The Solar System:


(Part I)

A nude statue of Mars in a garden setting, as depicted on a wall painting from Pompeii, 1st century CE.

Credit: Kleuske (Wikimedia Commons), CC BY 2.5 [link]; also see Schilling, R. 1992, "Mars", in Roman and European Mythologies, Y. Bonnefoy (ed.), W. Doniger (trans.) (Chicago: University of Chicago Press), p. 135 [link]

"Descanso de Marte" ("Resting Mars") by Diego Velázquez (1599-1660 CE; Spanish), 1640 CE.

Credit: Diego Velázquez; Prado Museum [link]

Images of Mars as a planet

Drawing of Mars by Christiaan Huygens (1629-1695 CE: Dutch) from 1659.

Credit: Christiaan Huygens (1659) [link]

Drawing of Mars by Giovanni Schiaparelli (1835-1910 CE; Italian) from 1890.

Credit: Giovanni Schiaparelli (1890); from Evans, J. E., & Maunder, E. W., 1903, Monthly Notices of the Royal Astronomical Society, 63, 488 - "Experiments as to the actuality of the 'Canals' observed on Mars" (1903MNRAS..63..488E)

Martian canals

Schiaparelli described “canali” on Mars. He meant “channels”; that is, natural features, like canyons. This was widely misinterpreted as “canals”; that is, artificial features (i.e., made by aliens).

Percival Lowell went all in on the “canals” interpretation, calling them:

“engineered works for irrigation”

Schiaparelli commented on the “canals” in Lowell’s drawings of Mars:


Drawing of Martian canals by Percival Lowell (1855-1916 CE; American) from c. 1895.

Credit: Percival Lowell (c. 1895) [link]

Percival Lowell (1855-1916 CE; American), c. 1904.

Credit: James E. Purdy; available from the United States Library of Congress's Prints and Photographs division under the digital ID cph.3c28068 [link]

Four faces of Mars in April-May 1999. Taking advantage of Mars's closest approach to Earth since eight years prior, astronomers used NASA's Hubble Space Telescope to obtain very sharp views of the Red Planet.

The telescope's Wide Field and Planetary Camera 2 snapped these images between April 27 and May 6, when Mars was 54 million miles (87 million kilometers) from Earth. From this distance the telescope could see Martian features as small as 12 miles (19 kilometers) wide.

The telescope obtained four images, which, together, show the entire planet. Each view depicts the planet as it completes one quarter of its daily rotation. In these views the north polar cap is tilted toward the Earth and is visible prominently at the top of each picture. The images were taken in the middle of the Martian northern summer, when the polar cap had shrunk to its smallest size. During this season the Sun shines continuously on the polar cap. Previous telescopic and spacecraft observations have shown that this summertime "residual" polar cap is composed of water ice, just like Earth's polar caps.

The upper-left image is centered near the location of the Pathfinder landing site. Dark sand dunes that surround the polar cap merge into a large, dark region called Acidalia. This area, as shown by images from the Hubble telescope and other spacecraft, is composed of dark, sand-sized grains of pulverized volcanic rock. Below and to the left of Acidalia are the massive Martian canyon systems of Valles Marineris, some of which form long linear markings that were once thought by some to be canals. Early morning clouds can be seen along the left limb of the planet, and a large cyclonic storm composed of water ice is churning near the polar cap.

The upper-right image is centered on the region of the planet known as Tharsis, home of the largest volcanoes in the solar system. The bright, ring-like feature just to the left of center is the volcano Olympus Mons, which is more than 340 miles (550 kilometers) across and 17 miles(27 kilometers) high. Thick deposits of fine-grained, windblown dust cover most of this hemisphere. The colors indicate that the dust is heavily oxidized ("rusted"), and millions (or perhaps billions) of years of dust storms have homogenized its composition. Prominent late afternoon clouds along the right limb of the planet can be seen.

The lower-left image is centered near another volcanic region known as Elysium. This area shows many small, dark markings that have been observed by the Hubble telescope and other spacecraft to change as a result of the movement of sand and dust across the Martian surface. In the upper left of this image, at high northern latitudes, a large chevron-shaped area of water ice clouds mark a storm front. Along the right limb, a large cloud system has formed around the Olympus Mons volcano.

The lower-right image is centered on the dark feature known as Syrtis Major, first seen telescopically by the astronomer Christian Huygens in the 17th century. Many small, dark, circular impact craters can be seen in this region, attesting to the Hubble telescope's ability to reveal fine detail on the planet's surface. To the south of Syrtis a large circular feature called Hellas. Viking and more recently Mars Global Surveyor have revealed that Hellas is a large and deep impact crater. These Hubble telescope pictures show it to be filled with surface frost and water ice clouds. Along the right limb, late afternoon clouds have formed around the volcano Elysium.

