How are Brown Dwarfs like jovian planets?
Brown Dwarfs are black in visible light, but in infrared, they appear as warm red and brown in color.
Brown Dwarfs are not exactly planets, they are not even close to be considered a Planet.
Brown Dwarfs are failed Stars. They start off as a Star but they simply lack the mass to further support fusion reactions. Lets explain it in terms of Jupiter.
Scientists believe that an object rough 75 times the mass of Jupiter ( the context of Jovian Planets) will almost lack the mass to sustain a Nuclear fusion reaction. After a little while they actual discovered objects with the above properties even a little less massive. These type of Stars begin their lives like normal Stars but then instead of sustaining fusion they simply cool down.
These Stars are cool and Black but the name Black Dwarf was already dubbed for another type of Object hence the term Brown Dwarf was taken. They are actually not Brown.
One Unique property that helped scientists discover Brown Dwarfs is that Brown Dwarfs will have Lithium inside their cores. AS actual Stars burn through their Lithium fuel quite rapidly.