novel! This giant exoplanet has been photographed by scientists, and its orbit is quite strange

Through the Young Exoplanet Survey (YSES) project, astronomers have directly photographed a gas giant in an orbit that is unusually large. It is as far from its star as Jupiter is 20 times from the Sun.

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Direct imaging of the exogiant planet YSES 2b (labeled "b" in the figure). The star is centered at the cluster of bright spots in the image, and its light is blocked.

Astronomers have previously discovered many giant planets similar to Jupiter and Saturn and orbiting their stars. Some of them -- known as "hot Jupiters" -- are not like any of the planets in our solar system, orbiting closer to their host stars than any planet in our solar system orbits.

This spring (April 2021), astronomers at Leiden University announced the discovery of an exoplanet of the opposite type, a massive exoplanet dubbed YSES 2b that orbits its star more than previously discovered A typical exoplanet orbits much farther. The researchers took a great effort to take a direct imaging picture of the planet. The planet orbits its star a full 20 times further than Jupiter orbits the sun. This distance is equivalent to 110 times the distance between the earth and the sun.

Details of the study were published in the peer-reviewed journal Astronomy & Astrophysics on April 19, 2021

YSES 2b is 360 light-years away, in the direction of the constellation Musca in the southern hemisphere. This is a young gas giant planet six times the mass of Jupiter. Many other similar extraterrestrial gas giants have been discovered before, but this one is very different.

Researchers have yet to figure out why the planet is so far away from its star. Scientists typically use two models—core accretion and disk instability—to explain the formation of such giant planets, but neither model seems to work well for the giant planet.

The first theory, the core accretion theory, explains that the planets formed in their place, as asteroid bodies gathered together to form a rocky core that, when massive enough to accrete large amounts of gas around it. But if this is the case, the mass of the YSES 2b is simply too great. Because usually at such a distance from the star, there is not enough material to form such a huge planet.

Another theory, the disk instability theory, says that the primordial accretion disk surrounding a young star (only 14 million years old, or a baby star, if you will) is gravitationally unstable Produces fragmentation, the process by which fragments form planets. However, the planet we see is not large enough for the above process to take place and produce itself.

Are there other possibilities? Scientists estimate that it is possible that the planet first formed its body through core accretion closer to the star, and then migrated outward to its current farther orbit. To justify it, the gravitational pull of a second planet is needed to influence it, yet this additional planet has yet to be discovered.

The exploration team was led by Alexander Bohn of Leiden University.

The discovery of YSES 2b is part of the Young Exoplanet Survey (YSES) project. Researchers will continue to study this unique world as they study more planets orbiting sun-like stars. According to first author Alexander Bohn at Leiden University:

By studying more Jupiter-like exoplanets in the near future, we will learn more about the formation process of gas giant planets around Sun-like stars.

At present, only giant planets like YSES 2b can be directly photographed, although it seems only a bright spot. The distant Earth-sized world is simply too small to observe with telescopes, but as technology advances, this will change in a few years.

In 2020, the Very Large Telescope (VLT) in Chile, used by the YSES project, also imaged the multi-planet system of the sun-like star TYC 8998-760-1, 300 light-years away. The star system was first detected between 2018 and 2020, the first-ever direct imaging of a multi-planet system. To obtain this image, a special planet-hunting instrument on the telescope called "Ball" was used. The instrument can capture the light emitted by exoplanets, either directly or indirectly. Bohn said at the time:

The discovery is a snapshot of a star system very similar to our solar system, but in the early stages of its evolution.

Two scenarios for planet formation, the core accretion model and the disk imbalance model. Currently, both models have difficulty explaining the formation of YSES 2b.

Co-author Matthew Kenworthy added:

Although astronomers have detected thousands of exoplanets indirectly in our galaxy, only a handful of them have been photographed directly. Direct observation is critical for studying the environments that support life.