Beyond Earth

Astronomers spy two growing exoplanets in photograph

CNN  — 

Astronomers have photographed two juvenile exoplanets that are still growing as they orbit a young star 370 light-years from Earth. This is only the second system with more than one planet to be captured in an image.

The star is known as PDS 70 and it’s 6 million years old. PDS 70 is smaller and less massive than our sun, and it’s still gathering material. Around the star, there’s a large disk made of gas and dust. And carving out a wide gap within that disk are the two planets, PDS 70 b and PDS 70 c. The gap is between 1.9 and 3.8 billion miles.

“This is the first unambiguous detection of a two-planet system carving a disk gap,” said Julien Girard of the Space Telescope Science Institute in Baltimore, Maryland.

Although this was detected in the image, the artist’s illustration makes what’s happening in this system more clear.

Two planets, represented by white balls of light, orbit the star at the center of the image.

PDS 70 b is the closest to the star, sitting about 2 billion miles out. This is comparable to Uranus in our solar system. First detected in 2018, it could weigh between 4 to 17 times as much as Jupiter.

PDS 70 c has just been discovered and it sits on the outer edge of the disk at 3.3 billion miles from the star. That’s about the distance from Neptune to our sun. It would only weigh in around 1 to 10 times as much as Jupiter. The astronomers were surprised to find the second planet.

The two planets have an orbital resonance, so the the closest planet to the star can orbit it twice in the time it takes the other planet for to orbit once.

The image is direct evidence of planets gathering so much material out of the disk around the star that they actually create an obvious gap.

The second exoplanet in the system was found using the ground-based European Southern Observatory’s Very Large Telescope MUSE spectrograph. The results were published Monday in the journal Nature.

“With facilities like ALMA, Hubble, or large ground-based optical telescopes with adaptive optics we see disks with rings and gaps all over. The open question has been, are there planets there? In this case, the answer is yes,” Girard said.