Shown here are color composites generated from data using three filters: blue (410 nanometers), green (502 nanometers), and red (673 nanometers). A total of 12 color filters, spanning ultraviolet to near-infrared wavelengths, were used in the observation.

Credit (image and some text): STScI OPO, S. Lee (University of Colorado), J. Bell (Cornell University), M. Wolff (Space Science Institute), NASA [link]

What does the surface of Mars look like?

'Raw,' 'Natural', and 'White-Balanced' views of Martian terrain. These three versions of the same image taken by the Mast Camera (Mastcam) on NASA's Mars rover Curiosity illustrate different choices that scientists can make in presenting the colors recorded by the camera. The left image is the raw, unprocessed color, as it is received directly from Mars. The center rendering was produced after calibration of the image to show an estimate of "natural" color, or approximately what the colors would look like if we were to view the scene ourselves on Mars. The right image shows the result of then applying a processing method called white-balancing, which shows an estimate of the colors of the terrain as if illuminated under Earth-like, rather than Martian, lighting.

Credit: NASA/JPL-Caltech/MSSS [link]

First visit to Mars

Thrust from a Titan 3/Centaur rocket launched NASA's Viking 1 spacecraft on a 505-million-mile journey to Mars on 20 August 1975. Viking 2 followed three weeks later. Each mission included both an orbiter and a lander, and all four components accomplished successes. On 20 July 1976, the Viking 1 lander returned the first photograph taken on the surface of Mars (see below). Located in a region called Chryse Planitia, the Viking 1 lander operated until 13 November 1982. The Viking 2 lander operated in the Utopia Planitia region from 3 September 1976 to 11 April 1980. The orbiters sent home images of the entire planet at resolutions of 300 meters or less per pixel.

Credit (adapted text): NASA/JPL [link]

Dr. Carl Sagan, best known for his acclaimed public television series "Cosmos," poses with a model of the Viking lander in Death Valley, California.

Credit: "Cosmos: A Personal Voyage"/Druyan-Sagan Associates, Inc. [link]

First image from the surface of Mars

The first image from the surface of Mars was obtained by the Viking 1 probe just minutes after the spacecraft landed successfully on 20 July 1976.

This is the original description provided by NASA with this historic image:

The center of the image is about 1.4 meters (five feet) from Viking Lander camera #2. We see both rocks and finely granulated material - sand or dust. Many of the small foreground rocks are flat with angular facets. Several larger rocks exhibit irregular surfaces with pits and the large rock at top left shows intersecting linear cracks. Extending from that rock toward the camera is a vertical linear dark band which may be due to a one-minute partial obscuration of the landscape due to clouds or dust intervening between the Sun and the surface. Associated with several of the rocks are apparent signs of wind transport of granular material. The large rock in the center is about 10 centimeters (4 inches) across and shows three rough facets. To its lower right is a rock near a smooth portion of the Martian surface probably composed of very fine-grained material. It is possible that the rock was moved during Viking 1 descent maneuvers, revealing the finer-grained basement substratum; or that the fine-grained material has accumulated adjacent to the rock. There are a number of other furrows and depressions and places with fine-grained material elsewhere in the picture. At right is a portion of footpad #2. Small quantities of fine grained sand and dust are seen at the center of the footpad near the strut and were deposited at landing. The shadow to the left of the footpad clearly exhibits detail, due to scattering of light either from the Martian atmosphere or from the spacecraft, observable because the Martian sky scatters light into shadowed areas.

Credit (image and some text): NASA/JPL [link]

Robotic exploration of Mars

Two spacecraft engineers join a grouping of vehicles providing a comparison of three generations of Mars rovers developed at NASA's Jet Propulsion Laboratory (JPL), located in Pasadena, California. The setting is JPL's Mars Yard testing area.

Front and center is the flight spare for the first Mars rover, Sojourner, which landed on Mars in 1997 as part of the Mars Pathfinder Project. On the left is a Mars Exploration Rover Project test rover that is a working sibling to Spirit and Opportunity, which landed on Mars in 2004. On the right is a Mars Science Laboratory test rover the size of that project's Mars rover, Curiosity, which is on course for landing on Mars in August 2012.

