Images of Neptune taken during twilight observing revealed an extremely large bright storm system near Neptune's equator (labeled 'cloud complex' in the upper figure), a region where astronomers have never seen a bright cloud. The center of the storm complex is about 9,000 km across, about 3/4 the size of Earth, or 1/3 of Neptune’s radius. The storm brightened considerably between June 26 and July 2, as noted in the logarithmic scale of the images taken on July 2. (N. MOLTER/I. DE PATER, UC BERKELEY/C. ALVAREZ, W. M. KECK OBSERVATORY)
SAN FRANCISCO - Ned Molter, an astronomy graduate student at University of California, Berkeley, has discovered a storm system nearly the size of Earth on Neptune.
The storm system, which was found near Neptune's equator where no bright cloud has ever been seen before, is about 9,000 kilometers in length, or one-third the size of Neptune's radius, spanning at least 30 degrees in both latitude and longitude.
"Seeing a storm this bright at such a low latitude is extremely surprising," said Molter.
"Normally, this area is really quiet and we only see bright clouds in the mid-latitude bands, so to have such an enormous cloud sitting right at the equator is spectacular."
Historically, very bright clouds have occasionally been seen on Neptune, but usually at latitudes closer to the poles, said Molter's advisor, Imke de Pater of UC Berkeley's Astronomy Department.
"Never before has a cloud been seen at, or so close to the equator, nor has one ever been this bright."
At first, de Pater thought it was the same Northern cloud complex seen by the Hubble Space Telescope in 1994, after the iconic Great Dark Spot, imaged by Voyager 2 in 1989, had disappeared. But measurements of its locale do not match, signaling that this cloud complex is different from the one Hubble first saw more than two decades ago.
Detailed images taken by NASA's Voyager 2 spacecraft in 1989 revealed bright, white clouds and two colossal storms whipping around the planet's atmosphere. (GODDARD SPACE FLIGHT CENTER / NASA / JPL)
Molter spotted the storm complex near Neptune's equator during a test run of twilight observing at W. M. Keck Observatory on Maunakea, Hawaii, and observed it getting much brighter between June 26 and July 2.
To astronomers, according to a UC Berkeley release announcing the finding, dusk and dawn are a waste of good observing time, as they want a truly dark sky.
Neptune is the windiest planet in our solar system, with the fastest observed wind speeds at the equator reaching up to 1,000 miles per hour. To put this into perspective, a Category 5 hurricane has wind speeds of 156 miles per hour.
De Pater noted that the first-year graduate student had never observed before.
Molter is one of eight scholars accepted into the new Keck Visiting Scholars Program, launched this summer, which gives graduate students and post-doctoral researchers experience working at the telescope.
His assignment during his six-week stay was to develop a more efficient method for twilight observing, making use of time that otherwise might not be used. Most observers there peer deep into the night sky and cannot observe their targets during twilight.