Planetary surface

A planetary surface is where the solid or liquid material of certain types of astronomical objects contacts the atmosphere or outer space.

The vast distances and complexities of space makes direct exploration of even near-Earth objects dangerous and expensive.

Indirect observations by flyby or orbit currently provide insufficient information to confirm the composition and properties of planetary surfaces.

Landers have explored several smaller bodies including 433 Eros (2001), 25143 Itokawa (2005), Tempel 1 (2005), 67P/Churyumov–Gerasimenko (2014), 162173 Ryugu (2018) and 101955 Bennu (2020).

Surface stability may be affected by erosion through Aeolian processes, hydrology, subduction, volcanism, sediment or seismic activity.

NEAR Shoemaker was the first to soft land on an asteroid – 433 Eros in February 2001 while Hayabusa was the first to return samples from 25143 Itokawa on 13 June 2010.

There have been many failed attempts, more recently Fobos-Grunt, a sample return mission aimed at exploring the surface of Phobos.

The remaining part of its surface consists of rocky or organic carbon and silicon rich compounds.

Liquid water as surface, beside on Earth, has only been found, as seasonal flows on warm Martian slopes, as well as past occurrences, and suspected at the habitable zones of other planetary systems.

Many of Earth's Igneous rocks are formed through processes rare elsewhere, such as the presence of volcanic magma and water.

Apart from water, many other abundant surface materials are unique to Earth in the Solar System as they are not only organic but have formed due to the presence of life – these include carbonate hardgrounds, limestone, vegetation and artificial structures although the latter is present due to probe exploration (see also List of artificial objects on extra-terrestrial surfaces).

As organic compounds are often volatile, their persistence as a solid or liquid on a planetary surface is of scientific interest as it would indicate an intrinsic source (such as from the object's interior) or residue from larger quantities of organic material preserved through special circumstances over geological timescales, or an extrinsic source (such as from past or recent collision with other objects).

Apollo 11 astronaut Buzz Aldrin walking on the surface of the Moon , which consists of lunar regolith (photographed by Neil Armstrong , July 1969).
OSIRIS-REx collecting a surface sample from asteroid 101955 Bennu in 2020
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First self-propelled flying extraterrestrial probe Ingenuity on Mars, hovering over its serface and being watched by its parent rover Perseverance rover.
Perspective radar view of Titan's Bolsena Lacus (lower right) and other northern hemisphere hydrocarbon lakes
Sand dunes in the Namib Desert on Earth (top), compared with dunes in Belet on Titan
Pluto's Tombaugh Regio (photographed by New Horizons flyby on July 14, 2015) appears to exhibit geomorphological features previously thought to be unique to Earth. [ 52 ]