new star's protoplanetary disk.

Therefore, the dust and metal content of the disk is absolutely
essential to the emergence of new worlds, the team concludes, quoted by Astrobiology Magazine.