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Debris Belts Around Vega
Infrared observations, debris
disks, exoplanet detection,
planetary systems
Spitzer, Herschel
Coordinated by
the NASA Astrophysics Forum
An Instructor’s Guide for using
the slide sets is available at the
ASP website
Vega is wearing 2 belts!
Infrared observations reveal the star
Vega has a “warm” inner dust belt in
addition to the previously-observed
outer “cold” dust belt.
The discovery can be explained by
two belts of leftover planetesimals
whose ongoing collisions produce
the detected dust--analogous to the
Sun’s asteroid and Kuiper Belts.
Could this also suggest a similar
planetary system for Vega?
Above: Image of the debris disk around the star Vega
taken in infrared light with the Herschel Space
Observatory. (Credit: Su et al., 2013)
Right: Artist’s illustration of debris belt around Vega.
(Credit: NASA/JPL-Caltech)
How was the Discovery Made?
The Spitzer Space Telescope and the
Herschel Space Observatory
detected infrared light in excess of that
expected from the star alone.
By comparing Vega to similar stars,
scientists subtracted the infrared
emission produced by the star itself,
leaving the emission radiated by
surrounding dust particles warmed by
the star.
The inner region of infrared excess
could not be resolved into a belt like the
outer one but the temperature of the
dust is consistent with an asteroid belt
about the same proportional distance
distance from Vega as ours is from our
smaller Sun.
Herschel Space Observatory infrared image of the
debris disk around the star Vega, after subtracting
the light of the star Vega itself. (Credit: Su et al.,
The Big Picture
Scientists have found other stars with similar inner and outer debris belts, with
the outer belt about ten times farther from the stars than the inner belt.
One such star,
HR8799, has been
found to have four
giant planets
orbiting in the gap
between belts.
Our own solar system
also has four giant
planets orbiting
between the rocky
asteroid belt and the
icy Kuiper belt.
No planets have yet been detected around Vega, but if the star were eventually
found to have several giant planets in orbit, this may suggest a common model
for how stars form planets and how their planetary systems evolve.
How does this discovery change our view?
In this diagram, the Vega system (left) is compared to our
Solar system scaled up by a factor of four (right). The inner
asteroid belt (orange) and Kuiper belt (red) are similar in
relative scale, with the distance from the stars to the outer
debris belts about ten times greater than the inner belts. The
true relative size of our solar system is illustrated by the small
drawing in the middle.
Other stars can host planetary
systems similar to the Sun. The
outer belts of both Vega and Sun are
about ten times more distant from the
star than the inner belts. Our solar
system has planets between debris
belts, and Vega may have planets in
the “gap” also.
Multiple debris belts may be a clue
to the presence of several planets.
o Our solar system may not be
Credit: NASA/JPL-Caltech
Press Release on this result:
Scientific Paper
o Su, et al., 2013, ApJ 763:118
Synopsis article
Additional Resources
o Exoplanet resource guide
o AAS announcement by Kate Su
o Extrasolar Planets Encyclopaedia
Debris Belts Around Vega
Why haven’t we found planets for Vega?
Vega is oriented on the plane of the
sky, so we’re looking at one of its poles,
and its debris disk is seen face-on, not
edge on.
We can’t detect planets by the
“transit” method since they wouldn’t
pass in front of the star from our
We can’t detect planets by the
“Doppler” method because stars like
Vega rotate very fast and have very
few narrow lines in their spectra for
noticing the tiny shifts in line position
caused by the gravitational tugs of
Image credit: NASA/JPL-Caltech
Direct visual searches have turned up empty, suggesting orbiting planets are too
small for us to yet detect by this method.
The more powerful James Webb Space Telescope or more sensitive groundbased searches may eventually find Jupiter-sized or smaller planets orbiting in
Vega’s gap.