Goddess For Sun
Sun is a king among nine planets and one who provides prestige, fame and leadership qualities to a native. Sun is also signifactor of soul. Goddess Siddhidaatri or Goddess Amba are the two best options for those with weak Sun who wish prestige, fame, leadership qualities as well as good health. Goddess Siddhidatri would provide fame and prestige while those with health and low self-esteem should pray to Goddess Amba. But the best Goddess for a weak Sun would still be Goddess Gayatri. Gayatri Mantra is a hymn not just to the Sun God but to all other Sun presents in our solar system. It is the best mantra in Vedas. If you have a weak Sun then praying to Gayatri and reciting the Gayatri Mantra is more then sufficient.
Goddess For Moon
Moon represents feminine grace, beauty, charm, elegance, caring nature and emotions. There is no better Goddess to pray for a weak Moon then the other half of Lord Shiva. Goddess Parvati or Goddess Tripurasundari or Goddess Mahagauri are the ideal goddess to worship for those with weak Moon. Moon also rules over mind. Goddess Parvati is half part of Ardh Nareshwar form of Shiva so those with weak mind automatically get blessings of Shiva by prayers to Goddess Parvati. Anyone with a weak mind should always pray to Lord Shiva or Goddess Parvati.
Goddess For Mars
Mars is a warrior, action-oriented, angry yet caring, strict but full of empathy for others. The only two Goddess that fit the bill are Goddess Chandi and Goddess Chamunda. They are the different forms of same Goddess. Mars has excess energy, is agile and prone to explode now and then. But even then those with prominent Mars are needed as they say the bitter truth and try to bring reform even if they have to fight for it. The feminine grace and at the same time eruption form of Chandi and Chamunda is something that those with weak Mars would cherish. Even those with strong Mars in horoscope should pray to Chamunda or Chandi form of Goddess Durga. That way they can keep anger in check and erupt when its needed the most. Also reciting of Chandi Patha is beneficial although not necessary. If one can't speak it then also its fine if you speak a mantra for Goddess Chandi or Chamunda.
Goddess For Mercury
Mercury is a Prince, a teen who has not yet matured but at the same time he is chatty, articulate, smart and quick thinker, passive but able to drive point across. Mercury also rules over skin and speech. So the best Goddess to pray is Goddess Saraswati. She is fair skinned, beautiful and at the same time the consort of Lord Brahma who is the creator of universe. She is the ultimate form of knowledge without whom the Lord Brahma cannot create the Universe. Prayers to Goddess Saraswati would bless a native with speech, intelligence, beauty and grace. She would also grant Mercurians with music and vocal talents if they are into music. She also rules over education and Mercurians often work as teachers or lecturers. Also prayers to Goddess Brahmacharini is a possible option.
Goddess For Jupiter
Jupiter is the significator of abudance and prosperity. There is no better Goddess to pray then Annapurna form of Goddess Parvati. She is the goddess who blesses the natives with good food and nourishment. Also prayers to the form Skanda Mata of Goddess Parvati is beneficial. Jupiter also blesses a native with progeny. So those who wish for a child should also pray to Goddess Parvati or one of her forms. Prayers to Goddess Saraswati are also advisable for those with weak Jupiter as Jupiter also rules over knowledge and Goddess Saraswati is herself the highest form of knowledge.
Goddess For Venus
Venus is the planet associated with music, arts, perfumes, sweets and luxuries. Venus also bestows a native with beauty and romance. There is no better Goddess to pray for Venus then Goddess Laxmi. She is the consort of Lord Vishnu. Without her even Lord Vishnu cannot perform his duty of feeding the Universe and keeping it in order. She is the ultimate form of Wealth. If you desire for comforts, luxuries and pleasures then there is no better goddess then Goddess Laxmi. Also possible are prayers to Goddess Rati who is the consort of Kamdeva who is the God Of Love. In Western Countries they call him The Cupid. Last but not least those who suffer from bad effects of Venus need to pray to Goddess Santoshi Maa. She is the one who grants a native with satisfaction and contentment.
Goddess For Saturn
Saturn is the most stern among the planets. He is ruthless and bestows judgement both good and bad on natives. Those whose karma are bad see hell at hands of Saturn. Similarly the Kali form of Goddess Parvati is the most fierce and mercilessly slays the evil doers. She is the best goddess to pray for those with weak Saturn. Although for Saturn a bit of Shiva, Ram or Hanuman's prayers are also advisable. A little strength and patience are needed by natives who pass through Saturn test and prayers to Goddess Adi Shakti help as she provides natives with strength, patience and endurance to pass the Saturn test.
Goddess For Rahu
Rahu represents black arts, mysticism and foreigners. Rahu represents the one that is illusion and magical but at the same time highly attractive and alluring native. Goddess Bhairavi is the consort of Lord Bhairava and goddess of black arts, mysticism and quite simple in her dressing sense. Those who have prominent Rahu need a bit of mysticism and magic to gain in the market place and prayers to Goddess Bhairavi are the best for them to gain mastery over mysticism and magic but at the same time remain simple enough to catch other people's attention.
Goddess For Ketu
Most text on Vedic Astrology would say the Goddess to pray to for Ketu is Goddess Dhumavati. They are correct to a point cause Goddess Dhumavati is smokey, old, ugly widow and represents in-auspiciousness as well the unattractive. Ketu is smokey, detached and doesn't like norms and regulations of society. So praying to Goddess Dhumavati maybe ideal. But what everyone forgets is Ketu is able to provide Moksha and detachment from social sphere. The ideal Goddess would be Goddess Radha as she is selfless bhakti. She is the highest form of Bhakti to the Supreme Deity called Lord Krishna.
Goddess Radha was never able to marry Lord Krishna but her love was so pure and transcendent that even today she hold place next to Lord Krishna in most temples and there is always Radha spoken before Krishna. Only Ketu among the planets is able to provide love on that platonic level where there is no sense of attachment or sense of possession. So the ideal Goddess to pray for a weak Ketu is Goddess Radha cause she is love and devotion without expectations.