The planet Mars has two moons, Phobos and Deimos.
They are very tiny, where the term "tiny" is in general the matter of opinion.
Phobos orbits closer to Mars, with diameter which is approximately 23 kilometers, where diameter of Deimos is approximately 13 kilometers. Their surface area is up close to some of the smallest states on Earth, like Luxembourg and Malta. The image below shows the two Moons analogically from the left; Phobos and Deimos.
Phobos and Deimos are in no way lightweight, total mass of Deimos is 2,244脳10^(15) kg , on the other hand, Phobos mass is 1.08脳10^(16) kg. In reality their gravitational pull isn't even strong enough to bring them into spherical form. So they looks more like huge potatoes than Moons. Both of them were discovered in 1877 by Asaph Hall. Their names are after the Greek mythological twin characters.
The most popular theory of their origin is that they were once part of the asteroid belt, until Jupiter's massive kicked them out of it. So Mars could catch them.
Phobos orbits Mars at a average distance of 9,400 kilometers, once every seven and a half hour. It's on collision course , and gets 2 meters closer to Mars every year. In 50 to 100 million years, it will probably be either ripped to pieces by Mars' gravity. The radius of the Phobos orbit is smaller than the radius of the synchronous orbit, which means that it orbits faster than Mars rotates around its own axis. A very frequent phenomenon in the Martian sky is the Fobos eclipse through the shadow of Mars. During that year, which lasts almost 687 Earth days, there are about 1,300 eclipses of Phobos. The duration of such eclipses can last no more than one hour.
Smaller Deimos, on the other hand, is slowly escaping Mars. It will probably leave the orbit of Mars, and leave a red planet behind. So, in a few hundred million years, Mars will be Moonless. Unless it will catch another asteroid over the years. The two largest craters on Deimos have a diameter of about 3 kilometers. They commemorate writers who mentioned the "two moons of Mars" before their discovery. These are the Swift craters (named after Jonathan Swift) and Voltaire (from the nickname of Voltaire).
References:
[1]https://www.researchgate.net/publication/275967177_Natural_motion_around_the_Martian_moon_Phobos
[2]http://planetary-science.org/mars-research/moons-of-mars/
[3]https://en.wikipedia.org/wiki/Moons_of_Mars
