Final answer:
The combined mass of Mars' moons, Phobos and Deimos, is 1.22 x 10^16 kilograms when expressed in scientific notation.
Step-by-step explanation:
To calculate the combined mass of Mars' moons, Phobos and Deimos, we simply need to add their masses together. The mass of Phobos is given as 1.07 x 1016 kilograms, and the mass of Deimos is 1.5 x 1015 kilograms. Using scientific notation, we can align the powers of ten to make the addition easier.
Add the two masses:
Phobos: 1.07 x 1016 kg
Deimos: 0.15 x 1016 kg (Deimos' mass shifted one decimal place to the left to match the exponent of Phobos' mass)
Combined mass: (1.07 + 0.15) x 1016 kg
= 1.22 x 1016 kg
Therefore, the combined mass of Mars' two moons is 1.22 x 1016 kilograms, expressed in scientific notation.