Planet That Shouldn't Exist Found
The exoplanet 8 Ursae Minoris b should not exist. It orbits its host star at just half the Earth-Sun distance, and by all indications, the star should have gone through a phase in which it bloated up enough to engulf that entire orbit and then some. Yet 8 Ursae Minoris b definitely appears to exist. From a report: There is a handful of potential explanations, none of them especially likely. The people who discovered the planet are suggesting that it survived because its host star got distracted by swallowing a white dwarf instead. 8 Ursae Minoris b was discovered using the radial velocity method, which watches for changes in a star's light that occur as planets tug the star back and forth as they orbit. This tugging creates a blue shift in the light when the planet is pulling the star in the direction of Earth and a red shift when the star is pulled away from Earth. But the planet is unlikely to be tugging the star directly toward Earth, so we tend to only measure the component of the star's motion that's in our direction. We'd see the same apparent motion of the star if a light planet's orbit was oriented directly toward Earth or a very heavy planet that has a relatively skewed orbit. At best, radial velocity measurements give us an estimate of the minimum mass of the planet; it could potentially be larger. So we know that, at minimum, 8 Ursae Minoris b is a big planet, at over 1.6 times the mass of Jupiter. It also resides close to its host star, completing a full orbit in just 93 days. That places it at half an Astronomical Unit (AU, the typical distance between Earth and the Sun) from its star. Observations also hint at a second body orbiting the star at least five AU. The evidence for that is weak given the current data, but it may have a significant role in shaping the system. On its own, there's nothing especially unusual about the 8 Ursae Minoris exosolar system. Where things get weird is when you consider the star at the center of the system.
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