Acknowledgment: M.H. Wong and J. Tollefson (UC Berkeley)
New images obtained on May 16, 2016, by NASA's Hubble Space Telescope confirm the presence of a dark vortex in the atmosphere of Neptune. Though similar features were seen during the Voyager 2 flyby of Neptune in 1989 and by the Hubble Space Telescope in 1994, this vortex is the first one observed on Neptune in the 21st century.
The discovery was announced on May 17, 2016, in a Central Bureau for
Astronomical Telegrams (CBAT) electronic telegram by University of
California at Berkeley research astronomer Mike Wong, who led the team
that analyzed the Hubble data.
Neptune's dark vortices are high-pressure systems and are usually
accompanied by bright "companion clouds," which are also now visible
on the distant planet. The bright clouds form when the flow of ambient
air is perturbed and diverted upward over the dark vortex, causing
gases to likely freeze into methane ice crystals. "Dark vortices coast
through the atmosphere like huge, lens-shaped gaseous mountains," Wong
said. "And the companion clouds are similar to so-called orographic
clouds that appear as pancake-shaped features lingering over mountains
on Earth."
Beginning in July 2015, bright clouds were again seen on Neptune by
several observers, from amateurs to astronomers at the W. M. Keck
Observatory in Hawaii. Astronomers suspected that these clouds might be
bright companion clouds following an unseen dark vortex. Neptune's
dark vortices are typically only seen at blue wavelengths, and only
Hubble has the high resolution required for seeing them on distant
Neptune.
In September 2015, the Outer Planet Atmospheres Legacy (OPAL)
program, a long-term Hubble Space Telescope project that annually
captures global maps of the outer planets, revealed a dark spot close
to the location of the bright clouds, which had been tracked from the
ground. By viewing the vortex a second time, the new Hubble images
confirm that OPAL really detected a long-lived feature. The new data
enabled the team to create a higher-quality map of the vortex and its
surroundings.
Neptune's dark vortices have exhibited surprising diversity over the
years, in terms of size, shape, and stability (they meander in
latitude, and sometimes speed up or slow down). They also come and go
on much shorter timescales compared to similar anticyclones seen on
Jupiter; large storms on Jupiter evolve over decades.
Planetary astronomers hope to better understand how dark vortices
originate, what controls their drifts and oscillations, how they
interact with the environment, and how they eventually dissipate,
according to UC Berkeley doctoral student Joshua Tollefson, who was
recently awarded a prestigious NASA Earth and Space Science Fellowship
to study Neptune's atmosphere. Measuring the evolution of the new dark
vortex will extend knowledge of both the dark vortices themselves, as
well as the structure and dynamics of the surrounding atmosphere.
The team, led by Wong, also included the OPAL team (Wong, Amy Simon,
and Glenn Orton), UC Berkeley collaborators (Imke de Pater, Joshua
Tollefson, and Katherine de Kleer), Heidi Hammel (AURA), Statia
Luszcz-Cook (AMNH), Ricardo Hueso and Agustin Sánchez-Lavega
(Universidad del Pais Vasco), Marc Delcroix (Société Astronomique de
France), Larry Sromovsky and Patrick Fry (University of Wisconsin), and
Christoph Baranec (University of Hawaii).
Contacts
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Robert Sanders
University of California, Berkeley, California
510-643-6998
rlsanders@berkeley.edu
Mike Wong
University of California, Berkeley, California
mikewong@astro.berkeley.edu
Source: HubbleSite
