Rod says - more testing is needed
Currently we have 4142 confirmed exoplanets according to my canonical reference site,
The Extrasolar Planets Encyclopaedia So far, I do not see any *confirmed exoplanets* that are in the habitable zone of a white dwarf star. WDs also have very high surface temperatures, some 30,000 K or so. The wavelength of light chiefly emitted will be very energetic, like UV or more compared to the Sun. Astronomer Tim, you may enjoy this note. Tonight from 1700-1830 EST, I was out viewing 4 Vesta asteroid in Cetus and the waxing gibbous Moon. I tracked 4 Vesta asteroid since 03-Nov-19 in Taurus, moving retrograde now through Cetus. Much fun. Visible in my 10x50 binoculars and also 90-mm refractor at 31x. I used Stellarium and Starry Night to create sky charts for my observation log showing the views and Telrad circles. While viewing in Cetus, I noticed a polar orbiting satellite near 2nd magnitude moving south, and later a meteor streak in the eyepiece while viewing 4 Vesta in Cetus. This is why I like to see a *confirmed* exoplanet in a WD habitable zone