Now, what does it mean to have 9th house lord sitting in 12th house?

It means the planet which rules/controls/owns the 9th house of your horoscope is sitting in the 12th house of horoscope.

Now, what is the impact of having 9th house lord sitting in 12th house?

Few things become very prominent with this position like Long Distance and Foreign Travels, Religion & Spirituality, Education & Wisdom. It shows that someone going to foreign lands to get his higher education. Someone getting a Guru in foreign lands. Someone works in Foreign Land/Companies with Foreigners. Someone who is highly imaginative. Someone who spends big part of life away from home land. But at the same time, 12th house is house of losses. It means that whichever planet you have in 12th house, you have to put extra efforts to gain anything out of it. If there are malefic planets in 12th house in wrong dignity and under further malefic impact, it shows that someone getting into illegal acts (9th house is Law too) and landing into jail or someone getting into drugs and all (12th house is escapism) and landing into hospitals.

Now, results may be different due to aspect, conjunctions of other planets or the planet being Retrograde or Combust. So again, Overall Chart Reading is important. Moreover, now we also need to check the strength of 12th house lord as 9th house lord is going in 12th house. So again, Overall Chart Reading is important.

So, let's see how different planets will behave differently as 9th house Lord in 12th house.

Sun - Suppose it is a Sagittarius Ascendant chart and Sun rules the 9th house with Leo sign and sits in the 12th house in Scorpio. It shows that person gets his confidence in life when he deals with matters of occult and mysticism in secluded/isolated places. This person wants to educate himself in matters of mysticism and other worldly affairs. At the same time, Sun in 12th house is Sun's Marana Karaka situation, they say Sun goes in 12th house to die. It means person's Father is always away from him and there is no benefit from Father. If there are benefic impacts on Sun then it will show Father performed all his duties well enough and was not irresponsible but still traveled a lot and could not give enough time to Family. But Soul is always seeking refuge in Spirituality, Occult and Mysticism.

Moon - So it is Scorpio Ascendant Chart and Moon rules the 9th house with Cancer sign and sits in 12th house in Libra. It shows that person will get his balance of mind when he is isolated. These people don't like staying among people. Isolation from worldly affairs makes their mind imaginative and creative. They will always be inclined towards higher education of religion and spirituality. Mother will be Spiritual too and on the basis of spirituality, they will find balance in relation with Mother. This also shows that Mother might have traveled to distant places a lot.

Mars - Mars can be 9th house ruler through its two signs. So, let's take both one after the other.

Leo Ascendant - So if it is Leo Ascendant, Mars rules 9th & 4th house and sits in 12th house in Cancer sign, where it is debilitated. If Mars is nearby the exact degree of debilitation, this is a position where person needs to be very careful and should not do anything against the law as high chances are there that he will end up in jails. Here, person will always have dominance struggle with his teachers. This person may get into legal trouble in Foreign Lands. These people also need to be careful against ways of escapism like Drugs and Alcohol, as it may cause them serious health issues.

Pisces Ascendant - Now if it is Pisces Ascendant, Mars rules 2nd & 9th house and sits in 12th house in Aquarius sign. We can see similar results here as Mars is still in enemy sign. But Aquarius is sign of Large Organizations and 12th house is Foreign Lands and Foreign Companies, so Mars's actions are getting some directions here. This person can gain by working in Large MNCs. They can be good in Real Estate Business in Foreign Lands. But dominance struggle and arguments with Teachers will remain as is.

Mercury - Mercury also can be 9th house ruler through its two signs. So, let's take both one after the other.

Libra Ascendant - If it is Libra Ascendant, Mercury rules 9th & 12th houses and sits in 12th house in Virgo, where it is exalted. This shows a prolific writer. This shows someone who wants to gain more and more of religious and spiritual knowledge. They are interested in gaining knowledge about different religions and different philosophies of the world, i.e. they will take info from anywhere. But when it comes to Spiritual knowledge they become very analytical, critical and perfectionist. This is the difference of Gemini and Virgo falling in these houses respectively. Amazing ability to become a great writer.

Capricorn Ascendant - If it is Capricorn Ascendant, then Mercury rules 6th and 9th house and sits in 12th house in Sagittarius. This shows a person dedicated to Higher Education as 9th house lord is sitting in Sagittarius (9th sign) which represents all the things which 9th house represents. As Mercury is all about collecting information, this shows someone who wants to learn more and more about religion, philosophy or law. As Mercury also represents Teaching/Counselling, it shows someone who is working as teacher/professor at Foreign Universities. This also shows a religious or spiritual preacher.

