Waves of magnetic energy may link far stars and extrasolar giant planets
Out on the toe of the Herdsman’s left boot, almost 50
light years from Earth and about 45 degrees across the sky from the Little
Dipper[*], a giant planet with more than five times the mass of Jupiter is
racing round and round its star, tau Bootes.
This boiling gas giant is so close to its star (about one-eighth as far as
from the sun to Mercury) that it completes an orbit in just over three days;
so close that it and similar extrasolar planets may actually “interact”
with both their stars and the layers of superheated plasma that surround
them, says a UAH astrophysicist.
Dr. Manfred Cuntz, an adjunct associate professor in UAH’s Center for Space
Plasma and Aeronomic Research (CSPAR), is part of a team that will search
for ultraviolet “signatures” to prove its theories correct.
“According to our theoretical calculations, there should be two types of
interactions: tidal interactions, which are gravitational, and magnetic,”
said Cuntz. “Of these, the more powerful will be the magnetic.”
Cuntz and his collaborators, Dr. Steven Saar from the Harvard-Smithsonian
Center for Astrophysics and Dr. Zdzislaw Musielak, a former UAH scientist
now in the physics department at the University of Texas at Arlington,
theorize that the magnetic fields of the giant extrasolar planets and
their stars “connect” as the planet circles in its orbit.
That surge of magnetic energy would sweep through the star’s lower outer
atmosphere, or chromosphere, adding energy to the superheated ions existing
there. With that extra energy, those ions would increase the rate at which
they emit ultraviolet radiation.
“We propose to measure it by looking at the extra ultraviolet light
produced in the chromosphere, which depends on the magnetic field strength
of the star and the planet,” Cuntz explained.”You would look for increased
UV radiation which would be cyclical in accordance with the planetary orbit.”
UV radiation is efficiently emitted by magnesium, carbon, iron and other
ions found in the chromospheres of stars. Because the power of the UV
radiation emitted by those ions depends on the strength of the magnetic
fields of both the star and the planet, the team hopes to use the UV data
to derive some information about the nature of the giant planets.
While the magnetic interaction is believed to be more powerful, the team
has also studied the gravitational effects of these huge planets orbiting
so close to their host stars. Just as the moon causes tides synchronized
to Earth’s spin and the lunar orbit, these massive planets might cause
gigantic tidal bulges that would sweep across the surface of the star.
These bulges might set up turbulence and shock waves that would race
through the star’s atmosphere, increasing heating and stellar activity,
strengthening magnetic fields and raising the level of UV emissions.
“At present this type of research is the only way to find out about the
magnetic field strengths of planets in far away systems,” Cuntz said. “It
may also help us to more thoroughly understand the magnetic structures of
Jupiter and Saturn, the gas planets in our own back yard.”
[*] To find Bootes, the Herdsman, and tau Bootes, follow a line from
the North Star through the cup of the Little Dipper. The Herdsman is
approximately 45 degrees across the sky, to the left of Ursa Major (the
Bear). Tau Boötes is by the toe of Boötes’ left foot.
