No Spring Picnic on Neptune
Neptune's spring: Three
Hubble photos taken over a six-year period
Imagine a spring where flowers don’t
bloom, birds don’t chirp, and children don’t run outside to play.
Welcome to springtime on Neptune.
Take your parka. Neptune’s springtime weather brings
blustery storms, temperatures of minus 400 degrees Fahrenheit at the
cloud tops, and fierce winds that sometimes gust to 900 miles per hour.
What is remarkable is that Neptune — the farthest and coldest of the
major planets — exhibits any evidence of seasonal change. After all,
the Sun is 900 times dimmer than it is on Earth.
Neptune's distance from the Sun
So, how can astronomers tell that springtime has arrived
at all? Researchers at the University of Wisconsin- Madison and NASA's
Jet Propulsion Laboratory in Pasadena, Calif., used NASA’s Hubble Space
Telescope to study the planet over time, making three sets of observations
in six years. The images reveal that the bands of clouds encircling the
planet’s Southern Hemisphere
increase in brightness over time. Astronomers believe the cloud bands
are getting brighter because the Sun is warming the atmosphere
in the south more than in the north. The amount of sunlight each
hemisphere receives at a given time plays a major role in determining
Tilting towards spring
Seasons on Neptune occur for the same reason as on
Earth. The seasonal changes on both planets occur because their axes
tilt slightly. Earth is inclined 23.5 degrees. Neptune is tipped at an
even greater angle: 29 degrees. As both planets circle the Sun, one
hemisphere is always tipped toward the Sun; the other is tilted away
from the Sun. When the Southern Hemisphere tips toward the Sun, it
receives more sunlight than the Northern Hemisphere. That means it’s
summer in the south and winter in the north. The opposite is true when
the Northern Hemisphere is tilted toward the Sun. The north receives
more sunlight, which means it’s summertime.
Unlike Earth, Neptune’s seasons last for years, not
months. A single season on the planet, which takes almost 165 years to
orbit the Sun, can last more than 40 years.