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The minimum distance between Earth and Mars has been declining over the years, and in 2003 the minimum distance was 55.76 million km, nearer than any such encounter in almost 60,000 years (57,617 BC). The record minimum distance between Earth and Mars in 2729 will stand at 55.65 million km.
The distance at close approach varies between about 54 and 103 million km (34 and 64 million mi) due to the planets' elliptical orbits, which causes comparable variation in angular size. [190] At their furthest Mars and Earth can be as far as 401 million km (249 million mi) apart. [191] Mars comes into opposition from Earth every 2.1 years.
The first two objects that were detected and had their Earth-MOID calculated before Earth impact were the small asteroids 2008 TC 3 and 2014 AA. 2014 AA is listed with a MOID of 0.00000045 AU (67 km; 42 mi), [5] and is the second smallest MOID calculated for an Apollo asteroid after 2020 QY 2 with an Earth-MOID of 0.00000039 AU (58 km; 36 mi). [6]
The actual distance between the Moon and Earth can change as quickly as 75 meters per second, [20] or more than 1,000 km (620 mi) in just 6 hours, due to its non-circular orbit. [21] There are other effects that also influence the lunar distance.
380 Earth radii (very inaccurate, true=16000 Earth radii) Aristarchus of Samos made a measurement of the distance of the Sun from the Earth in relation to the distance of the Moon from the Earth. The distance to the Moon was described in Earth radii (20, also inaccurate). The diameter of the Earth had been calculated previously.
While the Kármán line is defined for Earth only, several scientists have estimated the corresponding figures for Mars and Venus. Isidoro Martínez arrived at 80 km (50 miles) and 250 km (160 miles) high, respectively, [31] while Nicolas Bérend arrived at 113 km (70 miles) and 303 km (188 miles). [32]
Earth and Moon transiting the Sun in 2084, as seen from Mars. Image created using SpaceEngine Earth and Moon from Mars, as photographed by the Mars Global Surveyor. A transit of Earth across the Sun as seen from Mars takes place when the planet Earth passes directly between the Sun and Mars, obscuring a small part of the Sun's disc for an observer on Mars.
Several factors make placing a spacecraft into an areostationary orbit more difficult than a geostationary orbit. Since the areostationary orbit lies between Mars's two natural satellites, Phobos (semi-major axis: 9,376 km) and Deimos (semi-major axis: 23,463 km), any satellites in the orbit will suffer increased orbital station keeping costs due to unwanted orbital resonance effects.