Comet-Like Tail in WASP-69B Suggests Gas Leak in the Atmosphere of Hot Jupiter-Sized Planet

A team of astronomers have observed a shrinking exoplanet with a comet-like tail in its wake. The loss of atmosphere in its vast tail puzzled scientists and sparked new questions about the evolution of planets with their parent stars.

Boiling, Shrinking Planet

In 2014, NASA announced the discovery of an exoplanet 160 light years away from Earth. Known as WASP-69b, this gas giant orbits a K-type main-sequence star every 3.9 days at a distance of 0.04525 AU.

The planet was discovered on a tight, circular orbit with an equilibrium temperature of 886 K. Its planetary atmosphere is extremely hazy as it contains a partial cloud deck with cloud top rising to a pressure of 100 Pa. It is made mostly of hydrogen and helium, although sodium was also detected in low concentrations.

WASP-69b orbits to its host star so closely that its atmosphere starts to boil and shed away. The boiling is so intense, that the planet has developed a comet-like tail which stretches up to 350,000 miles behind it.

The intense radiation of its star causes the evaporation of helium gas in the planet's atmosphere. The star's "wind", or the stream of charged particles and magnetic fields that constantly hit the planet, sheds helium gas into a tail. This comet-like tail stretches at least seven times the planet's width.

The exoplanet sheds the equivalent of one Earth every billion years, or about 200,000 tons per second. Scientists believe that this kind of shedding may be common in the universe and could explain a mysterious gap in the sizes of exoplanets.

READ ALSO: Jupiter-Like Exoplanet Defies Doom Even After a Cosmic Cataclysm at the Hands of Its Own Sun

Explaining a Planetary Mystery

During its 30 years of space exploration, NASA has confirmed over 5,000 planets beyond our solar system. Some of these exoplanets are similar to planets in our solar system, while others are vastly different.

These discoveries suggest that two of the most common types of planets in the universe are super-Earths and sub-Neptunes. The former measures up to 1.6 times as wide as Earth, while the latter is about two to four times the Earth's width.

There are hardly any planets in between those sizes, probably because planets in between shrink so quickly that they turn into super-Earths. Scientists conclude that it could be due to the radiation from the planet's cores which pushes their atmospheres away. Another theory is that their host star boils the planet's outer layers away and causes mass evaporation over time.

Although WASP-69b is much bigger than a sub-Neptune, it demonstrates the exact boiling behavior that scientists suspect. Due to its massive size, it takes much longer to lose its atmosphere, and gives scientists plenty of time to study its unusual condition.

Studying this Jupiter-sized exoplanet and its long comet-like tail teaches us more about the physics of our universe. Astronomers consider the WASP-69b system as a gem because it provides a rare opportunity to study atmospheric mass-loss in real time and gives insights into the critical factors that shape thousands of other planets.

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