How are solar systems formed? A gas giant was found orbiting a very young star and this can help scientists answer that question.

Astronomy and cosmology are filled with big questions. How was the origin of the universe? How did life first start in our planet? How was our Solar System formed? Are there many systems such as our Solar System in the Universe or are we unique? Are there planetary systems that are not similar to ours?

These questions are very important for science and scientists but also for all of us. They are related to who we are, to what is our place in the universe. Some of these questions are partly answered and some are a matter of intense debate among scientists. And new things are found everyday.

In our Solar System, small rocky planets (Mercury, Venus, Earth, Mars) have orbits near the Sun, whereas gas giants (Jupiter, Saturn, Neptune, Uranus) are found much further out. However, in other solar systems astronomers have found different and surprising settings. For example, they were astonished to detect exoplanets that were gas giants but that were orbiting close to their host star. Why?

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Figure 1. In our Solar System, rocky planets are near the Sun and gas giants are further out. But that’s not the case for all solar systems.

In the beginning of the formation of a solar system a cloud of gas starts to spin and eventually turns into a disk known as protoplanetary disk. From this disk the central star and all its surrounding planets are born. Theoretical work indicates that gas giants can only form in the icy outer regions of the protoplanetary disk. That’s why scientists were so surprised to find gas giants so near their star. How can this be?

It turns out that some gas giants, called hot Jupiters, can migrate inwards and yet avoid falling into their host star. These giant planets are similar to Jupiter but they orbit their host star 100 times closer than Jupiter does the Sun. This increases their surface temperatures and that’s why they are called hot Jupiters.

But how and when in their history do the hot Jupiters migrate so close to their star? According to theoretical models this migration can occur either very early in the lives of giant planets (while they are still embedded within the protoplanetary disk) or much later (once multiple planets are formed they can interact with the gas giant flinging some of them into the vicinity of their star). Some of the hot Jupiters that were known so far had tilted or even backward orbits what suggests that they approached their star due to interaction with neighbor planets. A hot Jupiter that migrated during the early phases of its life hadn’t yet been found.

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Figure 2. Scientists have found a young hot Jupiter orbiting near a young star.

Now an international group of astronomers have discovered a very young hot Jupiter that is orbiting the vicinities of a very young star. This is the first time ever that scientists have found evidence that migration of hot Jupiters can, indeed, happen at the early stages of their lives.

The hot Jupiter in question was found orbiting a star called V830 Tau, located in the Taurus stellar nursery, about 430 light years away. They studied the star during a month and detected a regular fluctuation in the star’s velocity. The data was consistent with the presence of a planet almost as massive as Jupiter that was orbiting its host star at a distance one twentieth of that between the Earth and the Sun.

This is a major step forward in our understanding of how planetary systems form and evolve. Hopefully by studying distant planets such as this one we can learn more about our own Solar System and about our place in the universe.

By Kellen Manoela Siqueira

The work was led by researchers at the Institut de Recherche en Astrophysique et Planétologie (IRAP, CNRS/Université Toulouse III – Paul Sabatier) with colleagues at the Institut de Planétologie et d’Astrophysique de Grenoble (CNRS/Université Grenoble Alpes). The full paper can be found on the June 2016 edition of the journal Nature.

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