[…] ESA’s Venus Express spacecraft has discovered that our cloud-covered neighbour spins a little slower than previously measured. […] Over its four-year mission, Magellan was able to watch features rotate under the spacecraft, allowing scientists to determine the length of the day on Venus as being equal to 243.0185 Earth days. . However, surface features seen by Venus Express some 16 years later could only be lined up with those observed by Magellan if the length of the Venus day is on average 6.5 minutes longer than Magellan measured. […]
A quick back-of-the-envelope calculation indicates that 6.5 minutes in 16 years translates in 1.56 watt per hour on each square meter of Venus’ surface, if all the rotational energy is converted into heat (I couldn’t double-check the results though). If this process is cumulative, it will certainly have huge consequences.