A sapphire- or ruby-like planet?

55 Cancri e, HD219134 b, and WASP-47 e are three rocky planets – and they have something else in common: they might belong to a new class of super-Earths, according to arguments laid out by scientists from the University of Zurich and the University of Cambridge in a new paper. The astronomers looked at how planets are formed in protoplanetary disks. If they are formed, like the Earth, at a reasonable distance from their central star, then heavy elements, such as iron, magnesium, and silicon, condense.

If, however, the protoplanet has an orbit that is very close to its host star (HD219134 b, for example, needs only three days to complete one revolution), then the protoplanetary disk is much hotter there. Iron or silicon would remain in a gaseous state, while lighter elements, such as calcium or aluminum, would condense. Therefore, such planets might not have an iron core and thus might also not form a magnetic field.

Because they would have a completely different structure, this might also affect their cooling behavior and their atmosphere. The planets would have a ten to twenty percent lower density than that of the Earth. Seen from afar, they might shimmer like a ruby or sapphire – chemically, these gemstones are aluminum oxide.

Whether this new class of super-Earths actually exists has not yet been proven. 55 Cancri e, HD219134 b, and WASP-47 e, however, are interesting candidates of possible proof for this new class, because these planets have the properties determined by the scientists, among these the lower density that cannot be explained in some other way. Especially with 55 Cancri e (also known as Janssen), it was long assumed that this planet might be composed of carbon, possibly even in the form of diamond. That no longer fits the current results – but a sapphire planet would still be something special.

Artist’s depiction of 55 Cancri e, a planet that might shimmer like a sapphire or ruby (picture: Thibaut Roger)

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  • BrandonQMorris
  • Brandon Q. Morris es físico y especialista en el espacio. Lleva mucho tiempo preocupado por las cuestiones espaciales, tanto a nivel profesional como privado, y aunque quería ser astronauta, tuvo que quedarse en la Tierra por diversas razones. Le fascina especialmente el "qué pasaría si" y a través de sus libros pretende compartir historias convincentes de ciencia ficción dura que podrían suceder realmente, y que algún día podrían suceder. Morris es autor de varias novelas de ciencia ficción de gran éxito de ventas, como la serie Enceladus.

    Brandon es un orgulloso miembro de la Science Fiction and Fantasy Writers of America y de la Mars Society.