Source: "Word of Tarot" by Viktor Benkovski and Jelena Hajezkaja,
published 1993, Sankt-Petersburg, in russian.

Proserpina - hypotetic transpluto planet with year more than 600 years
of Earth. In astronomy Proserpina isn't discovered yet, but existing
of at least one planet behind Pluto is periodically under question.
But astrology used already Proserpina some time, and to Proserpina are
connected some properties of "Super-Saturn". Authors don't know source
of existing ephemerides of Proserpina. Proserpina rules Virgo, exalt
in Gemini.

What symbolizes this planet? First, such Saturn's functions, like
moving up, to fixed purpose, also hardships and losses connected with
this. Proserpina gives type of fanatics, who are absolutely pitiless
to self on the way to achieve purpose. At all, if influence of Saturn
can be directed inside or outside, influence on Proserpina is directed
mainly inside. On physical level Proserpina often influenced through
long isolation, voluntary or forced. Proserpina is like Saturn in square
and multiplied to Pluto. It gives fanaticism and inflexibility of
Saturn, mixed with superhuman vitality of Pluto, and often all has
typically eccentric Uranian forms.
Tommazo Campanella was monk, who taked part in rebellion. Inquisition
long time tortured him, but Campanella confessed nothing. Was sent to
treatment, there seduced nun, who looked after him, wrote "Sun town".
Was several ten of years in prisons. Inquisition was rather afraid of
new tortures, Campanella was stronger than torturers.

Proserpina symbolizes also unattainable heights, barriers. On organism's
level Proserpina is connected with immunity system. So, after conjunction
between Proserpina and Pluto we can see AIDS pandemy.

Proserpina symbolizes also total control (Saturn is simple control, but
Proserpina is total control). On other hand, Proserpina transforms like
Pluto, but not with extreme situations of Pluto, but gradually and
thoroughly. Say, we need overbuild house. Work a la Pluto : destroy all
and then build all anew. Work on Proserpina level - nothing can be
destroyed, but all, absolutely all must be overbuild, all bricks must
found new places. This planet gives great attention to details,
aspiration to control, analyze, calculation.

At the moment on most peoples Proserpina is manifested relatively feebly.
Activation of Proserpina taked place through extreme situations, most
often through clinic death. Life of such men is totally changed, they are
touched by Proserpina's influence.