Science News

Curated by RSF Research Staff

Planet types ‘missing link’

Why are some planets rocky and some gaseous? We may just be nearer to finding an answer through a new planet discovered by master’s student Merrin Peterson.

Have you ever wondered why the Earth is rocky and solid and planets like Jupiter and Neptune are gaseous? To add to the intrigue there are brown dwarfs which are neither planet or star, read more on brown dwarfs here.

So, what is it that classifies something as a planet and differentiates between rocky planets and gaseous planets.

Planets and stars are theorized to have formed in the collapsing dust of a nebulae, with the star forming in the centre of rotation and the planets forming in the corresponding disk. Obviously at the centre of rotation the angular momentum will be the greatest and the star will be experiencing significant energy production and emitting vast quantities of visible light. This is not the case for planets which by comparison will only be emitting small amounts of light and at a lower energy range - infrared.

Gaseous planets - such as Jupiter, Saturn, Uranus and Neptune - are believed to have first formed as rocky planets. However, their greater size allowed them to accrete and maintain a gaseous envelope – albeit not big enough to generate and sustain the energy production of a star. The size of the planet therefore seems to be the defining factor.

Last year, while studying the size of planets for his doctoral thesis, Benjamin Fulton noticed that planets of a specific size were less likely to exist - that is the population significantly decreases. This range is now known as the Fulton gap and is approximately 1- 4 times the Earths radius.

Utilizing data from the NASA’s Kepler telescope, Merrin Peterson, a master’s student at the Institute for Research on Exoplanets (iREx), has just discovered an exoplanet in this Fulton gap. The planet known as Wolf 503b has a radius twice that of Earths and is located 145 light-years away in the constellation of Virgo, making it the perfect laboratory for studying this ‘missing link’ between rocky and gaseous planets.

RSF—in perspective

The exact mechanism for star formation and planet formation is yet to be fully understood and is open for discussion. In the same way that supermassive black holes are now known to be at the centre of every galaxy – this could also be true for celestial bodies such as stars and planets. The characteristics of the celestial body defining it as a rocky planet, gaseous planet, star or a failed star could then be described in terms of the black hole dynamics, the size and the respective interactions with other celestial bodies.

Amira Val Baker



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