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Enlarge / The Keck telescopes, the place a few of the key observations had been accomplished.
The exoplanet 8 Ursae Minoris b mustn’t exist. It orbits its host star at simply half the Earth-Solar distance, and by all indications, the star ought to have gone by a part during which it bloated up sufficient to engulf that whole orbit after which some. But 8 Ursae Minoris b undoubtedly seems to exist.
There’s a handful of potential explanations, none of them particularly possible. The individuals who found the planet are suggesting that it survived as a result of its host star acquired distracted by swallowing a white dwarf as a substitute.
Huge and scorching
8 Ursae Minoris b was found utilizing the radial velocity methodology, which watches for modifications in a star’s mild that happen as planets tug the star forwards and backwards as they orbit. This tugging creates a blue shift within the mild when the planet is pulling the star within the course of Earth and a purple shift when the star is pulled away from Earth.
However the planet is unlikely to be tugging the star straight towards Earth, so we are likely to solely measure the element of the star’s movement that is in our course. We would see the identical obvious movement of the star if a lightweight planet’s orbit was oriented straight towards Earth or a really heavy planet that has a comparatively skewed orbit. At greatest, radial velocity measurements give us an estimate of the minimal mass of the planet; it might doubtlessly be bigger.
Commercial
So we all know that, at minimal, 8 Ursae Minoris b is a giant planet, at over 1.6 occasions the mass of Jupiter. It additionally resides near its host star, finishing a full orbit in simply 93 days. That locations it at half an Astronomical Unit (AU, the everyday distance between Earth and the Solar) from its star.
Observations additionally trace at a second physique orbiting the star at the very least 5 AU. The proof for that’s weak given the present information, however it might have a major function in shaping the system.
By itself, there’s nothing particularly uncommon concerning the 8 Ursae Minoris exosolar system. The place issues get bizarre is when you think about the star on the heart of the system.
This doesn’t add up
Observations recommend that 8 Ursae Minoris, the star, is about 1.5 occasions the mass of the Solar however is now considerably older. It seems to have already gone by the interval the place it began operating low on hydrogen gas and swelled up as a tenuous hydrogen-burning environment surrounded an ever-growing helium-rich core. Ultimately, 8 Ursae Minoris converted to burning helium and now exists as a warmer, extra compact star fueled by helium fusion.
And which means there’s an issue. Based mostly on the mass of the star, it ought to have grown till its outer edges prolonged to 0.7 AU. The planet orbits at 0.5 AU, that means it ought to have ended up contained in the envelope of the star. And so far as we will inform, planets cannot survive that. Calculations present they’re going to rapidly lose orbital velocity to friction and quickly spiral towards the star’s core. Observations have failed to point out any planets orbiting near a star of comparable age and dimension to eight Ursae Minoris, suggesting that these calculations are proper.
So the planet should not be there. Why is it?
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