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NASA’s Hubble Space Telescope
has been watching a large, dark

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storm on the planet Neptune
disappear before our very eyes –

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or, telescope mirror. The first
and only spacecraft to visit

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Neptune was NASA’s Voyager 2 in
1989. It discovered two immense,

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dark storms churning through
Neptune’s thick, blue

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atmosphere. Voyager 2 then
headed out of the solar system,

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and since then our primary means
of watching Neptune’s storms has

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been the Hubble Space Telescope.
Our atmosphere on Earth makes it

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hard to look at blue light in
high resolution, so Hubble is

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currently the only telescope
that is able to see these

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storms. The larger of the two
storms Voyager 2 discovered on

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Neptune was called the Great
Dark Spot, because it looked

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very similar to the Great Red
Spot on Jupiter. Jupiter’s Great

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Red Spot has existed for
hundreds of years, but when

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Hubble looked at Neptune in
1994, the Great Dark Spot was

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already gone. Instead there was
a new storm on the northern

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hemisphere, which was named the
Northern Great Dark Spot. Since

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then, that spot has also
disappeared, and now in total

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we’ve observed five different
dark spots on Neptune. We can

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see that large storms on Neptune
form and dissipate much more

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rapidly than storms on Jupiter,
and there’s a lot of diversity

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in what Neptune’s storms look
like and how they move. These

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dark vortices on Neptune present
atmospheric scientists with an

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amazing opportunity to learn
about how storms work on a

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different world. But because
there is so much in the universe

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that Hubble looks at, the
telescope had only been

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observing Neptune once every few
years, which wasn’t frequent

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enough to watch the formation or
demise of any one particular

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storm. Since 2014 however,
Hubble has begun a project

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called the Outer Planet
Atmospheres Legacy program, or

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OPAL, to gather global maps of
our gas giant planets every year

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for the remainder of Hubble’s
operation. Now for the first

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time, using data from OPAL and
additional Hubble observations,

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Hubble has captured time-lapse
images showing the gradual death

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of a storm on Neptune. The
vortex pictured here is dredging

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up material from deep inside
Neptune’s atmosphere, possibly

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such as hydrogen sulfide, which
would make for a pretty smelly

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storm. In the first image from
2015, the storm is over 3000

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miles across – big enough to
stretch across the entire

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Atlantic Ocean from Boston to
Portugal. The storm is dark in

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blue wavelengths, but
overshadowed at green and red

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wavelengths by nearby companion
clouds. The contrast of the dark

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vortex faded quite a bit by late
2017, though the feature was

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still over 2000 miles wide.
Seeing this storm unfold gives

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scientists a chance to test
their models of how they

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predicted an anticyclone may
interact with the wind jets on

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Neptune. This particular vortex
is not behaving how some

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dynamical simulations predicted,
which is great because that

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means there’s a lot left to
learn on Neptune. The Hubble

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Space Telescope is up to that
task of advancing scientists’

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understanding of planetary
atmospheres.

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www. nasa. gov/hubble
@NASAHubble