Hello Fred, after giving this much thought, we think we know what the issue is. Please correct me if we have this wrong.
The Exoplanet theme displays the footer immediately after the end of the page content, but you are looking to peg the footer to the absolute bottom of the screen, even when the page content is minimal or with not so much height, so you would see white space between the page content and the footer.
To accomplish this, can you please try adding the following to Customize > Additional CSS:
html, body {
height: 100%;
}
#page {
display: table;
width: 100%;
height: 100%;
}
#content {
height: auto;
}
#colophon {
display: table-row;
height: 1px;
}Please let me know whether this works or not.
Andy