Exoplanet with SO2 throws new light on planet formation

Newswand: An exoplanet with sulfur dioxide in its atmosphere is helping the astronauts to understand the process of formation of a planet.

Photo creidit: Department of Astronomy, UW–Madison

It is located about 96 light years away from our own solar system and became a prime target for scientists trying to understand how worlds are formed.

Astronomers discovered the planet, GJ 3470 b, in 2012 when the planet’s shadow crossed the star it orbits. GJ 3470 b is located in the constellation Cancer and is about half the size of Neptune, with a mass 10 times that of Earth. In the intervening years, researchers have compiled data on the planet using the Hubble and Spitzer space telescopes, culminating in a pair of recent observations with the James Webb Space Telescope.

They saw evidence of water, carbon dioxide, methane and sulfur dioxide. GJ 3470 b is the lightest and coldest (averaging a mere 325 degrees Celsius, or more than 600 Fahrenheit) exoplanet to harbor sulfur dioxide. The compound is likely a sign of the churn of active chemical reactions in the planet’s atmosphere, created when radiation from its nearby star blasts apart the components of hydrogen sulfide, which then go looking for new molecular partners.

Discovering sulfur dioxide in a planet as small as GJ 3470 b gives one more important item on the planet formation ingredient list, the astronauts opine.

In the case of GJ 3470 b, there are also other interesting features that might help fill out that recipe. The planet’s orbit around its star takes it nearly over the star’s poles, which is to say that it’s circling at a 90-degree angle to the expected path of planets in the system. It’s also surprisingly close to the star, close enough that the light from its star is blowing copious amounts of GJ 3470 b’s atmosphere away into space. The planet has probably lost about 40 percent of its mass since it was formed.

The close-in, off-kilter orbit is a sign that GJ 3470 b used to be somewhere else in its system, and at some point, the planet became entangled with the gravity of another and was pulled into a new path that eventually settled it in a different neighborhood.

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