NASA’s Hubble Space Telescope has been watching a large, dark
storm on the planet Neptune disappear before our very eyes –
or, telescope mirror. The first and only spacecraft to visit
Neptune was NASA’s Voyager 2 in 1989. It discovered two immense,
dark storms churning through Neptune’s thick, blue
atmosphere. Voyager 2 then headed out of the solar system,
and since then our primary means of watching Neptune’s storms has
been the Hubble Space Telescope. Our atmosphere on Earth makes it
hard to look at blue light in high resolution, so Hubble is
currently the only telescope that is able to see these
storms. The larger of the two storms Voyager 2 discovered on
Neptune was called the Great Dark Spot, because it looked
very similar to the Great Red Spot on Jupiter. Jupiter’s Great
Red Spot has existed for hundreds of years, but when
Hubble looked at Neptune in 1994, the Great Dark Spot was
already gone. Instead there was a new storm on the northern
hemisphere, which was named the Northern Great Dark Spot. Since
then, that spot has also disappeared, and now in total
we’ve observed five different dark spots on Neptune. We can
see that large storms on Neptune form and dissipate much more
rapidly than storms on Jupiter, and there’s a lot of diversity
in what Neptune’s storms look like and how they move. These
dark vortices on Neptune present atmospheric scientists with an
amazing opportunity to learn about how storms work on a
different world. But because there is so much in the universe
that Hubble looks at, the telescope had only been
observing Neptune once every few years, which wasn’t frequent
enough to watch the formation or demise of any one particular
storm. Since 2014 however, Hubble has begun a project
called the Outer Planet Atmospheres Legacy program, or
OPAL, to gather global maps of our gas giant planets every year
for the remainder of Hubble’s operation. Now for the first
time, using data from OPAL and additional Hubble observations,
Hubble has captured time-lapse images showing the gradual death
of a storm on Neptune. The vortex pictured here is dredging
up material from deep inside Neptune’s atmosphere, possibly
such as hydrogen sulfide, which would make for a pretty smelly
storm. In the first image from 2015, the storm is over 3000
miles across – big enough to stretch across the entire
Atlantic Ocean from Boston to Portugal. The storm is dark in
blue wavelengths, but overshadowed at green and red
wavelengths by nearby companion clouds. The contrast of the dark
vortex faded quite a bit by late 2017, though the feature was
still over 2000 miles wide. Seeing this storm unfold gives
scientists a chance to test their models of how they
predicted an anticyclone may interact with the wind jets on
Neptune. This particular vortex is not behaving how some
dynamical simulations predicted, which is great because that
means there’s a lot left to learn on Neptune. The Hubble
Space Telescope is up to that task of advancing scientists’
understanding of planetary atmospheres.
www. nasa. gov/hubble @NASAHubble