Venus - Venus also can be 9th house ruler through its two signs. So, let's take both one after the other.

Virgo Ascendant - If it is Virgo Ascendant, Venus rules 9th & 2nd house and sits in 12th house in Leo sign. This shows a person who finds beauty and love in travelling to different places and meeting people of different culture. This shows a guy who meets his future wife in Foreign Lands or Foreign Companies. Love interest can be Foreigner too. It can also be an online love story. But thing with Venus in Leo is that spouse may be highly demanding and that may end up in loss (12th house) of relation. So, people may need to take care of that.

Aquarius Ascendant - If it is Aquarius Ascendant, Venus rules 4th & 9th house and sits in 12th house in Capricorn. This is much better position of Venus as it is in friendly sign. It shows wealth from Foreign Lands, MNCs and from people of Authority. It again shows love and relationship in Foreign Lands or with Foreigner. This time relationship is expected to be stable as Venus is in Saturn ruled sign which represents Stability and Long Duration. So, relationship may be delayed in life but it will be stable.

Jupiter - Jupiter also can be 9th house ruler through its two signs. So, let's take both one after the other.

Aries Ascendant - If it is Aries Ascendant, Jupiter rules 9th & 12th house and sits in 12th house in Pisces Sign. This is a highly spiritual person. Jupiter ruling the 9th house and sitting in 12th house which again it rules with most Spiritual sign Pisces. This person is like a Gautam Buddha. This person will be regarded as highly Spiritual Guru to others who guide and counsel them. This is not a person of Bookish knowledge. They "know" what they say. A great position.

Cancer Ascendant - If it is Cancer Ascendant, Jupiter rules 6th & 9th house and sits in 12th house in Gemini. This person is more like a Professor/Teacher/Counselor in Foreign Lands as Jupiter is in sign of Gemini, a sign of communication/counselling. They can be good in counselling people in matters of Spirituality and Occult. As always, there is nothing much to say when planets are nicely placed.

Saturn - Saturn also can be 9th house ruler through its two signs.

In either sign (Capricorn/Aquarius) as 9th house lord, Saturn in 12th house (for Gemini/Taurus Ascendants respectively) surely indicates that access to foreign lands or foreign travels came late in life. In early life, they may have tried a lot to reach to foreign lands but their may be one or the other obstacles. Going to foreign land or returning from foreign land will be equally tough. For Taurus ascendant, Saturn is debilitated in 12th house. It shows some serious legal issues which forced person to be in jail for a long time. They might get into some legal issue in Foreign Lands too. It also shows that person is frugal or miser and doesn't spend a lot. In early life, they will never get good Spiritual Gurus but through age when they reach 30s, they get some old and wise Guru. Spirituality develops late in life.

Rahu - If Rahu is 9th house Lord through its sign Aquarius, as it co-rules Aquarius along with Saturn, and sits in 12th house in Taurus then 1st of all we need to make sure of Saturn's position as it is the main ruler. Rahu in Taurus in 12th house will transform Rahu as Venus as Rahu changes its nature as per the lord of sign it is placed in. At the same time, Rahu's basic nature of being insatiable will remain there. Rahu in Taurus in 12th house shows that person gains a lot of wealth from Foreign Lands or through Spirituality. They are those filthy rich people. As Rahu is involved, there may be some illusion regarding their source of earning, means they can be fooling around people in name of Spirituality. They can also be earning through Foreign Companies and Foreign Sources.

Ketu - Likewise, If Ketu is 9th house Lord through its sign Scorpio, as it co-rules Scorpio along with Mars, and sits in 12th house in Aquarius then 1st of all we need to make sure of Mars' position as it is the main ruler. As Ketu isolates/separates a person from the things related to the house Ketu is sitting, here it separates person from the concept of working in corporate :). It also separates person from the spiritual beliefs spread by others. They never find themselves agree with the concepts of spirituality of others and always find fault there. Similarly, they reach foreign land but don't find anything of interest there and feel isolated. At the same time, they are very research oriented and scientific people. They approach spirituality in scientific manner and through lots of research and study. It is one of the most prominent Moksha Margi position. They are here to seek truth their own way.