Phobos and Deimos, the two small moons of Mars, were discovered in 1877 by:

The American astronomer Asaph Hall discovered both moons of Mars in August 1877, using the 26-inch refracting telescope of the United States Naval Observatory in Washington, D.C.

The discovery:

• Hall discovered Deimos on 12 August 1877 and Phobos on 18 August 1877.
• He had almost given up the search, but his wife, Angeline Stickney, encouraged him to continue.
• The largest crater on Phobos is named Stickney in her honour.

Meaning of the names:

In Greek mythology, Phobos (fear) and Deimos (dread or terror) were the sons of Ares, the god of war, who is known to the Romans as Mars.

About Phobos:

• Phobos is the larger and inner moon, about 22 km across.
• It orbits very close to Mars, at about 6,000 km above the surface, and goes around the planet about three times a day.
• It is slowly spiralling towards Mars and is expected to break apart or crash into the planet in about 50 million years.

About Deimos:

Deimos is smaller, about 12 km across, and orbits farther away.

Origin of the moons:

• Both moons are irregular in shape, like potatoes.
• Many scientists think they may be captured asteroids, while others suggest they formed from debris after a large impact on Mars.

A prediction in fiction:

Jonathan Swift's "Gulliver's Travels" (1726) mentioned two moons of Mars, more than 150 years before they were discovered.

Missions:

About Mars:

• Mars is the fourth planet from the Sun and is called the Red Planet because of the reddish dust that covers its surface.
• It has Olympus Mons, the tallest volcano in the solar system.
• India's Mangalyaan (Mars Orbiter Mission) reached Mars orbit in September 2014 on its first attempt.

Why not the other options?

• ✗William Herschel discovered Uranus in 1781.
• ✗Giovanni Cassini discovered four moons of Saturn in the 17th century.
• ✗Johann Galle first observed Neptune in 1846.