The pink planet is so strange, astronomers are struggling to define it. They have just discovered that it is covered in salty clouds

There is a pink planet, a stone’s throw from Earth, that astronomers have been trying to decipher for more than a decade.

Known as the Pink Planet or officially GJ504b, this strange world orbits a sun-like star 57 light-years from Earth.

Astronomers aren’t even sure if it’s a planet at all. It has about 25 times the mass of Jupiter, and is so massive that it lies on the border between giant planets and brown dwarfs (a type of failed star).

But observations by the James Webb Space Telescope have revealed direct evidence of something rather strange on the pink planet: salty clouds.

Very cold planet

Because GJ504b is so massive, astronomers refer to it as a “planet-mass companion,” meaning it’s a planet-sized object orbiting a star.

The pink planet is one of the coldest known planetary mass companions ever directly imaged.

It’s too faint for astronomers to properly study it from Earth, but the James Webb Space Telescope has enabled a closer study of its atmosphere, revealing an atmosphere filled with strange chemistry and salty clouds.

“The pink planet is the coldest companion ever discovered using terrestrial instruments,” says Anish Babraj from Northwestern University in Illinois, USA, who led the study.

“Several teams around the world carried out follow-up observations to study its light, but it was too faint for ground-based instruments. This made it an ideal target for JWST.

“When we finally got its spectrum, it looked immediately interesting. But once we started digging deeper into the data, we realized it wasn’t like anything we’d analyzed before.”

These observations are considered some of the first direct evidence for the presence of salty clouds in the atmosphere of a cold body.

Astronomers say that this discovery is an important step towards studying cold cosmic objects that are too dim to be examined in detail using telescopes on Earth.

Big breakthrough

Attempts to study GJ504b with ground-based telescopes have proven fruitless.

GJ504b has a temperature of just 290°C (550°F) which, although it may seem hot, is very cold for a planet. It’s not a stretch to say that the temperature of a distant planet could be easily surpassed by a pizza oven.

Astronomers say its cold temperature is a result of its age. Planets are very hot when they form within dusty disks around newborn stars, but they cool over time.

The study estimates that GJ504b is between 2.5 billion and 4 billion years old. The James Webb Space Telescope was able to capture the faint light of the planet.

The team then used processing techniques to remove light from the bright host star, giving them a better view of the planet itself.

They were then able to analyze the light coming from the planet and thus identify the chemical elements and molecules present.

“In the past, other astronomers have observed the companion for an entire night using some of the largest telescopes in the world to obtain the spectrum,” says Baburaj.

“And they couldn’t see the object. With the James Webb Space Telescope, our entire observation took about two hours, and we were successful.”

The focus is on the pink planet

The data revealed chemicals including water vapor, methane, carbon dioxide and ammonia, among other molecules.

The team entered this information into a computer to produce a simulation of the planet, but they noticed something was missing.

Once the computer program attempted to build the model, the team found that the simulated atmosphere would only match what they actually saw if the planet had unusual and implausible features.

They added clouds to the model and the unusual characteristics disappeared.

The team says the salty clouds are likely suffocating the deeper layers of the atmosphere, which is consistent with what the James Webb Space Telescope has observed.

“We ran cloud simulations, and the results were consistent with what we know about cold planets,” Baburaj says.

“We tried three different types of clouds, and salt clouds were the best. When we took salt clouds into account, they subordinated the signature of molecules hidden deep in the atmosphere to the companion. Then, the results became physically possible.”

Webb notes that GJ504b is unusually rich in heavy elements or minerals.

But astronomers are still not sure how it formed. It may have formed as either a giant planet or a small star.

The team says the techniques used here could help study other cold and dim planets.

“This is the first time we have discovered that salt clouds play a crucial role in interpreting the spectrum of an object,” Baburaj said.

“It’s a good reminder to take drag into account in our models.”

Read the full paper at Astronomical magazine