Your question seems to contain a misconception. Mass is not a measure of weight, but a fundamental property of matter that describes the amount of matter in an object. Weight, on the other hand, is the force exerted on an object due to gravity. The relationship between mass and weight can be expressed by the equation F = mg, where F represents the force (weight) acting on the object, m represents its mass, and g represents the acceleration due to gravity (approximately 9.8 m/s^2 on Earth).

Therefore, it is not appropriate to ask how much a celestial body needs to weigh to have a mass of 1.9891e30 kilograms. If you have the mass of an object, you can calculate its weight by multiplying the mass by the acceleration due to gravity at the location of interest.