Radiogenic noble gas data provide valuable information on planetary evolution through their degassing histories. The relative abundance of ⁴⁰Ar in the Cytherean atmosphere is 0.26 of that in the Earth's atmosphere. Calculation of a ⁴⁰Ar degassing model along with mantle evolution and melt migration shows that the average magma production rate on Venus is about 5km³/yr. Duration of plate motion on Venus, if existed, would be less than several hundred million years. For Mars, estimated volume of erupted volcanic materials is compatible with the present Martian ⁴⁰Ar, which is about 1/20 of ⁴⁰Ar in the Earth's atmosphere. On the other hand, early degassing fraction estimated from Martian radiogenic ¹²⁹Xe is as much as 1/3 of that of the Earth. This early degassing may be due to the magma ocean cooling. Detection of Martian ⁴He will be evidence of current degassing activity on Mars. Abundant ⁴He in Venus atmosphere, showing much longer residence time than the Earth's ⁴He, should correspond to current absence of magnetic field.