Sojourner and its flight spare, named Marie Curie, are 2 feet (65 centimeters) long. The Mars Exploration Rover Project's rover, including the "Surface System Test Bed" rover in this photo, are 5.2 feet (1.6 meters) long. The Mars Science Laboratory Project's Curiosity rover and the "Vehicle System Test Bed" rover, on the right in this photo, are 10 feet (3 meters) long.

Credit (image and some text): NASA/JPL-Caltech [link]

Curiosity landed on Mars on 6 August 2012 and is still exploring as of November 2022!

This low-angle self-portrait of NASA's Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called "Buckskin" on lower Mount Sharp. The selfie combines several component images taken by Curiosity's Mars Hand Lens Imager (MAHLI) on Aug. 5, 2015, during the 1,065th Martian day, or sol, of the rover's work on Mars. For scale, the rover's wheels are 20 inches (50 centimeters) in diameter and about 16 inches (40 centimeters) wide.

Credit (image and some text): NASA/JPL-Caltech/MSSS [link]; Astronomy Picture of the Day on 2017 Nov 20 [link]

The team operating NASA's Curiosity Mars rover uses the Mars Hand Lens Imager (MAHLI) camera on the rover's arm to check the condition of the wheels at routine intervals. This image of Curiosity's left-middle and left-rear wheels is part of an inspection set taken on April 18, 2016, during the 1,315th Martian day, or sol, of the rover's work on Mars.

Holes and tears in the wheels worsened significantly during 2013 as Curiosity was crossing terrain studded with sharp rocks on its route from near its 2012 landing site to the base of Mount Sharp. Team members are keeping a close eye for when any of the zig-zag shaped treads, call grousers, begin to break. Longevity testing with identical wheels on Earth indicates that when three grousers on a given wheel have broken, that wheel has reached about 60 percent of its useful mileage.

The rectangular openings visible in the backs of the wheel treads in this image create a unique, repeating pattern in the sandy Martian surface, which the rover can use as a visual reference to drive more accurately in barren terrain. Incidentally, the pattern is Morse code for the letters JPL. [link]

Credit (image and some text): NASA/JPL-Caltech/MSSS [link]

Scenes from Mars

360 degree panorama image obtained by the Spirit rover in November 2005. Spirit acquired the 405 individual images that make up this 360-degree view of the surrounding terrain using five different filters on the panoramic camera. This image is an approximately true-color rendering using the camera's 750-, 530-, and 430-nanometer filters.

Credit: NASA/JPL-Caltech [link]

Sunset in Gusev Crater - Spirit (2005)

On 19 May 19, 2005, Mars Exploration Rover Spirit captured this stunning view as the sun sank below the rim of the Gusev crater on Mars. The filter combination used to take this image allows false color images to be generated that are similar to what the human eye would see, but with the colors slightly exaggerated. Because Mars is farther from the Sun than Earth is, the Sun appears only about two-thirds the size that it appears in a sunset seen from Earth. The floor of Gusev crater is visible in the distance, and the Sun is setting behind the wall of Gusev some 80 kilometers (50 miles) in the distance.

Credit (image and some text): NASA/JPL/Texas A&M/Cornell [link]

Sunset in Gale Crater - Curiosity (2015)

NASA's Curiosity Mars rover recorded this view of the sun setting at the close of the mission's 956th Martian day, or sol (15 April 2015), from the rover's location in Gale Crater.

This was the first sunset observed in color by Curiosity. The image comes from the left-eye camera of the rover's Mast Camera (Mastcam). The color has been calibrated and white-balanced to remove camera artifacts. Mastcam sees color very similarly to what human eyes see, although it is actually a little less sensitive to blue than people are.

Dust in the Martian atmosphere has fine particles that permit blue light to penetrate the atmosphere more efficiently than longer-wavelength colors. That causes the blue colors in the mixed light coming from the Sun to stay closer to the Sun's part of the sky, compared to the wider scattering of yellow and red colors. This effect is most pronounced near sunset, when light from the sun passes through a longer path in the atmosphere than it does at mid-day.

Credit (image and some text): NASA/JPL-Caltech/MSSS/Texas A&M University [link]

Solar eclipse on Mars

This set of three images shows views three seconds apart as the larger of Mars' two moons, Phobos, passed directly in front of the Sun as seen by NASA's Mars rover Curiosity. Curiosity photographed this annular, or ring, eclipse with the telephoto-lens camera of the rover's Mast Camera pair (right Mastcam) on 20 August 2013, the 369th Martian day, or sol, of Curiosity's work on Mars.

