Hubble’s OPAL Program Celebrates Decade of Tracking Solar System’s Giant Planets

The OPAL (Outer Planet Atmospheres Legacy) program obtains long-term baseline observations of Jupiter, Saturn, Uranus, and Neptune in order to understand their atmospheric dynamics and evolution.

Wandering across the heavens, the bright planets Jupiter and Saturn were named by the Romans after their most powerful gods.

Not until the 1700s and 1800s were two more planets uncovered, telescopically, far beyond Saturn.

They were named after the Greek god Uranus and the Roman god Neptune.

Early skywatchers could never have imagined that robotic emissaries would be sent along a perilous route from Earth to travel across millions and billions of miles to actually visit these wonder worlds.

The close-up pictures from NASA’s pair of Voyager spacecraft mesmerized an entire generation in the 1980s.

But these spacecraft visits were mere snapshots collecting precious data spanning just a few months — like a tour bus barreling across the United Sates.

“The Voyagers don’t tell you the full story,” said Dr. Amy Simon, an astronomer at NASA’s Goddard Space Flight Center.

“Hubble’s image sharpness is comparable to the Voyager views as they approached the outer planets, and Hubble spans wavelengths from ultraviolet to near-infrared light.”

“Hubble is the only telescope that can provide high spatial resolution and image stability for global studies of cloud coloration, activity, and atmospheric motion on a consistent time basis to help constrain the underlying mechanics of weather and climate systems.”

Jupiter, Saturn, Uranus, and Neptune have deep atmospheres and no solid surfaces.

Their churning atmospheres have their own unique weather systems, some with colorful bands of multicolored clouds, and with mysterious, large storms that pop up or linger for many years. Each outer planet also has seasons lasting many years.

Following the complex behavior is akin to understanding Earth’s dynamic weather as followed over many years, as well as the Sun’s influence on the Solar System’s weather.

The four distant worlds also serve as proxies for understanding the weather and climate on similar planets orbiting other stars.

Planetary scientists realized that any one year of data from Hubble, while interesting in its own right, doesn’t tell the full story of the outer planets.

Hubble’s OPAL program has routinely observed the planets once a year when they are closest to the Earth.

“Because OPAL now spans 10 years and counting, our database of planetary observations is ever growing,” Dr. Simon said.

“That longevity allows for serendipitous discoveries, but also for tracking long-term atmospheric changes as the planets orbit the Sun.”

“The scientific value of these data is underscored by the more than 60 publications to date that include OPAL data.”

This payoff continues to be a huge archive of data that has led to a string of remarkable discoveries to share with planetary astronomers around the world.

“OPAL also interfaces with other ground- and space-based planetary programs,” Dr. Simon said.

“Many papers from other observatories and space missions pull in Hubble data from OPAL for context.”