When was Phobos discovered by Asaph Hall?
American astronomer Asaph Hall spotted Phobos on the 18th of August 1877. The discovery occurred around 09:14 Greenwich Mean Time at the United States Naval Observatory in Washington D.C.
American astronomer Asaph Hall spotted Phobos on the 18th of August 1877. The discovery occurred around 09:14 Greenwich Mean Time at the United States Naval Observatory in Washington D.C.
Phobos measures roughly 22 kilometers across its longest dimension with a density near 1.88 grams per cubic centimeter. Spectral data reveals carbon-rich material similar to carbonaceous chondrites found among meteorites while voids occupy about 30 percent plus or minus 5 percent of its total volume.
The Stickney crater spans nine kilometers wide and likely shattered the moon before gravity reassembled it into its current irregular shape. Mars Express spacecraft data showed grooves radiate from the leading apex of orbit where boulders ejected during the Stickney impact rolled predictably across the surface compressing softer regolith layers.
Phobos orbits Mars below synchronous altitude completing a full revolution every seven hours and thirty-nine minutes while approaching Mars by approximately two centimeters per year through tidal deceleration effects. Scientists estimate breakup will occur within 30 to 50 million years when tidal forces overcome structural integrity to form a planetary ring system around Mars lasting between one million and 100 million years.
Mariner 7 photographed Phobos in close-up during 1969 followed by Mariner 9 in 1971 and Viking 1 captured images in 1977. Soviet probes Phobos 1 and 2 attempted dedicated study in 1988 while India's Mars orbiter captured photos from 4,200 kilometers away on the 1st of July 2020.