APPROACHING
GREEN COMET EXPLODES: A comet that could become visible to the naked
eye in August has just exploded in brightness.
Amateur astronomer
Michael Jäger of Austria reports that Comet PANSTARRS (C/2017 S3)
brightened 16-fold during the late hours of July 2nd, abruptly
increasing in magnitude from +12 to +9.
"The
gas cloud around the comet's nucleus is about 4 arc minutes wide," says
Jäger. That means the comet's atmosphere is 260,000 km in diameter,
almost twice as wide as the planet Jupiter.
These dimensions make it a
relatively easy target for backyard telescopes.
Comet
PanSTARRS is falling toward the sun from the Oort cloud, a vast
reservoir of fresh comets in the distant outer solar system.
It has
never visited the inner planets before, and, as a result, no one can
say what will happen when its fragile ices are exposed to solar heat as
it approaches the sun in August.
Previous estimates of the comet's
brightness max out at magnitude +4--that is, barely visible to the
unaided eye from dark-sky sites. Additional outbursts could boost its
visibility even more.
The
comet was discovered on Sept. 23, 2017, by the PanSTARRS telescope on
the summit of the Haleakalā volcano in Maui.
PanSTARRS's primary
mission is to detect near-Earth asteroids that threaten our planet. In
the process,it sweeps up variable stars, supernovas, and comets like
this one.
With almost a year of data in hand, astronomers have been
able to nail down the comet's orbit. Click on the image to launch an
interactive 3D visualization from JPL:
Comet
PanSTARRS is approaching the sun on a hyperbolic orbit--a narrow
open-ended path that will ultimately fling it back to the outer solar
system.
At
perihelion (closest approach to the sun) on August 15-16, the
comet will be inside the orbit of Mercury, blasted by solar
radiation at point-blank range. What will happen then? Stay tuned.