Artist rendering of a red dwarf , with three exoplanets orbiting. About 75% of all stars in the sky are the cooler, smaller red dwarfs. (NASA)

Two giant planets have been found orbiting a tiny star, defying our theories for how planets are formed.

To be entirely truthful, there is nothing new in an exoplanet discovery shredding our current ideas about how planets are built. The first extrasolar planets ever discovered orbit a dead star known as a pulsar. Pulsars end their regular starry life in a colossal supernova explosion that should incinerate or eject any orbiting worlds. This discovery was followed a few years later by the first detection of a hot Jupiter; a gas giant planet orbiting its star in just a few days, defying theories that said such planets should form on long orbits where there is more building material to make massive worlds. Exoplanet hunting is a field full of surprises and now, it has one more.

GJ 3512 is a red dwarf star with a luminosity only around a thousandth (0.0016L☉) of our sun. The small size of these stars makes it easier to detect the presence of a planet, and many of our most famous exoplanet discoveries have been found orbiting red dwarf stars, including Proxima Centauri b and the seven worlds in the TRAPPIST-1 system. But a notable attribute of these systems is that the planets are small. Unlike our own sun which boasts four gas giant worlds, planets around red dwarfs are typically smaller than Neptune.

Artist impression of the seven planets of Trappist-1 that also orbit a red dwarf star. These are small worlds. Jupiter-sized gas giants were not previously thought to form around the small red dwarf stars (NASA/JPL-Caltech).

This preference for downsized worlds is assumed to be due to the protoplanetary disk; the disk of dust and gas that swirls around young stars out of which planets are born. Protoplanetary disks around small stars tend to be low mass and puffy. This limits and spreads out the solid material, making it difficult for a young planet to grow.

Yet the two planets discovered around GJ 3512 are not small.
Led by Juan Carlos Morales at the IEEC Institute of Space Studies of Catalonia, the announcement of the discovery was published in the journal Science today.

The team detected these two new worlds using the radial velocity technique which measures the wobble in the position of the star due to the gravitational tug of the orbiting planet.… Read more