We present an analysis of 4.5 years of high precision ( 0.1 % ) space-based photometric measurements of the Cepheid variable Polaris , obtained by the broad band Solar Mass Ejection Imager ( SMEI ) instrument on board the Coriolis satellite .
The data span from April 2003 to October 2007 , with a cadence of 101 minutes and a fill factor of 70 % .
We have measured the mean peak to peak amplitude across the whole set of observations to be 25 mmag .
There is , however , a clear trend that the size of the oscillations has been increasing during the observations , with peak to peak variations less than 22 mmag in early 2003 , increasing to around 28 mmag by October 2007 , suggesting that the peak to peak amplitude is increasing at a rate of 1.39 \pm 0.12 mmag yr ^ { -1 } .
Additionally , we have combined our new measurements with archival measurements to measure a rate of period change of 4.90 \pm 0.26 s yr ^ { -1 } over the last 50 years .
However , there is some suggestion that the period of Polaris has undergone a recent decline , and combined with the increased amplitude , this could imply evolution away from an overtone pulsation mode into the fundamental or a double pulsation mode depending on the precise mass of Polaris .