The rover's observations of Phobos help researchers to make measurements of the moon's orbit even more precise. Because this eclipse occurred near mid-day at Curiosity's location on Mars, Phobos was nearly overhead, closer to the rover than it would have been earlier in the morning or later in the afternoon. This timing made Phobos' silhouette larger against the Sun - as close to a total eclipse of the Sun as is possible from Mars.

Credit: NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M University [link]

Geographic features of the Martian surface

It's all downhill... (form the south pole anyway)

The Mars Orbiter Laser Altimeter (MOLA) aboard the Mars Global Surveyor produced the first global map of the topography of Mars. MOLA operated by shining a laser at the planet and timing its reflection. The most obvious feature of this map is the major contrast in elevation between the southern highlands (mostly orange) and northern lowlands (blue). The highest elevations are found in the Tharsis volcanic province at about 250°E, while the lowest elevations are in the Hellas basin at about 60°E.

This contrast between the hemispheres is probably the result of a giant impact of a Pluto-sized object near the north pole of Mars early in its history. There are fewer craters in the north hemisphere, indicating that the terrain was "repaved" by melting or being covered with sub-surface lava as a result of the impact. This event might have contributed to the rapid shut-off of Mars’ global magnetic field.

Credit (image and some text): NASA/JPL/GSFC [link]

Olympus Mons

Largest volcano in the Solar System

Viking 1 orbiter image of Olympus Mons. The dimensions of the volcano and related terrain are approximately 640x840 km, roughly the size of the state of Arizona.

Credit: NASA [link]

Olympus Mons is so massive that it is slowly collapsing under its own weight, even in the comparatively low gravity of Mars (40% of Earth's gravity). The steep cliffs visible along the right side of the volcano's base in this side-view image constructed from Viking data were caused by collapse. Heights in this image are exaggerated by a scale of 10:1.

Credit: NASA/MOLA Science Team [link]

Comparison of large mountains on Earth and Mars. Mauna Kea is shown starting from the sea floor; the part that is underwater is shaded blue.

Credit: attribution unknown; revised elevations by D. W. Hoard (2018), using data from Plescia, J. B., 2004, Journal of Geophysical Research (Planets), 109, E03003 - "Morphometric properties of Martian volcanoes" (2004JGRE..109.3003P) [Olympus Mons: 21.1 km peak, 21.9 km relief, 840x640 km base, MRO]; USGS, 2018 (Nov 20), "How big are the Hawaiian volcanoes?" [link] [Mauna Kea: 10.2 km, USGS]; and BBC News, 2010 (Apr 8), "Nepal and China agree on Mount Everest's height" [link] [Mt. Everest: 8.8 km]

Valles Marineris

Now that's a grand canyon!

Mosaic of the Valles Marineris hemisphere of Mars projected into point perspective, a view similar to that which one would see from a spacecraft. The distance is 2,500 kilometers from the surface of the planet. The mosaic is composed of 102 Viking Orbiter images of Mars. The center of the scene shows the entire Valles Marineris canyon system, over 3000 kilometers long and up to 8 kilometers deep. The three Tharsis volcanoes (dark red spots), each about 25 kilometers high, are visible to the west (left).

Credit (image and some text): NASA/JPL-Caltech [link]
  • Valles Marineris started as a very large tectonic "crack" in the Martian crust.

  • Subsequently widened by erosion by wind and liquids.

  • Some channels may have been formed by water or carbon dioxide (or lava!).

How the Grand Canyon on Earth compares to Valles Marineris on Mars.

Credit: attribution unknown; data from NASA, National Park Service [link]

The Ophir Chasma region of Valles Marineris, the northernmost of the connected valleys. For scale, the large impact crater in the lower right corner is about 30 km (18.5 miles) wide. Ophir Chasma itself is a large west-northwest-trending trough about 100 km (62 miles) wide. The Chasma is bordered by high-walled cliffs, most likely tectonic faults, showing the effect of numerous past landslides.

Credit: NASA/JPL/USGS [link]


Valles Marineris

  • Lin, A., 2012, Lithosphere, 4, 286 - "Structural analysis of the Valles Marineris fault zone: Possible evidence for large-scale strike-slip faulting on Mars” (2012Lsphe...4..286Y)

Olympus Mons collapsing under its own weight

  • Musiol, S., Holohan, E. P., Cailleau, B., et al. 2016, Journal of Geophysical Research: Planets, 2016, 121, 255 - “Lithospheric flexure and gravity spreading of Olympus Mons volcano, Mars” (DOI:10.1002/2015JE004896)