The disconcerting discovery of a young star orbited by four planets the size of Jupiter and Saturn has challenged current theories about planetary formation and the cosmos.
In addition, astronomers say that the newly-found star system has also set a new record for the most extreme range of orbits observed so far: the outermost planet is more than a thousand times farther from the star than the innermost one, which also raises interesting questions about how such a planet could have formed in this type of solar system.
A Young Star
Astronomers explain that the star is only two million years old, which means it is a ‘baby’ in astronomical terms.
The star is surrounded by a huge disk of dust and ice.
This disk, known as a protoplanetary disk, is where planets, moons, asteroids and other astronomical objects are formed in solar systems.
It was already known that the star was remarkable because it is home to the first planet referred to by astronomers as a hot Jupiter, a massive planet orbiting very close to its ‘extremely young’ parent star
Although hot Jupiter’s were the first type of exoplanet to be discovered, their existence has intrigued astronomers because they are often thought to be too close to their progenitor stars to have formed in situ.
ALMA searching the Cosmos
To understand more about the anomalous star system as well as its hot Jupiter, a team of researchers led by the University of Cambridge has used the ALMA telescope in Chile to search for planetary “brothers” in the vicinity of this hot Jupiter.
The cosmic images obtained by ALMA revealed three distinct spaces on the disk, which, according to the theoretical model, were probably caused by three additional giant gas planets that also orbited the young star.
The host star in question, CI Tau, is about 500 light-years away, in a highly productive stellar “nursery” region of the galaxy.
Its four planets differ greatly in their orbits: the closest one (hot Jupiter) is within the equivalent of Mercury’s orbit, while the farthest orbits the star more than three times the distance between our sun and Neptune.
The two outer planets are roughly the mass of Saturn, while the two inner planets are, respectively, about one and ten times the mass of Jupiter.
The discovery raises numerous questions for astronomers.
It is believed that around 1% of the stars harbor hot Jupiter’s, but most of the known hot Jupiter’s are hundreds of times older than CI Tau.
“It is currently impossible to say whether the extreme planetary architecture seen in CI Tau is common in hot Jupiter systems because the way that these sibling planets were detected – through their effect on the protoplanetary disc – would not work in older systems which no longer have a protoplanetary disc,” said Professor Cathie Clarke from Cambridge’s Institute of Astronomy, the study’s first author.
The research has been supported by the European Research Council.