Very Short Day

Astronomers have been able to measure the length of day of an exoplanet.  It's a short day.  It's also a huge world.  At ten times the mass of Jupiter, a day on this world is only about eight hours long.  By comparison, a day on Jupiter is a bit more than nine hours long.

That's not all.  The exoplanet seems to be very young-- maybe only 20 million years old-- and astronomers think the day there will get even shorter.