'Should Not Exist:' Giant Planet Orbiting Tiny Star Changes Everything We Know About How Planets Form

Friday, 27 September 2019 - 11:49AM
Friday, 27 September 2019 - 11:49AM
'Should Not Exist:' Giant Planet Orbiting Tiny Star Changes Everything We Know About How Planets Form
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Guillem Anglada-Escude IEEC/Science Wave SpaceEngine.org. (CC BY 4.0)

An international team of scientists has just discovered a disproportionately massive gas giant orbiting a tiny host star located thirty short light-years away from Earth according to the BBC. The team published their findings yesterday in the journal Science.


"Our most up-to-date models could never allow the formation of even one massive planet, let alone two,'' admits Alexander Mustill, a research team member from Lund Observatory.


The star, GJ 3512, is an M-type red dwarf. These are the most common stars in our galaxy. They are also the smallest, dimmest, and coolest stars – which also makes them the longest-lasting, because they burn through their hydrogen at a slower rate and can linger for trillions of years (stars like our Sun only last approximately ten billion years.) Proxima Centauri, our closest star after the Sun, is a red dwarf.


"Around such stars there should only be planets the size of the Earth or somewhat more massive Super-Earths," says Christoph Mordasini, a coauthor of the study from the University of Bern in Switzerland.


This planet, on the other hand, is much – much – larger than Earth or Super-Earths. We still know relatively little about it, but GJ 3512b is about half the size of Jupiter and has a long 204-day elliptical orbit. This ellipsis is an extreme oval, which indicates that there could be other even more massive undiscovered planets that we can't see exerting their gravitational pull.


Credit: Guillem Anglada-Escude - IEEC/Science Wave, using SpaceEngine.org. (CC BY 4.0)


The question is, how did it get there? This particular red dwarf star is only one-tenth the size of our Sun, but this gas giant is half the size of Jupiter. Planets form from the debris within a protoplanetary disc – a rotating cloud of dust and gas surrounding newborn stars. First, a rocky core is formed as debris snowballs onto itself, held together by sheer gravity. Once enough solid mass has accumulated, the planet may then take on large amounts of gas. "GJ 3512b, however, is...at least one order of magnitude more massive than the planets predicted by theoretical models for such small star," added Mordasini.


But this star isn't dense enough to have held enough material in its protoplanetary disc for such a large planet to form, and the implications are astounding. "I find it fascinating how a single anomalous observation has the potential to produce a paradigm shift in our thinking," said Juan Carlos Morales, the lead author of the study, "in something as essential as the formation of planets and, therefore, in the big picture of how our own Solar System came into existence."

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