Giant planets around young star defy model predictions


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The uncertainty of science: The recent discovery of four Saturn/Jupiter-sized planets orbiting a star only about two million years old throws a wrench into all existing solar system formation theories.

The star, CI Tau, is located 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 (the hot Jupiter) is within the equivalent of the orbit of Mercury, while the farthest orbits at a distance more than three times greater than that of Neptune. The two outer planets are about the mass of Saturn, while the two inner planets are respectively around one and 10 times the mass of Jupiter.

The discovery raises many questions for astronomers. Around 1% of stars host hot Jupiters, but most of the known hot Jupiters 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.

According to the researchers, it is also unclear whether the sibling planets played a role in driving the innermost planet into its ultra-close orbit, and whether this is a mechanism that works in making hot Jupiters in general. And a further mystery is how the outer two planets formed at all.

“Planet formation models tend to focus on being able to make the types of planets that have been observed already, so new discoveries don’t necessarily fit the models,” said Clarke. “Saturn mass planets are supposed to form by first accumulating a solid core and then pulling in a layer of gas on top, but these processes are supposed to be very slow at large distances from the star. Most models will struggle to make planets of this mass at this distance.” [emphasis mine]

In other words, the present models are absurdly premature. We simply don’t know enough to formulate any theory that can be taken seriously.

This is not to say that models shouldn’t be formulated, only to emphasize that no one should consider them predictive of any part of reality. They give astronomers some guidance on what to look for, but if they take them too seriously they might not look in the right places.

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3 comments

  • Could some or all of the planets been captured? That region sky seems relatively star dense, albeit with young stars. Planets may orbit several stars before ‘settling down’ due to gravitational interaction between stars.

  • wodun

    They could create models that are predictive of the unknown but that would make smart people look stupid.

  • pzatchok

    How can you have an accurate computer model if you have no idea of the exact data to input?

    So far all I am sure of is that there are infinite possibilities out there in the universe. There are exceptions to EVERY model and rule.

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