You cannot tell the mass, because what you are doing now is appealing to the notion of mass as something that's related to the pull of the Earth on the object.

你无法测出质量,因为你现在所做的是把质量,用地球对物体的引力给替代了

耶鲁公开课 - 基础物理课程节选

They estimate that at least a third of the planet's mass is diamond - the equivalent of three times Earth's mass.

BBC: Oddballs: The strange worlds beyond our Solar System

The geodetic effect is caused by a distortion that the Earth's mass makes in the fabric of space.

ECONOMIST: A new satellite will test Einstein's magnum opus

Almost two-thirds of the stars likely host a planet measuring about five times Earth's mass, and half of them harbor a planet about the mass of Neptune.

WSJ: Galaxy Hosts 100 Billion Planets, in New Estimate