In Brief
  • 51 Eridani b is the smallest gas giant ever to be imaged around another star, and is only 20 million years old (for comparison Jupiter is about 4.5 billion years old).
  • It is only two times more massive than Jupiter, and is unusually cool at just 400° C – in fact it is one of the coldest planets of its type to be discovered.

Meet 51 Eridani b, the smallest gas giant ever imaged around another star. The tiny giant resembles Jupiter in its infancy and could yield clues to the formation of our own solar system’s gas giants, helping to unlock the secrets that are hidden deep beneath the gaseous layers of their atmospheres.

This exoplanet shows the strongest methane signature ever detected on an alien planet, which should provide important information on how 51 Eridani b, and other gas giants, are formed.

Julien Rameau, a postdoctoral researcher at the University of Montreal and a member of the team that discovered the planet, is confident about the importance of the new findings.

“This is the first time we directly see a planet with a lot of methane in its atmosphere and a mass close to Jupiter. The previously imaged planets were more massive and have atmospheres very different from our gas giants, with a lot of thick clouds and not, or a little, methane content,” Rameau told Futurism. “51 Eridani b is, therefore, unique to understand the atmospheres of Jupiter-like planets. We are now able to probe systems which have the same scale that our solar system. It is extremely important to understand their formations, evolution, and the physics of their atmospheres.”

As already mentioned, 51 Eridani b is young by astronomical standards – only 20 million years old (Jupiter is about 4.5 billion years old). It is approximately two times more massive than Jupiter, whereas other directly imaged planets tend to have masses that are at least five times greater than our solar system’s biggest gas giant. At 400° C, it is also one of the coldest planets of its type to be discovered. These factors, along with the previously mentioned atmospheric methane signal, indicate to researchers that 51 Eridani b strongly resembles a young Jupiter.

smallest gas giant
This image is the discovery photo of alien planet 51 Eridani b (labeled as “b”) as seen in near-infrared light. Image Credit: J. Rameau (UdeM) and C. Marois (NRC Herzberg)

“The planet shares properties that resemble those of Jupiter when it was young,” Rameau said. “One way to understand Jupiter formation is too look at young planets which still carry information about their formations.”

It is believed that the gas giants in our solar system formed by building up a large core over a few million years and then pulling in a huge amount of hydrogen and other gasses to form an atmosphere. The core-buildup process can also form rocky planets like Earth, though a fast and hot collapse might only make giant gassy planets. 51 Eridani b is young enough that it could “remember” its formation.

But still, a lot of work needs to be done to fully understand the newly discovered planet’s composition and, therefore, better understand our solar system’s gas giants. Scientists will have to employ more powerful scientific instruments for this ambitious task.

“The modeling of the spectrum gave us its temperature, its pressure, and its rough composition – hydrogen and helium with methane and water. Directly seeing the presence of methane and water in this faint and close-in planet is already a challenge that the Gemini Planet Imager (GPI) [the instrument used to discovered 51 Eridani b] was able to overcome. It is currently not possible to qualitatively measure the actual composition or detect other elements because the resolution and sensitivity of GPI is too low. This requires extremely powerful instruments,” Rameau said.

Rameau believes that this discovery will certainly push the international community to learn more about the planet and the architecture and history of the system. Astronomers will monitor the orbit of the planet with new imagine technology like the European Southern Observatory’s (ESO) Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) and Very Large Telescope (VLT) to improve the quality of the spectrum and observe at different wavelengths to refine the measurements of its mass, temperature, and pressure. They will also search for additional giant planets which might be present in the system.

Rameau concluded, “51 Eridani b will certainly be one of the most studied planets in the coming years.”